Remote sensing is the science and art of obtaining information about a phenomena without being in contact with it. Remote sensing deals with the detection and measurement of phenomena with devices sensitive to electromagnetic energy
There are two kinds of remote sensing. Passive sensors detect natural energy (radiation) that is emitted or reflected by the object or surrounding area being observed. Reflected sunlight is the most common source of radiation measured by passive sensors. Examples of passive remote sensors include film photography, infra-red, charge-coupled devices and radiometers. Active collection, on the other hand, emits energy in order to scan objects and areas whereupon a passive sensor then detects and measures the radiation that is reflected or backscattered from the target and the examples are Radar.
Remote sensing makes it possible to collect data on dangerous or inaccessible areas where it is not possible to take data , photos, or nay information we want to take, that is not possible to reach there, remote sensing helps in that areas and evaluate all observations we need from that. Some examples are like the effects of climate change on glaciers and Arctic and Antarctic regions, and depth sounding of coastal and ocean depths.
There are some very useful applications of remote sensing as follows:
- It provides a unique perspective from which to observe large regions.
- Sensors can measure energy at wavelengths which are beyond the range of human vision (ultra-violet, infrared, microwave
- Global monitoring is possible from nearly any site on earth.
Generally, speaking remote sensing works on the principle of inverse evaluation. The common example of this is to verify the type of animal from it’s footprints. The quality of remote sensing data consists of its spatial, spectral, radiometric and temporal resolutions. Using these four types of data, the results taken out from remote sensing are very accurate and significant. Evaluation from size of a pixel that is recorded in a raster image – typically pixels may correspond to square areas ranging in side length from 1 to 1000 meters comes under spatial significance. The number of different frequency bands recorded comes under the spectral significance. Radiometric resolution refers to the number of different intensities of radiation the sensor is able to distinguish. The temporal resolution is simply the frequency of flyovers by the satellite or plane, and is only relevant in time-series studies or those requiring an averaged or mosaic image as in deforesting monitoring. So, by the combination of all these four types of significances we are getting out the results from remote sensing which are very helpful to us.
As we can see in the military, in the time of war, remote sensing plays a very important role which can help in many ways. Digital image processing with help of remote sensing also plays a vital role in processing of satellite images. Object-Based Image Analysis is a sub-discipline devoted to partitioning remote sensing (RS) imagery into meaningful image-objects, and assessing their characteristics through spatial, spectral and temporal scale.