Improvement to above_classifier in ATL08 PhoREAL Processing

[ejguenther]

It has been found that only applying the above_classifier flag when optical depth is low improves the classification - restricting the algorithm to only operating in clear sky conditions and reduces the likelihood of false positives in low-cloud/foggy conditions.

Optical depth will be added as a new field to ATL08 in v007, however, currently, the optical depth information is column_od_asr in ATL09. When column_od_asr are lower than 0.05 then the above_classifier flag can be active, when values are above 0.05 then the flag needs to be deactivated for photons in the related segments.