Strangely high sst values

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oscar_holon
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Joined: Tue Mar 08, 2022 11:25 am America/New_York
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Strangely high sst values

by oscar_holon » Wed Dec 07, 2022 2:02 pm America/New_York

Hi all, I am just learning how to process satellite images, particularly, learning how to convert L2 images to raster (tif). For this, I am developing a mixed, very basic, R/bash routine (if anyone is interested, you can visit my github: https://github.com/oscarIM/imgsatEasy), that for some reason that I still don't understand or see, I get abnormally high values for sst for a given area.

The only thing the routine does (after downloading the daily l2 files manually) is to go from individual L2 files to individual L3 mapped files, which I then transform to raster, group and calculate according to what I need.
Here is a processing scheme (since the original one is an R loop invoking the binaries of seadas for each file) for a given file:

####L2bin####
infile = 20221201T185501.L2.SST.NRT.x.nc
ofile = 20221201T185501.L2.SST.NRT_1km_L3b_tmp.nc
prodtype="day"
l3bprod ="sst"
resolve =1
verbose="off",
flaguse ="LAND,HISOLZEN",
qual_max=0,
latnorth=-35,
latsouth=-40,
loneast =-75,
lonwest = -70,
area_weighting=0

l2bin infile=${infile} ofile=${ofile} prodtype=${prodtype} l3bprod=${l3bprod} resolve=${resolve} verbose=${verbose} flaguse=${flaguse} qual_max=${qual_max} latnorth=${latnorth} latsouth=${latsouth} loneast=${loneast} lonwest=${lonwest} area_weighting=${area_weighting} > ${infile}"_l2binlog.txt"
####L3bin####
infile = 20221201T185501.L2.SST.NRT_1km_L3b_tmp.nc
ofile = 20221201T185501.L2.L2.SST.NRT_1km_L3m_tmp.nc
prod="sst"
oformat ="netCDF4"
verbose = "off"
l3bin infile=${infile} ofile=${ofile} prod=${prod} oformat=${oformat} verbose=${verbose} > ${infile}"_l3binlog.txt"
####L3mapgen####
ifile=20221201T185501.L2.L2.SST.NRT_1km_L3m_tmp.nc
ofile=20221201T185501.L2_sst_1km_L3mapped.nc
product="sst"
oformat="netcdf4"
resolution="1km"
projection="platecarree"
interp="area"
north=-35
south=-40
west=-75
east=-70
quiet="true"
mask_land="no"
fudge=2

l3mapgen ifile=${ifile} ofile=${ofile} product=${product} oformat=${oformat} resolution=${resolution} projection=${projection} interp=${7} north=${north} south=${south} west=${west} east=${east} quiet=${quiet} mask_land=${mask_land} fudge=${fudge}> ${ifile}"_l3mapgenlog.txt"


Then, in R (in another routine), I group the L3 mapped files according to the temporality I need, convert them to raster, stacked them and calculate some measure (mean, median, etc.). The result of all this, is that some pixels are generated with very high sst values (they are high compared to 4km L3 images downloaded from https://oceancolor.gsfc.nasa.gov/l3/order/ for the same geographic extent and time) or compared to the “expected” for this latitudes

If anyone finds any errors in the L2 to L3 process, I would be very grateful if you could let me know.
Regards

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OB.DAAC - SeanBailey
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Answers: 1

Re: Strangely high sst values

by OB.DAAC - SeanBailey » Thu Dec 08, 2022 2:43 pm America/New_York

Nothing jumps out, although you are binning at 1km, while our standard processing does so at 4km - so more values go into any given bin, thus minimizing the impact of a spuriously high (or low) value affecting the mean.

If you have spurious values in the L3, they came from the L2. Since you have the L2 files, I suggest you look at those to see what the SST value is in those (you can apply the same flags to mask the L2 as are applied in the binning).

Regards,
Sean

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