Science Seminars

6/4/2009 – Gregor Morfill, Max-Planck Institut für extraterrestrische Physik Germany

Speaker: Dr Grant Matthews, ITT Space Systems Division
Date: Saturday, Jun 06, 2009
Time: 4:00pm
Location: LSTB

Seminar Abstract:

It is essential to maintain global measurements of the Earth’s Radiation Budget (ERB) from space, which are the scattered solar and emitted thermal radiative fluxes leaving the planet. These are required for purposes of validating current climate model predictions of our planet’s future response to anthropogenic greenhouse gas forcing. The measurement accuracy and calibration stability required to resolve the magnitude of model suggested cloud climate feedbacks on the ERB has recently been estimated. The suggestion is for ERB data to strive for a calibration stability of ±0.3%/decade for scattered solar, ±0.5%/decade for emitted thermal and an overall absolute accuracy of 1Wm−2. The Clouds and the Earth’s Radiant Energy System (CERES) is currently the only satellite program to maintain global ERB measurements, beginning in January 1998. However the new climate calibration standards are beyond those originally specified by the NASA CERES program for its Edition 2 data release. Furthermore the CERES instrument optics have been discovered to undergo substantial in-flight degradation due to contaminant issues. This is not directly detectable using established calibration methods. Hence user applied revisions for Edition 2 SW data were derived to compensate for this effect, described as ‘spectral darkening’. Also an entirely new in-flight calibration protocol has been developed for CERES that uses Deep Convective Cloud albedo as a primary solar wavelength stability metric. This is then combined with a sophisticated contamination mobilization/polymerization model. The intention is to assign spectral coloration to any optical degradation occurring to the different CERES Earth observing telescopes. This work quantifies the stability of revised Edition 2 data. It also calculates stability which the new protocols could give CERES measurements if used. The conclusion is that the Edition 2 revisions restore the originally specified stability of CERES SW data. It is also determined that the climate calibration stability goals are reachable using the new in-flight methodologies presented. This will however require data sets of longer than approximately 10 years. It shall also require obtaining regular raster scans of the Moon by all operational CERES instruments.