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Remote Sensing

15 Feb 2017Science and Technology Essays

Introduction

For more than 40 years, satellites have been the best way to see the Earth's ever-changing atmospheric processes in motion. Today, who could imagine a hurricane season without the watchful eye of the Geostationary Operational Environmental Satellite (GOES) to warn of the approach of storms like Hurricane Andrew.

Thanks to some extent to satellite technology, advanced weather and climate information helps farmers decide when to plant or harvest their crops. Satellite information may warn citrus growers of frost and sugar cane farmers of rain that may affect harvesting and growth. An accurate weather forecast also can allow engineers to schedule the best time for construction of large-scale projects such as bridges, highways, and dams.

Satellite images help forecast when and where tropical storms, hurricanes, floods, cyclones, forest fires, and even El Niño may strike.

Satellites have evolved from simply "staring at Earth's weather" to exploiting the electromagnetic spectrum to fully understand, link, and forecast alters in the global atmospheric systems. Satellites serve as a sort of "MRI of the atmosphere." And like the MRI readings doctors use, satellite images are not simply scientific curiosities but are a vital part of the toolbox scientists need to help diagnose and analyze the atmosphere.

Today's weather satellites give meteorologists immense power to see into the processes driving our weather and climate. This power promises to help forecasters broaden their understanding of developing weather patterns and fine-tune their forecasts further into the future. Moreover, the utility of satellites has grown beyond synoptic weather forecasts that enable us to plan for coming events.

We are entering a new era in which satellites will help society deal with the larger subjects of climate alter, resource management, and economic and environmental policy. Satellites today provide us with a comprehensive global viewpoint that could enable us to make intelligent and informed decisions for the health of our planet and its people.

Entering a New Era

There are four distinct eras in the evolution of Earth observations from space. The 1960s, 1970s, and 1980s were a time for exploring possibilities, demonstrating the technology, and seeing what we could do.

The decade of the 1990s was a time for surveying the Earth system. The concept of Earth as a composite of interdependent, related systems emerged, as scientists discovered the connections among weather, climate, land, ocean, and ice. The objective was to document how the Earth is changing and the consequences of those alters. For example, if climate alter is occurring, how will weather patterns, hurricane intensity, or flood frequency alter?

In the current period, from 2000 to 2020, the focus will shift from empirical science to national needs. Striving to make science serve society, researchers aim to answer questions that have an impact on national or international societal and economic guidelines. For example, how can global precipitation measurements from space be used to improve freshwater resource management or agriculture? How will global measurement of aerosols add to pollution regulation?

In NASA's view, the period beyond 2020 will be marked by broad use of the view from space, by making space information available to users in a timely and affordable manner. For example, a weekend gardener might access NASA satellite rainfall data to find the best location for his or her vegetable garden.

Remote Sensing

The objective of ocean color remote sensing algorithms is to differentiate various types of water, and the constituents that establish a particular color. Preferably, a helpful algorithm would calculate the concentration of suspended particulates in the muddy water, and the concentration of chlorophyll in both turbid and clear water.

The propagation of multilateral environmental accords, up from about 140 in 1970 to more than 350 today, has augmented the demand for information on almost every characteristic of the Earth's biophysical systems. On the other hand, correct and up-to-date environmental information for treaty monitoring, national reporting, and global environmental assessments are limited.

In current years, analysts have begun to judge the potential of remote-sensing technologies to meet the information needs of environmental treaties. Remote-sensing refers to the collection of information on Earth systems (land, atmosphere, and oceans) and human activities from a platform located above the surface of the Earth. Remote-sensing instruments are located on various types of platforms, including manned and unmanned aircraft, satellites, and, more currently, the space shuttle. The scope of remote-sensing is broad—additionally to environmental monitoring, it is used in fields as diverse as weather forecasting, humanitarian assistance, urban planning, agriculture, archaeology, and arms control. Environmental information that remote-sensing offers comprises information on land use, land cover alter, carbon monoxide pollution, and the carbon density of ecosystems. Progress in remote-sensing technologies permit the assembly of a wide array of formerly unavailable information that are pertinent to global environmental policy, and the figure and variety of remote-sensing tools in the sky at any given time keeps increasing.

Remote-sensing imagery has many striking qualities. It is usually correct and objective; it has globally consistent coverage over relatively long time periods; it can focus on ecological regions of various scales; and, because it is sensed from space, it can present a wide variety of pertinent information synoptically and without infringing on national autonomy. On the other hand, remote-sensing is not devoid of boundaries. It must be interpreted by people with enough technical expertise; the process of interpretation is still prone to subjective biases; it is expensive to get; and it will not get rid of core political obstruction to environmental protection.

