Land and Water Measurements with Passive Techniques

2 Land and Water Measurements with Passive Techniques 

In passive monitoring of land or water surfaces the reflective properties or the IR thermal emission are normally used. In earth resource monitoring the selective reflection properties of different types of materials, exposed to sunlight, are used. In Fig. 6.76 some reflectance curves are shown. 

Many substances and materials have characteristic spectral signatures in that part of the IR region which is not covered by photographic emulsions. As a general-purpose technique in wide wavelength regions Multi-Spectral Scanning (MSS) performed from an aeroplane, or better still a satellite, can be used. The principle of this technique is illustrated in Fig.6.77. 

Different points on the earth s surface are sensed sequentially using a scanner mirror placed in front of a light-collecting telescope. As the sensor platform moves forward, a certain strip ( swath ) on the surface is covered in a manner resembling the scanning on a TV screen. The radiation is divided up into different wavelength bands that are recorded in parallel detectors. After digitizing, the information is stored on a recorder or trans- 

IR measurements for assessing surface temperature are of interest in many contexts. One application is to monitor heat plumes in the sea outside nuclear power plants. The measurements can be performed with scanners in suitable wavelength bands or with special heat cameras, which are also used for monitoring heat leaks from houses in cold regions, and for industrial 

Multi-spectral aerial photography represents the simplest type of reflective remote sensing. A number of ahgned identical cameras equipped with different filters, are activated at the same time. This technique produces images directly and can be used to monitor land vegetation, and oil, algae and turbidity in water. The sensitivity of photographical materials only extends 

Receiving stations are distributed around the globe. The digital data must first be rectified to a normal map grid to eliminate the influence of the 

---