1 | % ================================================================ |
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2 | % Chapter observation operator (OBS) |
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3 | % ================================================================ |
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4 | \chapter{Observation and model comparison (OBS)} |
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5 | \label{OBS} |
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6 | |
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7 | Authors: D. Lea, M. Martin, K. Mogensen, A. Vidard, A. Weaver... % do we keep that ? |
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8 | |
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9 | \minitoc |
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10 | |
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11 | |
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12 | \newpage |
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13 | $\ $\newline % force a new line |
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14 | |
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15 | The observation and model comparison code (OBS) reads in observation files (profile |
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16 | temperature and salinity, sea surface temperature, sea level anomaly, sea ice concentration, |
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17 | and velocity) and calculates an interpolated model equivalent value at the observation |
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18 | location and nearest model timestep. The resulting data are saved in a ``feedback'' file (or |
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19 | files). The code was originally developed for use with the NEMOVAR data assimilation code, but |
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20 | can be used for validation or verification of model or any other data assimilation system. |
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21 | |
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22 | The OBS code is called from \np{opa.F90} for model initialisation and to calculate the model |
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23 | equivalent values for observations on the 0th timestep. The code is then called again after |
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24 | each timestep from \np{step.F90}. To build with the OBS code active \key{diaobs} must be |
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25 | set. |
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26 | |
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27 | For all data types a 2D horizontal interpolator is needed to interpolate the model fields to |
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28 | the observation location. For {\em in situ} profiles, a 1D vertical interpolator is needed in |
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29 | addition to provide model fields at the observation depths. Currently this only works in |
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30 | z-level model configurations, but is being developed to work with a generalised vertical |
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31 | coordinate system. Temperature data from moored buoys (TAO, TRITON, PIRATA) in the |
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32 | ENACT/ENSEMBLES data-base are available as daily averaged quantities. For this type of |
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33 | observation the observation operator will compare such observations to the model temperature |
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34 | fields averaged over one day. The relevant observation type may be specified in the namelist |
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35 | using \np{endailyavtypes}. Otherwise the model value from the nearest timestep to the |
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36 | observation time is used. |
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37 | |
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38 | The code is controlled by the namelist \textit{nam\_obs}. See the following sections for more |
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39 | details on setting up the namelist. |
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40 | |
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41 | Section~\ref{OBS_example} introduces a test example of the observation operator code including |
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42 | where to obtain data and how to setup the namelist. Section~\ref{OBS_details} introduces some |
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43 | more technical details of the different observation types used and also shows a more complete |
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44 | namelist. Section~\ref{OBS_theory} introduces some of the theoretical aspects of the |
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45 | observation operator including interpolation methods and running on multiple processors. |
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46 | Section~\ref{OBS_obsutils} introduces some utilities to help working with the files produced |
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47 | by the OBS code. |
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48 | |
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49 | % ================================================================ |
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50 | % Example |
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51 | % ================================================================ |
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52 | \section{Running the observation operator code example} |
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53 | \label{OBS_example} |
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54 | |
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55 | This section describes an example of running the observation operator code using |
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56 | profile data which can be freely downloaded. It shows how to adapt an |
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57 | existing run and build of NEMO to run the observation operator. |
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58 | |
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59 | \begin{enumerate} |
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60 | \item Compile NEMO with \key{diaobs} set. |
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61 | |
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62 | \item Download some ENSEMBLES EN3 data from |
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63 | \href{http://www.hadobs.org}{http://www.hadobs.org}. Choose observations which are |
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64 | valid for the period of your test run because the observation operator compares |
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65 | the model and observations for a matching date and time. |
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66 | |
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67 | \item Add the following to the NEMO namelist to run the observation |
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68 | operator on this data. Set the \np{enactfiles} namelist parameter to the |
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69 | observation file name: |
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70 | \end{enumerate} |
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71 | |
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72 | %------------------------------------------namobs_example----------------------------------------------------- |
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73 | \namdisplay{namobs_example} |
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74 | %------------------------------------------------------------------------------------------------------------- |
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75 | |
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76 | The options \np{ln\_t3d} and \np{ln\_s3d} switch on the temperature and salinity |
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77 | profile observation operator code. The \np{ln\_ena} switch turns on the reading |
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78 | of ENACT/ENSEMBLES type profile data. The filename or array of filenames are |
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79 | specified using the \np{enactfiles} variable. The model grid points for a |
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80 | particular observation latitude and longitude are found using the grid |