Remote-sensing has already made noteworthy contributions to global environmental guideline. Pictures from space have raised the profile of certain subjects by waning alarming trends or by providing a fresh viewpoint. The first images of Earth from the Apollo 8 mission in 1968 stimulated a united sense of planetary stewardship that led to Earth Day in 1970 and the Stockholm Conference on the Environment in 1972. Tropospheric ozone reduction is one more case in point. reduction of the ozone layer was first revealed by a ground-based study team in 1984 and was later established by information from sensors aboard the National Aeronautics and Space Administration's (NASA) Nimbus-7 satellite. Imagery from the Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) tool was used to manuscript the seasonal depletion of ozone over the Antarctic, and the media's employment of the images led to public consciousness and a call for action. These actions cemented the way for the Montreal Protocol on Substances that Deplete the Ozone Layer, widely judged one of the most effectual environmental accords. Images from TOMS have given intuitive support to other scientific proof that was critical in increasing the protocol (Uhlir, 1995). These examples propose that remote-sensing imagery can help generate the public support requisite for treaty growth and can encourage even loath politicians to take action.

Through information from satellite imaging tools such as the coastal zone color scanner, SeaWiFS, MODIS and others, oceanographers increased a insightful of shifts in seasonal models over large parts of the global ocean and revealed important dissimilarities between plankton cycles in the Southern Ocean and in Northern Hemisphere oceans. Many spacecraft, including NOAA's operational meteorological satellites and the currently launched Moderate Resolution Imaging Spectroradionieter (MODIS) tool aboard the Terra spacecraft, measure sea surface temperature.

Since the knowledge of future C02 concentrations is so crucial, a corresponding knowledge of the global biosphere and its role in partitioning C02 between its reservoirs on the land, in the oceans, and in the atmosphere is also critical. Until currently, on the other hand, knowledge of the distribution of biospheric activity over the entire Earth surface was lacking. Satellite information have totally altered that picture, on the other hand, and hold the guarantee of future alters. Images from the SeaWifs sensor aboard the commercially-operated SeaStar satellite have offered images of the land and oceanic surface - approximately whole maps every 2 days - and allowed for quantitative studies of spatial, seasonal, and interannual variations. Especially, the SeaWifs observations of "ocean color'- actually the sharing of chlorophyll-containing phytoplankton in the uppermost deposit of the ocean - have transformed our familiarity of the division of plant matter in the ocean. The reaction of oceanic life to alters in the physical characteristics of the ocean has been marvelously acknowledged. Examples include the "bloom" of the tropical Pacific Ocean that took place in mid-1998 when the cooler, nutrient-rich waters connected with La Nina relocated the warmer, nutrient-poor waters connected with the former El Nino.

Enhanced observations of the terrestrial biosphere are anticipated with the Moderate-resolution Imaging Spectroradiometer (MODIS) tool aboard the Terra platform -launched. The blend of spectral resolution (more than 30 bands) and spatial resolution (typically 1 km x 1 km; in some cases 250m x 250m) is exclusive and should proffer scientists with the unparalleled aptitude to document the land cover at the Earth's surface. Combined with a major venture in information and information systems, these information can be dispersed quickly and routinely to users in the scientific and applications communities.

Tools

The most important tools used by NASA to scrutinize ocean color are SeaWiFS and MODIS:

- SeaWiFS

The point of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project is to present helpful information on ocean color to the Earth science society. SeaWiFS flies on the OrbView-2 satellite, but afar the tool itself, the SeaWiFS Project has urbanized and functions a study information system that processes, standardizes, validates, archives and distributes information acknowledged from an Earth-orbiting ocean color sensor.

- MODIS

MODIS, an tool so helpful it has been located on two satellites (Terra and Aqua), is ideal for observing large-scale alters in the biosphere to defer new insights into the global carbon cycle. MODIS can calculate the photosynthetic movement of land and marine plants (phytoplankton) to acquiesce better estimates of how much of the greenhouse gas is being absorbed and used in plant production. Joined with the sensor's surface temperature measurements, MODIS' measurements of the biosphere are serving scientists track the sources and sinks of carbon dioxide in reply to climate alters.

Sea-viewing Wide Field-of-view Sensor (SeaWiFS)

The new satellite monitor, named the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS), accumulates every day images of every point on Earth in eight separate wavelengths of light. By determining the color of the oceans, the tool can circuitously calculate the absorption of tiny marine plants called phytoplankton, which fasten the marine food chain.

