This release provides, for the first time within SeaDAS, the ability to process and display MODIS/Aqua data. We plan to provide the ability to process MODIS/Terra data in the near future. But for now, SeaDAS 4.5 provides the capability to:
- create a Geolocation file from MODIS Aqua Level 1A data
- create a Level 1B file from MODIS Aqua Level 1A data
- create a Level 2 file from MODIS Aqua Level 1B data
We also plan to provide the capability to produce various MODIS Aqua Level 3 files in the near future. This initial release only supports RedHat Linux 7.3. Support for RedHat 7.2 and 7.1 will be forthcoming shortly, followed by support for Solaris 2.8, Solaris 2.7, and Irix 6.5. We do not anticipate being able to provide support for RedHat 8.0 or 9.0, but we are planning on providing support for Fedora 1.0 sometime within the next few months. The format of the Level 1A and Level 1B Aqua data is very similar to the format of the data that is available from the Goddard DAAC, with the exception that it does not have the 250m or 500m data which are being used currently primarily for land studies.
Users can obtain the global Level 1A 1km data from our Ocean Color website at https://oceancolor.gsfc.nasa.gov through the Level 1 and 2 Browser link and through the Data Subscription service. There is also a link on this page for the Oceans FTP site, where you can find ancillary MET/OZONE files, attitude and ephemeris files, Aqua Level 3 SMI files, and recent Aqua day and nighttime files. Further detailed information on the format of the various data files is described at the link for "Overview of MODIS Processing with the SatelliteData Processing System" available at: https://oceancolor.gsfc.nasa.gov/products/. Support for processing of additional Level-1 formats, including IMAPP Direct Broadcast format, will be added in a future release and we are going to work closely with the Direct Broadcast community and software developers towards this goal. The Geolocation and Level-1B processing software provided with this release is the standard institutional code produced by SDST and MCST, respectively. The Level-1B code has been slightly modified to ignore the missing 250 and 500-meter data. The Level-1B look-up table for the reflective solar bands has also been modified in an effort to improve the extrapolation of sensor calibration into the future. This extrapolation is being actively monitored by the MODIS Oceans Cal/Val team, and updates to the Level-1B look-up table will be provided when necessary through periodic updates that you will be notified of. The Level-2 processing software for MODIS makes use of the same multi-sensor code used for SeaWiFS, OCTS, MOS, and OSMI. A description of the differences between this software and the code used in the past to produce the GDAAC products is available here:
https://oceancolor.gsfc.nasa.gov/reproc ... erview.pdf
A note about creating Geolocation files:
In order to successfully create a Geolocation file from a Level1A file, you must have the proper Attitude and Ephemeris files loaded onto your hard drive in the proper location. The Attitude and Ephemeris files should go under the $SEADAS/data/modisnpp/atteph directory. They should be further divided in subdirectories by year and day. To get the Attitude and Ephemeris files. The first way is through the Oceans FTP site. Navigate down through MODISA/ATTEPH, and then to the year and day desired. The Attitude files have the string "ATT" in them, and the Ephemeris file has the string "EPH" in it. There is only one Ephemeris file per day at noon, and there are twelve attitude files per day, one per two-hour period. An Ephemeris file covers a 24-hour period beginning with the day and time in the file name. An Attitude file covers a 2-hour period beginning with the day and time in the filename. Here is an example of a command that would help you to easily download files for 2004 day 044:
ncftpget -R oceans.gsfc.nasa.gov . MODISA/ATTEPH/2004/044
The second way to obtain the files is through the SeaDAS ftp site, which provides them in compressed tar file format in 30-day chunks. The files are in the same location as the SeaDAS software. The format for the filenames is seadas_modisaeYYYYDDDDDD.tar.gz. The "modisae" part of the filename stands for "MODIS Attitude Ephemeris". The "YYYY" is the 4-digit year. The first three "DDD" stand for the beginning julian day of the chunk, and the last three "DDD" stand for the ending julian day for the chunk. For example, seadas_modisae2004001030.tar.gz contains all of the Aqua Attitude and Ephemeris files for Jan. 1 to Jan. 30, 2004 (day 001 to 030). There are different rules for what attitude and ephemeris files are required depending on the start time of the Level 1A input file, but those rules are handled by the processing scripts. For your purposes, it would probably be best just to ensure that you have all of the attitude and ephemeris files for the day of the file you are processing, plus for the day before and the day after. In order to properly install the attitude and ephemeris files from these compressed tar files, download the appropriate compressed tar file into your $SEADAS directory, then use the following command (as an example) to put them into the appropriate directory:
gunzip -c seadas_modisae2004001030.tar.gz | tar xvf -
This will automatically put them in the correct location under the $SEADAS/data/modisnpp/atteph directory. A note about errors/bugs within SeaDAS 4.5:
The addition of the MODIS Aqua processing and display capabilities to SeaDAS has required a fair amount of effort. We have completed a significant amount of testing to try to bring you the most stable and error-free software package possible. However, we are a team of only two developers, so we are unable to guarantee that you will not find any errors or problems with the software. We want to work with the user community to find and resolve any problems that may come up. If you discover a bug or an error, or if you simply have a suggestion that would make the software more useful, please let us know.
We will evaluate and prioritize all problems and suggestions, and try to provide you with the most expedient updates possible. User support for bugs and general questions are handled through our user support e-mail address: firstname.lastname@example.org
General announcements concerning SeaDAS are available both at our main website:
https://seadas.gsfc.nasa.gov and also through the Ocean Color Forum website at: https://oceancolor.gsfc.nasa.gov/forum/ ... um_show.pl.
We have also established a forum for SeaDAS questions at the same location. We hope that this might serve as a site for Frequently Asked Questions.
The SeaDAS Development Group