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81 | searching part of the code. This can be expensive, particularly for large |
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82 | numbers of observations, setting \np{ln\_grid\_search\_lookup} allows the use of |
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83 | a lookup table which is saved into an ``xypos`` file (or files). This will need |
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84 | to be generated the first time if it does not exist in the run directory. |
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85 | However, once produced it will significantly speed up future grid searches. |
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86 | Setting \np{ln\_grid\_global} means that the code distributes the observations |
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87 | evenly between processors. Alternatively each processor will work with |
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88 | observations located within the model subdomain (see section~\ref{OBS_parallel}). |
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89 | |
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90 | A number of utilities are now provided to plot the feedback files, convert and |
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91 | recombine the files. These are explained in more detail in section~\ref{OBS_obsutils}. |
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92 | |
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93 | \section{Technical details} |
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94 | \label{OBS_details} |
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95 | |
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96 | Here we show a more complete example namelist and also show the NetCDF headers |
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97 | of the observation |
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98 | files that may be used with the observation operator |
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99 | |
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100 | %------------------------------------------namobs-------------------------------------------------------- |
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101 | \namdisplay{namobs} |
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102 | %------------------------------------------------------------------------------------------------------------- |
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103 | |
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104 | This name list uses the "feedback" type observation file input format for |
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105 | profile, sea level anomaly and sea surface temperature data. All the |
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106 | observation files must be in NetCDF format. Some example headers (produced using |
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107 | \mbox{\textit{ncdump~-h}}) for profile |
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108 | data, sea level anomaly and sea surface temperature are in the following |
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109 | subsections. |
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110 | |
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111 | \subsection{Profile feedback type observation file header} |
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112 | |
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113 | \begin{alltt} |
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114 | \tiny |
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115 | \begin{verbatim} |
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116 | netcdf profiles_01 { |
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117 | dimensions: |
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118 | N_OBS = 603 ; |
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119 | N_LEVELS = 150 ; |
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120 | N_VARS = 2 ; |
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121 | N_QCF = 2 ; |
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122 | N_ENTRIES = 1 ; |
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123 | N_EXTRA = 1 ; |
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124 | STRINGNAM = 8 ; |
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125 | STRINGGRID = 1 ; |
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126 | STRINGWMO = 8 ; |
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127 | STRINGTYP = 4 ; |
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128 | STRINGJULD = 14 ; |
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129 | variables: |
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130 | char VARIABLES(N_VARS, STRINGNAM) ; |
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131 | VARIABLES:long_name = "List of variables in feedback files" ; |
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132 | char ENTRIES(N_ENTRIES, STRINGNAM) ; |
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133 | ENTRIES:long_name = "List of additional entries for each variable in feedback files" ; |
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134 | char EXTRA(N_EXTRA, STRINGNAM) ; |
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135 | EXTRA:long_name = "List of extra variables" ; |
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136 | char STATION_IDENTIFIER(N_OBS, STRINGWMO) ; |
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137 | STATION_IDENTIFIER:long_name = "Station identifier" ; |
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138 | char STATION_TYPE(N_OBS, STRINGTYP) ; |
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139 | STATION_TYPE:long_name = "Code instrument type" ; |
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140 | double LONGITUDE(N_OBS) ; |
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141 | LONGITUDE:long_name = "Longitude" ; |
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142 | LONGITUDE:units = "degrees_east" ; |
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143 | LONGITUDE:_Fillvalue = 99999.f ; |
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144 | double LATITUDE(N_OBS) ; |
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145 | LATITUDE:long_name = "Latitude" ; |
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146 | LATITUDE:units = "degrees_north" ; |
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147 | LATITUDE:_Fillvalue = 99999.f ; |
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148 | double DEPTH(N_OBS, N_LEVELS) ; |
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149 | DEPTH:long_name = "Depth" ; |
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150 | DEPTH:units = "metre" ; |
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151 | DEPTH:_Fillvalue = 99999.f ; |
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152 | int DEPTH_QC(N_OBS, N_LEVELS) ; |
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153 | DEPTH_QC:long_name = "Quality on depth" ; |
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154 | DEPTH_QC:Conventions = "q where q =[0,9]" ; |
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155 | DEPTH_QC:_Fillvalue = 0 ; |
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156 | int DEPTH_QC_FLAGS(N_OBS, N_LEVELS, N_QCF) ; |
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157 | DEPTH_QC_FLAGS:long_name = "Quality flags on depth" ; |
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158 | DEPTH_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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159 | double JULD(N_OBS) ; |
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160 | JULD:long_name = "Julian day" ; |
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161 | JULD:units = "days since JULD_REFERENCE" ; |
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162 | JULD:Conventions = "relative julian days with decimal part (as parts of day)" ; |
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163 | JULD:_Fillvalue = 99999.f ; |
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164 | char JULD_REFERENCE(STRINGJULD) ; |
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165 | JULD_REFERENCE:long_name = "Date of reference for julian days" ; |
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166 | JULD_REFERENCE:Conventions = "YYYYMMDDHHMMSS" ; |
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167 | int OBSERVATION_QC(N_OBS) ; |
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168 | OBSERVATION_QC:long_name = "Quality on observation" ; |
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169 | OBSERVATION_QC:Conventions = "q where q =[0,9]" ; |
