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REMOTE SENSING STUDIES
According to the National Aeronautics and Space Administration, remote sensing refers to instrument-based techniques used in the acquisition and measurement of spatially distributed data depicting features, objects and materials obtained at a substantial distance from the target. Remote sensing (RS) surveys are typically conducted with aerial-mounted instrumentation or obtained from earth satellites. The available instrumentation includes cameras, radiometers and scanners, lasers, radar systems, thermal devices, scintillometers, and other sensing equipment. D’Appolonia has analyzed data from both aerial and satellite platforms to evaluate surface characteristics including land use/cover, agricultural practices, soil erosion/desertification, vegetation health, urbanization, and water quality. D’Appolonia analyzes remote sensing data with state-of-the-practice software and typically uses GIS-based software for manipulating and presenting data.
Some important applications of RS include the following:
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Land Use/Cover Changes – Urbanization is a fact of life in the U.S. and other industrialized nations. Satellite data that can be used to evaluate the type of land use/cover has been available (Landsat) since 1972. Typically, land cover for a study area is assigned to one of a number of class types and the results are mapped using GIS software. Classifications are performed at regular intervals, and the changes are displayed on the GIS map.
Vegetation/Tree Canopy Health – RS imagery can be used to determine the types and health of vegetation cover and tree canopy. Factors such as brightness, greeness and moisture content can be detected with visible band and infrared images. Unhealthy vegetation/tree canopy can be detected by characteristic coloring and shades. Factors such as time of day, sun angle, shadow, atmospheric haze, and clouds must be taken into consideration when selecting and interpreting images.
Agricultural Practices – Similar to use for vegetation detection, RS images can be used to assess the distribution of various types of crops and their condition. RS analysis is increasingly being employed as part of "precision agriculture." For this purpose aerial imagery obtained below cloud level is much more useful than satellite imagery.
Water Qualtiy – Water quality can be assessed from RS imagery through the application of sophisticated software. Parameters that can be quantified include chlorophyll, suspended minerals, colored dissolved organic carbon, Secchi depth, turbidity, and Trophic Status Index (TSI). Use of RS imagery allows large areas to be covered without extensive sampling. Sampling is then performed on a limited basis to validate the RS interpretation.
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