Remote Sensing - a tool for environmental observation

Lrr laser reflectometer for measure orbit altitude

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- LRR: Laser Reflectometer for measure orbit altitude calibration of the Envisat platform - SCIAMACHY: Scanning Imaging Absorption Spectrometer for Atmospheric Chartography for measuring the concentration of trace gasses in the atmosphere - AATSR: Advanced Along Track Scanning Radiometer for measure sea surface temperature to study ocean currents and El Nino - DORIS: Doppler Orbitography for Radiopositioning Integrated by Satellite. for measuring ocean surface topography and variations in ice coverage. Envisat has a sun-synchronous orbit with a mean altitude of 800 km. More information on Envisat and its launch can be found on the internet pages: http://www.esa.int and http://envisat.esa.int 2.4 Airborne Sensors Remote sensing observations are not only made from out of space but are also frequently carried out by sensor systems mountend in an aircraft. The systems used is always a trade off between technical possibilities, costs and the image specifications requested by the users. Furthermore, sensors in an experimental stage of development are often first tested in an aircraft before they are planned aboard satellites. Physical Geography of Utrecht is for example involved in feasibility studies of imaging spectrometers such as AVIRIS, DAIS7915 and GERIS. Some examples of airborne sensors are presented in the next sessions. CAESAR CAESAR is an acronym for CCD Airborne Experimental Scanner for Applications in Remote Sensing and is developed and built by the Dutch NLR and TNO. It can be used for terrestrial and marine surveys. For that purpose, it has a modular design in such a way that the sensors can be changed following the user’s requirements. The ‘land mode’ of Caesar has 3 spectral
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35 channels centred on 0.55, 0.67 and 870 μm. The spatial resolution depends on the altitude of the aircraft. At nominal altitude of 3000 m, the pixel size is around 0.75 m. A detailed study to the usefulness of CAESAR for vegetation survey is carried out by Kloosterman et al. (1991). Daedalus Another well-known airborne scanner is the Daedalus scanner. In its basic mode it has twelve channels from which seven in the visible wavelengths, three in the near infrared red part of the spectrum and two in the thermal bands. The spatial resolution at the nominal aircraft altitude of 19.5 km is around 25 m. GERIS and AVIRIS GERIS (Geophysical Environmental Research Imaging Spectrometer) developed by the GER- company and AVIRIS (Airborne Visible and Infrared Imaging Spectrometer) developed by the Jet Propulsion Laboratory (JPL) of NASA are so-called imaging spectrometers. Imaging spectroscopy refers to the acquisition of images in many, very narrow, contiguous spectral bands in the optical part of the spectrum: the visible, near-infrared and mid-infrared portions of the spectrum (Goetz et al., 1985). Spectral reflectance curves of minerals and some vegetation tissues have diagnostic, narrow absorption bands which allow their identification by remote observation (figure 2.5). Imaging spectroscopy requires a bandwidth of approximately 15 nm,
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