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170 | OBSERVATION_QC:_Fillvalue = 0 ; |
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171 | int OBSERVATION_QC_FLAGS(N_OBS, N_QCF) ; |
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172 | OBSERVATION_QC_FLAGS:long_name = "Quality flags on observation" ; |
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173 | OBSERVATION_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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174 | OBSERVATION_QC_FLAGS:_Fillvalue = 0 ; |
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175 | int POSITION_QC(N_OBS) ; |
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176 | POSITION_QC:long_name = "Quality on position (latitude and longitude)" ; |
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177 | POSITION_QC:Conventions = "q where q =[0,9]" ; |
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178 | POSITION_QC:_Fillvalue = 0 ; |
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179 | int POSITION_QC_FLAGS(N_OBS, N_QCF) ; |
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180 | POSITION_QC_FLAGS:long_name = "Quality flags on position" ; |
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181 | POSITION_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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182 | POSITION_QC_FLAGS:_Fillvalue = 0 ; |
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183 | int JULD_QC(N_OBS) ; |
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184 | JULD_QC:long_name = "Quality on date and time" ; |
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185 | JULD_QC:Conventions = "q where q =[0,9]" ; |
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186 | JULD_QC:_Fillvalue = 0 ; |
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187 | int JULD_QC_FLAGS(N_OBS, N_QCF) ; |
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188 | JULD_QC_FLAGS:long_name = "Quality flags on date and time" ; |
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189 | JULD_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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190 | JULD_QC_FLAGS:_Fillvalue = 0 ; |
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191 | int ORIGINAL_FILE_INDEX(N_OBS) ; |
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192 | ORIGINAL_FILE_INDEX:long_name = "Index in original data file" ; |
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193 | ORIGINAL_FILE_INDEX:_Fillvalue = -99999 ; |
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194 | float POTM_OBS(N_OBS, N_LEVELS) ; |
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195 | POTM_OBS:long_name = "Potential temperature" ; |
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196 | POTM_OBS:units = "Degrees Celsius" ; |
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197 | POTM_OBS:_Fillvalue = 99999.f ; |
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198 | float POTM_Hx(N_OBS, N_LEVELS) ; |
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199 | POTM_Hx:long_name = "Model interpolated potential temperature" ; |
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200 | POTM_Hx:units = "Degrees Celsius" ; |
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201 | POTM_Hx:_Fillvalue = 99999.f ; |
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202 | int POTM_QC(N_OBS) ; |
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203 | POTM_QC:long_name = "Quality on potential temperature" ; |
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204 | POTM_QC:Conventions = "q where q =[0,9]" ; |
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205 | POTM_QC:_Fillvalue = 0 ; |
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206 | int POTM_QC_FLAGS(N_OBS, N_QCF) ; |
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207 | POTM_QC_FLAGS:long_name = "Quality flags on potential temperature" ; |
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208 | POTM_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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209 | POTM_QC_FLAGS:_Fillvalue = 0 ; |
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210 | int POTM_LEVEL_QC(N_OBS, N_LEVELS) ; |
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211 | POTM_LEVEL_QC:long_name = "Quality for each level on potential temperature" ; |
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212 | POTM_LEVEL_QC:Conventions = "q where q =[0,9]" ; |
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213 | POTM_LEVEL_QC:_Fillvalue = 0 ; |
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214 | int POTM_LEVEL_QC_FLAGS(N_OBS, N_LEVELS, N_QCF) ; |
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215 | POTM_LEVEL_QC_FLAGS:long_name = "Quality flags for each level on potential temperature" ; |
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216 | POTM_LEVEL_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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217 | POTM_LEVEL_QC_FLAGS:_Fillvalue = 0 ; |
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218 | int POTM_IOBSI(N_OBS) ; |
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219 | POTM_IOBSI:long_name = "ORCA grid search I coordinate" ; |
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220 | int POTM_IOBSJ(N_OBS) ; |
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221 | POTM_IOBSJ:long_name = "ORCA grid search J coordinate" ; |
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222 | int POTM_IOBSK(N_OBS, N_LEVELS) ; |
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223 | POTM_IOBSK:long_name = "ORCA grid search K coordinate" ; |
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224 | char POTM_GRID(STRINGGRID) ; |
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225 | POTM_GRID:long_name = "ORCA grid search grid (T,U,V)" ; |
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226 | float PSAL_OBS(N_OBS, N_LEVELS) ; |
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227 | PSAL_OBS:long_name = "Practical salinity" ; |
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228 | PSAL_OBS:units = "PSU" ; |
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229 | PSAL_OBS:_Fillvalue = 99999.f ; |
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230 | float PSAL_Hx(N_OBS, N_LEVELS) ; |
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231 | PSAL_Hx:long_name = "Model interpolated practical salinity" ; |
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232 | PSAL_Hx:units = "PSU" ; |
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233 | PSAL_Hx:_Fillvalue = 99999.f ; |
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234 | int PSAL_QC(N_OBS) ; |
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235 | PSAL_QC:long_name = "Quality on practical salinity" ; |
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236 | PSAL_QC:Conventions = "q where q =[0,9]" ; |
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237 | PSAL_QC:_Fillvalue = 0 ; |
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238 | int PSAL_QC_FLAGS(N_OBS, N_QCF) ; |
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239 | PSAL_QC_FLAGS:long_name = "Quality flags on practical salinity" ; |
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240 | PSAL_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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241 | PSAL_QC_FLAGS:_Fillvalue = 0 ; |
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242 | int PSAL_LEVEL_QC(N_OBS, N_LEVELS) ; |
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243 | PSAL_LEVEL_QC:long_name = "Quality for each level on practical salinity" ; |
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244 | PSAL_LEVEL_QC:Conventions = "q where q =[0,9]" ; |
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245 | PSAL_LEVEL_QC:_Fillvalue = 0 ; |
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246 | int PSAL_LEVEL_QC_FLAGS(N_OBS, N_LEVELS, N_QCF) ; |
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247 | PSAL_LEVEL_QC_FLAGS:long_name = "Quality flags for each level on practical salinity" ; |
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248 | PSAL_LEVEL_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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249 | PSAL_LEVEL_QC_FLAGS:_Fillvalue = 0 ; |
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250 | int PSAL_IOBSI(N_OBS) ; |
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251 | PSAL_IOBSI:long_name = "ORCA grid search I coordinate" ; |
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252 | int PSAL_IOBSJ(N_OBS) ; |
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253 | PSAL_IOBSJ:long_name = "ORCA grid search J coordinate" ; |
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254 | int PSAL_IOBSK(N_OBS, N_LEVELS) ; |
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255 | PSAL_IOBSK:long_name = "ORCA grid search K coordinate" ; |
