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Remote Sensing - Down The Memory Lane…
The technology of modern remote sensing began with the invention of the camera more than 150 years ago. Although the first, rather primitive photographs were taken as "stills" on the ground, the idea and practice of looking down at the Earth's surface emerged in the 1840s when pictures were taken from cameras secured to tethered balloons for purposes of topographic mapping.
 A photograph of aeronaut (hot air balloonist) Gaspard Felix Tournachon, who on October 23, 1858 applied for a patent for what we today call aerial survey. (Source http://www.correodelmaestro.com/anteriores/2005/abril/2artistas107.htm)  (The earliest aerial photograph still in existence (left): Obtained by aeronauts James W. black and Samuel A. King from a tethered balloon at an altitude of 1,200 ft on October 13, 1860 of downtown Boston. Source http://arch.ced.berkeley.edu/kap/1997_images/Background/History/boston.gif (Right) A satellite imagery of the same area (downtown Boston, MA, USA today, Source: Google Earth. The zest for viewing the terrain as a bird would lead man to think of rather novel ways, since the first airplane was still to be successfully flown. In 1903 probably a few months before the success of the Wright brothers, Julius Neubronner from Germany patented a breast-mounted aerial camera for carrier pigeons. The results were not very spectacular, but it was still an attempt at aerial photography.  A pigeon equipped with a lightweight camera (left), and an oblique aerial photograph obtained from a camera carried by a pigeon. (Source: http://latteier.com/pigeoncam/) Aerial Photography - The dawn of Photogrammetry The airplane was invented in 1903 but was not used as a camera platform until 1909, when the first aerial motion pictures were taken during a flight by Wilbur Wright in Italy. With the advent of World War I, aerial photography became indispensable for military reconnaissance. By the First World War, cameras mounted on airplanes provided aerial views of fairly large surface areas that proved invaluable in military reconnaissance. The science of extracting quantitative data about terrain height, slope and dimensions of objects on ground using overlapping aerial photographs was perfected, giving birth to the field of Photogrammetry. From then until the early 1960s, the aerial photograph remained the single standard tool for depicting the earth's surface from a vertical or oblique perspective. The greatest advances in aerial photography and photointerpretation came with the Second World War, and the majority of subsequent advances in the field were an outgrowth of military development. Today, digital aerial photography and digital photogrammetry are still unbeaten contenders for quantitative data extraction though Satellite remote sensing is more popular due to easy availability and low cost. Satellite Remote Sensing Remote sensing from space received its first impetus through remote sensing from rockets. As early as 1891, the Germans were developing rocket propelled camera systems, and by 1907 gyro-stabilization had been added to improve picture quality. Space remote sensing began in earnest in the period 1946-50 when many cameras were carried on rockets and ballistic missiles. In 1946, V-2 rockets acquired from Germany after World War II were launched to high altitudes from White Sands, New Mexico. These rockets, while never attaining orbit, contained automated still or movie cameras that took pictures as the vehicle ascended. The development of meteorological satellites provided the impetus for most modern remote sensing. TIROS-1 was launched by US in 1960 and returned the first coarse views of cloud patterns. With refinements in imaging sensors meteorologists began to collect information on terrestrial features as well and the concept of looking through the atmosphere evolved.  The first non-photo sensors were television cameras mounted on unmanned spacecraft and were devoted mainly to looking at clouds. The first U.S. meteorological satellite, TIROS-1, launched by an Atlas rocket into orbit on April 1, 1960 is seen on the left. The image on the right is one of the first (May 9, 1960) returned by TIROS-1; Superimposed on the cloud patterns is a generalized weather map for the region. Source: http://rst.gsfc.nasa.gov The early 60' saw the development of the Corona orbital satellite reconnaissance program by the CIA and U.S. Air Force while the Soviets launched the Zenit-2, keeping in tune with the cold war between the two then super powers and the atmosphere of suspicion and paranoid fear. . The manned space flights of the 1960's and 70's yielded spectacular photographs of the earth's surface where earth-orbiting cosmonauts and astronauts acted much like tourists by taking photos out the window of their spacecraft and lead to the first use of multi-spectral and microwave instruments from space. Following the success of these missions the first earth resources satellites were planned in 1967 and the ERTS-1 (later renamed Landsat 1) satellite was launched by NASA in 1972, in what was to become the forerunner to the Landsat program becoming the first readily available satellite imagery to be commercially exploited, and which continues to be so.  First Corona Satellite Reconnaissance photograph (left): Mys Schmidta Air Field, U.S.S.R on August 18, 1960. (Source: http://www.nro.gov/corona/corona2.jpg, Credit - American Society of Photogrammetry). These images were declassified in 1996. On the right is a satellite imagery (at a much higher resolution) of the same area, readily accessible to public (Source: Google Earth) The availability of the Landsat 1 data, in the mid 70's, led to a boom in development of digital image processing techniques. The first satellite borne multispectral scanners on board the Landsat 1, 2 and 3 were opto-mechanical. The Landsat 4 (1982) was the first to be equipped with a solid state CCD array scanner in its seven band Thematic Mapper sensor (TM). In the last 35 years, satellite remote sensing has reached a level of resolution finer than 1m. What began in 1971 with a course resolution of 79m has today reached sub-meter levels.  The first multispectral photography from space happened during the famous 1968 Apollo 9 mission. Scientist mounted four Hasselblad cameras in a holder such that they all aimed at the same target point when an astronaut triggered their shutters simultaneously. Below are three filtered b & w photos of southern California around San Diego, which the astronauts took in the 1.green, 2. red, 3. photo IR bands, and 4. is a (false) color IR picture generated from a combination of 1,2 and 3. Source: http://rst.gsfc.nasa.gov/Intro The demand for geometrically corrected and georeferenced, very high-resolution multi spectral data is ever increasing. With the supply barely meeting the requirements and demand, the market for such data is large. India is today a global player in the field of remote sensing. With the launching of IRS 1C in 1995, ISRO, made available for the first time 5m panchromatic data, which was available earlier at a resolution of 10m from the SPOT 1 (1986), 2 and 3 satellites.  The Mumbai International Airport seen in false colour composites made from IRS data at various resolutions. 1. IRS 1A LISS I (72.5m), 2. IRS 1B LISS II (36.25m), 3. IRS 1C LISS III (23.5), 4 IRS 1C LISS III + PAN (5m) The use of space borne sensors is today not limited to obtaining data about the earths land surface alone. Specifically designed sensors acquire data about ocean surface characteristics, land surface temperatures, cloud formations, snow caps, magnetic and gravity anomalies, biomass content in oceans, ocean color to name just a few. Though development of satellite remote sensing systems was mainly from governmental organizations of various countries, in 1995 a private company, Orbimage launched the first commercial remote sensing satellite. This has been followed by Digitalglobe and Space Imaging launching their own satellites. |