Thursday 28 May 2015

Remote sensing

 Remote Sensing 
                 Beyond the primitive methods of remote sensing our earliest ancestors used to standing on a high mountains or tree to view the landscape.  The modern discipline arose with the development of flight.  The balloonist made photographs of cities from their balloons. The first tactical use was during the civil war. Messenger pigeons, kites, rockets and unmanned balloons were also used for early images. With the exception of balloons, these first, individual images were not particularly useful for map making or for scientific purposes. 
               Systematic aerial photography was developed for military use beginning in World War I and reaching a climax during the Cold War with the use of modified combat aircraft.  A more recent development is that of increasingly smaller sensor pods such as those used by law enforcement and the military, in both manned and unmanned platforms. The advantage of this approach is that this requires minimal modification to a given airframe. Later imaging technologies would include Infra-red, conventional, doppler and synthetic aperture radar 
                 The development of artificial satellites in the latter half of the 20th century allowed remote sensing to progress to a global scale. Instrumentation aboard various Earth observing and weather satellites such as Landsat, the Nimbus and more recent missions such as RADARSAT and UARS provided global measurements of various data for civil, research, and military purposes. Space probes to other planets have also provided the opportunity to conduct remote sensing studies in extra-terrestrial environment, synthetic aperture radar aboard the Magellan spacecraft provided detailed topographic maps of Venus. 
                 Recent developments include, beginning in the 1960s and 1970s with the development of image processing of satellite images. Several research groups in Silicon Valley including NASA, developed Fourier transform techniques leading to the first notable enhancement of imagery data. 
The introduction of online web services for easy access to remote sensing data in the 21st century mainly low/medium-resolution images, like Google Earth, has made remote sensing more familiar to the every one and has popularized the science