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Topic Frequently Asked Questions / Data Products & Algorithms FAQ / Are SeaDAS-generated products identical to OBPG-distributed products? (locked)
Are SeaDAS-generated products identical to those distributed by the OBPG?
Other than very slight machine/OS dependencies (e.g. floating point math nuances), SeaDAS can generate the exact products that are available on the Ocean Color Web (we check all our platform distributions to ensure this).
However, for this to occur you must be using a version of the SeaDAS binaries, data support files (e.g. calibration coefficients, gains, etc.), and ancillary data files that exactly match the versions used by production to create the file you are processing. This isn't always easy to do. The most important thing is to have the most current version of SeaDAS. Once you have that installed you can consult the processing versions table to compare your versions with those in the forward stream of our production system. (It is possible even the newest version of SeaDAS may be a bit behind what is being used in production's forward stream.)
If your binary versions, L1B calibration look-up tables, and gains all match, then you should be getting identical product values to those of production (other than slight machine/OS dependencies) for recent MODIS products. I say recent because until a complete reprocessing occurs, a file from the Ocean Color Web may have been processed at an earlier date when versions were older than what is shown in the processing versions table. (Also, since older L1B data isn't distributed you'll have no way of knowing what L1B LUTs were used for an older file.) Also be careful not to compare Quicklook MODIS products with products you've generated using Refined attitude and ephemeris, otherwise slight geolocation differences will make the data appear slightly different.
If all versions appear to match and you're still not getting an identical product, take a look in the meta-data of the Level 2 file (using "ncdump -h"). Make sure everything matches as it should.. for example the MET/OZONE input files should be exactly the same for your file as for the Ocean Color Web file.
If you still get a difference, then this might indicate a problem, so please let us know and we'll look into it.
Other than very slight machine/OS dependencies (e.g. floating point math nuances), SeaDAS can generate the exact products that are available on the Ocean Color Web (we check all our platform distributions to ensure this).
However, for this to occur you must be using a version of the SeaDAS binaries, data support files (e.g. calibration coefficients, gains, etc.), and ancillary data files that exactly match the versions used by production to create the file you are processing. This isn't always easy to do. The most important thing is to have the most current version of SeaDAS. Once you have that installed you can consult the processing versions table to compare your versions with those in the forward stream of our production system. (It is possible even the newest version of SeaDAS may be a bit behind what is being used in production's forward stream.)
If your binary versions, L1B calibration look-up tables, and gains all match, then you should be getting identical product values to those of production (other than slight machine/OS dependencies) for recent MODIS products. I say recent because until a complete reprocessing occurs, a file from the Ocean Color Web may have been processed at an earlier date when versions were older than what is shown in the processing versions table. (Also, since older L1B data isn't distributed you'll have no way of knowing what L1B LUTs were used for an older file.) Also be careful not to compare Quicklook MODIS products with products you've generated using Refined attitude and ephemeris, otherwise slight geolocation differences will make the data appear slightly different.
If all versions appear to match and you're still not getting an identical product, take a look in the meta-data of the Level 2 file (using "ncdump -h"). Make sure everything matches as it should.. for example the MET/OZONE input files should be exactly the same for your file as for the Ocean Color Web file.
If you still get a difference, then this might indicate a problem, so please let us know and we'll look into it.
Topic Frequently Asked Questions / Data Products & Algorithms FAQ / Are SeaDAS-generated products identical to OBPG-distributed products? (locked)