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Intermediary files
The files required to run the main ORAC processor are,
| # | Default name | Descriptive name | Type | Purpose |
|---|---|---|---|---|
| 1 | User_defined.txt | Driver file | ASCII | Specifies data files, relevant folders, and channels to consider |
| 2 | INST_ChX.sad | Channel specification file | ASCII | Defines the principal characteristics of a particular instrument channel |
| 3 | INST_CLASS_LUT_ChX.sav | LUT file | ASCII | Look-up table LUT of cloud radiative properties for particle model CLASS |
| 4 | User_defined.alb.nc | Albedo file | NCDF | Surface albedo data by pixel |
| 5 | User_defined.clf.nc | Cloud flag file | NCDF | Cloud flagging bit map by pixel |
| 6 | User_defined.geo.nc | Geometetry file | NCDF | Satellite/solar/relative viewing angles by pixel |
| 7 | User_defined.loc.nc | Geolocation file | NCDF | Lat/lon by pixel |
| 8 | User_defined.lsf.nc | Land-sea file | NCDF | Land-sea flag by pixel |
| 9 | User_defined.lwrtm.nc | LW-RTM file | NCDF | Atmospheric RT results in the longwave |
| 10 | User_defined.msi.nc | Imagery file | NCDF | Multi-spectral imagery data by pixel |
| 11 | User_defined.prtm.nc | RTM profile file | NCDF | Profile data (T,p) used in RTM calculations |
| 12 | User_defined.swrtm.nc | SW-RTM file | NCDF | Atmospheric RT results in the shortwave |
| 13 | User_defined.config.nc | Configuration file | NCDF | Summarises the channel configuration |
This is the driver file for the ORAC system, outlined here.
Using MODIS as an example the default value for Ctrl%ReChans is
Ctrl%ReChans=20,6,7,5
Ctrl%ReChans must have 4 elements based on the length of
Ctrl%r_e_chans=5,6,7,20 (the set of candidate Re channels).
If 5,6,7,20 are given to ORAC (with the bits for all Re channel set in the channel bit mask in the driver file) then it will choose one Re channel based on availability and decreasing priority in the Ctrl%ReChans list. So if 20 is available then 20 is used or if 20 and 6 are not available then 7 is used. If for example you don't want 6 to ever be used then use
Ctrl%ReChans = 20,0,7,5
For Aqua you might want to use
Ctrl%ReChans = 20,7,6,5
If you want more control and don't want ORAC to chose just one effective radius channel then use
Ctrl%ReChans = 0,0,0,0
which basically turns this feature off. In which case it will use whatever is set in the channel bit mask even if more than one Re channel is set.
Each channel for each instrument has an associated file giving its principal characteristics. The file name is constructed as in the section title using the instrument code and the channel identifier. The identifier convention is that ascending number corresponds to increasing wavelength. However, this need not be strictly adhered to. The only requirement is that all channels with solar contributions are numbered below those with only thermal contributions. (For example, the order [Ch1=0.67, Ch2=0.87, Ch3=11] is conventional, [Ch1=0.87, Ch2=0.67, Ch3=11] is acceptable, while [Ch1=0.67, Ch2=11, Ch3=0.87] is not acceptable.) Modifications to these files should be limited to the system administrator. A sample specification file for the ATSR-2 3.7um channel is given below.
ATSR-2_Ch5.sad % Channel characterisation file
3.7 um % Descriptor SAD_CHAN()%Desc
Ch5 % File ID SAD_CHAN()%Fileid
2715.30 % Central wavenmuber SAD_CHAN()%Wvn
1 % Thermal source flag SAD_CHAN()%Thermal%Flag
238452.0 % Planck coefficient 1 SAD_CHAN()%Thermal%B1
3885.87 % Planck coefficient 2 SAD_CHAN()%Thermal%B2
-2.041717 % Planck coefficient 3 SAD_CHAN()%Thermal%T1
1.005042 % Planck coefficient 4 SAD_CHAN()%Thermal%T2
.5,.5,1.,.5,.5 % Thermal noise Eqv Homog SAD_CHAN()%Thermal%NeHomog
.15,.15,1.,.25,.25 % Thermal noise Eqv Coreg SAD_CHAN()%Thermal%NeCoreg
0.28 % Thermal NeBT SAD_CHAN()%Thermal%NeBT
1 % Solar source flag SAD_CHAN()%Solar%Flag
5.39,0.177 % Solar constant SAD_CHAN()%Solar%F0,F1
.5,.5,1.,.5,.5 % Solar noise Eqv Homog SAD_CHAN()%Solar%NeHomog
.15,.15,1.,.25,.25 % Solar noise Eqv Coreg SAD_CHAN()%Solar%NeCoreg
0.0 % Solar NeFR SAD_CHAN()%Solar%NeFR
0.01 1.0 % 'typical' sea/land refl SAD_CHAN()%Solar%Rs(2)
This channel is chosen as an example because it has both solar and thermal components and hence the characterisation file is more complete than most other channels. If a source (thermal or solar) is not present, then the detail following the flag for that source is omitted; the file below is for the ATSR-2 0.67um channel which has only solar sources.
