Publication Abstracts

Brest et al. 1997

Brest, C.L., W.B. Rossow, and M.D. Roiter, 1997: Update of radiance calibrations for ISCCP. J. Atmos. Ocean. Technol., 14, 1091-1109, doi:10.1175/1520-0426(1997)014<1091:UORCFI>2.0.CO;2.

Since July 1983 ISCCP has collected, normalized and calibrated radiance data (visible and thermal infrared) from the imaging radiometers on the NOAA polar orbiters and from the geostationary staellites, GOES, METEOSAT and GMS. Although analyzed by ISCCP to obtain information about clouds, this global radiance dataset also represents a valuable resource for other remote sensing studies. Examination of the 8-year cloud climatology produced with the first version of the ISCCP calibration revealed artifacts in the global means that coincided with the changes in the afternoon polar orbiters (used as a reference standard), as well as some localized anomalies related to occasional errors in the geostationary normalizations. This paper reports the changes to the ISCCP normalization and calibration procedures (originally reported in Brest and Rossow 1992) that have been made to reduce these artifacts and errors and to produce a revised calibration. The key assumption, made after examining more than 10 years of global data, is that the mean proporties of Earth are more nearly constant over this time scale than are calibrations of these radiometers. We conclude that the relative calibrations of the radiances used by ISCCP are now uncertain on average by no more than ±0.01-0.02 absolute, ±3-5% relative, for VIS radiances and ±1-2K absolute, ±0.3-1.0% relative, for IR radiances. We estimate the absolute calibration uncertainty to be about 10% for VIS and 2% for IR. The history of efforts to calibrate AVHRR points to some lessons important to future spacecraft observations of climate change: real decadal scale changes of Earth are much smaller in magnitude than uncertainties in calibration change and cannot be reliable detected without significant improvements of instrument calibration; infrequent aircraft calibration results for AVHRR with their attendant uncertainties make it difficult to distinguish real interannual variability from short-term calibration changes and suggest that something more will be required to obtain the needed accuracy; and finally, even calibrations based on on-board targets may not be sufficient, given that still find differences in IR calibrations of more than 1K. these results suggest, in particular, that reliance on one method of calibration for future spacecraft missions is unlikely to reduce calibration uncertainties enough for climate change monitoring. Even with improvements in all of these areas, the relative accuracy attained will only be apparent in the contect of a long data record.

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BibTeX Citation

  author={Brest, C. L. and Rossow, W. B. and Roiter, M. D.},
  title={Update of radiance calibrations for ISCCP},
  journal={J. Atmos. Ocean. Technol.},

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RIS Citation

ID  - br03000u
AU  - Brest, C. L.
AU  - Rossow, W. B.
AU  - Roiter, M. D.
PY  - 1997
TI  - Update of radiance calibrations for ISCCP
JA  - J. Atmos. Ocean. Technol.
VL  - 14
SP  - 1091
EP  - 1109
DO  - 10.1175/1520-0426(1997)014%3C1091%3AUORCFI%3E2.0.CO;2
ER  -

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