In the broadest sense, remote sensing is the measurement or acquisition of information of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object. In practice, remote sensing is the utilization at a distance (as from aircraft, spacecraft, satellite, or ship) of any device for gathering information about the environment. Thus an aircraft taking photographs, Earth observation and Weather satellites, monitoring of a fetus in the womb via ultrasound, and space probes are all examples of remote sensing. In modern usage, the term generally refers to techniques involving the use of instruments aboard aircraft and spacecraft rather than other fields which are considered to be under medical imaging or photogrammetry.

While all astronomy could be considered remote sensing (in fact, extremely remote sensing) the term "remote sensing" is normally only applied to terrestrial observations.

Data acquisition techniques

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Data may be acquired through a variety of devices depending upon the object or phenomena being observed. Most remote sensing techniques make use of emitted or reflected electromagnetic radiation of the object of interest in a certain frequency domain (infrared, visible light, microwaves). This is possible due to the fact that the examined objects (plants, houses, water surfaces, air masses ...) reflect or emit radiation in different wavelengths and in different intensity according to their current condition. Some remote sensing systems use sound waves in a similar way, and others measure variations in gravitational or magnetic fields.

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USGS Newsroom

Science that Weathers the Storm...USGS Scientists in the Field Preparing for Hurricane Ike
OC_Web@usgs.gov (Office of Communications Web Group)Reporters: Want to accompany USGS scientists as they install storm surge sensors? Contact Leroy Pearman at 321-354-5248 or lpearman@usgs.gov. US Geological Survey (USGS) scientists will be installing storm-surge sensors to prepare for Hurricane Ike. These temporary devices are installed just hours before an impending storm and provide additional monitoring data in critical areas needed for effective forecasting and emergency response. "We could not accurately forecast river flows and water-levels without the data and support we receive from the USGS," said Dave Reed, Hydrologist-In-Charge of the National Weather Service Lower Mississippi River Forecast Center in Slidell, LA. "When river and tide data are not available, our job of forecasting is much more difficult and typically results in diminished accuracy of those forecasts." USGS scientists will be installing storm surge sensors to prepare for Hurricane Ike. A special interactive USGS Water Hazards Map will be available soon, which will provide real-time flooding and storm surge data from streamgages and temporary devices. This information is imperative to local, State and Federal officials in order to forecast floods and coordinate flood-response activities in the affected area. Track streamflow and water levels and access other USGS Hurricane Ike efforts by visiting http://www.usgs.gov/ike. Access real-time data from over 7,500 streamgages across the country by visiting the USGS Water Watch Website at http://water.usgs.gov/waterwatch/. USGS has a network of rugged, inexpensive water-level and barometric-pressure sensors, called storm-surge sensors, which will be installed right before Ike hits land. These sensors provide information about storm surge duration, times of surge arrival and retreat, and maximum depths, which is useful in forecasting and modeling future events. Tropical Storms Katrina and Rita vividly demonstrated that coastal storm surge can be as dangerous as inland flooding caused by rain. For more than 125 years, the USGS has monitored flow in selected streams and rivers across the United States and does so in cooperation with over 850 federal, state and local agencies. Contacts: If you would like to know more specific information about USGS Hurricane Ike response activities in your area, please contact the appropriate person listed below. Alabama: Athena Clark, 334-395-4141, athclark@usgs.gov Florida: Barry Rosen, 407-803-5508, brosen@usgs.gov Georgia: Ed Martin, 770-903-9166, ehmartin@usgs.gov Louisiana: Charles Demas, 225-298-5481 Ext. 3117, crdemas@usgs.gov Mississippi: Michael Plunkett, 601-933-2940, plunkett@usgs.gov South Carolina, Eric Strom, 803-750-6109, ewstrom@usgs.gov Texas: Robert Joseph, 512-927-3500, rljoseph@usgs.gov National Flood Specialist: Robert Holmes, 573-308-3581, bholmes@usgs.gov
Science that Weathers the Storm...Track Flooding During Tropical Storm Hanna in Real-Time
