1. Sun as a Source of Energy: Sun is the prime source of energy to the world. It is the resource for all activities of the life forms.
2. Emission of Sun's Energy : Solar energy is emitted into the space. The emission is in the form of various electromagnetic waves. It consists of gamma rays to radio waves (short wave length). This band of rays is called the 'electromagnetic radiation' (EMR).
3. Interaction of Solar Energy with Atmospheric Elements: When the solar energy passes through the atmosphere, many elements await to meet the energy. A portion of the 'electromagnetic radiation' is absorbed by carbon di oxide, ozone, moisture and dust and reflected back. So, the balance of electromagnetic radiation reaches the earth's surface as sunlight.
4. Interaction of Sunlight with Terrestrial Features: Electromagnetic waves in sunlight have different wave lengths. A number of bands can be identified based on the wave lengths. These bands of radiation fall on the objects of the earth and get reflected, differently by different objects. The reflectance varies according to the wave length. Through such reflectance, various wave lengths help in remote sensing to identify various elements over the earth. Thus, the spectral reflectances from the earth, in fact earth objects, are of many thousand types.
5. Terrestrial Radiation of the Earth's Element: The solar energy, along with the energy already stored in the elements on the earth, are radiated back into the atmoshpere. Any object, with a temperature of about 0o K (273o C) will emit energy. Thus, all objects over the earth have temperatures above 0o K and therefore emit energy at varying levels.
6. Collection of Information/Data: The energy thus reflected and emitted by the earth's features are recorded by cameras and sensors fitted onto the various platforms. The cameras record the energy in films and the sensors convert the energy into electrical signals and send them to the earth's receiving stations.
7. Data Acquisition by the Earth Station: The electrical pulses from the remote sensors are converted into 'digital' numbers. Each point or picture element gets different (pixel) digital numbers. Thus, a satellite image is composed different digital values or pixels.
8. Remotely Sensed Data Supply: Satellite images and the aerial photographs can be obtained from three organisations or places in India as indicated below:
National Remote Sensing Agency, Hyderabad
Indian Air Force, New Delhi
Air Survey Company, Calcutta.