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RE: The reflectance output of ENVISAT Product Reader API for C
I'm trying to read an AATSR Level-1B file with epr_api ( and I have a general question.

I'd like to calculate Top of atmosphere reflectance:

When we read data using epr_api, the reflectance values are already multiplied by pi and divided by cosine of solar zenith angle? which means we already have TOA reflectance?

or reflectance values are just sun normalized radiance? which means we need to multiply them by pi and divide them by cosine of solar zenith angle?

Best regards,
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RE: The reflectance output of ENVISAT Product Reader API for C
6/8/18 1:23 PM as a reply to soheila jafari.
The sun angle is not considered. Probably the following two links can help you.
Here is described what is done in the ground segment: AATSR Products User Guide - Algorithms

The following quote is taken from AATSR Products User Guide - - 1.6 micron forward view MDS
"The calibrated reflectance of each pixel on the image row (numbers 0 to 511) in the selected visible channel, measured in the forward view. The reflectance is not corrected for solar illumination angle."

In the EPR API only scaling factor and offset are applied to calculate the geophysical values from the raw counts.

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