ATSR-2_Ch2.sad % Channel characterisation file
0.67 um % Descriptor SAD_CHAN()%Desc
Ch2 % File ID SAD_CHAN()%Fileid
14925.4 % Central wavenmuber SAD_CHAN()%Wvn
0 % Thermal source flag SAD_CHAN()%Thermal%Flag
1 % Solar source flag SAD_CHAN()%Solar%Flag
21.46, 0.703 % Solar constant SAD_CHAN()%Solar%F0,F1
.5, .75,2.,1.,.75 % Solar noise Eqv Homog SAD_CHAN()%Solar%NeHomog
1.5,2., 3.,1.,1. % Solar noise Eqv Coreg SAD_CHAN()%Solar%NeCoreg
0.0058 % Solar NedR SAD_CHAN()%Solar%NedR
0.1 5.0 % 'typical' sea/land refl SAD_CHAN()%Solar%Rs(2)
LUT file names are constructed from the instrument, channel, cloud class and radiative properties codes. Thus the water cloud bidirectional reflectance file for the SEVIRI 0.8um channel is named SEVIRI-1_WAT_RBD_Ch2.sad. Files are ASCII formatted for portability. Each file has header information describing its contents and allowing for some consistency checks between it and the requested parameters. The header contents are described in the following table; see following sections for full details.
| LUT | Description | Solar | Thermal | Wavelength | Tau | Sat zen | Sun zen | Rel azi | Re | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Needed for ? | Header information present ? | ||||||||||||||||
| grid descriptors (nX, dX, X) | |||||||||||||||||
| Rbd | Bidirection reflectance | * | * | * | * | * | * | * | |||||||||
| Tb | Beam direct transmission | * | * | * | * | * | |||||||||||
| Tbd + Tfbd | Beam diffuse transmission + flux | * | * | * | |||||||||||||
| Td + Tfd | Diffuse transmission + flux | * | * | * | * | * | * | ||||||||||
| Rd + Rfd | Diffuse reflection + flux | * | * | * | * | * | * | ||||||||||
| Em | Emission | * | * | * | * | * | |||||||||||
The exact contents of the LUT files depend on which grid descriptors apply to the LUT in question (see table above). However, the general structure is the same in each case:
- Line 1: Wavelength (f8.2). Store in SAD_LUT()%wavelength
- Line 2: Grid descriptor 1: number of values (integer), grid step size for this descriptor (float)
- Line 3: Grid descriptor 1: grid descriptor values
- Line 4: Grid descriptor 2: as above
- Line 5 etc as above for all relevant grid descriptors
- Line n to end of file: LUT values (f8.3); stored in SAD_LUT( )%LUT(x, y, z, ...)
