I tried to solve this issue. FLAASH defines azimuth as +/-180 deg.
We need to input azimuth from ground perspective, while our met file usually mentions azimuth from sensor.
So if metfile shows azimuth and zenith of 158.16 and 52.95 degrees respectively, then for flaash, it wud be 338.16 deg and 142.95 deg respectively. Is it right?

Hi..you can use the PCI Geomatica software or GRASS. For the atmospheric correction you will need the orbital parameters of the satellite when capturing images. otherwise in Help of these software, there are explanations.