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Remote Sensing - a tool for environmental observation

T shadow sites or sun exposed sites active

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T (shadow sites or sun-exposed sites, active evapotranspiration of vegetation, changes in the water content during subsequent observations etc.). Thermal diffusivity (k) refers to the ability of a material to transfer solar heating from the surface to the interior during daytime and at night, during a period of cooling, from the interior to the surface. It is defined as the ratio between the thermal conductivity and the thermal capacity times the density. Table 4.1 Kinetic versus radiant temperature for four material types. 4.5 Thermal sensors
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59 Thermal sensors used to record thermal images are often aboard aircrafts. Commercial applications of thermal imagery are the detection of heat losses from houses, buildings and factories and the survey of hot spots of buried pipelines that may indicate leakages. Furthermore, thermal images are used to survey evapotranspiration and to map geologic formation with different thermal properties. A number of satellites have also thermal scanners aboard. The Landsat TM has a thermal infrared scanner (10.4-12.5 μm) with a spatial resolution of 120 m. It is used for soil moisture mapping and evapotranspiration survey. The Enhanced Thematic Mapper (ETM+) of Landsat 7 carries a thermal infrared scanner with a spatial resolution of 60 m. NOAA-AVHRR has thermal infrared scanners in the two thermal atmospheric windows (3.55-3.93 μm and 10.5-11.5 μm) with a ground resolution at nadir of 1.1 km to measure top- cloud temperature and seawater temperatures. Figure 4.4 Effect of differences in thermal inertia on surface temperature during diurnal solar cycles. 4.6 Heat Capacity Mapping Mission: HCMM The data of the HCMM were intended initially for conversion to thermal inertia mapping of geological features. However, the images were also applied for vegetation survey and evapo- transpiration mapping (Curran, 1985; Galli de Paratesi & Reiniger, 1987). The HCMM satellite contained a scanning radiometer in visible and near infrared (0.55-1.10 μm) and a thermal infrared waveband (10.5-12.5 μm) with a ground resolution of 600 m to 1 km (depending on the viewing angle). The orbits of the satellite were arranged to ensure that images (of the United States and Europe) were obtained during times of maximum and minimum surface temperature (near 1:30 p.m. and 2:30 a.m.). The HCMM-satellite was launched in April 1978 and lasted until end 1980. Examples and a detailed description of HCMM can be found in Sabins (1987) and Galli de Paratesi & Reiniger (1987). 4.7 Interpretation of thermal infrared images
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60 On most thermal infrared images the brightest tones represent the warmest radiant (!) temperatures and the darkest tones represents the coolest temperatures. However be careful: as you will notice during the exercise, image processing techniques allow you to give every colour or grey tone to any digital number (reflectance value or temperature) in an digital image.
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