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Selasa, 17 Januari 2012
remote sensing
Remote sensing
A. Introduction
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. Perhaps the most novel platform at the end of the last century is the famed pigeon fleet that operated as a novelty in Europe. By the first World War, cameras mounted on airplanes provided aerial views of fairly large surface areas that proved invaluable in military reconnaissance. From then until the early 1960s, the aerial photograph remained the single standard tool for depicting the surface from a vertical or oblique perspective.
Satellite remote sensing can be traced to the early days of the space age (both Russian and American programs) and actually began as a dual approach to imaging surfaces using several types of sensors from spacecraft. 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. Then, with the emergence of the space program in the 1960s, Earth-orbiting cosmonauts and astronauts acted much like tourists by taking photos out the window of their spacecraft.
The term "remote sensing," first used in the United States in the 1950s by Ms. Evelyn Pruitt of the U.S. Office of Naval Research, is now commonly used to describe the science—and art—of identifying, observing, and measuring an object without coming into direct contact with it. This process involves the detection and measurement of radiation of different wavelengths reflected or emitted from distant objects or materials, by which they may be identified and categorized by class/type, substance, and spatial distribution.
B. Discussion
From Wikipedia, the free encyclopedia
Remote sensing is the acquisition of information about an object or phenomenon, without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth (both on the surface, and in the atmosphere and oceans) by means of propagated signals (e.g. electromagnetic radiation emitted from aircraft or satellites).
There are two main types of remote sensing: passive remote sensing and active remote sensing. Passive sensors detect natural 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, infrared, charge-coupled devices, and radiometers. Active collection, on the other hand, emits energy in order to scan objects and areas whereupon a sensor then detects and measures the radiation that is reflected or backscattered from the target. RADAR and LiDAR are examples of active remote sensing where the time delay between emission and return is measured, establishing the location, height, speed and direction of an object.
Remote sensing makes it possible to collect data on dangerous or inaccessible areas. Remote sensing applications include monitoring deforestation in areas such as the Amazon Basin, glacial features in Arctic and Antarctic regions, and depth sounding of coastal and ocean depths. Military collection during the Cold War made use of stand-off collection of data about dangerous border areas. Remote sensing also replaces costly and slow data collection on the ground, ensuring in the process that areas or objects are not disturbed.
Orbital platforms collect and transmit data from different parts of the electromagnetic spectrum, which in conjunction with larger scale aerial or ground-based sensing and analysis, provides researchers with enough information to monitor trends such as El NiƱo and other natural long and short term phenomena. Other uses include different areas of the earth sciences such as natural resource management, agricultural fields such as land usage and conservation, and national security and overhead, ground-based and stand-off collection on border areas.[4]
By satellite, aircraft, spacecraft, buoy, ship, and helicopter images, data is created to analyze and compare things like vegetation rates, erosion, pollution, forestry, weather, and land use. These things can be mapped, imaged, tracked and observed. The process of remote sensing is also helpful for city planning, archaeological investigations, military observation and geomorphological surveying.
Applications of remote sensing data
• Conventional radar is mostly associated with aerial traffic control, early warning, and certain large scale meteorological data. Doppler radar is used by local law enforcements’ monitoring of speed limits and in enhanced meteorological collection such as wind speed and direction within weather systems. Other types of active collection includes plasmas in the ionosphere. Interferometric synthetic aperture radar is used to produce precise digital elevation models of large scale terrain (See RADARSAT, TerraSAR-X, Magellan)
• Laser and radar altimeters on satellites have provided a wide range of data. By measuring the bulges of water caused by gravity, they map features on the seafloor to a resolution of a mile or so. By measuring the height and wave-length of ocean waves, the altimeters measure wind speeds and direction, and surface ocean currents and directions.
• Light detection and ranging (LIDAR) is well known in examples of weapon ranging, laser illuminated homing of projectiles. LIDAR is used to detect and measure the concentration of various chemicals in the atmosphere, while airborne LIDAR can be used to measure heights of objects and features on the ground more accurately than with radar technology. Vegetation remote sensing is a principal application of LIDAR.
• Radiometers and photometers are the most common instrument in use, collecting reflected and emitted radiation in a wide range of frequencies. The most common are visible and infrared sensors, followed by microwave, gamma ray and rarely, ultraviolet. They may also be used to detect the emission spectra of various chemicals, providing data on chemical concentrations in the atmosphere.
• Stereographic pairs of aerial photographs have often been used to make topographic maps by imagery and terrain analysts in trafficability and highway departments for potential routes.
• Simultaneous multi-spectral platforms such as Landsat have been in use since the 70’s. These thematic mappers take images in multiple wavelengths of electro-magnetic radiation (multi-spectral) and are usually found on Earth observation satellites, including (for example) the Landsat program or the IKONOS satellite. Maps of land cover and land use from thematic mapping can be used to prospect for minerals, detect or monitor land usage, deforestation, and examine the health of indigenous plants and crops, including entire farming regions or forests.
• Hyperspectral imaging produces an image where each pixel has full spectral information with imaging narrow spectral bands over a contiguous spectral range. Hyperspectral imagers are used in various applications including mineralogy, biology, defence, and environmental measurements.
• Within the scope of the combat against desertification, remote sensing allows to follow-up and monitor risk areas in the long term, to determine desertification factors, to support decision-makers in defining relevant measures of environmental management, and to assess their impacts.
NASA Remote Sensing Accomplishments
Beginning with the April 1, 1960 launch of the Television and Infrared Observation Satellite (TIROS 1), which proved that satellites can observe Earth's weather patterns, NASA has been studying the global perspective of our environment. Other NASA accomplishments in observing the Earth include:
1966: Environmental Science Services Administration (ESSA) I and II gave the United States its first global weather satellite system.