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256 | char PSAL_GRID(STRINGGRID) ; |
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257 | PSAL_GRID:long_name = "ORCA grid search grid (T,U,V)" ; |
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258 | float TEMP(N_OBS, N_LEVELS) ; |
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259 | TEMP:long_name = "Insitu temperature" ; |
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260 | TEMP:units = "Degrees Celsius" ; |
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261 | TEMP:_Fillvalue = 99999.f ; |
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262 | |
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263 | // global attributes: |
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264 | :title = "NEMO observation operator output" ; |
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265 | :Convention = "NEMO unified observation operator output" ; |
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266 | } |
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267 | \end{verbatim} |
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268 | \end{alltt} |
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269 | |
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270 | \subsection{Sea level anomaly feedback type observation file header} |
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271 | |
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272 | \begin{alltt} |
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273 | \tiny |
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274 | \begin{verbatim} |
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275 | netcdf sla_01 { |
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276 | dimensions: |
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277 | N_OBS = 41301 ; |
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278 | N_LEVELS = 1 ; |
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279 | N_VARS = 1 ; |
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280 | N_QCF = 2 ; |
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281 | N_ENTRIES = 1 ; |
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282 | N_EXTRA = 1 ; |
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283 | STRINGNAM = 8 ; |
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284 | STRINGGRID = 1 ; |
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285 | STRINGWMO = 8 ; |
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286 | STRINGTYP = 4 ; |
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287 | STRINGJULD = 14 ; |
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288 | variables: |
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289 | char VARIABLES(N_VARS, STRINGNAM) ; |
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290 | VARIABLES:long_name = "List of variables in feedback files" ; |
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291 | char ENTRIES(N_ENTRIES, STRINGNAM) ; |
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292 | ENTRIES:long_name = "List of additional entries for each variable in feedback files" ; |
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293 | char EXTRA(N_EXTRA, STRINGNAM) ; |
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294 | EXTRA:long_name = "List of extra variables" ; |
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295 | char STATION_IDENTIFIER(N_OBS, STRINGWMO) ; |
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296 | STATION_IDENTIFIER:long_name = "Station identifier" ; |
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297 | char STATION_TYPE(N_OBS, STRINGTYP) ; |
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298 | STATION_TYPE:long_name = "Code instrument type" ; |
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299 | double LONGITUDE(N_OBS) ; |
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300 | LONGITUDE:long_name = "Longitude" ; |
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301 | LONGITUDE:units = "degrees_east" ; |
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302 | LONGITUDE:_Fillvalue = 99999.f ; |
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303 | double LATITUDE(N_OBS) ; |
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304 | LATITUDE:long_name = "Latitude" ; |
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305 | LATITUDE:units = "degrees_north" ; |
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306 | LATITUDE:_Fillvalue = 99999.f ; |
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307 | double DEPTH(N_OBS, N_LEVELS) ; |
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308 | DEPTH:long_name = "Depth" ; |
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309 | DEPTH:units = "metre" ; |
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310 | DEPTH:_Fillvalue = 99999.f ; |
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311 | int DEPTH_QC(N_OBS, N_LEVELS) ; |
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312 | DEPTH_QC:long_name = "Quality on depth" ; |
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313 | DEPTH_QC:Conventions = "q where q =[0,9]" ; |
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314 | DEPTH_QC:_Fillvalue = 0 ; |
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315 | int DEPTH_QC_FLAGS(N_OBS, N_LEVELS, N_QCF) ; |
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316 | DEPTH_QC_FLAGS:long_name = "Quality flags on depth" ; |
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317 | DEPTH_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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318 | double JULD(N_OBS) ; |
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319 | JULD:long_name = "Julian day" ; |
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320 | JULD:units = "days since JULD_REFERENCE" ; |
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321 | JULD:Conventions = "relative julian days with decimal part (as parts of day)" ; |
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322 | JULD:_Fillvalue = 99999.f ; |
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323 | char JULD_REFERENCE(STRINGJULD) ; |
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324 | JULD_REFERENCE:long_name = "Date of reference for julian days" ; |
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325 | JULD_REFERENCE:Conventions = "YYYYMMDDHHMMSS" ; |
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326 | int OBSERVATION_QC(N_OBS) ; |
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327 | OBSERVATION_QC:long_name = "Quality on observation" ; |
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328 | OBSERVATION_QC:Conventions = "q where q =[0,9]" ; |
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329 | OBSERVATION_QC:_Fillvalue = 0 ; |
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330 | int OBSERVATION_QC_FLAGS(N_OBS, N_QCF) ; |
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331 | OBSERVATION_QC_FLAGS:long_name = "Quality flags on observation" ; |
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332 | OBSERVATION_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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333 | OBSERVATION_QC_FLAGS:_Fillvalue = 0 ; |
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334 | int POSITION_QC(N_OBS) ; |
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335 | POSITION_QC:long_name = "Quality on position (latitude and longitude)" ; |
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336 | POSITION_QC:Conventions = "q where q =[0,9]" ; |
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337 | POSITION_QC:_Fillvalue = 0 ; |
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338 | int POSITION_QC_FLAGS(N_OBS, N_QCF) ; |
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339 | POSITION_QC_FLAGS:long_name = "Quality flags on position" ; |
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340 | POSITION_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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341 | POSITION_QC_FLAGS:_Fillvalue = 0 ; |
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342 | int JULD_QC(N_OBS) ; |
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343 | JULD_QC:long_name = "Quality on date and time" ; |
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344 | JULD_QC:Conventions = "q where q =[0,9]" ; |
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345 | JULD_QC:_Fillvalue = 0 ; |
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346 | int JULD_QC_FLAGS(N_OBS, N_QCF) ; |
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347 | JULD_QC_FLAGS:long_name = "Quality flags on date and time" ; |
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348 | JULD_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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349 | JULD_QC_FLAGS:_Fillvalue = 0 ; |
