Data from Remote Sensing
Earth resource information satellites have been operated by space agencies since the beginning of the 70’s. The 1999 updated and improved earthwatch satellite Landsat-7 with the high-resolution and multi-spectral remote sensing system “ETM+ (Enhanced Thematic Mapper)” orbits the earth in an almost-true polar orbit at an altitude of 705 km (for detailed information: www.nasa.gov). Landsat 7 carries a multi-spectral scanning system called the “Thematic Mapper” ™. The satellite images a 185 km-wide strip along the earth during each orbital cycle of 1-1/2 hours. The entire surface of the earth is thus surveyed in 16 days. The satellite passes over Berlin and environs in about 20 seconds. Data is digitalized and radio-transmitted to ground stations, which record it on magnetic tape. Since April 1999 Landsat7 has a thermal resolution quality about 3,100 points, or pixels, per line. Each point equals a surface area of 60 m x 60 m. This means dissolution is higher a 4-fold opposite than the overflight with Landsat 5 in the year 1991 (cf. map 04.06 edition 1993). Flight patterns during the day and night are not identical, resulting in different image sectors in the resulting maps. Night scans of this area must be specially ordered by way of the ground station of the European Space Agency (ESA) in Italy.
The seven total spectral ranges of the Landsat-TM are in wavelengths from the 0.45 µm of blue-green light, to the 12.5 µm of heat-infrared. Two spectral canals are available in the thermal infra-red on that occasion. The spectral interpretation of both canals is the same and corresponds to Landsat 5 TM.
The longwave spectrum between 10.4 and 12.5 µm was selected for the imaging of surface temperatures. This portion of longwave radiation emanating from the earth itself can pass relatively undisturbed through the atmospheric layers. It is called the “infrared window”.
Choices for the two imaging scans were coupled to the time periods that the satellite was over the Berlin area (the time periods could not be changed) during the early evening and the morning of the following day. The selection was also coupled to certain meteorlogical requirements. A recording of the behavior of surface structures as precisely as possible requires that there will be no influence on the area to be examined by clouds, previous precipitation, or too high wind velocity. Consideration of these requirements during the summer half-year of 2000 allowed usable images only during the time periods of the evening of 13 August 2000, 21:45 and the following day of 14 August 2000, 10:30. The meteorological conditions measured at the Dahlem Station of the Free University of Berlin were:
- 13 August, 22:00 CET: Cloudiness, 0/8; wind velocity, 3.0 m/s; air temperature at 2 m altitude, 19.2°C
- 14 August, 10:00 CET: Cloudiness, 1/8; wind velocity, 2.0 m/s; air temperature at 2 m altitude, 24,2°C
The conditions were different in the comparison to the preceding satellite picture reception from the year 1991, that fell into a phase of extreme dryness, in the run-up to this reception. The weather was embossed in the first half of the August in Germany of a change of different air masses and corresponding precipitation activities. A high pressure area led to beginning of the second monthly half to dry and increasingly warmer weather, with temperatures at the 14.08. of more than 30 °C. So some stations reached its monthly maximum. This time coincided with the Landsat-remote sensing fortunately.
Geometrical correction of the scenes was executed by means of passport point regulation opposite the vector data of the land-use structures of the Information System Urban and Environment. Also the panchromatic bond 8 with a grid of 15 m standing with Landsat 7 was used for the improvement of all other relating data.
Data from Terrestrial Measurement
At the same time experts from the Institute of Ecology conducted a climate survey. Measurements were taken of air temperature, wind, and vapor pressure at an altitude of 2 m. The surface temperatures of homogenous structures, such as surface waters and on open areas south of Berlin, were determined by analogic technology. It was thus possible to compare calculated with actually measured surface temperatures.