Extended Abstract (224K)P5.28
INTERCOMPARISON OF CERES SCANNING AND ERBS WFOV NON-SCANNING RADIOMETERS
David A. Rutan, AS&M, Hampton, VA; and G. L. Smith, R. B. Lee, and T. Wong
Measurements from the Clouds and Earth's Radiant Energy System (CERES) scanners aboard the Tropical Rainfall Measurement Mission (TRMM) and the Earth Observing System (EOS) Terra satellites are compared with measurements from wide field-of-view (WFOV) radiometers aboard the Earth Radiation Budget Spacecraft (ERBS) on a quasi-instantaneous basis. The different satellite orbits are collocated in space and time then CERES radiances are numerically integrated within the field of view of the non-scanner to compute longwave and shortwave fluxes which simulate the observations measured by the WFOV instruments. The difference in direction of the radiation between that measured by the scanning radiometer and that measured by the WFOV radiometer is taken into account by the use of bidirectional reflectance distribution functions for the shortwave and limb-darkening functions for the longwave radiation.
The ERBS has an altitude of 620 km. TRMM is much lower at 350 km and Terra is slightly higher at 705 km. As a consequence the swath width measured by the TRMM/CERES scanner is narrower than the field of view of the WFOV radiometers for ERBS. It is thus necessary to extrapolate the scanner results to cover the WFOV observation, adding to the random scatter of the results. Because of Terra's higher altitude, coverage of the WFOV footprint by the Terra/CERES scanner is near complete.
At night, longwave radiation measurements come from total radiation channels of both instruments. The mean longwave flux at ERBS altitude at night for the orbit intersection points is found to be 212 W-m**-2 for the WFOV and the CERES/TRMM result is 1.7 W-m**-2 higher so that the total channels of the two instruments agree to better than 1 percent. The mean shortwave flux measured by the shortwave WFOV radiometer is 162 W-m**-2 and the TRMM/CERES result is 2.4 W-m**-2 lower for an agreement of better than 2.0 percent. The daytime longwave results depend on the total and shortwave channels for each instrument. The mean daytime longwave flux at the ERBS spacecraft is measured by the WFOV to be 221 W-m**-2 and the result computed from CERES radiances is 4.0 W-m**-2 higher, or 1.7 percent. Results of comparisons between the Terra/CERES instrumentation and the ERBS WFOV will be presented.
Poster Session 5, New Technology and Methods
Wednesday, 17 October 2001, 2:15 PM-4:00 PM
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