Hi

I've downloaded some L1A data from the L1 Browser but for some reason I got a msg telling that it was not possible extract the geographical area I indicated.

So I had to download the full scenes and now I'm trying to subcene the L1A and process it to L2. First I have to create a Geolocation file. The problem is that I get several error msgs.

What is the predefined directory for Attitude and Ephemeris files which I have also downloaded? I've tried /seadas5.1/data/common/benchmarks/ancilliary.

Regards

Akli

Akli,

As long as you have an internet connection, you don't need to worry about
retrieving the attitude and ephemeris files. SeaDAS internal scripts will
automatically do so for you to create a geolocation file.

What is the error message? What is the area you are interested ?

Long

SeaDAS's predefined directory (where the attitude and ephemeris data
gets downloaded) should be located in $SEADAS/var/modis/atteph.

Hi long

Thanks for the reply but I've solved the problem it had to do with write permissions. I've been able to process L1A->GEo; L1A subscene, L1A->L1B.

Now, I have one question the SST is scaled right? When I display it the slope appears 0.005 and intercept = 0.

Regards,

Akli

Another thing, my SeaDas is downloading the atteph files to $SEADAS /data/modis/atteph/year and not the path you mentioned.

I'm worried about this, because I've downloaded all ancilliary files previously

Don't worry, SeaDAS 5.1 uses your path $SEADAS /data/modis/atteph/year.
SeaDAS 5.2 uses a new path.

Yes, those data are scaled. You can do rescale in image display:

display image -> Functions -> Rescale -> Log Scale or reset Min/Max.

Thanks

Hi

How can I automate the L1A->GEO procedure using a SeaDAS script to run in batch mode.

Regards

Akli

Just found it, if anyones interested:

http://oceancolor.gsfc.nasa.gov/forum/oceancolor/topic_show.pl?pid=6778;hl=l1a%20geo#pid6778

One doubt has come uP:

subscene,l1afile,north,south,west,east,1,1,subscene_file,/ll_flag & $

1) What does the two "1" mean?
2) How can I output and define the name of the correspondent subcened GEO file ?

Regards

Akli

That "1, 1 " are pixel & scan line subsampling rate.
"Subsene" program has been renamed in SeaDAS 5.2.

   http://oceancolor.gsfc.nasa.gov/seadas/name_changes.html

For MODIS files, it is "l1aextract_modis".

For SeaWiFS files, subscene program "l1aextract_seawifs" usage:

l1aextract_seawifs infile spix epix sscan escan pix_sub sc_sub outfile

       pix_sub  - pixel subsampling rate
       sc_sub   - scan line subsampling rate

       spix     - start pixel number
       epix     - end pixel number
       sscan    - start scan line
       escan    - end scan line

Please refer a helping massage for Geo file names in command script:

http://oceancolor.gsfc.nasa.gov/forum/oceancolor/topic_show.pl?pid=9050;hl=automat#pid9050

Hi

Can I have access to the "old" subscene comand documentation? I can only find the docs for the new comand modisl1a_extract

http://oceancolor.gsfc.nasa.gov/seadas/doc/l1aextract_modis/l1aextract_modis.html

I've noticed that some parameters have different names, I'm using the 5.1version.

Regards

For any SeaDAS IDL command you can use the "/help" argument on the SeaDAS command-line. You can also click on any particular GUI window's Help button to access web help. And for old versions of SeaDAS to extract MODIS data you'd actually want to use the modis_subscene command:

SeaDAS> modis_subscene,/help

Usage: modis_subscene, ifile="ifile", geofile="geofile", ofile="ofile", outgeo="outgeo",
       swlon=SWlon, swlat=SWlat, nelon=NElon, nelat=NElat, wait=wait, help=hlp
(Note use of quotes around path/filenames)

Example:
modis_subscene, ifile="$SDSDEMO/A2005191123500.L1A_LAC", $
                geofile="$SDSDEMO/A2005191123500.GEO", $
                ofile="A2003160140000.L1A_sub", $
                outgeo="A2003160140000.GEO_sub", $
                swlon=11, swlat=-27, nelon=18, nelat=-22

Hi

I was using the comand "subscene" and not "modis_subscene" following this topic:

http://oceancolor.gsfc.nasa.gov/forum/oceancolor/topic_show.pl?pid=9050;hl=automat#pid9050

Great help Mike, thank you very much.

Regards

Akli

Akli,

Your scaling equation is correct.  I'm not sure why some of your values are so low, but I suspect they probably failed at some point in the algorithm, maybe atmospheric correction or something else.  The L2 Flags Display might give you some idea what's happening, if you can isolate a pixel and check its l2_flags value using the tool, maybe it will be an SSTWARN or SSTFAIL flagged pixel.  SSTWARN means that there was a retrieval but it is suspect for some reason, and SSTFAIL means there was no retrieval.  You can also check the qual_sst flags and get some ideas there.  You can also set the sst_qual_ix so that seadas doesn't load in these suspect values.  Do a search in the seadas forum and the data products and algorithms forum for sst_qual_ix and SSTFAIL, and you will see some relevant info.

Mark

Hi

I read your post now, a couple of hours ago I understood the reason: The values are negative because they are masked. For chl-a I think that flagged values are not displayed in the Geo. Variable map. The qual_sst flags are enough to understand that the negative temperature values are flagged ones.

Thanks!

Regards