Remote Sensing - a tool for environmental observation

Ers european remote sensing satellite a very

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ERS: European Remote Sensing satellite A very important satellite is ERS-1. ERS-1 is the first European satellite of the European Space Agency ESA was launched on 17 July 1991 and retired in March 2000. ERS-1 is shown in figure 3.11. Apart from a radar remote sensing system this satellite has several other instruments, which are briefly described here. A detailed description is given by ESA (1993). ERS-1 carries three principal sensors: 1. AMI: the Active Microwave Instrumentation with three modes, a Synthetic Aperture Radar (SAR) in the C-band (5.7 cm) in image mode and in wave mode and a Wind Scatterometer. 2. RA: the Radar Altimeter 3. ATSR: Along Track Scanning Radiometer with two instruments, a thermal infrared radiometer (IRR) and a microwave sounder (MWS). This satellite and its planned successors are aimed at worldwide monitoring of oceans, coastal waters, polar seas and ice and also will, to a more limited extent, be of significance to land applications e.g. agricultural statistics. The most important properties of ERS-1 for environmentalists are: ERS: 1. AMI: SAR-C system Altitude: 785 km 2. RA: Radar Altimeter: K u -band Inclination: 98.5 ° 3. ATSR-thermal radiometer Revisit period: ± 16 days SAR pixel size: ± 30 m ATSR pixel size: ± 50 km
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51 Figure 3.11 The ERS-1 satellite in the test room at ESTEC in Noordwijk NL. The AMI in image mode, SAR , obtains strips of high-resolution images (± 30 m), 100 km in width to the right of the satellite track with a nominal angle of 23 ° . Figure 3.12 shows an example of an ERS-1 SAR image. The AMI in wave mode measures the change in reflectivity of the sea surface due to surface waves and provides information on wavelength and direction of wave systems. The wind scatterometer uses three sideways looking antennae to measure radar backscatter from the sea surface for 50 km resolution overlapping cells. A mathematical model is used to compute surface wind vectors: speed and direction (ESA, 1993). The radar altimeter is a radar system looking straight down under the satellite and measure echoes from oceans and ice surfaces. It is used to derive information on wave height and sea surface elevation and/or on ice field topography. The ATSR, Along Track Scanning Radiometer has a thermal infrared radiometer to measure sea-surface and cloud-top temperatures over areas of approximately 50 by 50 km at an accuracy of 0.5 K. Many papers will soon be published on the technical performance and usefulness for environmental studies of ERS-1.
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52 A new instrument for ERS-2 is GOME: Global Ozone Monitoring Experiment . GOME is a nadir-viewing spectrometer which will observe solar radiation (240 to 790 nm with a spectral resolution of 0.2-0.4 nm) transmitted through or scattered from the earth’s atmosphere (stratos- phere). The recorded spectra will be used to derive information on the atmosphere’s content on ozone, nitrogen oxide, water vapour and other trace gases. This instrument is not designed to monitor the earth’s surface, therefore it uses spectral regions outside the atmospheric windows to collect information on the gases atmosphere using absorption spectra. A more advanced version
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