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Home • Re: SNPP VIIRS issue processing SST

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I have finally figured out that l3mapgen has a small problem (or I'm missing something). When I generate a TIFF image with l3mapgen with:

Code:

 l3mapgen interp=area projection='EPSG:3857' threshold=0.5 ofile=SST-l3mapgen-out.tif ifile=SNPP_VIIRS.20240619T204200.sst.L3b.nc oformat=tiff fudge=5.0 suite=SST product=sst apply_pal=0 quiet=0 resolution=qkmLoading default parameters from /u/ocssw//share/viirs/npp/l3mapgen_defaults.parLoading default parameters from /u/ocssw//share/common/l3mapgen_defaults_SST.parl3mapgen 2.4.0-T2024.20 (Jun  6 2024 21:11:08)ifile      : SNPP_VIIRS.20240619T204200.sst.L3b.ncofile      : SST-l3mapgen-out.tifoformat    : tiffprojection : EPSG:3857resolution : 289.895mproduct    : sstqual_prod  :north      :   25.974south      :    2.589east       : -100.127west       : -125.586image size : 9342 x 977899% completeactual data min       : -5.000000actual data max       : 32.980000num filled pixels     : 16901924percent filled pixels : 18.50%
I'm not clear on what values should exist to indicate not actual data values, but it would be convenient to be able to specify something like nodata=-32768 to override the default output. This would make it much easier to work with the gdal tools.

Below is a gdalinfo report of the tif.

Code:

$ gdalinfo -stats -hist SST-l3mapgen-out.tifDriver: GTiff/GeoTIFFFiles: SST-l3mapgen-out.tifSize is 9778, 9342Coordinate System is:PROJCRS["WGS 84 / Pseudo-Mercator",    BASEGEOGCRS["WGS 84",        ENSEMBLE["World Geodetic System 1984 ensemble",            MEMBER["World Geodetic System 1984 (Transit)"],            MEMBER["World Geodetic System 1984 (G730)"],            MEMBER["World Geodetic System 1984 (G873)"],            MEMBER["World Geodetic System 1984 (G1150)"],            MEMBER["World Geodetic System 1984 (G1674)"],            MEMBER["World Geodetic System 1984 (G1762)"],            MEMBER["World Geodetic System 1984 (G2139)"],            ELLIPSOID["WGS 84",6378137,298.257223563,                LENGTHUNIT["metre",1]],            ENSEMBLEACCURACY[2.0]],        PRIMEM["Greenwich",0,            ANGLEUNIT["degree",0.0174532925199433]],        ID["EPSG",4326]],    CONVERSION["Popular Visualisation Pseudo-Mercator",        METHOD["Popular Visualisation Pseudo Mercator",            ID["EPSG",1024]],        PARAMETER["Latitude of natural origin",0,            ANGLEUNIT["degree",0.0174532925199433],            ID["EPSG",8801]],        PARAMETER["Longitude of natural origin",0,            ANGLEUNIT["degree",0.0174532925199433],            ID["EPSG",8802]],        PARAMETER["False easting",0,            LENGTHUNIT["metre",1],            ID["EPSG",8806]],        PARAMETER["False northing",0,            LENGTHUNIT["metre",1],            ID["EPSG",8807]]],    CS[Cartesian,2],        AXIS["easting (X)",east,            ORDER[1],            LENGTHUNIT["metre",1]],        AXIS["northing (Y)",north,            ORDER[2],            LENGTHUNIT["metre",1]],    USAGE[        SCOPE["Web mapping and visualisation."],        AREA["World between 85.06°S and 85.06°N."],        BBOX[-85.06,-180,85.06,180]],    ID["EPSG",3857]]Data axis to CRS axis mapping: 1,2Origin = (-13980489.748659253120422,2996145.823402185924351)Pixel Size = (289.894507274305511,-289.894507274305511)Metadata:  AREA_OR_POINT=Area  OBPG_version=UnspecifiedImage Structure Metadata:  COMPRESSION=LZW  INTERLEAVE=BANDCorner Coordinates:Upper Left  (-13980489.749, 2996145.823) (125d35'19.95"W, 25d58'34.68"N)Lower Left  (-13980489.749,  287951.336) (125d35'19.95"W,  2d35' 9.00"N)Upper Right (-11145901.257, 2996145.823) (100d 7'31.20"W, 25d58'34.68"N)Lower Right (-11145901.257,  287951.336) (100d 7'31.20"W,  2d35' 9.00"N)Center      (-12563195.503, 1642048.580) (112d51'25.58"W, 14d35'25.71"N)Band 1 Block=9778x9342 Type=Float32, ColorInterp=Gray  Minimum=-32767.000, Maximum=32.980, Mean=-26699.336, StdDev=12734.1140...10...20...30...40...50...60...70...80...90...100 - done.  256 buckets from -32831.3 to 97.2937:  74444152 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 16901924  Metadata:    STATISTICS_MAXIMUM=32.979999542236    STATISTICS_MEAN=-26699.336323204    STATISTICS_MINIMUM=-32767    STATISTICS_STDDEV=12734.11371322    STATISTICS_VALID_PERCENT=100
Ideally, I want to use gdal_translate to set NODATA=-32768 but since there are other values near that like -32767 and maybe others this doesn't work. I was able to work around this issue with the following to set all values < -5 to -32768 and then asserting the NoDataValue=-32768.

Code:

gdal_calc.py -A SST-l3mapgen-out.tif --outfile=SST-out.tif --calc="where(A<-5,-32768,A)" --NoDataValue=-32768 --overwrite
Now gdalinfo on SST-out.tif report (truncated) is much more accurate WRT the actual data values:

Code:

...Corner Coordinates:Upper Left  (-13980489.749, 2996145.823) (125d35'19.95"W, 25d58'34.68"N)Lower Left  (-13980489.749,  287951.336) (125d35'19.95"W,  2d35' 9.00"N)Upper Right (-11145901.257, 2996145.823) (100d 7'31.20"W, 25d58'34.68"N)Lower Right (-11145901.257,  287951.336) (100d 7'31.20"W,  2d35' 9.00"N)Center      (-12563195.503, 1642048.580) (112d51'25.58"W, 14d35'25.71"N)Band 1 Block=9778x1 Type=Float32, ColorInterp=Gray  Min=-5.000 Max=32.980  Minimum=-5.000, Maximum=32.980, Mean=4.728, StdDev=9.999  NoData Value=-32768  Metadata:    STATISTICS_MAXIMUM=32.979999542236    STATISTICS_MEAN=4.728431679632    STATISTICS_MINIMUM=-5    STATISTICS_STDDEV=9.9994284060557    STATISTICS_VALID_PERCENT=100

Statistics: Posted by woodbri — Tue Jul 09, 2024 11:19 am America/New_York



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