I downloaded the MODIS AOD data from Terra. One HDF file has several (203 * 135) matrices depicting various things.
Now if I wish to find the value of the products at a certain location (coordinates are known), I am simply locating the pixel nearest to that location (from Latitude and Longitude subdatasets in the HDF file). Say the pixel is at row number r and column number c in the (203 * 135) matrix.
To find the AOD calculated by Deep Blue algorithm, can I simply open the subdataset [203 * 135] Deep_Blue_Aerosol_Optical_Depth_550_Land mod04 (16-bit integer), and refer to the value at row number r and column number c? Is this value the AOD I am looking for?
Thanks for helping out.
Nimish Mishra:
See these articles if it can help:
Yes Nimish, the AOD number at row r and colomn c is exactly what you are looking for.
Some times a 'scaling factor' is introduced, which is indicated in the file. But for AOD scaling factor is usually 1, so you do not need to make any correction to that number.
Hope this helps.
Francesca Barnaba
Thank you for your answer. I extracted the data and found AOD values to be in hundreds, some even greater than thousand. I think we have a scaling factor of 0.001 out here.
ok, if so, you should find mentioned in the file that the scaling factor is 0.001.
Dear Nimish Mishra
MODIS Conversion Tool Kit (MCTK) automatically apply scale factor and offset to provide actual values of AOD and reproject the data into geographic/UTM map projection. After getting data in projected coordinates, you can extract AOD values for your desired location (latitude/longitude).
Kind regards,
Bilal
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