hi!! i'm working on modis L2 images, extracting data with envi 4.3. after applying slope-intercept to chl data, are the values in log format or do i still have to log transorm after the slope-intercept step??

thanks...

mimoy

thanks a lot norman!! that clears up some things.
mimoy

I downloaded data of chlorophyll maped 8-daily of Seawfis and I am reading the data with matlab. I applyed the data the scaling equation
base^(data*slope+intercept), but the colormap of the images are homogeneous and almost cero. I dont' understand why the images are not with a color scle similar to obtained by giovvani in his homepage. http://reason.gsfc.nasa.gov/OPS/Giovanni/ocean.swf8D.2.shtml.
The question is: Is there necesary some conversion with the data moreover of the scaling equation?

thanks

Nieves Lorenzo

Hi Nieves,

I'm not familiar with Matlab, but I suspect that the problem may be arising
when Matlab applies a color lookup table to the data.  I used hdp and perl
to extract reasonable looking chlorophyll values from a recent 8-day SeaWiFS
chlorophyll file.

hdp dumpsds -n l3m_data -d S20070572007064.L3m_8D_CHLO_9 | \
perl -e 'undef $/;' \
     -e '$data=<STDIN>;' \
     -e '@chl=split " ",$data;' \
     -e '$incr=360/4320;' \
     -e '$i=-1;' \
     -e 'for($lat=  90-$incr/2; $lat>-90; $lat-=$incr){' \
     -e 'for($lon=-180+$incr/2; $lon<180; $lon+=$incr){' \
     -e '$i++;' \
     -e 'next if $chl[$i]==255;' \
     -e '$c=10**(0.01524*$chl[$i]-2);' \
     -e 'printf "%7.3f %8.3f %7.3f\n",$lat,$lon,$c;' \
     -e '}}'

Note the scaling equation in the third to last line above.
Executing the above on the unix commandline results in records
that look like this.

62.958  -40.458   0.178
62.958  -40.375   0.178
62.958  -40.292   0.101
62.958  -40.208   0.101
62.958  -40.125   0.113
62.958  -40.042   0.113
62.958   -9.292   0.346
62.958   -9.208   0.346
62.875  -40.708   0.134
62.875  -40.625   0.134
...


Regards,

Norman

Ok, Norman I try to compare the data and change the color scale

Post Script

During our most recent reprocessing we switched to
storing 32-bit floating point geophysical values in our
standard-mapped data products, so you can now
remove the aforementioned scaling equation as
shown in the attachment.

Norman