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- 2017-12-14T15:48:12+01:00 (6 years ago)
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branches/2017/dev_merge_2017/DOC/TexFiles/Chapters/Chap_OBS.tex
r6997 r9052 27 27 is set to true. 28 28 29 For all data types a 2D horizontal interpolator is needed to interpolate the model fields to29 For all data types a 2D horizontal interpolator or averager is needed to interpolate/average the model fields to 30 30 the observation location. For {\em in situ} profiles, a 1D vertical interpolator is needed in 31 addition to provide model fields at the observation depths. Currently this only works in 32 z-level model configurations, but is being developed to work with a generalised vertical 31 addition to provide model fields at the observation depths. This now works in a generalised vertical 33 32 coordinate system. 34 33 35 34 Some profile observation types (e.g. tropical moored buoys) are made available as daily averaged quantities. 36 The observation operator code can be set-up to calculate dthe equivalent daily average model temperature fields35 The observation operator code can be set-up to calculate the equivalent daily average model temperature fields 37 36 using the \np{nn\_profdavtypes} namelist array. Some SST observations are equivalent to a night-time 38 37 average value and the observation operator code can calculate equivalent night-time average model SST fields by … … 40 39 observation time is used. 41 40 42 The code is controlled by the namelist \textit{nam \_obs}. See the following sections for more41 The code is controlled by the namelist \textit{namobs}. See the following sections for more 43 42 details on setting up the namelist. 44 43 … … 560 559 \label{OBS_theory} 561 560 562 \subsection{Horizontal interpolation methods} 563 561 \subsection{Horizontal interpolation and averaging methods} 562 563 For most observation types, the horizontal extent of the observation is small compared to the model grid size 564 and so the model equivalent of the observation is calculated by interpolating from the four surrounding grid 565 points to the observation location. Some satellite observations (e.g. microwave satellite SST data, or satellite SSS data) 566 have a footprint which is similar in size or larger than the model grid size (particularly when the grid size is small). 567 In those cases the model counterpart should be calculated by averaging the model grid points over the same size as the footprint. 568 NEMO therefore has the capability to specify either an interpolation or an averaging (for surface observation types only). 569 570 The main namelist option associated with the interpolation/averaging is \np{nn\_2dint}. This default option can be set to values from 0 to 6. 571 Values between 0 to 4 are associated with interpolation while values 5 or 6 are associated with averaging. 572 \begin{itemize} 573 \item \np{nn\_2dint}=0: Distance-weighted interpolation 574 \item \np{nn\_2dint}=1: Distance-weighted interpolation (small angle) 575 \item \np{nn\_2dint}=2: Bilinear interpolation (geographical grid) 576 \item \np{nn\_2dint}=3: Bilinear remapping interpolation (general grid) 577 \item \np{nn\_2dint}=4: Polynomial interpolation 578 \item \np{nn\_2dint}=5: Radial footprint averaging with diameter specified in the namelist as \np{rn\_???\_avglamscl} in degrees or metres (set using \np{ln\_???\_fp\_indegs}) 579 \item \np{nn\_2dint}=6: Rectangular footprint averaging with E/W and N/S size specified in the namelist as \np{rn\_???\_avglamscl} and \np{rn\_???\_avgphiscl} in degrees or metres (set using \np{ln\_???\_fp\_indegs}) 580 \end{itemize} 581 The ??? in the last two options indicate these options should be specified for each observation type for which the averaging is to be performed (see namelist example above). 582 The \np{nn\_2dint} default option can be overridden for surface observation types using namelist values \np{nn\_2dint\_???} where ??? is one of sla,sst,sss,sic. 583 584 Below is some more detail on the various options for interpolation and averaging available in NEMO. 585 586 \subsubsection{Horizontal interpolation} 564 587 Consider an observation point ${\rm P}$ with 565 588 with longitude and latitude $({\lambda_{}}_{\rm P}, \phi_{\rm P})$ and the … … 660 683 661 684 \end{enumerate} 685 686 \subsubsection{Horizontal averaging} 687 688 For each surface observation type: 689 \begin{itemize} 690 \item The standard grid-searching code is used to find the nearest model grid point to the observation location (see next subsection). 691 \item The maximum number of grid points is calculated in the local grid domain for which the averaging is likely need to cover. 692 \item The lats/longs of the grid points surrounding the nearest model grid box are extracted using existing mpi routines. 693 \item The weights for each grid point associated with each observation are calculated, either for radial or rectangular footprints. For grid points completely within the footprint, the weight is one; for grid points completely outside the footprint, the weight is zero. For grid points which are partly within the footprint the ratio between the area of the footprint within the grid box and the total area of the grid box is used as the weight. 694 \item The weighted average of the model grid points associated with each observation is calculated, and this is then given as the model counterpart of the observation. 695 \end{itemize} 696 697 Examples of the weights calculated for an observation with rectangular and radial footprints are shown in Figs.~\ref{fig:obsavgrec} and~\ref{fig:obsavgrad}. 698 699 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 700 \begin{figure} \begin{center} 701 \includegraphics[width=0.90\textwidth]{Fig_OBS_avg_rec} 702 \caption{ \label{fig:obsavgrec} 703 Weights associated with each model grid box (blue lines and numbers) for an observation at -170.5E, 56.0N with a rectangular footprint of 1\deg x 1\deg.} 704 \end{center} \end{figure} 705 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 706 707 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 708 \begin{figure} \begin{center} 709 \includegraphics[width=0.90\textwidth]{Fig_OBS_avg_rad} 710 \caption{ \label{fig:obsavgrad} 711 Weights associated with each model grid box (blue lines and numbers) for an observation at -170.5E, 56.0N with a radial footprint with diameter 1\deg.} 712 \end{center} \end{figure} 713 %>>>>>>>>>>>>>>>>>>>>>>>>>>>> 714 662 715 663 716 \subsection{Grid search}
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