Landsat Applications to Agricultural and Urban Feature Analysis
Brief History of Remote Sensing
The term remote sensing, if interpreted literally, could include any type of photography or sensing device that is at some distance, and thus not in direct contact, with the subject of interest, but that is capable of providing some information about that subject. However, now when the term remote sensing is used, it is mostly with respect to the discipline of acquiring reflected electromagnetic radiation through the use of sensors that are mounted on satellites or manned earth orbiting platforms at altitudes above the Earth’s atmosphere. The electromagnetic radiation utilized could be passive (naturally occurring) or active (generated by the remote sensing instrument). Also included is imagery acquired at high altitudes within earth’s atmosphere as well as some applications that utilize sonar signals. Generally, aerial photography from conventional airplanes is not considered remote sensing as the term is currently used, although strictly speaking, it is also a form of remote sensing.
Examining the history of remote sensing involves looking at the development of three different types of technologies. One technology involves the ability to create a record of a scene that can be saved and displayed visually at some point in the future. Another technology involves the capacity to place a sensing device at some altitude above the scene of interest. Integral to the development of the two mentioned technologies, as it relates to the current state of remote sensing, is the development of data processing technologies. As each one of these is an extensive topic in itself, we will only take a quick look at the development of these three technologies: photography, aviation, and computer science.
The first permanent photograph was acquired by Jospeh Niepce in 1826. The first aerial photographs were acquired beginning in the 1860’s from balloons and kites. Later, airplanes provided the ability to cover specific areas but also provided a greater range accessible per flight session. The first aerial photograph from a plane appears to have been taken in 1908 by Wilbur Wright of the Wright brothers who were also responsible for the first powered airplane piloted by Orville Wright in 1903.
The first electronic transmission of a visual scene was conducted by Arthur Korn in 1906.
The first US high altitude images taken from above the earth’s atmosphere were acquired in 1947 from a video camera mounted on a V-2 rocket that had been acquired from Germany during WW-II. The first digital image was produced on a computer in 1957 by Russell Kirsch at U.S. National Bureau of Standards. Kirsch is also recognized as one of the contributors to the first programmable computer built in the US.
Computing technology has a long history beginning with the development of the Sumerian abacus more than 4,000 years ago but the development of the modern electronic computer is generally said to have occurred in the late 1930’s to early 1940’s. It is not possible to say which one person invented the computer but a few events are noteworthy. Iowa State University Professor John Atanasoff and graduate student Clifford Berry built the world's first electronic-digital computer at Iowa State University during the years 1939 and 1942. However, Presper Eckert and John Mauchly were the first to patent a digital computing device in 1947. A legal battle over the legitimacy of the patent arose in 1967, with one of the key end results of the proceedings being that the computer as a concept was declared un-patentable, which result is sometimes referred to as the "dis-invention of the computer.
Remote sensing today requires the high speed processing of enormous amounts of data and would not be possible without sophisticated computers and electronic equipment, not only to record and process the electromagnetic radiation signals, but also to control the advanced aviation technology that places the sensors in precise orbits about the surface of the earth.
One of the most well known and utilized remote sensing programs is the Landsat program, operated jointly by NASA and the USGS. In 1965-66 the Landsat program was proposed by the director of the U.S. Geological Survey (USGS), William Pecora, largely as a result of recognizing the potential of remote sensing as demonstrated by the NASA Mercury and Gemini photography of the Earth from space program. However, in the beginning, there was disagreement between agencies with competing interests, including the Bureau of Budget, the Department of Defense, the Department of the Interior, and the Department of Agriculture. It was not until 1970 that NASA was able to begin construction of the first Landsat satellite which was subsequently launched in 1972.
To date there have been 7 Landsat satellites however the Landsat 6 failed to orbit and thus produced no imagery. Currently, there are two operational Landsat platforms in orbit and transmitting imagery back to Earth, Landsat 5 and Landsat 7. Landsat 5 was launched in 1984 with a primary mission of three years. As of today it has exceeded that mission by 23 years. Landsat 7 was launched in 1999 and is also exceeding its original planned life expectancy of 5 years. NASA and the USGS are working jointly on the next generation of the Landsat program, the Landsat Data Continuity Mission (LDCM) which has a planned launch date of December, 2012.
To date the Landsat program has utilized 4 different image acquisition technologies. The first three missions included a Return Beam Vidicon (RBV) and a Multispectral Scanner. The RBV was originally anticipated as being the primary system but it quickly became apparent that the experimental MSS system was superior. The MSS system recorded data in 4 spectral bands: green, red, and two infra-red bands.
The RBV system was retired in the Landsat 4 and subsequent missions however the Thematic Mapper (TM) was added beginning with Landsat 4. The TM system utilizes 7 spectral bands: blue, green, red, near-infrared, two mid-infrared bands, and a thermal infrared band.
The Landsat 6 mission was equipped with the Enhanced Thematic Mapper (ETM) but as previously mentioned, it failed to obtain orbit. However, the Landsat 7 mission utilized the Enhanced Thematic Mapper Plus (ETM+). The ETM+, like the ETM of the failed Landsat 6 mission, mirrors but improves upon the capabilities of the TM instrument of Landsat 4 and 5. It has improved resolution in the Thermal IR band and also includes a b/w panchromatic band.
The French SPOT-1 and SPOT-2 are Landsat like systems that record in similar bands and have similar spatial and temporal resolutions, and ground swath widths. One notable difference is that SPOT is a commercially oriented program whereas the Landsat is government operated program whose mission is to make remotely sensed imagery available to the public at as low a cost as possible.