GPT results in no-data value of 0 instead of NaN pixels

Microwave Toolbox
#1

I am trying to get a graph running that produces Sentinel-1 GRD backscatter images in decibels. Regions outside what is imaged should get a NaN (in Float32 format), but persistently get a “0”. This is bad, as 0 is a perfectly valid value and should definitely not be used as no-data value. I tried to uncheck the “no-data value used” in the graph, I tried to set it to “0”, but none of these have any effect. Pixels in the exported image are still “0”. Any idea what I can do?

#2

So, no suggestions? Someone put this thread under s1tbx, which I think is a pity since it is a general SNAP issue I face; no data in SNAP becomes 0 in an exported image, no matter the format.

NaN values in SNAP toolbox
#3

I did not test it but if you look at the metadata file (the dim one), you can observe that there is a Xml tag corresponding to no-data value. Maybe compare this with a generated file created by SNAP-Desktop and a file generated using GPT.

    <Spectral_Band_Info>
        <BAND_INDEX>0</BAND_INDEX>
        <BAND_DESCRIPTION />
        <BAND_NAME>i_IW1_VV_mst_14Nov2017</BAND_NAME>
        <BAND_RASTER_WIDTH>20911</BAND_RASTER_WIDTH>
        <BAND_RASTER_HEIGHT>13401</BAND_RASTER_HEIGHT>
        <DATA_TYPE>int16</DATA_TYPE>
        <PHYSICAL_UNIT>real</PHYSICAL_UNIT>
        <SOLAR_FLUX>0.0</SOLAR_FLUX>
        <BAND_WAVELEN>0.0</BAND_WAVELEN>
        <BANDWIDTH>0.0</BANDWIDTH>
        <SCALING_FACTOR>1.0</SCALING_FACTOR>
        <SCALING_OFFSET>0.0</SCALING_OFFSET>
        <LOG10_SCALED>false</LOG10_SCALED>
        <NO_DATA_VALUE_USED>false</NO_DATA_VALUE_USED>
        <NO_DATA_VALUE>0.0</NO_DATA_VALUE>
    </Spectral_Band_Info>
#4

@kristofvt Did you find a solution for the issue you reported?

#5

@lveci @jun_lu can you check if this is still the case?

#6

Could you provide more details (processing chain, product, graph etc.) of your test so that we can repeat the problem? Thanks.

Jun