OC_Web@usgs.gov (Office of Communications Web Group)Real-time flooding and storm surge information is available as Tropical Storm Hanna approaches the east coast by visiting the interactive US Geological Survey (USGS) Water Hazards Map. The map provides immediate flooding and storm surge data from real-time streamgages in the affected area, which is imperative to local, State and Federal officials in order to forecast floods and coordinate flood-response activities in the affected area. "These coordinated actions will ensure timely and uninterrupted water information for forecasters, emergency managers, scientists and the general public," says Matthew Larsen, USGS Associate Director for Water. "Improved flood monitoring and assessment will help reduce the risks to coastal communities, property and human life." Access current streamflow in the context of historical conditions, as well as real-time water quality and groundwater information by visiting http://water.usgs.gov/waterwatch/hanna.  Access other USGS Tropical Storm Hanna efforts by visiting http://www.usgs.gov/hanna. For more than 125 years, the USGS has monitored flow in selected streams and rivers across the U.S. The USGS, in cooperation with 1400 federal, state and local agencies, collects data from more than 7,500 continuous recording streamgages, most of which provide near real-time data in 15-minute increments. These data are used to develop flood forecasts, to manage flood control and coordinate flood response activities, to manage water supplies and droughts, to keep our waters clean, and to provide information for many recreational activities. Contacts: National Flood Specialist: Robert Holmes, 573-308-3581, bholmes@usgs.gov. If you would like to know more specific information about USGS Tropical Storm Hanna response activities in your area, please contact the appropriate person listed below. Delaware, Holly Weyers, 302-734-2506 (ext. 224), hsweyers@usgs.gov Florida, Barry Rosen, 407-803-5508, brosen@usgs.gov Georgia, Brian McCallum, 404-375-2505, bemccall@usgs.gov Maryland, Ed Doheny, 443-498-5535, ejdoheny@usgs.gov North Carolina, Jerad Bales, 919-571-4048, jdbales@usgs.gov South Carolina, Eric Strom, 803-750-6109, ewstrom@usgs.gov Virginia, Mark Bennett, 804-261-2643, mrbennet@usgs.gov  
Study: Undiscovered Minerals in the Andes
OC_Web@usgs.gov (Office of Communications Web Group)South America holds treasure of Copper, Molybdenum, Gold and Silver Deposits of undiscovered copper, molybdenum, gold and silver may be present in the Andes Mountains of South America, according to a new scientific assessment. The assessment estimates that the Andes may hold 750 million metric tons of copper in undiscovered porphyry copper deposits. Mining from these types of deposits provides more than 50 percent of world copper supply. The undiscovered porphyry copper deposits also have the potential to contain 20 million tons of molybdenum, 13,000 tons of gold and 250,000 tons of silver. Molybdenum, known to occur naturally with copper, is used in industry to harden steel and for catalysts, lubricants, and pigments. Estimated undiscovered molybdenum resources in the Andes represent more than double the current world reserves of 8.6 million tons. The Andes were studied as part of the first global mineral resource assessment, which is being led by the U.S. Geological Survey. The USGS jointly prepared and published the Andes assessment with experts from the Geological Surveys of Argentina, Chile, Colombia and Peru. The partnership that contributed to the assessment is "a hallmark of international scientific collaboration," said USGS Director Mark Myers. "The expertise of our international collaborators is indispensable to our ability to undertake a worldwide assessment of numerous undiscovered mineral commodities in a variety of geologic environments." The estimated copper resources in the Andes represent about 2.5 times the amount of undiscovered copper resources that was estimated for the United States in a 1998 USGS assessment of all major types of copper deposits. Not all of the estimated undiscovered mineral deposits are likely to be discovered and developed. The USGS Mineral Resources Program provides scientific information for objective resource assessments and unbiased research results on mineral potential, production, consumption and environmental effects. This program is the sole federal source for this information. The complete report, Quantitative Mineral Resource Assessment of Copper, Molybdenum, Gold, and Silver in Undiscovered Porphyry Copper Deposits in the Andes Mountains of South America, by C.G. Cunningham and others, is available online at http://pubs.usgs.gov/of/2008/1253.
