You might want to confirm these terms with the data provider but the 'Sensor look angle' may be the same as the Zenith. If the data provider assumes nadir is 0 and the image is 'looking' at the ground 18 degrees off nadir, then in FLAASH you would subtract 18 degrees from 180 degrees, where 180 degrees is nadir in FLAASH. You do not have appropriate information for azimuth since it is the sensor azimuth, not the sun azimuth.

Thanks MariM for your support. I requested to the data provider information related to the Azimuth angle of the sensor. Kind regards,

Did you ever get an answer to that question? I'd also like to know the answer.

Hi guy.serbin, Yes, somebody from USGS-EROS Centre provided the following explanation: "The look angle should be equivalent to the satellite's zenith angle. The azimuth angle of the satellite can be found from the satellite's inclination angle, which is also a metadata field, and should be approximately 98 degrees measured from due west for day scenes. Off-nadir collections are always made perpendicular to the satellite's inclination. This means the satellite azimuth angle should always be approximately -82 or +98 degrees for day scenes, measured from true north." I hope it is useful for you, Paul

Thanks for information, I use 98 degrees as azimuth angle. however it is suggested to compute azimuth as the angle between side of the image and north, I think it will not change much Also check this thesis: https://helda.helsinki.fi/bitstream/h...