The ACOS/OCO-2/OCO-3 ABSCO tables are “lookup tables” that supply cross section values for absorbing gases in the Level 2 algorithm (L2) retrieval process. They record molecular absorption cross-sections over the range of relevant wavelengths, temperatures, and pressures in units of cm^2 /mol for the gases O2, H2O, and CO2. During the L2 generation process the retrieval algorithm computes atmospheric absorption at each relevant temperature, pressure, and wavelength using linear interpolation. Successive versions have refined these tables by incorporating new laboratory results and theoretical models for increasingly accurate absorption coefficients. ABSCO tables are released together with each major build of the OCO-2 Level 2 algorithm.
The tables can be computed at a spectral resolution of 0.002 cm^-1 (required for validation of the tables using high resolution laboratory spectra) but the current L2 retrieval code uses a spectral resolution of 0.01 cm-1.