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350 | int ORIGINAL_FILE_INDEX(N_OBS) ; |
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351 | ORIGINAL_FILE_INDEX:long_name = "Index in original data file" ; |
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352 | ORIGINAL_FILE_INDEX:_Fillvalue = -99999 ; |
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353 | float SLA_OBS(N_OBS, N_LEVELS) ; |
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354 | SLA_OBS:long_name = "Sea level anomaly" ; |
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355 | SLA_OBS:units = "metre" ; |
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356 | SLA_OBS:_Fillvalue = 99999.f ; |
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357 | float SLA_Hx(N_OBS, N_LEVELS) ; |
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358 | SLA_Hx:long_name = "Model interpolated sea level anomaly" ; |
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359 | SLA_Hx:units = "metre" ; |
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360 | SLA_Hx:_Fillvalue = 99999.f ; |
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361 | int SLA_QC(N_OBS) ; |
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362 | SLA_QC:long_name = "Quality on sea level anomaly" ; |
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363 | SLA_QC:Conventions = "q where q =[0,9]" ; |
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364 | SLA_QC:_Fillvalue = 0 ; |
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365 | int SLA_QC_FLAGS(N_OBS, N_QCF) ; |
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366 | SLA_QC_FLAGS:long_name = "Quality flags on sea level anomaly" ; |
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367 | SLA_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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368 | SLA_QC_FLAGS:_Fillvalue = 0 ; |
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369 | int SLA_LEVEL_QC(N_OBS, N_LEVELS) ; |
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370 | SLA_LEVEL_QC:long_name = "Quality for each level on sea level anomaly" ; |
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371 | SLA_LEVEL_QC:Conventions = "q where q =[0,9]" ; |
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372 | SLA_LEVEL_QC:_Fillvalue = 0 ; |
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373 | int SLA_LEVEL_QC_FLAGS(N_OBS, N_LEVELS, N_QCF) ; |
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374 | SLA_LEVEL_QC_FLAGS:long_name = "Quality flags for each level on sea level anomaly" ; |
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375 | SLA_LEVEL_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
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376 | SLA_LEVEL_QC_FLAGS:_Fillvalue = 0 ; |
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377 | int SLA_IOBSI(N_OBS) ; |
---|
378 | SLA_IOBSI:long_name = "ORCA grid search I coordinate" ; |
---|
379 | int SLA_IOBSJ(N_OBS) ; |
---|
380 | SLA_IOBSJ:long_name = "ORCA grid search J coordinate" ; |
---|
381 | int SLA_IOBSK(N_OBS, N_LEVELS) ; |
---|
382 | SLA_IOBSK:long_name = "ORCA grid search K coordinate" ; |
---|
383 | char SLA_GRID(STRINGGRID) ; |
---|
384 | SLA_GRID:long_name = "ORCA grid search grid (T,U,V)" ; |
---|
385 | float MDT(N_OBS, N_LEVELS) ; |
---|
386 | MDT:long_name = "Mean Dynamic Topography" ; |
---|
387 | MDT:units = "metre" ; |
---|
388 | MDT:_Fillvalue = 99999.f ; |
---|
389 | |
---|
390 | // global attributes: |
---|
391 | :title = "NEMO observation operator output" ; |
---|
392 | :Convention = "NEMO unified observation operator output" ; |
---|
393 | } |
---|
394 | \end{verbatim} |
---|
395 | \end{alltt} |
---|
396 | |
---|
397 | The mean dynamic |
---|
398 | topography (MDT) must be provided in a separate file defined on the model grid |
---|
399 | called {\it slaReferenceLevel.nc}. The MDT is required in |
---|
400 | order to produce the model equivalent sea level anomaly from the model sea |
---|
401 | surface height. Below is an example header for this file (on the ORCA025 grid). |
---|
402 | |
---|
403 | \begin{alltt} |
---|
404 | \tiny |
---|
405 | \begin{verbatim} |
---|
406 | dimensions: |
---|
407 | x = 1442 ; |
---|
408 | y = 1021 ; |
---|
409 | variables: |
---|
410 | float nav_lon(y, x) ; |
---|
411 | nav_lon:units = "degrees_east" ; |
---|
412 | float nav_lat(y, x) ; |
---|
413 | nav_lat:units = "degrees_north" ; |
---|
414 | float sossheig(y, x) ; |
---|
415 | sossheig:_FillValue = -1.e+30f ; |
---|
416 | sossheig:coordinates = "nav_lon nav_lat" ; |
---|
417 | sossheig:long_name = "Mean Dynamic Topography" ; |
---|
418 | sossheig:units = "metres" ; |
---|
419 | sossheig:grid = "orca025T" ; |
---|
420 | \end{verbatim} |
---|
421 | \end{alltt} |
---|
422 | |
---|
423 | \subsection{Sea surface temperature feedback type observation file header} |
---|
424 | |
---|
425 | \begin{alltt} |
---|
426 | \tiny |
---|
427 | \begin{verbatim} |
---|
428 | netcdf sst_01 { |
---|
429 | dimensions: |
---|
430 | N_OBS = 33099 ; |
---|
431 | N_LEVELS = 1 ; |
---|
432 | N_VARS = 1 ; |
---|
433 | N_QCF = 2 ; |
---|
434 | N_ENTRIES = 1 ; |
---|
435 | STRINGNAM = 8 ; |
---|
436 | STRINGGRID = 1 ; |
---|
437 | STRINGWMO = 8 ; |
---|
438 | STRINGTYP = 4 ; |
---|
439 | STRINGJULD = 14 ; |
---|
440 | variables: |
---|
441 | char VARIABLES(N_VARS, STRINGNAM) ; |
---|
442 | VARIABLES:long_name = "List of variables in feedback files" ; |
---|
443 | char ENTRIES(N_ENTRIES, STRINGNAM) ; |
---|
444 | ENTRIES:long_name = "List of additional entries for each variable in feedback files" ; |
---|
445 | char STATION_IDENTIFIER(N_OBS, STRINGWMO) ; |
---|
446 | STATION_IDENTIFIER:long_name = "Station identifier" ; |
---|
447 | char STATION_TYPE(N_OBS, STRINGTYP) ; |
---|
448 | STATION_TYPE:long_name = "Code instrument type" ; |
---|
449 | double LONGITUDE(N_OBS) ; |
---|
450 | LONGITUDE:long_name = "Longitude" ; |
---|
451 | LONGITUDE:units = "degrees_east" ; |
---|
452 | LONGITUDE:_Fillvalue = 99999.f ; |
---|
453 | double LATITUDE(N_OBS) ; |
---|
454 | LATITUDE:long_name = "Latitude" ; |
---|
455 | LATITUDE:units = "degrees_north" ; |
---|
456 | LATITUDE:_Fillvalue = 99999.f ; |
---|
457 | double DEPTH(N_OBS, N_LEVELS) ; |
---|
458 | DEPTH:long_name = "Depth" ; |
---|
459 | DEPTH:units = "metre" ; |
---|
460 | DEPTH:_Fillvalue = 99999.f ; |
---|
461 | int DEPTH_QC(N_OBS, N_LEVELS) ; |
---|
462 | DEPTH_QC:long_name = "Quality on depth" ; |
---|
463 | DEPTH_QC:Conventions = "q where q =[0,9]" ; |
---|
464 | DEPTH_QC:_Fillvalue = 0 ; |
---|
465 | int DEPTH_QC_FLAGS(N_OBS, N_LEVELS, N_QCF) ; |
---|
466 | DEPTH_QC_FLAGS:long_name = "Quality flags on depth" ; |
---|
467 | DEPTH_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
---|
468 | double JULD(N_OBS) ; |
---|
469 | JULD:long_name = "Julian day" ; |
---|
470 | JULD:units = "days since JULD_REFERENCE" ; |
---|
471 | JULD:Conventions = "relative julian days with decimal part (as parts of day)" ; |
---|
472 | JULD:_Fillvalue = 99999.f ; |
---|
473 | char JULD_REFERENCE(STRINGJULD) ; |
---|
474 | JULD_REFERENCE:long_name = "Date of reference for julian days" ; |
---|
475 | JULD_REFERENCE:Conventions = "YYYYMMDDHHMMSS" ; |
---|
476 | int OBSERVATION_QC(N_OBS) ; |
---|
477 | OBSERVATION_QC:long_name = "Quality on observation" ; |
---|
478 | OBSERVATION_QC:Conventions = "q where q =[0,9]" ; |
---|
479 | OBSERVATION_QC:_Fillvalue = 0 ; |
---|
480 | int OBSERVATION_QC_FLAGS(N_OBS, N_QCF) ; |
---|
481 | OBSERVATION_QC_FLAGS:long_name = "Quality flags on observation" ; |
---|
482 | OBSERVATION_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
---|
483 | OBSERVATION_QC_FLAGS:_Fillvalue = 0 ; |
---|
484 | int POSITION_QC(N_OBS) ; |
---|
485 | POSITION_QC:long_name = "Quality on position (latitude and longitude)" ; |
---|
486 | POSITION_QC:Conventions = "q where q =[0,9]" ; |
---|
487 | POSITION_QC:_Fillvalue = 0 ; |
---|
488 | int POSITION_QC_FLAGS(N_OBS, N_QCF) ; |
---|
489 | POSITION_QC_FLAGS:long_name = "Quality flags on position" ; |
---|
490 | POSITION_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
---|
491 | POSITION_QC_FLAGS:_Fillvalue = 0 ; |
---|
492 | int JULD_QC(N_OBS) ; |
---|
493 | JULD_QC:long_name = "Quality on date and time" ; |
---|
494 | JULD_QC:Conventions = "q where q =[0,9]" ; |
---|
495 | JULD_QC:_Fillvalue = 0 ; |
---|
496 | int JULD_QC_FLAGS(N_OBS, N_QCF) ; |
---|
497 | JULD_QC_FLAGS:long_name = "Quality flags on date and time" ; |
---|
498 | JULD_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
---|
499 | JULD_QC_FLAGS:_Fillvalue = 0 ; |
---|
500 | int ORIGINAL_FILE_INDEX(N_OBS) ; |
---|
501 | ORIGINAL_FILE_INDEX:long_name = "Index in original data file" ; |
---|
502 | ORIGINAL_FILE_INDEX:_Fillvalue = -99999 ; |
---|
503 | float SST_OBS(N_OBS, N_LEVELS) ; |
---|
504 | SST_OBS:long_name = "Sea surface temperature" ; |
---|
505 | SST_OBS:units = "Degree centigrade" ; |
---|
506 | SST_OBS:_Fillvalue = 99999.f ; |
---|
507 | float SST_Hx(N_OBS, N_LEVELS) ; |
---|
