System Noise in the NESDIS TOVS Forward Model. Part II: Consequences

Abstract

To utilize satellite radiance sounding data, in either explicit or implicit retrieval algorithms, a proper understanding of the noise in the measurements is required. Conventionally, to define the expected accuracy of atmospheric profiles inferred from sounder data, instrument noise equivalent temperature difference (NE?T) noise specifications have been used to simulate spacecraft data. Here it is demonstrated that NE?T noise specifications are inappropriate for this purpose. Instead, total system noise estimates should be employed since use of sounding data in any type of physical retrieval algorithm implies application of a radiative transfer model, which in turn must be ?calibrated? against in situ and satellite data. It is demonstrated that the accuracy of atmospheric retrievals inferred from the TIROS Operational Vertical Sounder radiometers is limited by the total system noise rather than NE?T noise, and that modeled radiance temperatures perturbed by Gaussian total system noise very nearly replicate the accuracy statistics of retrievals computed from satellite measurements. The implications of these results for planned high-resolution infrared sounding instruments are briefly discussed.