Remote Sensing

Remote sensing

            Remote sensing is the acquisition or obtaining information about an object by a device that is not in contact with the object.

Remote sensing is used in numerous fields, including geography, land surveying and most Earth Science disciplines (for example, hydrology, ecology, meteorology, oceanography, glaciology, geology

Principles of Remote Sensing:

Remote sensing involves the detection and measurement of the radiations of different wavelengths reflected or emitted from distant objects or materials, which helps in their identification and categorization.

It offers four basic components to measure, which include:

i) The energy source

(ii) The transmission path

(iii) The target

(iv) The satellite sensor

Among these, the energy source or electromagnetic energy, is very important, as it serves as the crucial medium for transmitting information from the target to the sensor. 

Types of Remote Sensing:

Satellite remote sensing involves gathering information about features on the Earth’s surface from orbiting satellites, which may carry either of the following two types of sensor systems:

(i) Passive System:

It generally consists of an array of small sensors or detectors, which records the amount of electro-magnetic radiation reflected and/or emitted from the Earth’s surface. Thus, passive remote sensing relies on naturally reflected or emitted energy of the imaged surface.

Most remote sensing instruments fail into this category, obtaining pictures of visible, near-infrared and thermal infrared energy. A multi-spectral scanner is an example of a passive system (Fig. 11.3). Passive visible and near-infrared data are used in a variety of GIS applications, for example in the classification of vegetation and land-use, and may be performed at a variety of temporal and spatial scales.

(ii) Active System:

This type of a system propagates its own electro-magnetic radiation and measures the intensity of the return signal. Thus, active remote sensing means that the sensor provides its own illumination and measures what comes back. Remote sensing technologies that use this type of system include lidar (laser) and radar.

Synthetic Aperture Radar (SAR) is an example of an active system.

As for example, radar images are sensitive to the shape, orientation and size of leaves and their moisture content, rather than the vegetation color. Similarly, airborne lidars have been largely used for mapping surface topography in three dimensions. Existing and planned radar and lidar altimeters will also help in monitoring closely the elevation of the world’s ice caps and sea level with centimeter precision

Applications of Remote Sensing:

Satellite data allows the proper management of our renewable and non-renewable resources as it provides timely and detailed information about the Earth’s surface.

Following are a few examples of some of the important uses of satellite data:

(i) Assessment and monitoring of vegetation types and their status.

(ii) Agricultural property management planning and crop yield assessment.

(iii) Soil surveys including mineral and petroleum exploration.

iv) Litho logic mapping.

(v) Monitoring and planning of water resources and groundwater exploration.

(vi) Geographic information

(vii) Map making and revision and production of thematic maps.

(viii) Weather and agricultural forecasts and assessment of environment and natural disasters.

(ix) Urban planning.

(x) Image processing.

(xi) Precision geo-referencing.

(xii) Laser film writing and printing.

Applications of Remote Sensing in Forest Resource Management:

(i) Satellite imagery can provide the visible boundaries of soil types, while remote sensing provide for a shallow penetration of soils. Additional physical data can be obtained from spectral signatures for the soil surfaces.

ii. Multi temporal techniques can be used to map dynamical features, erosion and soil moisture.

(iii) Remote sensing can also be used in combination with ground radar, to detect changes of diagnostic soil horizons such as albic, spodic and argillic horizons or soil/rock boundaries.

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