CALIBRATION OF THE NOAA AVHRR SHORTWAVE CHANNELS USING SPLIT PASS IMAGERY .1. PILOT-STUDY

A method of deriving in-flight calibration factors for Channels 1 and 2 of the AVHRR radiometer is described. The technique utilizes the dual views of a selected area of the ocean obtained from consecutive satellite overpasses, coupled with a radiative transfer model whose aerosol properties are constrained by surface measurements. The method is applied to a sample NOAA 11 data set obtained about 18 months after launch, and the sensitivity of the recovered calibration drift factors to uncertainties in the data and model parameters is examined. Best estimates of the calibration factors, defined as the fractional sensitivity relative to the preflight calibration, are 0.75 +/- 0.04 in Channel 1 and 0.76 +/- 0.06 in Channel 2. The Channel 2 result is subject to additional error due to uncertainty in the water vapor loading, and observational constraints on the water vapor profile will be necessary to ensure the success of the method in this channel.