508 | SST_Hx:long_name = "Model interpolated sea surface temperature" ; |
---|
509 | SST_Hx:units = "Degree centigrade" ; |
---|
510 | SST_Hx:_Fillvalue = 99999.f ; |
---|
511 | int SST_QC(N_OBS) ; |
---|
512 | SST_QC:long_name = "Quality on sea surface temperature" ; |
---|
513 | SST_QC:Conventions = "q where q =[0,9]" ; |
---|
514 | SST_QC:_Fillvalue = 0 ; |
---|
515 | int SST_QC_FLAGS(N_OBS, N_QCF) ; |
---|
516 | SST_QC_FLAGS:long_name = "Quality flags on sea surface temperature" ; |
---|
517 | SST_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
---|
518 | SST_QC_FLAGS:_Fillvalue = 0 ; |
---|
519 | int SST_LEVEL_QC(N_OBS, N_LEVELS) ; |
---|
520 | SST_LEVEL_QC:long_name = "Quality for each level on sea surface temperature" ; |
---|
521 | SST_LEVEL_QC:Conventions = "q where q =[0,9]" ; |
---|
522 | SST_LEVEL_QC:_Fillvalue = 0 ; |
---|
523 | int SST_LEVEL_QC_FLAGS(N_OBS, N_LEVELS, N_QCF) ; |
---|
524 | SST_LEVEL_QC_FLAGS:long_name = "Quality flags for each level on sea surface temperature" ; |
---|
525 | SST_LEVEL_QC_FLAGS:Conventions = "NEMOVAR flag conventions" ; |
---|
526 | SST_LEVEL_QC_FLAGS:_Fillvalue = 0 ; |
---|
527 | int SST_IOBSI(N_OBS) ; |
---|
528 | SST_IOBSI:long_name = "ORCA grid search I coordinate" ; |
---|
529 | int SST_IOBSJ(N_OBS) ; |
---|
530 | SST_IOBSJ:long_name = "ORCA grid search J coordinate" ; |
---|
531 | int SST_IOBSK(N_OBS, N_LEVELS) ; |
---|
532 | SST_IOBSK:long_name = "ORCA grid search K coordinate" ; |
---|
533 | char SST_GRID(STRINGGRID) ; |
---|
534 | SST_GRID:long_name = "ORCA grid search grid (T,U,V)" ; |
---|
535 | |
---|
536 | // global attributes: |
---|
537 | :title = "NEMO observation operator output" ; |
---|
538 | :Convention = "NEMO unified observation operator output" ; |
---|
539 | } |
---|
540 | \end{verbatim} |
---|
541 | \end{alltt} |
---|
542 | |
---|
543 | \section{Theoretical details} |
---|
544 | \label{OBS_theory} |
---|
545 | |
---|
546 | \subsection{Horizontal interpolation methods} |
---|
547 | |
---|
548 | Consider an observation point ${\rm P}$ with |
---|
549 | with longitude and latitude $({\lambda_{}}_{\rm P}, \phi_{\rm P})$ and the |
---|
550 | four nearest neighbouring model grid points ${\rm A}$, ${\rm B}$, ${\rm C}$ |
---|
551 | and ${\rm D}$ with longitude and latitude ($\lambda_{\rm A}$, $\phi_{\rm A}$), |
---|
552 | ($\lambda_{\rm B}$, $\phi_{\rm B}$) etc. |
---|
553 | All horizontal interpolation methods implemented in NEMO |
---|
554 | estimate the value of a model variable $x$ at point $P$ as |
---|
555 | a weighted linear combination of the values of the model |
---|
556 | variables at the grid points ${\rm A}$, ${\rm B}$ etc.: |
---|
557 | \begin{eqnarray} |
---|
558 | {x_{}}_{\rm P} & \hspace{-2mm} = \hspace{-2mm} & |
---|
559 | \frac{1}{w} \left( {w_{}}_{\rm A} {x_{}}_{\rm A} + |
---|
560 | {w_{}}_{\rm B} {x_{}}_{\rm B} + |
---|
561 | {w_{}}_{\rm C} {x_{}}_{\rm C} + |
---|
562 | {w_{}}_{\rm D} {x_{}}_{\rm D} \right) |
---|
563 | \end{eqnarray} |
---|
564 | where ${w_{}}_{\rm A}$, ${w_{}}_{\rm B}$ etc. are the respective weights for the |
---|
565 | model field at points ${\rm A}$, ${\rm B}$ etc., and |
---|
566 | $w = {w_{}}_{\rm A} + {w_{}}_{\rm B} + {w_{}}_{\rm C} + {w_{}}_{\rm D}$. |
---|
567 | |
---|
568 | Four different possibilities are available for computing the weights. |
---|
569 | |
---|
570 | \begin{enumerate} |
---|
571 | |
---|
572 | \item[1.] {\bf Great-Circle distance-weighted interpolation.} The weights |
---|
573 | are computed as a function of the great-circle distance $s(P, \cdot)$ |
---|
574 | between $P$ and the model grid points $A$, $B$ etc. For example, |
---|
575 | the weight given to the field ${x_{}}_{\rm A}$ is specified as the |
---|
576 | product of the distances from ${\rm P}$ to the other points: |
---|
577 | \begin{eqnarray} |
---|
578 | {w_{}}_{\rm A} = s({\rm P}, {\rm B}) \, s({\rm P}, {\rm C}) \, s({\rm P}, {\rm D}) |
---|
579 | \nonumber |
---|
580 | \end{eqnarray} |
---|
581 | where |
---|
582 | \begin{eqnarray} |
---|
583 | s\left ({\rm P}, {\rm M} \right ) |
---|
584 | & \hspace{-2mm} = \hspace{-2mm} & |
---|
585 | \cos^{-1} \! \left\{ |
---|
586 | \sin {\phi_{}}_{\rm P} \sin {\phi_{}}_{\rm M} |
---|
587 | + \cos {\phi_{}}_{\rm P} \cos {\phi_{}}_{\rm M} |
---|
588 | \cos ({\lambda_{}}_{\rm M} - {\lambda_{}}_{\rm P}) |
---|
589 | \right\} |
---|
590 | \end{eqnarray} |
---|
591 | and $M$ corresponds to $B$, $C$ or $D$. |
---|
592 | A more stable form of the great-circle distance formula for |
---|
593 | small distances ($x$ near 1) involves the arcsine function |
---|
594 | ($e.g.$ see p.~101 of \citet{Daley_Barker_Bk01}: |
---|
595 | \begin{eqnarray} |
---|
596 | s\left( {\rm P}, {\rm M} \right) |
---|
597 | & \hspace{-2mm} = \hspace{-2mm} & |
---|
598 | \sin^{-1} \! \left\{ \sqrt{ 1 - x^2 } \right\} |
---|
599 | \nonumber |
---|
600 | \end{eqnarray} |
---|
601 | where |
---|
602 | \begin{eqnarray} |
---|
603 | x & \hspace{-2mm} = \hspace{-2mm} & |
---|
604 | {a_{}}_{\rm M} {a_{}}_{\rm P} + {b_{}}_{\rm M} {b_{}}_{\rm P} + {c_{}}_{\rm M} {c_{}}_{\rm P} |
---|
605 | \nonumber |
---|
606 | \end{eqnarray} |
---|
607 | and |
---|
608 | \begin{eqnarray} |
---|
609 | {a_{}}_{\rm M} & \hspace{-2mm} = \hspace{-2mm} & \sin {\phi_{}}_{\rm M}, |
---|
610 | \nonumber \\ |
---|
611 | {a_{}}_{\rm P} & \hspace{-2mm} = \hspace{-2mm} & \sin {\phi_{}}_{\rm P}, |
---|
612 | \nonumber \\ |
---|
613 | {b_{}}_{\rm M} & \hspace{-2mm} = \hspace{-2mm} & \cos {\phi_{}}_{\rm M} \cos {\phi_{}}_{\rm M}, |
---|
614 | \nonumber \\ |
---|
615 | {b_{}}_{\rm P} & \hspace{-2mm} = \hspace{-2mm} & \cos {\phi_{}}_{\rm P} \cos {\phi_{}}_{\rm P}, |
---|
616 | \nonumber \\ |
---|
617 | {c_{}}_{\rm M} & \hspace{-2mm} = \hspace{-2mm} & \cos {\phi_{}}_{\rm M} \sin {\phi_{}}_{\rm M}, |
---|
618 | \nonumber \\ |
---|
619 | {c_{}}_{\rm P} & \hspace{-2mm} = \hspace{-2mm} & \cos {\phi_{}}_{\rm P} \sin {\phi_{}}_{\rm P}. |
---|
620 | \nonumber |
---|
621 | \nonumber |
---|
622 | \end{eqnarray} |
---|
623 | |
---|
624 | \item[2.] {\bf Great-Circle distance-weighted interpolation with small angle |
---|
625 | approximation.} Similar to the previous interpolation but with the |
---|
626 | distance $s$ computed as |
---|
627 | \begin{eqnarray} |
---|
628 | s\left( {\rm P}, {\rm M} \right) |
---|
629 | & \hspace{-2mm} = \hspace{-2mm} & |
---|
630 | \sqrt{ \left( {\phi_{}}_{\rm M} - {\phi_{}}_{\rm P} \right)^{2} |
---|
631 | + \left( {\lambda_{}}_{\rm M} - {\lambda_{}}_{\rm P} \right)^{2} |
---|
632 | \cos^{2} {\phi_{}}_{\rm M} } |
---|
633 | \end{eqnarray} |
---|
634 | where $M$ corresponds to $A$, $B$, $C$ or $D$. |
---|
635 | |
---|
636 | \item[3.] {\bf Bilinear interpolation for a regular spaced grid.} The |
---|
637 | interpolation is split into two 1D interpolations in the longitude |
---|
638 | and latitude directions, respectively. |
---|
639 | |
---|
640 | \item[4.] {\bf Bilinear remapping interpolation for a general grid.} An |
---|
641 | iterative scheme that involves first mapping a quadrilateral cell |
---|
642 | into a cell with coordinates (0,0), (1,0), (0,1) and (1,1). This |
---|
643 | method is based on the SCRIP interpolation package \citep{Jones_1998}. |
---|
644 | |
---|
645 | \end{enumerate} |
---|
646 | |
---|
647 | \subsection{Grid search} |
---|
648 | |
---|
649 | For many grids used by the NEMO model, such as the ORCA family, |
---|
650 | the horizontal grid coordinates $i$ and $j$ are not simple functions |
---|
651 | of latitude and longitude. Therefore, it is not always straightforward |
---|
652 | to determine the grid points surrounding any given observational position. |
---|
653 | Before the interpolation can be performed, a search |
---|
654 | algorithm is then required to determine the corner points of |
---|
655 | the quadrilateral cell in which the observation is located. |
---|
656 | This is the most difficult and time consuming part of the |
---|
657 | 2D interpolation procedure. |
---|
658 | A robust test for determining if an observation falls |
---|
659 | within a given quadrilateral cell is as follows. Let |
---|
660 | ${\rm P}({\lambda_{}}_{\rm P} ,{\phi_{}}_{\rm P} )$ denote the observation point, |
---|
661 | and let ${\rm A}({\lambda_{}}_{\rm A} ,{\phi_{}}_{\rm A} )$, |
---|
662 | ${\rm B}({\lambda_{}}_{\rm B} ,{\phi_{}}_{\rm B} )$, |
---|
663 | ${\rm C}({\lambda_{}}_{\rm C} ,{\phi_{}}_{\rm C} )$ |
---|
664 | and |
---|
665 | ${\rm D}({\lambda_{}}_{\rm D} ,{\phi_{}}_{\rm D} )$ denote |
---|
666 | the bottom left, bottom right, top left and top right |
---|
667 | corner points of the cell, respectively. |
---|
668 | To determine if P is inside |
---|
669 | the cell, we verify that the cross-products |
---|
670 | \begin{eqnarray} |
---|
671 | \begin{array}{lllll} |
---|
672 | {{\bf r}_{}}_{\rm PA} \times {{\bf r}_{}}_{\rm PC} |
---|
673 | & = & [({\lambda_{}}_{\rm A}\; -\; {\lambda_{}}_{\rm P} ) |
---|
674 | ({\phi_{}}_{\rm C} \; -\; {\phi_{}}_{\rm P} ) |
---|
675 | - ({\lambda_{}}_{\rm C}\; -\; {\lambda_{}}_{\rm P} ) |
---|
