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Last Post 12 Jun 2014 04:57 PM by  anon
VIIRS DNB Values (ENVI 5.1)
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anon



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12 Jun 2014 04:57 PM
    Hello, I am trying to work with the day night band on VIIRS sensor. I can open and view the images with no problems and the image looks fine. However when I try to view the values they all appear as 0. I am assuming this is because the values of the pixels are in nanowatts (10^-9) and the values scale only shows number up to 10^-6. I have tried to use the band math option to multiply the values by 10^9 in order to try and normalize them but I end up with number on the order of 10^-6 for some reason and the image turns black. I have tried stretching it but also to no avail. I was wondering if there was a known problem with working with small number in ENVI and what the solution is. I am pretty much new to ENVI and have no programming skills. I would appreciate any help I could get. Thanks!

    MariM



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    17 Jun 2014 02:31 PM
    The data values are displayed as they are stored in the file as W/(cm^2*sr) but are just very tiny because the radiance is much lower at night. Additionally the background value (-9999) is much different than the rest of the dynamic range of the data. ENVI is probably treating it as "no data' in the display when it is first imported. If you scale the data by a large value, the background value will also get very large and no longer treated as 'no data' when displayed. This new background value should be masked, and then set to a "data ignore value" in the header. This should allow the data to display appropriately.
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