analyse mean chlorophyll

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nada31
Posts: 37
Joined: Tue Sep 26, 2017 9:30 am America/New_York

analyse mean chlorophyll

by nada31 » Tue Jan 02, 2018 4:45 am America/New_York

i have this image A20173052017334.L3b_MO_CHL.nc
i have two working method which is the most reliable for anlayser the average of chlorophyll
The first :
Data images --> Cropped images --> Correction Preview images --> Vector Import shape file --> Export Mask Pixel --> Data Ascii --> Analyse mean Chlorophyll

The second :

Dta images --> Cropped--> correction Preview images --> L3bin processing --> L3mapgen --> Reprojecting --> L3bindump --> Data Ascii --> analyse mean chlorophyll

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OB WebDev - norman
Subject Matter Expert
Subject Matter Expert
Posts: 142
Joined: Tue Feb 09, 2021 8:19 am America/New_York

analyse mean chlorophyll

by OB WebDev - norman » Wed Jan 03, 2018 11:05 am America/New_York

Hi,

If I were you, I would choose your second method but leave out
the L3mapgen and reprojecting steps.  The L3bindump program
reads level-3 bin files directly, so you do not need to make mapped
versions of the data.

Regards,
Norman

nada31
Posts: 37
Joined: Tue Sep 26, 2017 9:30 am America/New_York

analyse mean chlorophyll

by nada31 » Thu Jan 04, 2018 3:35 am America/New_York

Thank you for your suggestion..:wink:

nada31
Posts: 37
Joined: Tue Sep 26, 2017 9:30 am America/New_York

analyse mean chlorophyll

by nada31 » Thu Jan 04, 2018 5:04 pm America/New_York

hi
I chose your suggetion of the file directly the program l3bindump for the image A20173052017334.L3b_MO_CHL.nc but first it does not work, it tells me error of parametrage but the problem is that: my need is:
to have a mapped image of my region and to extract the average of cholorohylle at the same time,
how do i do to have pixel x and y longitude and latitude and mean chl-a
is it the right method
think's

OB WebDev - norman
Subject Matter Expert
Subject Matter Expert
Posts: 142
Joined: Tue Feb 09, 2021 8:19 am America/New_York

analyse mean chlorophyll

by OB WebDev - norman » Tue Jan 09, 2018 1:27 pm America/New_York

There are many ways to handle the output of l3bindump.
Here is one that I would use involving Perl to parse the l3bindump output.

# To get the mean value of chlorophyll concentration for an arbitrary region.
l3bindump ifile=A20173052017334.L3b_MO_CHL.nc l3bprod=chlor_a \
          north=25 south=17 west=60 east=66 \
| perl \
-e '<STDIN>;<STDIN>;<STDIN>;' \
-e 'while(<STDIN>){' \
-e '  $s+=(split " ")[12];' \
-e '  $n++;' \
-e '}' \
-e '$mean=sprintf "%.3f",$s/$n;' \
-e 'print "mean chlor_a = $mean milligrams per cubic meter\n";'

# The above commandline prints out the following.
mean chlor_a = 0.911 milligrams per cubic meter

# To make a colored image of the extracted region, I would use
# gmt, gs, and convert to generate the attached PNG image.
l3bindump ifile=A20173052017334.L3b_MO_CHL.nc l3bprod=chlor_a \
          north=25 south=17 west=60 east=66 \
| perl \
-e '<STDIN>;<STDIN>;<STDIN>;' \
-e 'while(<STDIN>){' \
-e '  ($n,$s,$w,$e,$chl)=(split " ")[3,4,5,6,12];' \
-e '  print "> -Z$chl\n$w $n\n$e $n\n$e $s\n$w $s\n";' \
-e '}' \
| gmt psxy -Cchl.cpt -L -R59/67/16/26 -JM15 -P -X0 -Y0 -B1g1 \
      --FORMAT_GEO_MAP=DF --FONT=16p --MAP_FRAME_TYPE=inside \
| gs -sDEVICE=ppmraw -sOutputFile=- -q -r100 -g1500x2000 -dTextAlphaBits=4 - \
| convert - regional_chl.png

I just picked an arbitrary region using the file you specified since you weren't
specific about the type of problem you were encountering.  I hope this is helpful.

Norman

P.S. I am also attaching the color palette table (cpt) that I used to color the
      chlorophyll image.

attachment 2

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