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Unformatted text preview: Two important advantages of multi-spectral scanning are: - Objects at the surface of the earth have varying reflection behaviour through the optical spectrum, they can be recognized and/or identified more easily using several spectral bands than using just one band. - A large number of objects do not reflect radiation very well in the visible part of the spectrum. Remote sensing observations outside the visible wavelengths or in combination with observations in the visible spectrum produce a much more contrasting image, which is helpful to identify objects or to determine their condition. 2.2 Meteorological Satellites and their Sensors NOAA-AVHRR The first satellite for remote sensing observations was launched in 1960 and was called TIROS: Television and Infrared Observation Satellite. It was developed for meteorological purposes by the National Oceanic and Atmospheric Administration (NOAA) of the USA. This early weather satellite sent down rather coarse views of cloud patterns. NOAA refined the sensors and the orbits of TIROS and has continued and will continue to launch weather satellites. One of their most famous series of satellites among environmentalists is the NOAA-AVHRR (NOAA- AVHRR 12 was launched on 14 may 1991). AVHRR stands for Advanced Very High Resolution Radiometer and was also built for meteorological observation. It has a near-polar, sun-synchronous orbit at an altitude of approximately 830 k. Due to its large field of view, its 25 spatial resolution is low (i.e. its pixel size is large: ± 1.1 k). Lillesand & Kiefer (1994), page 502 and colour plate 16, 17 and 18 show examples of NOAA-AVHRR images. It has the following five spectral bands: NOAA-AVHRR: 1. 0.58 - 0.68 μm Altitude: 830 k 2. 0.72 - 1.10 μm Orbit incl.: 98.9 ° 3. 3.55 - 3.93 μm Repeat time: 1 day 4. 10.5 - 11.5 μm IFOV: ± 1.1 k 5. 11.5 - 12.5 μm NOAA-AVHRR are used by environmentalists to monitor changes in vegetation cover at a continental scale e.g. Tucker et al. (1986) and Tucker et al. (1984). NOAA-AVHRR data are also used for the ARTEMIS project (the Africa Real Time Environmental Modelling using Imaging Systems). This project of the Food and Agricultural organization (FAO) was funded by the Netherlands and aims at supplying a continuous, real-time overview of the ecological conditions of the African continent. This enables planners to avoid famine due to bad harvests. The point of contact in the Netherlands to obtain NOAA images is the KNMI at de Bilt. NIMBUS The NIMBUS satellite, the first NIMBUS was launched in 1964 and NIMBUS-7 was put in orbit in 1978, was developed by NASA for meteorological and oceanographic research: measuring sea water temperature, to map phytoplankton concentration and suspended materials....
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- Winter '12
- Remote Sensing, Electromagnetic spectrum, µm, Infrared