Cloud Screening Using Proxy Photon Path Length Distributions Derived from High Resolution Spectra in the Near Infra-red
Abstract
Measurement of column amounts of trace gases from space using high resolution spectra of reflected sunlight in the near infra-red requires almost clear sky, and therefore reliable cloud screening. In a clear sky, photons will follow the direct path from sun to surface to satellite, because Rayleigh scattering is negligible in the near infra-red, so the distribution of photon path lengths will be a delta-function. A proxy for the photon path length distribution under any sky condition is recovered from high resolution spectra by representing the distribution as a weighted sum of delta-functions. Scenes are classified as clear or cloudy according to how closely the distribution approximates the ideal single delta-function for the direct path. An algorithm using the strong CO2 absorption band at 2 micrometers is described, and the efficiency and accuracy of the algorithm are characterized for observations over sun-glint using simulated spectra generated for multiple orbits of the Orbiting Carbon Observatory.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A43D..06O
- Keywords:
-
- 0360 ATMOSPHERIC COMPOSITION AND STRUCTURE / Radiation: transmission and scattering