676 | ({\phi_{}}_{\rm A} \; -\; {\phi_{}}_{\rm P} )] \; \widehat{\bf k} \\ |
---|
677 | {{\bf r}_{}}_{\rm PB} \times {{\bf r}_{}}_{\rm PA} |
---|
678 | & = & [({\lambda_{}}_{\rm B}\; -\; {\lambda_{}}_{\rm P} ) |
---|
679 | ({\phi_{}}_{\rm A} \; -\; {\phi_{}}_{\rm P} ) |
---|
680 | - ({\lambda_{}}_{\rm A}\; -\; {\lambda_{}}_{\rm P} ) |
---|
681 | ({\phi_{}}_{\rm B} \; -\; {\phi_{}}_{\rm P} )] \; \widehat{\bf k} \\ |
---|
682 | {{\bf r}_{}}_{\rm PC} \times {{\bf r}_{}}_{\rm PD} |
---|
683 | & = & [({\lambda_{}}_{\rm C}\; -\; {\lambda_{}}_{\rm P} ) |
---|
684 | ({\phi_{}}_{\rm D} \; -\; {\phi_{}}_{\rm P} ) |
---|
685 | - ({\lambda_{}}_{\rm D}\; -\; {\lambda_{}}_{\rm P} ) |
---|
686 | ({\phi_{}}_{\rm C} \; -\; {\phi_{}}_{\rm P} )] \; \widehat{\bf k} \\ |
---|
687 | {{\bf r}_{}}_{\rm PD} \times {{\bf r}_{}}_{\rm PB} |
---|
688 | & = & [({\lambda_{}}_{\rm D}\; -\; {\lambda_{}}_{\rm P} ) |
---|
689 | ({\phi_{}}_{\rm B} \; -\; {\phi_{}}_{\rm P} ) |
---|
690 | - ({\lambda_{}}_{\rm B}\; -\; {\lambda_{}}_{\rm P} ) |
---|
691 | ({\phi_{}}_{\rm D} \; - \; {\phi_{}}_{\rm P} )] \; \widehat{\bf k} \\ |
---|
692 | \end{array} |
---|
693 | \label{eq:cross} |
---|
694 | \end{eqnarray} |
---|
695 | point in the opposite direction to the unit normal |
---|
696 | $\widehat{\bf k}$ (i.e., that the coefficients of |
---|
697 | $\widehat{\bf k}$ are negative), |
---|
698 | where ${{\bf r}_{}}_{\rm PA}$, ${{\bf r}_{}}_{\rm PB}$, |
---|
699 | etc. correspond to the vectors between points P and A, |
---|
700 | P and B, etc.. The method used is |
---|
701 | similar to the method used in |
---|
702 | the SCRIP interpolation package \citep{Jones_1998}. |
---|
703 | |
---|
704 | In order to speed up the grid search, there is the possibility to construct |
---|
705 | a lookup table for a user specified resolution. This lookup |
---|
706 | table contains the lower and upper bounds on the $i$ and $j$ indices |
---|
707 | to be searched for on a regular grid. For each observation position, |
---|
708 | the closest point on the regular grid of this position is computed and |
---|
709 | the $i$ and $j$ ranges of this point searched to determine the precise |
---|
710 | four points surrounding the observation. |
---|
711 | |
---|
712 | \subsection{Parallel aspects of horizontal interpolation} |
---|
713 | \label{OBS_parallel} |
---|
714 | |
---|
715 | For horizontal interpolation, there is the basic problem that the |
---|
716 | observations are unevenly distributed on the globe. In numerical |
---|
717 | models, it is common to divide the model grid into subgrids (or |
---|
718 | domains) where each subgrid is executed on a single processing element |
---|
719 | with explicit message passing for exchange of information along the |
---|
720 | domain boundaries when running on a massively parallel processor (MPP) |
---|
721 | system. This approach is used by \NEMO. |
---|
722 | |
---|
723 | For observations there is no natural distribution since the |
---|
724 | observations are not equally distributed on the globe. |
---|
725 | Two options have been made available: 1) geographical distribution; |
---|
726 | and 2) round-robin. |
---|
727 | |
---|
728 | \subsubsection{Geographical distribution of observations among processors} |
---|
729 | |
---|
730 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
731 | \begin{figure} \begin{center} |
---|
732 | \includegraphics[width=10cm,height=12cm,angle=-90.]{./TexFiles/Figures/Fig_ASM_obsdist_local} |
---|
733 | \caption{ \label{fig:obslocal} |
---|
734 | Example of the distribution of observations with the geographical distribution of observational data.} |
---|
735 | \end{center} \end{figure} |
---|
736 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
737 | |
---|
738 | This is the simplest option in which the observations are distributed according |
---|
739 | to the domain of the grid-point parallelization. Figure~\ref{fig:obslocal} |
---|
740 | shows an example of the distribution of the {\em in situ} data on processors |
---|
741 | with a different colour for each observation |
---|
742 | on a given processor for a 4 $\times$ 2 decomposition with ORCA2. |
---|
743 | The grid-point domain decomposition is clearly visible on the plot. |
---|
744 | |
---|
745 | The advantage of this approach is that all |
---|
746 | information needed for horizontal interpolation is available without |
---|
747 | any MPP communication. Of course, this is under the assumption that |
---|
748 | we are only using a $2 \times 2$ grid-point stencil for the interpolation |
---|
749 | (e.g., bilinear interpolation). For higher order interpolation schemes this |
---|
750 | is no longer valid. A disadvantage with the above scheme is that the number of |
---|
751 | observations on each processor can be very different. If the cost of |
---|
752 | the actual interpolation is expensive relative to the communication of |
---|
753 | data needed for interpolation, this could lead to load imbalance. |
---|
754 | |
---|
755 | \subsubsection{Round-robin distribution of observations among processors} |
---|
756 | |
---|
757 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
758 | \begin{figure} \begin{center} |
---|
759 | \includegraphics[width=10cm,height=12cm,angle=-90.]{./TexFiles/Figures/Fig_ASM_obsdist_global} |
---|
760 | \caption{ \label{fig:obsglobal} |
---|
761 | Example of the distribution of observations with the round-robin distribution of observational data.} |
---|
762 | \end{center} \end{figure} |
---|
763 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
764 | |
---|
765 | An alternative approach is to distribute the observations equally |
---|
766 | among processors and use message passing in order to retrieve |
---|
767 | the stencil for interpolation. The simplest distribution of the observations |
---|
768 | is to distribute them using a round-robin scheme. Figure~\ref{fig:obsglobal} |
---|
769 | shows the distribution of the {\em in situ} data on processors for the |
---|
770 | round-robin distribution of observations with a different colour for |
---|
771 | each observation on a given processor for a 4 $\times$ 2 decomposition |
---|
772 | with ORCA2 for the same input data as in Fig.~\ref{fig:obslocal}. |
---|
773 | The observations are now clearly randomly distributed on the globe. |
---|
774 | In order to be able to perform horizontal interpolation in this case, |
---|
775 | a subroutine has been developed that retrieves any grid points in the |
---|
776 | global space. |
---|
777 | |
---|
778 | \subsection{Vertical interpolation operator} |
---|
779 | |
---|
780 | Vertical interpolation is achieved using either a cubic spline or |
---|
781 | linear interpolation. For the cubic spline, the top and |
---|
782 | bottom boundary conditions for the second derivative of the |
---|
783 | interpolating polynomial in the spline are set to zero. |
---|
784 | At the bottom boundary, this is done using the land-ocean mask. |
---|
785 | |
---|
786 | \newpage |
---|
787 | |
---|
788 | \section{Observation Utilities} |
---|
789 | \label{OBS_obsutils} |
---|
790 | |
---|
791 | Some tools for viewing and processing of observation and feedback files are provided in the |
---|
792 | NEMO repository for convenience. These include OBSTOOLS which are a collection of Fortran |
---|
793 | programs which are helpful to deal with feedback files. They do such tasks as observation file |
---|
794 | conversion, printing of file contents, some basic statistical analysis of feedback files. The |
---|
795 | other tool is an IDL program called dataplot which uses a graphical interface to visualise |
---|
796 | observations and feedback files. OBSTOOLS and dataplot are described in more detail below. |
---|
797 | |
---|
798 | \subsection{Obstools} |
---|
799 | |
---|
800 | A series of Fortran utilities is provided with NEMO called OBSTOOLS. This are helpful in |
---|
801 | handling observation files and the feedback file output from the NEMO observation operator. |
---|
802 | The utilities are as follows |
---|
803 | |
---|
804 | \subsubsection{corio2fb} |
---|
805 | |
---|
806 | The program corio2fb converts profile observation files from the Coriolis format to the |
---|
807 | standard feedback format. The program is called in the following way: |
---|
808 | |
---|
809 | \begin{alltt} |
---|
810 | \footnotesize |
---|
811 | \begin{verbatim} |
---|
812 | corio2fb.exe outputfile inputfile1 inputfile2 ... |
---|
813 | \end{verbatim} |
---|
814 | \end{alltt} |
---|
815 | |
---|
816 | \subsubsection{enact2fb} |
---|
817 | |
---|
818 | The program enact2fb converts profile observation files from the ENACT format to the standard |
---|
819 | feedback format. The program is called in the following way: |
---|
820 | |
---|
821 | \begin{alltt} |
---|
822 | \footnotesize |
---|
823 | \begin{verbatim} |
---|
824 | enact2fb.exe outputfile inputfile1 inputfile2 ... |
---|
825 | \end{verbatim} |
---|
826 | \end{alltt} |
---|
827 | |
---|
828 | \subsubsection{fbcomb} |
