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Last Post 10 Mar 2021 11:07 AM by  MariM
ROI Statistics
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Cole Miller



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13 Feb 2021 03:54 PM
    Hello all,

    I am new to this online community and may be asking some random general questions in the coming months.

    I would like to be able to interpret the statistics of an ROI, using ASTER L2 Surface Temperature (AST_08) data. My main objective is to be able to extract the average temperature within a 100 pixel area. I understand that this can be done by right clicking on the ROI layer and exporting the Statistics to a text file. When I do this, however, I can't make sense of any of the data.

    In Statistics, There shows a histogram. Below that it gives basic stats for band 1 (ROI): min, max, mean, std dev, yielding the values 2430, 2484, 2457.240000, and 12.2577786 respectively. What do these values refer to?

    Below this, they show the stats for the above histogram. DN, count, total, percent, Acc Pct. What does all of this mean?

    I understand this is a rather elementary question, but I couldn't find these variables defined anywhere on the ENVI website.

    I appreciate any guidance.

    MariM



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    10 Mar 2021 11:07 AM
    According to the data provider:
    https://lpdaac.usgs.gov/products/ast_08v003/

    You need to first apply a scale factor of 0.1 to the data to convert the integer values to floating point surface temperature in Kelvin. Then, when you extract the pixels of the ROI, the values will represent the min/max/mean/sd of the pixels in the ROI - which will be the min/max/mean temperature values within the ROI per band.

    The histogram represents the number of pixels that represent that value or 'range of values' set by the bin size.
    DN is 'digital number' which is a generic way of saying 'pixel value'
    Count is the number of pixels falling within that bin range for that band
    Total is the total number of pixels accounted for so far for that band
    Percent is the percent of pixels within a bin range
    Acc Pct is the accumulated percent of pixels for all bins in that band
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