Earth Observation Data Group

Abstract:

The differing path lengths of AATSR's forward and nadir views can be used to separate the contributions from aerosol scattering and surface reflectance in the observed top-of-atmosphere (TOA) radiance. The nadir-view Oxford-RAL retrieval of Aerosols and Clouds (ORAC) scheme has been extended to take advantage of the dual-view capabilities AATSR offers. The new algorithm uses optimal estimation to retrieve aerosol optical depth at 550 nm, effective radius and the white-sky surface albedo at AATSR visible channel wavelengths. A comparison of retrieval results for the month of September 2004 with AERONET and MISR measurements is presented, along with some applications of the data to the Amazon region.

Abstract:

Envisat MERIS and AATSR data have been acquired in the framework of the Eurorisk-Preview project. The project addresses European civil protections and proposes to develop, at the European scale, new information services to support the risk management. In Italy one of the most important natural risks is due to the presence of volcanoes. Mt. Etna in Sicily, displays persistent activity, periodically interrupted by eruptions, which emit volcanic aerosol and ash to different altitudes in troposphere affecting the central Mediterranean area. In order to test the use of MERIS and AATSR data to derive emitted particles parameters as optical depth, effective radius and the ash mass of particles, the already developed remote sensing techniques has been adapted. MERIS and AATSR data acquired during the Mt. Etna 2002-2003 volcanic eruption has been chosen. The use of VIS and TIR bands of the two sensor demonstrates the potential to derive useful information on plume particles and to monitor the volcanic plume during eruption if frequent and high resolution data is available in near real time.

Abstract:

We use satellite observations of aerosol optical depth tau(a) and cloud effective radius r(e) from the ATSR-2 instrument in 1997 to investigate the Twomey indirect effect ( IE, -partial derivative ln r(e)/partial derivative ln tau(a)) in regions of continental outflow. We generally find a negative correlation between tau(a) and r(e), with the strongest inverse relationships downwind of Africa. North American and eastern Asian continental outflow exhibits a strong seasonal dependence, as expected. Global values for IE range from 0.10 to 0.16, consistent with theoretical predictions. Downwind of Africa, we find that the IE is unphysically high but robust ( r = -0.85) during JJA associated with high aerosol loading, and attribute this tentatively to the Twomey hypothesis accounting only for a limited number of physical properties of aerosols.