---|
829 | |
---|
830 | The program fbcomb combines multiple feedback files produced by individual processors in an |
---|
831 | MPI run of NEMO into a single feedback file. The program is called in the following way: |
---|
832 | |
---|
833 | \begin{alltt} |
---|
834 | \footnotesize |
---|
835 | \begin{verbatim} |
---|
836 | fbcomb.exe outputfile inputfile1 inputfile2 ... |
---|
837 | \end{verbatim} |
---|
838 | \end{alltt} |
---|
839 | |
---|
840 | \subsubsection{fbmatchup} |
---|
841 | |
---|
842 | The program fbmatchup will match observations from two feedback files. The program is called |
---|
843 | in the following way: |
---|
844 | |
---|
845 | \begin{alltt} |
---|
846 | \footnotesize |
---|
847 | \begin{verbatim} |
---|
848 | fbmatchup.exe outputfile inputfile1 varname1 inputfile2 varname2 ... |
---|
849 | \end{verbatim} |
---|
850 | \end{alltt} |
---|
851 | |
---|
852 | |
---|
853 | \subsubsection{fbprint} |
---|
854 | |
---|
855 | The program fbprint will print the contents of a feedback file or files to standard output. |
---|
856 | Selected information can be output using optional arguments. The program is called in the |
---|
857 | following way: |
---|
858 | |
---|
859 | \begin{alltt} |
---|
860 | \footnotesize |
---|
861 | \begin{verbatim} |
---|
862 | fbprint.exe [options] inputfile |
---|
863 | |
---|
864 | options: |
---|
865 | -b shorter output |
---|
866 | -q Select observations based on QC flags |
---|
867 | -Q Select observations based on QC flags |
---|
868 | -B Select observations based on QC flags |
---|
869 | -u unsorted |
---|
870 | -s ID select station ID |
---|
871 | -t TYPE select observation type |
---|
872 | -v NUM1-NUM2 select variable range to print by number |
---|
873 | (default all) |
---|
874 | -a NUM1-NUM2 select additional variable range to print by number |
---|
875 | (default all) |
---|
876 | -e NUM1-NUM2 select extra variable range to print by number |
---|
877 | (default all) |
---|
878 | -d output date range |
---|
879 | -D print depths |
---|
880 | -z use zipped files |
---|
881 | \end{verbatim} |
---|
882 | \end{alltt} |
---|
883 | |
---|
884 | \subsubsection{fbsel} |
---|
885 | |
---|
886 | The program fbsel will select or subsample observations. The program is called in the |
---|
887 | following way: |
---|
888 | |
---|
889 | \begin{alltt} |
---|
890 | \footnotesize |
---|
891 | \begin{verbatim} |
---|
892 | fbsel.exe <input filename> <output filename> |
---|
893 | \end{verbatim} |
---|
894 | \end{alltt} |
---|
895 | |
---|
896 | \subsubsection{fbstat} |
---|
897 | |
---|
898 | The program fbstat will output summary statistics in different global areas into a number of |
---|
899 | files. The program is called in the following way: |
---|
900 | |
---|
901 | \begin{alltt} |
---|
902 | \footnotesize |
---|
903 | \begin{verbatim} |
---|
904 | fbstat.exe [-nmlev] <filenames> |
---|
905 | \end{verbatim} |
---|
906 | \end{alltt} |
---|
907 | |
---|
908 | \subsubsection{fbthin} |
---|
909 | |
---|
910 | The program fbthin will thin the data to 1 degree resolution. The code could easily be |
---|
911 | modified to thin to a different resolution. The program is called in the following way: |
---|
912 | |
---|
913 | \begin{alltt} |
---|
914 | \footnotesize |
---|
915 | \begin{verbatim} |
---|
916 | fbthin.exe inputfile outputfile |
---|
917 | \end{verbatim} |
---|
918 | \end{alltt} |
---|
919 | |
---|
920 | \subsubsection{sla2fb} |
---|
921 | |
---|
922 | The program sla2fb will convert an AVISO SLA format file to feedback format. The program is |
---|
923 | called in the following way: |
---|
924 | |
---|
925 | \begin{alltt} |
---|
926 | \footnotesize |
---|
927 | \begin{verbatim} |
---|
928 | sla2fb.exe [-s type] outputfile inputfile1 inputfile2 ... |
---|
929 | |
---|
930 | Option: |
---|
931 | -s Select altimeter data_source |
---|
932 | \end{verbatim} |
---|
933 | \end{alltt} |
---|
934 | |
---|
935 | \subsubsection{vel2fb} |
---|
936 | |
---|
937 | The program vel2fb will convert TAO/PIRATA/RAMA currents files to feedback format. The program |
---|
938 | is called in the following way: |
---|
939 | |
---|
940 | \begin{alltt} |
---|
941 | \footnotesize |
---|
942 | \begin{verbatim} |
---|
943 | vel2fb.exe outputfile inputfile1 inputfile2 ... |
---|
944 | \end{verbatim} |
---|
945 | \end{alltt} |
---|
946 | |
---|
947 | \subsection{building the obstools} |
---|
948 | |
---|
949 | To build the obstools use in the tools directory use ./maketools -n OBSTOOLS -m [ARCH]. |
---|
950 | |
---|
951 | \subsection{Dataplot} |
---|
952 | |
---|
953 | An IDL program called dataplot is included which uses a graphical interface to visualise |
---|
954 | observations and feedback files. It is possible to zoom in, plot individual profiles and |
---|
955 | calculate some basic statistics. To plot some data run IDL and then: |
---|
956 | \begin{alltt} |
---|
957 | \footnotesize |
---|
958 | \begin{verbatim} |
---|
959 | IDL> dataplot, "filename" |
---|
960 | \end{verbatim} |
---|
961 | \end{alltt} |
---|
962 | |
---|
963 | To read multiple files into dataplot, for example multiple feedback files from different |
---|
964 | processors or from different days, the easiest method is to use the spawn command to generate |
---|
965 | a list of files which can then be passed to dataplot. |
---|
966 | \begin{alltt} |
---|
967 | \footnotesize |
---|
968 | \begin{verbatim} |
---|
969 | IDL> spawn, 'ls profb*.nc', files |
---|
970 | IDL> dataplot, files |
---|
971 | \end{verbatim} |
---|
972 | \end{alltt} |
---|
973 | |
---|
974 | Fig~\ref{fig:obsdataplotmain} shows the main window which is launched when dataplot starts. |
---|
975 | This is split into three parts. At the top there is a menu bar which contains a variety of |
---|
976 | drop down menus. Areas - zooms into prespecified regions; plot - plots the data as a |
---|
977 | timeseries or a T-S diagram if appropriate; Find - allows data to be searched; Config - sets |
---|
978 | various configuration options. |
---|
979 | |
---|
980 | The middle part is a plot of the geographical location of the observations. This will plot the |
---|
981 | observation value, the model background value or observation minus background value depending |
---|
982 | on the option selected in the radio button at the bottom of the window. The plotting colour |
---|
983 | range can be changed by clicking on the colour bar. The title of the plot gives some basic |
---|
984 | information about the date range and depth range shown, the extreme values, and the mean and |
---|
985 | rms values. It is possible to zoom in using a drag-box. You may also zoom in or out using the |
---|
986 | mouse wheel. |
---|
987 | |
---|
988 | The bottom part of the window controls what is visible in the plot above. There are two bars |
---|
989 | which select the level range plotted (for profile data). The other bars below select the date |
---|
990 | range shown. The bottom of the figure allows the option to plot the mean, root mean square, |
---|
991 | standard deviation or mean square values. As mentioned above you can choose to plot the |
---|
992 | observation value, the model background value or observation minus background value. The next |
---|
993 | group of radio buttons selects the map projection. This can either be regular latitude |
---|
994 | longitude grid, or north or south polar stereographic. The next group of radio buttons will |
---|
995 | plot bad observations, switch to salinity and plot density for profile observations. The |
---|
996 | rightmost group of buttons will print the plot window as a postscript, save it as png, or exit |
---|
997 | from dataplot. |
---|
998 | |
---|
999 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
1000 | \begin{figure} \begin{center} |
---|
1001 | %\includegraphics[width=10cm,height=12cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_main} |
---|
1002 | \includegraphics[width=9cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_main} |
---|
1003 | \caption{ \label{fig:obsdataplotmain} |
---|
1004 | Main window of dataplot.} |
---|
1005 | \end{center} \end{figure} |
---|
1006 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
1007 | |
---|
1008 | If a profile point is clicked with the mouse button a plot of the observation and background |
---|
1009 | values as a function of depth (Fig~\ref{fig:obsdataplotprofile}). |
---|
1010 | |
---|
1011 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
1012 | \begin{figure} \begin{center} |
---|
1013 | %\includegraphics[width=10cm,height=12cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_prof} |
---|
1014 | \includegraphics[width=7cm,angle=-90.]{./TexFiles/Figures/Fig_OBS_dataplot_prof} |
---|
1015 | \caption{ \label{fig:obsdataplotprofile} |
---|
1016 | Profile plot from dataplot produced by right clicking on a point in the main window.} |
---|
1017 | \end{center} \end{figure} |
---|
1018 | %>>>>>>>>>>>>>>>>>>>>>>>>>>>> |
---|
1019 | |
---|
1020 | |
---|
1021 | |
---|
1022 | |
---|