1972: NASA began the Landsat series with the launch of the Earth Resources Technology Satellite 1, which was later renamed Landsat 1.
1975: The Synchronous Meteorological Satellites (SMS)-A, the first spacecraft to observe the Earth from geosynchronous orbit, and SMS-B started producing cloud cover pictures every 30 minutes for weather forecasters.
1976: Laser Geodynamic Satellite I (LAGEOS 1) provided scientists with the ability to track very precisely the movements of the Earth's surface, increasing our understanding of earthquakes and other geological activity.
1978: The Heat Capacity Mapping Mission (HCMM) satellite demonstrated the ability to measure variations in the Earth's temperature from space, paving the way for future climate studies.
1978: Seasat demonstrated techniques for global monitoring of the Earth's oceans.
1978: Nimbus 7, the final satellite in that series, was launched carrying a Total Ozone Mapping Spectrometer (TOMS) instrument that provided 14 years of data on the Earth's ozone layer. Data from the TOMS were part of the scientific basis for the Montreal Protocol and other treaties banning the manufacture and use of ozone-depleting chemicals. In addition, Nimbus 7's Coastal Zone Color Scanner (CZCS) obtained a data set that is widely used to study the links between the oceans' biology and the Earth's climate.
TOMS image of antarctic ozone, October, 1985. White areas are high ozone levels, black areas represent low ozone. (Image by Robert Simmon)
1984: The Earth Radiation Budget (ERBE) satellite began its study of how the Earth absorbs and reflects the Sun's energy.
1991: The Upper Atmosphere Research Satellite (UARS) began its study of the chemistry and physics of the Earth's atmosphere. UARS data are used to create global maps of ozone-destroying chemicals and to understand the processes related to ozone depletion better. By 1994, UARS' comprehensive data set provided conclusive evidence that human-made chemicals are responsible for the annual Antarctic ozone depletion.
1992: Data from the U.S.-French TOPEX/Poseidon satellite began to detail the links between the Earth's ocean and climate. By 1994, TOPEX data indicated that the Earth's average global sea level had risen in the two previous years.
Spring 1992: The first Atmospheric Laboratory for Applications and Science (ATLAS) flew on the Space Shuttle Atlantis. The mission carried fourteen experiments to study the chemistry of the Earth's upper atmosphere and the Sun's energy, and the effect of those two elements on ozone levels. Two additional ATLAS payloads were carried on subsequent shuttle missions in 1993 and 1994.
1994: The Space Radar Laboratory, which flew on two shuttle missions, demonstrated the uses of a complex radar to study the Earth's surface, with applications in ecology, geology, water-cycle studies, and other areas. Related research released in 1996 shed new light on the Great Wall of China and the geological history of the Nile River.
1997: The Sea-viewing Wide-field-of-view sensor, the only sensor onboard the OrbView-2 satellite, was launched into low-Earth orbit from a Pegasus rocket attached to the belly of a modified Lockheed L-1011 aircraft. Data gathered from SeaWiFS is helping scientists identify oceanic "hot spots" of biological activity, measure global phytoplankton biomass, and estimate the rate of oceanic carbon uptake. This information will yield a better understanding of the sources and sinks in the carbon cycle and the processes that shape global climatic and environmental change.
SeaWiFS ocean chlorophyll data from 1998. Low concentrations of phytoplankton are represented by purple and blue shades, high concentrations are yellow, orange, and red. (Image courtesy NASA SeaWiFS project)
1997: NASA, along the National Space Development Agency of Japan, launched the Tropical Rainfall Measuring Mission (TRMM) from the Tanegashima Space Center in Japan. TRMM houses five separate instruments including the first-ever precipitation radar to fly in space. Designed to help our understanding of the role that the water cycle plays in the current climate system, TRMM is providing much-needed data on rainfall and the associated heat released during the condensation-precipitation process in the tropics and sub-tropics.
1999: The latest mission in the Landsat series—Landsat 7—launched from Vandenberg Air Force Base. Landsat 7 is continuing the flow of global change information to users worldwide. Scientists use the Landsat satellites to gather remotely-sensed images of the land surface and surrounding coastal regions for global change research, regional environmental change studies, and other civil and commercial purposes.
1999: The QuikSCAT satellite was launched from Vandenberg Air Force Base atop a U.S. Air Force Titan II launch vehicle. QuikSCAT houses a scatterometer called SeaWinds that is being used to acquire all-weather, high-resolution measurements of near-surface winds over the Earth's oceans. These data will be combined with measurements from scientific instruments in other disciplines to help us better understand the mechanisms of global climate change and weather patterns.
Beginning in late 1999, NASA will launch the Terra satellite (formerly EOS AM-1), the flagship of the Earth Observing System (EOS)—a series of spacecraft that represent the next landmark steps in NASA's leadership role to observe the Earth from the unique vantage point of space. Focused on key measurements identified by a consensus of U.S. and international scientists, Terra will enable new research into the ways that Earth's lands, oceans, air, ice, and life function as a total environmental system. Terra is scheduled to launch from Vandenberg Air Force Base, California.
References
The Remote Sensing Tutorial
Virtually Hawaii
NASA Observatorium
Terra Website
NASA's Earth Science Enterprise CD-ROM (NP-1999-01-005-GSFC)
Looking at Earth From Space
Teacher's Guide with Activities for Earth and Space Science
Kamis, 05 Januari 2012
optik-gasing
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