Abstract. Information content analysis is used to select channels
for a marine liquid cloud retrieval using the high-spectral-resolution oxygen
A-band instrument on NASA's Orbiting Carbon Observatory-2 (OCO-2). Desired
retrieval properties are cloud optical depth, cloud-top pressure and
cloud pressure thickness, which is the geometric thickness expressed in hectopascals.
Based on information content criteria we select a micro-window of 75 of the
853 functioning OCO-2 channels spanning 763.5–764.6 nm and perform a series
of synthetic retrievals with perturbed initial conditions. We estimate
posterior errors from the sample standard deviations and obtain ±0.75
in optical depth and ±12.9 hPa in both cloud-top pressure and cloud
pressure thickness, although removing the 10 % of samples with the highest
χ2 reduces posterior error in cloud-top pressure to ±2.9 hPa
and cloud pressure thickness to ±2.5 hPa. The application of this
retrieval to real OCO-2 measurements is briefly discussed, along with
limitations and the greatest caution is urged regarding the assumption of a
single homogeneous cloud layer, which is often, but not always, a reasonable
approximation for marine boundary layer clouds.