SSEC forums

Several MODIS direct broadcast users have noticed that in passes where some missing data is present, the MODIS geolocation data (i.e., latitudes and longitudes) can be incorrect for the rest of the pass (starting where the missing data was found). It appears that a particular kind of missing and/or invalid Level 0 CCSDS APID 64 packet data from Terra causes the MODIS geolocation code to produce incorrect geolocation results. Typically a small section of missing data within the satellite pass causes bad geolocation data to be created for the remaining data in the pass, even if the remaining data are good. It is reproducible in the sense that I have been able to process Terra Level 0 data from other direct broadcast sites and observe the same problem.

The following correspondence is from the NASA Ocean Color Forums, and it describes an example of the problem:
http://oceancolor.gsfc.nasa.gov/forum/o ... l?tid=2960
http://oceancolor.gsfc.nasa.gov/forum/o ... l?tid=2963

I have asked the MODIS Calibration Support Team to take a look at this issue and see if there is a change or fix that can be made to the geolocation software to fix it. I'll let you all know when I have more information.

Liam.

Liam, could you post such a pds data sample to public ftp site?
It is interesting to look at it

The Level 0 file for this pass is available at

ftp://ftp.ssec.wisc.edu/pub/gumley/geolocation/

Liam.

Just an update on this topic.

I have been in contact with the developers of the MODIS L1B geolocation code, and with the developers of MODISL1DB/SeaDAS. It appears that the "vertical stripes" problem is fixed in the new version of the MODIS L1B geolocation code (program "geogen_modis"), and it will be included in the next release of SeaDAS and MODISL1DB. I do have a preview copy of the geogen_modis binary file if anyone is interested. On my system, I just replaced the existing version of geogen_modis in the modisl1db/bin directory, and the problem went away in the test cases I examined.

Liam.

Hi Liam,

We at the Finnish Meteorological Insitute are interested in the geogen_modis binary file to use it in our Sodankylä receiving station. I am not sure do we have had these vertical stripe problems but if we can prevent them to occur in future, that would be great.
How can I get these files? Via ftp or email...?

Omit,

The NASA OBPG team will be releasing a new version of MODISL1DB very soon, and it will include the fix for the "vertical stripes" problem. I recommend waiting until the new version becomes available. I will be releasing a new version of the IMAPP Virtual Appliance shortly afterwards that will contain the new version of MODISL1DB.

Regards,
Liam.