Evaluating the Absolute Calibration Accuracy and Stability of AIRS Using the CMC SST

Hartmut H Aumann,Evan M Manning,Robert C Wilson,Steven E Broberg,Thomas S Pagano

doi:10.3390/rs12172743

Hartmut H Aumann, Evan M Manning + Show 3 more

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https://doi.org/10.3390/rs12172743

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Abstract

We compare the daily mean and standard deviation of the difference between the sea surface skin temperature (SST) derived from clear sky Atmospheric InfraRed Sounder (AIRS) data from seven atmospheric window channels between 2002 and 2020 and collocated Canadian Meteorological Centre (CMC) SST data from the tropical oceans. After correcting the mean difference for cloud contamination and diurnal effects, the remaining bias relative to the CMC SST, is reasonably consistent with estimates of the AIRS absolute accuracy based on the uncertainty of the pre-launch calibration. The time series of the bias produces trends well below the 10 mK/yr level required for climate change evaluations. The trends are in the 2 mK/yr range for the five window channels between 790 and 1231 cm−1, and +5 mK/yr for the shortwave channels. Between 2002 and 2020, the time series of the standard deviation of the difference between the AIRS SST and the CMC SST dropped fairly steadily to below 0.4 K in several AIRS window channels, a level previously only seen in gridded SST products relative to the Argo buoys.

Highlights

The absolute radiometric calibration accuracy of any sounder is a complicated function of its design, its on-orbit thermal environment, likely degradation on orbit, and the scene temperature
We compare the daily mean and standard deviation of the difference between surface skin temperature (SST) derived from clear Atmospheric InfraRed Sounder (AIRS) data and collocated Canadian Meteorological Centre (CMC) data from the tropical oceans
After correcting the mean for cloud contamination and diurnal effects, the remaining bias relative to the CMC at the 100 mK level is reasonably consistent with estimates of the AIRS absolute accuracy based on the uncertainty of the pre-launch calibration

Summary

Introduction

The absolute radiometric calibration accuracy of any sounder is a complicated function of its design, its on-orbit thermal environment, likely degradation on orbit, and the scene temperature. Lower bounds on the absolute accuracy can be established by noting that most sounders make measurements in channels which have identical or functionally identical spectral response functions. The Atmospheric Infrared Sounder, AIRS [5], has several channels with nearly identical spectral response functions Differences between these nominally identical channels and trends in the differences constitute lower bounds on the absolute accuracy and stability of the calibration. They are lower bounds because there are shared elements in the calibration, which cancel in the difference. Another method is to note that all hyperspectral sounders make measurements in many atmospheric window channels. The differences between the derived temperatures and a reliable surface truth can be used as a measure of the absolute radiometric accuracy and stability

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