High-resolution cloud motion analysis with Meteosat-6 Rapid Scans, MISR and ASTER

In this study, coincident images of Meteosat-6, MISR (on EOS Terra) and ASTER (on EOS Terra) are used to analyze the cloud motion field in high temporal and spatial resolution. The Multi-angle Imaging SpectroRadiometer (MISR) has nine cameras at different viewing angles, -70.5° (named DA), -60.0° (CA), -45.6° (BA), -26.1° (AA), 0.0° (AN), 26.1° (AF), 45.6° (BF), 60.0° (CF), and 70.5° (DF), and a spatial resolution of 275 m. The time delay between the MISR camera views is 40-55 s, resulting in a total time span of about 7 minutes between DF and DA. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) VNIR subsystem provides nadir and backward looking stereo images of channel 3 (870 nm), with a spatial resolution of 15 m. The stereo configuration is given with the setting angle of 27.6° between the nadir and the backward telescope. The ASTER nadir view (3N) is simultaneously acquired with the MISR AN view, while the backward view (3B) is taken about 55 s later. In the presented case study, the coincident images from the three sensors allow a precise characterization of the cloud motion field on different spatial scales. The stereo matching and tracking is done with a cloud-adapted leastsquares matching (LSM) algorithm, developed at our Institute. The retrieved cloud motion winds (CTW) from the Meteosat-6 10-minute Rapid Scans have an accuracy of 2 m/s in East-West direction and an accuracy of 3 m/s in North-South direction; the MISR CTWs have a cross-track accuracy of about 2 m/s and an acrosstrack accuracy of 5-6 m/s and the ASTER cross-track winds can be retrieved with an accuracy of 0.5 m/s. This study shows that the Meteosat-6 10-minute Rapid Scan Service is an important component for the comparison of cloud motion products from geostationary and polar-orbiting satellites; in the near future, the MSG 15-minute Scans will further increase the comparison and validation possibilities of cloud motion winds over Europe.