Surveying

Introduction

In environmental science, a survey refers to the examination of a site to precisely determine selected characteristics such as the presence of certain wildlife; type and condition of the soil; presence and extent of features such as wetlands, grassland, and lakes; indications of the presence of minerals in the subsurface (by measurement of variations in radiation levels); and information on the surface geology (by measurement of fluctuations in magnetism).

Surveys can be done on foot, but are most easily carried out from the air, typically using equipment onboard the aircraft or towed behind the aircraft.

Historical Background and Scientific Foundations

Environmental science survey techniques are generally known as geophysical surveys, which refer to the physical aspects of Earth’s surface and immediate subsurface.

A common environmental science geophysical survey is the aeromagnetic survey. In a typical aeromagnetic survey, an instrument called a magnetometer is carried onboard or towed behind an aircraft. Magnetometers are portable and so can be carried during on-foot surveys. However, the use of an aircraft permits a much broader territory to be examined in a day, while examination of the same area on foot would likely require weeks, even if the terrain is hospitable enough to permit easy access to the survey area.

In an aeromagnetic survey, the aircraft flies in a regular and pre-determined pattern over the region of interest. Typically, the flight path is a grid pattern, with the aircraft flying back and forth, for example north-south followed by south-north, to form one area of the grid,before paths at 90 degrees to the first pattern (for example, west-east followed by east-west) to complete the grid. Geographic information system (GIS) technology allows the location of the aircraft to be determined at any point during the flight, and this geographic information can be correlated with the aeromagnetic findings to precisely map findings of interest.

A magnetometer measures small variations in the magnetic field at Earth’s surface. When the contributions of Earth’s magnetic field are filtered out, the resulting variations correspond to a difference on local magnetic energy due to the minerals present at the surface or the immediate subsurface. In this way a map of the geological composition can be generated.

Another environment survey is known as an aerora-diometric survey. This can be done in exactly the same way as an aeromagnetic survey, except for the use of a different piece of equipment that measures optical radiation such as the ultraviolet, visible, and infrared portions of the light spectrum. A common use of the survey is to measure variations in surface temperature. This can also be done using radiometers positioned onboard satellites orbiting Earth. The latter surveys permit the examination of huge swaths of the surface during each orbit.

Surveys can also be done by eye or photographically. These are useful when the intent is to monitor an area to roughly gauge the population of a target species such as elk or to gauge the success of a species re-introduction campaign.

Impacts and Issues

Aeromagnetic surveys are important in generating detailed geological maps of Earth’s surface, and they are commercially important in mineral exploration. Deposits of minerals such as iron are magnetic, while other nonmagnetic minerals will produce a fluctuation in the local magnetic field when they are present in abundance.

WORDS TO KNOW

ANTHROPOGENIC: Made by humans or resulting from human activities.

GREENHOUSE GAS: A gas that accumulates in the atmosphere and absorbs infrared radiation, contributing to the greenhouse effect.

HABITAT: The natural location of an organism or a population.

PRIMARY POLLUTANT: Any pollutant released directly from a source to the atmosphere.

Aeroradiometric surveys can be conducted over water, which can be useful in revealing locations where colder and deeper water is moving upward (upwelling). This can be helpful in revealing potential fishing sites, since the upwelling water brings nutrients to the surface.

Surveys of the surface temperature of the ocean that have been conducted in satellite studies since the 1970s have revealed the increasing surface temperature of the ocean in certain regions. In tropical regions this change may be influencing the frequency and intensity of extreme weather events such as hurricanes. Additionally, some modeling studies have indicated that the changing ocean temperature could alter currents such as the Gulf Stream.

The data from environmental surveys are also useful in generating models that attempt to predict other effects of climatic change that includes weather patterns, the frequency of heat waves, and rise of sea level.

See Also Climate Modeling; Geospatial Analysis

BIBLIOGRAPHY

Books

Berg, Linda, and Mary Catherine Hager. Visualizing Environmental Science. New York: Wiley, 2006.

Pepper, Ian, Charles Gerba, and Mark Brusseau. Environmental and Pollution Science. New York: Academic Press, 2006.

Web Sites

Appalachian Mountain Club“Ecological Survey and Land Management Planning on the Katahdin Iron Works Property.” http://www.outdoors.org/conservation/wherewework/maine/ecological-inventory.cfm (accessed May 2, 2008).