DEVELOPMENT OF A NEW ALGORITHM FOR THE DETECTION AND CLASSIFICATION OF CLOUDS THROUGH SATELLITE IMAGERYAuthor:
Casanova Mateo Carlos.
Year:
2006.
University:
VALLADOLID [
www.uva.es].
Place of defense: Facultad de Ciencias.
Place of preparation: Facultad de Ciencias.
Summary: It has developed a new method for classifying clouds based on the traditional analysis of radiances of channels Visible and Infrared Thermal by setting thresholds over the height of the cloud. The radiances were obtained directly from the information provided by the relevant channels and height of the cloud through the analysis of the atmospheric soundings. The combination of the two sources of information has led to some very satisfying results. The method has been applied to the sensor MVIRI, aboard the satellite Meteosat-7, with data from the probe A / TOVS, flying aboard NOAA satellites. The results have been validated by analyzing different situations synoptic and mesoescalares, resulting in a large classified correspondence between the clouds and clouds are expected in situations analyzed. Also Metar data have been used for validation, with a match exceeds 85%. The method has been applied to the sensor satellites NOAA-AVHRR, using polls vertical probes A / TOVS with very satisfactory results. The emergence MODIS sensor, which flies aboard satellites and AQUA TERRA has led us to apply the method to this sensor. As a source of atmospheric soundings has chosen to use the probe AIRS, which gives better results that polls MODIS when compared with direct atmospheric soundings. To analyze the validity of our results seemed appropriate comparison with the algorithm institutional NASA, NOAA and the University of Wisconsin have developed for the detection of cloud pixels by MODIS but we find that the band 6 presented a problem bandeado (stripping) 14 of its 20 lines. We decided then bandeado correct this by applying a correlation between the lines well and the corresponding measures of the band 7. After verifying the validity of the procedure, we applied the algorithm for classifying clouds nominated sensor MODIS-AQUA with data from the probe AIRS. By validating the results compared to those resulting from the implementation of institutional MODIS algorithm, it was found that this is ill-suited to the Iberian Peninsula, which proceeded to adjust through foto-interpretación various subescenas duly selected as a 'pilot areas '. Finally there was a coincidence of 96'8% between the two procedures. Currently Meteosat Second Generation, MSG, or Meteosat-8, has replaced Meteosat-7. As the sensor SEVIRI has 12 channels, compared to 3 of the former Meteosat, the procedure has been applied to the sensor SEVIRI but adding an additional series of tests that are included in the algorithm institutional MODIS. Moreover, the atmospheric soundings are still getting the probe AIRS. The new test implemented are: - The difference between the temperature of brightness wavelengths 10.8 and 3.9 micrometers. - Quotient among reflectividades of 0.6 and 0.8 micrometers. - Test in the area of absorption of Carbon Dioxide (13.4 micrometers). We have established the appropriate thresholds for these new tests that have been included in our algorithm, in addition to those for the usual test channels Visible and Infrared Thermal, and the results have been validated by comparing the outputs of this new method with expanded and with the previous corresponding RGB compositions, with very satisfactory results.