Unexplored Arctic Region to be Mapped
OC_Web@usgs.gov (Office of Communications Web Group)Reporters: You will have access to a journal, photographs and video during and after this expedition. Information is available at the Arctic Chronicles Web site. A scientific expedition this fall will map the unexplored Arctic seafloor where the U.S. and Canada may have sovereign rights over natural resources such as oil and gas and control over activities such as mining. Both countries will use the resulting data to establish the outer limits of the continental shelf, according to the criteria set out in the Convention on the Law of the Sea. The extended continental shelf, the seafloor and subsoil beyond 200 nautical miles from shore that meet those criteria, is an area of great scientific interest and potential economic development. The expedition will be collaboratively undertaken by the U.S. and Canada using two ships. The U.S. Geological Survey will lead data collection from September 6-October 1 on the U.S. Coast Guard Cutter Healy to map the Arctic seafloor. The Geological Survey of Canada, Natural Resources Canada will follow Healy on the Canadian Coast Guard ship Louis S. St. Laurent (Louis) and study the geology of the sub-seafloor. "The two-ship experiment allows both the U.S. and Canada to collect and share complementary data in areas where data acquisition is costly, logistically difficult, and sometimes dangerous," said USGS scientist Deborah Hutchinson, who will sail aboard Louis. "Both countries benefit through sharing of resources and data as well as increasing likelihood of success by utilizing two ice-breaker ships in these remote areas of the Arctic Ocean." "Healy will utilize an echo sounder, which emits sounds signals in the water, to map the seafloor. This will be done using a multibeam bathymetry system," said USGS scientist Jonathan Childs, chief scientist on Healy during the September cruise. "Unlike conventional echo sounders, which measure the water depth at a point directly beneath the ship, the multibeam system collects a ‘swath' of depth information about 3 km wide along the ship's path, creating a three-dimensional view of the seafloor." The National Oceanic and Atmospheric Administration funded U.S. participation in the U.S.-Canadian mission and collaborated with the University of New Hampshire to collect bathymetric data in the Arctic Ocean on Healy from August 14-September 5. Research is coordinated by the Extended Continental Shelf Task Force, a government-wide group headed by the U.S. Department of State. Participants in this Task Force include the USGS, NOAA, U.S. Coast Guard, National Science Foundation, Joint Chiefs of Staff, U.S. Navy, Department of Energy, Environmental Protection Agency, Executive Office of the President, Minerals Management Service, and the Arctic Research Commission. For more information about the Convention on the Law of the Sea, visit http://www.un.org/Depts/los/index.htm.
Fish Pesticide May Control Unwanted Round Goby
OC_Web@usgs.gov (Office of Communications Web Group)Scientists have discovered that certain chemicals may be useful in slowing the spread of the round goby, an invasive fish species that is threatening parts of the Great Lakes and Mississippi River. When released near the bottom of a river or lake, two fish pesticides are effective in controlling this bottom-dwelling invader, particularly where dissolved oxygen is low, while leaving native species unharmed. "Selective removal of round gobies may be possible with bottom-release pesticides," said Theresa Schreier, lead author of this research, published in the Journal of Great Lakes Research. "This work shows the value of understanding how an invasive species differs from native populations in the way that it lives in an ecosystem and basing control measures on a unique vulnerability of the invader." For this study, researchers at the U.S. Geological Survey (USGS) Upper Midwest Environmental Sciences Center in La Crosse, Wis. evaluated four currently registered fish pesticides (antimycin, rotenone, 3-trifluoromethyl-4-nitrophenol (TFM), and Bayluscide) for their toxicity to round gobies. Round gobies were sensitive to all four chemicals; unfortunately, the level of sensitivity was similar to native fish species tested.  Further testing revealed that formulations of Bayluscide and antimycin that can be released near the bottom of a body of water showed promise as control agents because round gobies did not react or appear to detect the presence of these chemicals. USGS scientists also evaluated the effect of dissolved oxygen concentrations on toxicity to determine if a modification of the current design of the Illinois Waterway could be an effective tool in the management and control of round gobies. Round goby can withstand low dissolved oxygen concentrations, and during lab tests gobies showed increased sensitivity to bottom-release fish pesticides at lower oxygen levels.  