HR: 1340h
AN: A33D-0107    [Abstracts]
TI: Validation of Calibration Corrections Applied to EarthProbe TOMS in Response to Significant Instrument Degradation
AU: * Haffner, D P
EM: dhaffner@ssaihq.com
AF: SSAI, 10210 Greenbelt Rd., Suite 400, Greenbelt, MD 20706 United States
AU: Taylor, S L
EM: staylor@ssaihq.com
AF: SSAI, 10210 Greenbelt Rd., Suite 400, Greenbelt, MD 20706 United States
AU: McPeters, R D
EM: richard.d.mcpeters@nasa.gov
AF: NASA Goddard Space Flight Center, Code 916, Greenbelt, MD 20771 United States
AU: Labow, G J
EM: labow@chapman.gsfc.nasa.gov
AF: SSAI, 10210 Greenbelt Rd., Suite 400, Greenbelt, MD 20706 United States
AU: Jaross, G
EM: gjaross@ssaihq.com
AF: SSAI, 10210 Greenbelt Rd., Suite 400, Greenbelt, MD 20706 United States
AU: Bhartia, P K
EM: pawan.k.bhartia@nasa.gov
AF: NASA Goddard Space Flight Center, Code 916, Greenbelt, MD 20771 United States
AU: Wellemeyer, C G
EM: cwellemeyer@ssaihq.com
AF: SSAI, 10210 Greenbelt Rd., Suite 400, Greenbelt, MD 20706 United States
AB: EarthProbe TOMS solar calibration data show a dramatic, time-dependent decrease in instrument sensitivity of nearly 50% between 2000 and 2002. A simple thin film interference model suggests that contaminant build-up on the scan mirror is responsible. Also, analysis of unusual total ozone patterns across scans reveal a scan angle-dependent, wavelength-dependent instrument error in radiance sensitivity that developed at the same time. The angular dependence of radiance measurements interferes with on-board calibration, which requires equal radiance sensitivity across the angular range between the solar calibration diffuser and Earth-viewing scan angles. Soft calibration methods and inter-satellite comparisons have been used to assess these instrument changes. The scan angle dependence is captured assuming average longitudinal homogeneity of ozone at the equator across the 2200 km wide TOMS scan swath, and then characterizing radiances at all scan angles using ozone sensitivities. Overall trends in instrument sensitivity are determined using spectral discrimination analysis and total ozone comparisons with SBUV/2 instruments at the equator. Based on these results, calibration corrections were applied uniformly with latitude in the official reprocessing of the EarthProbe TOMS data using the new Version 8 algorithm. We have now extended the corrected dataset through June 2004. Results show 1-3% agreement with NOAA-11 and 16 SBUV/2 data at the equator, and independent comparisons with Brewer ground measurements show differences of 1-2%. However, these corrections are less effective at high latitudes, and measurements of ice radiance over Greenland and Antarctica suggest signal level-related issues may play a role. Users should exercise caution and evaluate the latter EarthProbe data (2000-present) for their specific purpose. Analysis of these data for long-term trends is discouraged. Overall however, the instrument has stabilized, and our corrections make TOMS data useful for inter-comparison with OMI in the coming year.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0341 Middle atmosphere--constituent transport and chemistry (3334)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting