Remote Sensing basics and Remote Sensing satellites
This page of satellite tutorial covers remote sensing basics and provides very useful information on remote sensing satellites.
Remote sensing is a technique for studying the land,ocean and atmosphere using instruments called as sensors mounted on satellites and aircrafts. The sensors help create the images of any location of the earth. There are two types of sensors viz. passive and active.
Passive sensors require natural energy and can detect energy falling on them. The passive sensors such as high definition cameras and electro-optic scanners record the sunlight reflected by objects in the form of a photograph/data which can be converted to an imagery. The sun's heat reflected by objects(i.e. reflective infrared radiation) and the temperature of hot objects(i.e. thermal infrared radiation) are recorded using infrared film and infrared scanners. Often low levels of very high frequency radio waves emitted by objects are detected by sensors referred a radiometers.
Different objects emit different wavelength and hence distinguised by different colors in the image as mentioned in the following table.
| Color | Earth resource |
|---|---|
| Black | Clear water |
| Blue | Turbid water |
| Cyan | Base soil and buildings |
| Green | dense forest |
| Orange | Grass |
| Red | Base soil/Builtup area |
| White | Buildings |
| Yellow | Shrubs and less dense forests |
Active sensors provide their own source of energy. These type of sensors emit radiation towards the target and detects the reflected radiation from the target.
Following are the silent features of a typical remote sensing satellite or radiometer.
• They are placed in a orbit at a distance of 800 to 900 Km
• Orbit period is usually about 90 to 100 minutes.
• Placed in sun-synchronous with inclination of 99o.
• Wavelength band 0.4 to 0.9 µm
• Swath: 180/70/40 Km
• Resolution:80/40/15 meters
• Repetivity:once in 20 days
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