Some portions of the Illinois Waterway have low oxygen levels and are mechanically aerated, providing an option to manage a segment of the waterway as an anoxic barrier.  Managers could explore the option of maintaining a low dissolved oxygen zone that could be treated with selective fish pesticides to control congregations of the bottom-dwelling round goby. Since 1990 the round goby has been following the path of the invasive zebra mussel spreading throughout the Great Lakes basin and into the interior of North America. First found in the St. Clair River near Detroit, the small fish was introduced most likely by the release of unregulated ballast water from transatlantic shipping.  It is one of more than 180 non-indigenous organisms that have invaded the Great Lakes from Eurasia, many of which cause ecological and economic consequences. The round goby competes with native fish for spawning and foraging habitats. If left unchecked, this small fish might have a big impact on the Great Lakes recreational and commercial fishing industry, which generates approximately $5 billion per year.  As round gobies continue to spread down the Illinois Waterway connecting the Great Lakes to the Mississippi River basin, consequences are imminent on a larger scale.  USGS began this research in 2000 in response to a request by natural resource agencies to evaluate chemicals to combat invasive species. Funding for this study came from the U.S. Army Corps of Engineers, the U.S. Environmental Protection Agency, and the U.S. Fish and Wildlife Service. Nationwide, fishery managers have limited tools for use in control of nuisance species like the round goby. Selective application of these promising fish pesticides may limit the range expansion of this invasive species providing protection for freshwater fish. State and federal natural resource agencies responsible for fish programs benefit from effective and safe chemicals, allowing them to maintain recreational and commercially valuable fish, and protect endangered and threatened species. The Upper Midwest Environmental Sciences Center has been a leader in the research and development of fishery-management chemicals and drugs since 1959. The Center works within a consortium of agencies, including the U.S. Food and Drug Administration, the U.S. EPA, the Great Lakes Fishery Commission, and the Association of Fish and Wildlife Agencies.  For more information on the Invasive Species Research Program at the USGS Upper Midwest Environmental Sciences Center go to http://www.umesc.er.usgs.gov/invasive_species.html Reporters: The full article "Effectiveness of Piscicides for Controlling Round Gobies (Neogobius melanostomus)," is available from the author tschreier@usgs.gov. The abstract is available at: http://www.iaglr.org/
Hurricane Gustav: USGS Maps Potential for Coastal Change
OC_Web@usgs.gov (Office of Communications Web Group)With Gustav approaching the Northern Gulf Coast, many communities are preparing for the impact. The combination of many Americans living along the coastline and the cumulative effects of previous storms makes the Northern Gulf region vulnerable to tropical storms and hurricanes.  The U.S. Geological Survey (USGS) is working to provide scientific information on coastal vulnerability to extreme storms that helps forecast possible impacts and damages. Hurricane landfall and associated elevated water levels, waves, and currents can lead to severe coastal change through erosion and re-deposition. In order to understand the vulnerability of coasts to storms, USGS scientists monitor U.S. coasts before and after impacts to determine the severity and patterns of erosion and accretion. Depending on storm characteristics and coastal elevations, as well as other factors, impacts can vary. The most extreme coastal change regime is associated with inundation, when storm surge exceeds the elevation of the primary dune or beach berm and the entire beach system is submerged. For Gustav, the USGS Hurricane and Extreme Storms Research Group has conducted pre-storm analyses of potential impacts in five major areas along the Northern Gulf of Mexico coastline where Gustav is likely to make landfall. "These maps describe the potential changes that may occur on the coast that threaten communities and critical wildlife habitats," said Abby Sallenger, USGS oceanographer. To view these maps and learn more about USGS coastal hazard research activities associated with Hurricane Gustav, please visit: http://coastal.er.usgs.gov/hurricanes/gustav

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