Laboratory for
Climatology and Remote Sensing

Abstract:

Human activities during the last decades provoked a notable reduction in global forest cover. Knowing that forest stands act as stock and sinks for carbon and other greenhouse gases, it is important to determine the existing forest cover at country level and to calculate annual deforestation rates. This work uses NOAA satellite images in a resolution of 1 km x 1 km to classify the surface of continental Ecuador in “forest” – “non-forest” pixels and to estimate the annual deforestation rate from 1986 to 2001 as well as from 2001 to 2008. The method is based on a decision tree algorithm that includes different spectral bands of the NOAA-AVHRR sensor and additional topographic and meteorological parameters. The results show that the total forest cover of continental Ecuador was reduced from 48.1 % in 1986 to 36.8 % in 2008. The calculated annual deforestation rates indicate that forest reduction increased during the last decade. The most affected area is the Coastal Lowland, due to the enhanced population pressure, followed by the Amazon Basin, not only caused by the governmental supported oil and mining industry, but also due to the uncontrolled timber extraction. The Andean Highland has been less affected, because the major parts of this region were deforested before, during the Pre-Columbian-Era.

Abstract:

Two schemes for the determination of fog horizontal visibility using AVHRR data both, day and night, are presented. Ground truth has been performed by the comparison of calculated visibilities and simultaneous transmissometer measurements. The daytime approach is based on the calculation of fog albedo from AVHRR #1 and the relation of fog optical depth and geometrical thickness to spectral extinction and horizontal visibility. The mean deviation between observed and calculated visibilities is about 56 m. The nighttime approach uses the relation between fog and air temperature derived from AVHRR # 4 and 5 and a simple model for the approximation of the fog droplet distribution. The resulting fog extinction is directly related to horizontal visibility. Because fog optical depth is not available at night, the calculation of horizontal visibility using the nighttime approach is only valid if fog extinction is nearly homogeneous over the whole fog layer. Mean deviations between observed and calculated visibilities therefore slightly increase to about 61 m.

Abstract:

The development of a 4D GIS application for the realistic rendering of fog clearance is presented. The system comprises of a 2D raster GIS, a 3D volume rendering technique and a 4D animation procedure. The application extensively uses NOAA-AVHRR data to provide a realistic view of fog coverage and fog optical properties.