SeaWiFS substitutes a color-scanning satellite sensor that closed working in 1986. Not like the older edition, on the other hand, SeaWiFS can calculate the amount of plant life on land in addition to in the oceans. (Monastersky, 1997)

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS)--which was initiated in August 1997, aboard the Orbital Sciences Corporation (OSC; Dulles, VA) SeaStar spacecraft--took its first picture of the world's oceans on September 16, 1997. The whirling compound image below rep, dislikes the first 24 hours of information taken from an altitude of 440 miles (705 kilometers).

The colors specify unstable concentrations of chlorophyll in the oceans. Reds show high concentrations of chlorophyll, yellows and greens specify transitional concentrations, and blues and purples signify low concentrations, The black swaths specify gaps amid the orbits, where no information was composed. SeaWiFS monitors the Earth from a midday sun-synchronous orbit, which means that the sensor is at all times screening the Earth at local noon for utmost solar enlightenment.

This orbit is most sought-after for sensing concentrations of phytoplankton, microscopic green plants that live just under the ocean surface. Phytoplankton are vital in the global carbon cycle, and knowing their circulation will help scientists envisage the dynamics of ocean and coastal currents, the physics of amalgamation, and the associations between ocean physics and comprehensive models of ocean production. (Peach, 1997)

The SeaWiFS consists of an electronic module and an optical scanner receptive to eight central wavelengths ranging from 412 to 865 nm. The tool was customized to create a bilinear response. The inventive sensitivity is maintained up to 80% of the digital productivity variety and then changed intermittently to expand the dynamic variety considerably. The net result is not anticipated saturation over clouds.

Scanning methods drive an off-axis folded telescope and a rotating half-angle mirror that is phase-synchronized with, and rotating at half the speed of, the folded telescope. The rotary scanning telescope, joined with the half-angle scan mirror, permits a least level of polarization devoid of field-of-view rotary motion, over the highest scan angle requirement of 58.3 degrees.

The plan is element of NASA's Mission to Planet Earth Enterprise, a long-standing, matched study attempt to study the Earth as a global system. The SeaWiFS is the report on ocean color tool to the Coastal Zone Color Scanner (CZCS), which was taken out of commission in 1986 after an eight-year mission. Via the vantage point of space, NASA is observing, monitoring, and assessing comprehensive environmental processes such as ocean efficiency, focusing on climate change. (Peach, 1997)

Moderate Resolution Imaging Spectrometer: MODIS

Elevated shadowy resolution (that is, narrow, contiguous bands) is also accomplished by the Moderate Resolution Imaging Spectrometer (MODIS), which was launched by NASA in December 1999 as one of the flagship tools on the Terra satellite stand. MODIS consists of 36 shadowy bands from 620 nm to 14,385 nm, and spatial resolution varieties from 250 meters for Bands 1 and 2 (620-670 nm and 841-876 nm, correspondingly) to 1 km for most other observable and infrared bands. Though more responsive to sun-glint as of its wide scan angle variety (±55°), MODIS has previously shown assurance in ocean color mapping as confirmed by NASA's early MODIS ocean-color yields.

An exclusive observational tool called MODIS (Moderate-Resolution Imaging Spectroradiometer) now allows climatologists to learn how aerosols move across the planet.

"MODIS was designed to track, fine aerosols through the atmosphere," says Yoram Kaufman, the principal investigator for MODIS aerosol study at the National Aeronautics and Space Administration (NASA). In 1999, when NASA launched Terra, the first of three Earth-observing satellites to study atmospheric pollution (among other things), MODIS technology was onboard. MODIS also is on the Aqua satellite launched in 2002.

MODIS measures aerosol optical thickness (AOT), which indicates how much sunlight is prevented from traveling through the atmosphere. An AOT of 0.2 means that 20% of the overhead sunlight will be blocked by the aerosol layer--roughly equivalent to a mildly hazy day. By comparison, during the summer in Washington, D.C., the AOT typically varietys from 0.4 to 0.8.

MODIS lets researchers decide the absorptions and dimensions of atmospheric aerosols. This, joint with acquaintance of wind models and surface population distributions, can disclose basis of these contaminants. That will, sequentially, tell how contaminants move across the Earth's surface, their residence time in definite parts, and the contact of other climatological factors, and will expose more about how all of these diverse particulate forms interrelate.

