The Radiometric Calibration Budget for the High-Resolution Dynamics Limb Sounder

C. W. P. Palmer Atmospheric, Oceanic, and Planetary Physics, Oxford University, United kingdom

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J. G. Whitney Atmospheric, Oceanic, and Planetary Physics, Oxford University, United kingdom

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Abstract

The High-Resolution Dynamics Limb Sounder is a 21-channel infrared filter radiometer due to be launched on the Earth Observing System Chemistry platform in 2002. The channels range in wavelength from 6.1 to 17.8 μm, with fractional widths of between 1% and 8%. The scientific objectives include the retrieval of atmospheric temperature and distributions of a range of minor constituents, the retrieval of geopotential height gradients, and the detection of atmospheric wave activity, by sounding the atmospheric radiance viewed at the earth's limb. These objectives require extremely accurate radiometry, with stringent limits on both errors that scale with the radiance and systematic offsets. The analysis presented shows explicitly how systematic errors in the in-flight calibration propagate into radiometric errors. Initial budget allocations to these error sources are made. An indirect calibration view of a small blackbody, rather than a full-aperture calibrator, is shown to have advantages in the case that the blackbody and the telescope optics are at the same temperature. The origins of scan-dependent offsets are discussed and shown to be significant error sources unless in-flight correction is possible. Two approaches for this are discussed.

Abstract

The High-Resolution Dynamics Limb Sounder is a 21-channel infrared filter radiometer due to be launched on the Earth Observing System Chemistry platform in 2002. The channels range in wavelength from 6.1 to 17.8 μm, with fractional widths of between 1% and 8%. The scientific objectives include the retrieval of atmospheric temperature and distributions of a range of minor constituents, the retrieval of geopotential height gradients, and the detection of atmospheric wave activity, by sounding the atmospheric radiance viewed at the earth's limb. These objectives require extremely accurate radiometry, with stringent limits on both errors that scale with the radiance and systematic offsets. The analysis presented shows explicitly how systematic errors in the in-flight calibration propagate into radiometric errors. Initial budget allocations to these error sources are made. An indirect calibration view of a small blackbody, rather than a full-aperture calibrator, is shown to have advantages in the case that the blackbody and the telescope optics are at the same temperature. The origins of scan-dependent offsets are discussed and shown to be significant error sources unless in-flight correction is possible. Two approaches for this are discussed.

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