Remote Sensing - a tool for environmental observation

Otherwise the spectral signature with absorption

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otherwise the spectral signature with absorption features is lost in the overall reflectance (De Jong, 1994). Therefore, GERIS and AVIRIS have narrow bands in the optical range of the spectrum e.g.: Technical specifications of GERIS: ────────────────────────────── Wavelength range Module Channels Bandwidth ────────────────────────────── 0.477 - 0.843 μm VIS/NIR 31 12.3 nm 1.440 - 1.800 μm SWIR I 4 120 nm 2.005 - 2.443 μm SWIR II 28 16.2 nm ────────────────────────────── Average altitude: 3000 m Instantaneous field of view (IFOV): 90 ° Nominal ground resolution: 10 x 10 m Pixels per scanline: 512 Dynamic range: 16 bits AVIRIS has 224 contiguous spectral bands with a bandwidth of 10 nm between 0.4 and 2.5 μm and a nominal pixel size of 20 meters. Examples and applications of imaging spectroscopy will be discussed in the following sections. Intelligence Systems Apart from Earth observation systems and sensors available for the civil sector, there is a wide range of sensor systems used for intelligence purposes. There is only little information available about these sensor systems. CORONA was a very advanced intelligence system developed in
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36 the US in 1960 and was operational until 1972. It already provide B&W photos of the Earth surface at a resolution of approximately 50 cm. A Corona image of 1961 of Utrecht province is available in the course directory. Figure 2.6 shows a diagram of some intelligence sensors used today. Figure 2.5 Concept of imaging spectroscopy.
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37 Figure 2.6 Intelligence sensor systems as they are used today (NRC, 11 November 2001)
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38 Chapter 3 Remote Sensing in the Microwave Region (RADAR) 3.1 Introduction Radar is most often an active remote sensing system, it provides its own source of electromag- netic energy. The radar system ‘illuminates’ the terrain with electromagnetic energy with intervals of wavelengths between 1 mm and 1 m and detects the energy returning form the objects in the terrain. Passive Radar systems exists but the amount of energy emitted by objects (Stefan Boltzmann equation) in the microwave part of the spectrum is very small, consequently pixels must be large and bands must be wide. Radar is an acronym for Radio Detection and Ranging. Radar was developed during World War II for navigation and target location (Sabins 1987). These systems use the familiar rotating antenna and circular CRT (Cathode-Ray-Tube) display. Radar systems have a few important advantages over other remote sensing systems (FAO, 1993): 1. Due to its own energy source radar systems operate independent of the sun. Hence, observations are possible during day and night. 2. Control of the emitted electromagnetic energy in terms of frequency or wavelength, power and polarization.
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