For example, the RBD LUT files contain the following information:
Wavelength (f8.2). Store in ''SAD_LUT()%wavelength''
no. of tau (i2), delta_Tau (f8.2). Check against ''SAD_CloudClass()%nTau''),
Tau values (nTau * f8.3). First (1) stored in ''SAD_LUT()%Grid%!MinTau'', last (nTau) stored in ''%!MaxTau''
No. of Satzen values, dSatzen i4, f8.2 check nsat against ''SAD_CloudClass()%nSat'', dsat stored in ''SAD_LUT()%Grid%dSatzen'', nsat stored in ''SAD_LUT()%Grid%nSatzen''
Satzen values (nSat * f8.2) satz(1) stored in ''SAD_LUT()%Grid%!MinSatzen'', satz(nsat) stored in !MaxSatzen
No. of Sunzen values, dSunzen (i4, f8.2) check nsun against ''SAD_CloudCLass()%nSun'', dsun stored in ''SAD_LUT()%dSunzen'', nsun stored in ''SAD_LUT()%nSunzen''
Sunzen values (nsun* f8.2) sunz (1) stored in ''SAD_LUT()%Grid%!MinSunzen'', sunz(nsun) in !MaxSunzen
No. of Relazi values, dRelazi (i4, f8.2) check nazi against ''SAD_CloudCLass()%nAzi'', dRelazi stored in ''SAD_LUT()%Grid%dRelazi'',
Relazi values (nazi * f8.2) azi(1) stored in ''SAD_LUT()%Grid%!MinRelazi'', azi(nazi) stored in ''!MaxRelazi'' No. of Re values, dRe (i4, f8.2) check nr against ''SAD_CloudCLass()%nRe'', dr stored in ''SAD_LUT()%Grid%nRe'',
Re values (nre * f8.2), Re(1) stored in ''SAD_LUT()%Grid%!MinRe'', re(nre) stored in ''!MaxRelazi''
RBD (f8.3) stored in ''SAD_LUT()%Solar%Rbd'' (chan_index, 1:ntau, 1:nsat, 1:nsun,1:nazi,1:nr) (written left indices first)
Provides the surface albedo and emissivity information. The variables in the file are: alb_abs_ch_numbers, emis_abs_ch_numbers, alb_data, emis_data, rho_0d_data, rho_0v_data, rho_dd_data, rho_dv_data.
Cloud flags are assumed to be provided in a file separately to the MSI data. For ATSR-2 data, pre-processor code will generate a cloud flag file. See the section on image segmentation above. The variables in the file are: ann_phase, ann_phase_uncertainty, cccot_pre, cflag, cldmask, cldmask_uncertainty, cldtype, cphcot.
ATSR MSI data includes geometric information, but in order to retain the functionality required for other data sources, it is assumed that a separate pixel-based geometry file will be available. The variables in the file are: solzen, satzen, solaz, sataz, relazi.
Latitude and longitude for each pixel, taken from the geolocation considerations of the original satellite data. The variables in the file are: lat, lon.
ORAC will not obtain the underlying surface character for a particular pixel but will assume a pixel-based map is available via this file. For ATSR-2 processing, this will obtained by the pre-processor code. See the section on image segmentation below. The variables in the file are: dem, lsflag, lusflag, nisemask.
The longwave radiative transfer file supplies the atmospheric channel transmittances and radiance terms (see the ATBD) for the channels with thermal emission sources. The source of this file for ORAC prototyping and testing will be the Eumetsat RTM model. See the !Read_Lw_RTM module description for details of the Lw RTM file format and contents. The variables in the file are: lw_channel_abs_ids, lw_channel_instr_ids, lw_channel_wvl, emiss_lw, tac_lw, tbc_lw, rbs_up_lw, rac_up_lw, rac_down_lw.
To avoid the difficulties of ingesting multiple data formats from different imagers within the retrieval itself, this is managed within the pre-processing to produce this file summarising only the desired spectral information in a format appropriate to ORAC. The variables in the file are: msi_instr_ch_numbers, msi_abs_ch_wl, msi_ch_swflag, msi_ch_lwflag, msi_ch_view, time_data, msi_data, sd_data.
This file contains the level pressure and temperature information that was used in the RTM models. See the Read_Lw_RTM module description for details of the RTM profile file format and contents. The variables in the file are: lon_rtm, lat_rtm, hprofile_rtm, o3profile_rtm, pprofile_rtm, qprofile_rtm, tprofile_rtm.
The shortwave radiative transfer file supplies the atmospheric channel transmittances and radiance terms (see the ATBD) for the channels without thermal emission sources. The source of this file for ORAC prototyping and testing will be a modified LOWTRAN7 RTM model. See the Read_Sw_RTM module description for details of the Sw RTM file format and contents. The variables in the file are: sw_channel_abs_ids, sw_channel_instr_ids, sw_channel_wvl, tac_sw, tbc_sw.
Provides dimension and arrays needed to initialise the reading of all the other files. The variables in the file are: alb_abs_ch_numbers, emis_abs_ch_numbers, msi_abs_ch_wl, msi_ch_lwflag, msi_ch_swflag, msi_ch_view, msi_instr_ch_numbers.
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