A number of changes must be made to the code if it is to be used with a different operating system, or with satellite data from a satellite ocean color sensor other than MODIS. This section was written specifically to address changes that may need to be made to the code to enable processing data from the Global Imager (GLI), a Japanese ocean color sensor to be launched in the near future. However, the details listed in this section are also applicable to changes that would be required to the code for processing of data from other ocean color sensors. A comparison of the MODIS and GLI sensor characteristics can be found in Table 4 : General Characteristics of MODIS and GLI and Table 5 : Wavebands of MODIS and GLI. Note that code converting SeaWiFS to MODIS data is currently available from Bob Evans.
If the code is used on a different operating system, some changes may need to be made, particularly to the SDP toolkit which may be incompatible with the system used. The type of floating point number usage can be changed in ocean_build.csh or ocean_build.ksh by changing the variable BRAND from sgi32 (new-style 32 bit) to sgi (old-style 32 bit) or sgi64 (64 bit).
The paths listed in ocean_build.csh or ocean_build.ksh must be altered to correspond to the paths of the files and toolkits at the local site.
Code must be written to generate PCFs as required. These files contain the paths and filenames, appropriate to the location and time of data acquisition, of the input satellite and ancillary data and of the output files. The format of PCFs can be checked using
$PGSBIN/pccheck.sh -i PCFname,
where $PGSBIN is a variable defined to be the location of the toolkit
directory (defined in ocean_build.csh or ocean_build.ksh) and PCFname is the
name of the PCF. Note that Perl scripts exist to generate the PCFs for PGE 20, 53
and 54 - they are located in the STORE/PGE*/scf_cfg directories.
This code uses ancillary climatological data from the National Meteorological Center (NMC) and TOVS measurements, and linearly interpolates them to retrieve data at the time and place of the satellite data. The relevant routines may need to be changed to accommodate a different data set or a different interpolation scheme, if used. The current ancillary datafile formats are described in the Input File Format Description - MODCOL, Input File Format Description - MODSST and Input File Format Description - MSBIN, MTBIN, MSPC, and MMAP documents.
Geolocation data must be obtained (including the solar and azimuth zenith angles, latitude and longitude).
If the input level 1 radiance data is not formatted in a similar style to the MODIS data, different programs will need to be created to read in the data. Care must also be taken that the input data is in appropriate units of radiance (W m-2 um-1 sr-1).
The MODIS programs are designed for use with a specific number of visible and infrared bands, which are referred to by band number (see subroutine anlyopi). Adjustments would need to be made if the extra visible GLI bands are to be incorporated. These adjustments affect the input files as well as dimensionality within the program (for example vector dimensions and DO loop indices). Note : Howard Gordon (University of Miami) has code to generate appropriate ancillary coefficient files at different wavelengths.
The wavelengths and bandpasses need to be known for some of the atmospheric correction calculations. In the infrared, the spectral shapes of the sensors are required. These parameters can be changed in the external input file called spectra.
Adjustments may need to be made to account for instrumental effects that are not removed by the calibration process used to derive the level 1B data. Potential effects are the scan angle and wavelength dependence of the scan mirror, and spectral and spatial crosstalk between channels.
Additional corrections may need to be made to account for different atmospheric effects at wavebands not used by MODIS. Examples include a correction for high Rayleigh scattering at the GLI wavebands below 412 nm, and correction for water absorption effects at the 565 and 625 nm GLI wavebands.
Documented by Jasmine S. Bartlett, COAS, Oregon State University.