MODIS yields information on the ratio between finer particles (with a radius roughly less than 0.5 micrometer) and coarser particles (1 micrometer and larger). This is important, says Didier Tanre, director of the Laboratoire d'Optique Atmospherique at France's Universite des Sciences et Technologies de Lille and one of the developers of the algorithms that power MODIS, because most of the aerosols that are produced by human activity are finer. MODIS therefore helps to differentiate between naturally occurring and anthropogenic aerosols, Tanre says. (Frazer, 2003)

But MODIS can paint only part of the atmospheric portrait, and so works best in conjunction with other, similar tools. For example, the system has a hard time detecting dust over the deserts of Asia because these regions reflect so much light, says Steven Massie, an atmospheric chemist with the National Center for Atmospheric Study. On the other hand, a tool known as the Total Ozone Mapping Spectrometer, or TOMS, can detect desert dust because it uses a various system to measure various wavelengths of light. Other systems offer complementary information on other contaminants. Measurements of Pollution in the Troposphere (MOPITT) is a system developed by the Canadian Space Agency to measure carbon monoxide and methane.

When MODIS information are shared with information from other satellite-based systems, such as TOMS, MOPITT, and Global Ozone Monitoring Experiment, it yields a more complete atmospheric representation. For instance, says John Gille, chief of the Global Observations, Modeling, and Optical Techniques Section of the National Center for Atmospheric Study and the principal U.S. researcher for MOPITT, scientists can use information from these assorted sources to learn relationships between contaminant sources and their relative size and concentrations. They can also see how contaminants' sources impact their arrangement and the quantity of each produced relative to the other. Combining those information with wind information presents a clearer picture of how contaminants are transported through the atmosphere.

To realize the interface of aerosols with water vapor in the atmosphere, one preferably would recognize the vertical distribution of aerosols and dampness. Kaufman says that MODIS measures only the whole column absorption of aerosols and water vapor. On the other hand, other tools aboard the Aqua satellite accumulate moisture profiles, and other missions will use additional technologies to compile the aerosol vertical outline. This will permit scientists to study the outcome of moisture on aerosol particles.

"The dust particles are also an subject," says Tanre. "They are not spherical, when our algorithm assumes they are. Aerosol models that are assumed in the algorithm may be improved." (Frazer, 2003) according to Kaufman, "I think MODIS is a very competent element of a priceless [observational satellite] program that's going to offer a greater perceptive of our atmospheric dynamics over the coming years." (Frazer, 2003)

Products

As information from SeaWiFS and MODIS are acknowledged, they are routed through numerous "levels". Level 2 products, such as chlorophyll, water clarity, and fluorescence, apply sensor calibration information and atmospheric alteration to analyze Earth exterior radiances from the radiances calculated at the satellite.

Conclusion

As Earth alters, we must understand the forcing mechanisms of the alters (human and/or natural), the consequences of the alters, and how to better forecast the alters. We are entering an era of unparalleled observation and forecast of our everyday weather and enduring climate that in due course will benefit every farmer, planner, guideline maker, and citizen of planet Earth.

References

Lance Frazer, 2003, MODIS Operandi for Mapping Haze. Environmental Health Viewpoints. Volume: 111. Subject: 9. 458 P. F. Uhlir, 1995, "From Spacecraft to Statecraft," GIS Law 2, no. 3 Peach, Laurie Ann, 1997, SeaWiFS colors the world's oceans., Laser Focus World, 10438092, Vol. 33, Subject 11 Monastersky, R., 1997, Satellite views Earth's living plumage., Science News, 00368423, Vol. 152, Subject 14

Bibliography

  • Conant, Francis P. 1994 Human ecology and space age technology: Some predictions. Human Ecology 22(3):405-413.
  • Gemmill, W.H. and V.M. Krasnopolsky, 1999, "The Use of SSM/I Data in Operational Marine Analisis", Weather and Forecasting, Vol. 14, No.5, pp. 789-800
  • Krasnopolsky, V.M., W.H. Gemmill, and L.C. Breaker, 1999, "A multi-parameter empirical ocean algorithm retrievals", Technical Note, OMB Contribution No. 154, NOAA/NCEP/EMC, 1998, Canadian Journal of Remote Sensing,, Vol. 25, No. 5, pp. 486-503
  • Oreopoulos, L., 2005, The impact of subsampling on MODIS level-3 statistics of cloud optical thickness and effective radius, GeoRS(43), No. 2, pp. 366-373
  • Pearson, Robert A. and Donald D. Bustamante, 1998. "Improving Error Structure in Temperature Profile Retrievals from Satellite Observations," AIRIES'98: Artificial Intelligence Research in Environmental Sciences, October 21-23, Victoria, B.C

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