Remote sensing satellite images in coastal environments

Remote Sensing (satellite Images) in Coastal Environments

Remote sensing in costal environments: Methodology and uses

The methods for using remote sensing in coastal environments

Remote sensing "involves the measurement of electromagnetic radiation reflected from or emitted by the Earth's surface and the relating of these measurements to the types of habitat or the water quality in the coastal area being observed by the sensor" (Edwards 2009). "Remote sensing provides a synoptic portrait of the Earth's surface by recording numerical information on the radiance measured in each pixel in each spectral band of the image being studied. To create a habitat map, the operator must instruct the computer to treat certain reference pixels as belonging to specific habitats. The computer then creates a 'spectral signature' for each habitat and proceeds to code every other pixel in the image accordingly, thus creating a thematic map" (Mumby & Green 2009).

The results of using remote sensing in coastal environments and the role of remote sensing in changing the understanding of coastal environments

The use of remote sensing to assess the damage done to costal environments has become increasingly important, and has been facilitated by the greater ease of use of computer-based self-tutoring packages. Remote sensing is a relatively unobtrusive, zero-impact, yet comprehensive method of assessing an environment's current conditions and future needs. For example, it has recently proved effective in understanding the damage done to the coastal and marine environment of the Gulf States. This is critical "given the important commercial interests" in the region's natural resources combined with the potential that exists for the exploitation of the "fragile" coast (Sudarshana 2009).

The use of airborne and space-borne imaging sensors over the last two decades has also played a role in mapping areas difficult to reach by sea or land, such as the complex landscapes of French Guiana (Polidori, 2009, p. 627). "The permanent evolution of this environment is a concern for decision makers, since the population and the economic activity of this region are concentrated along the coast. Sea defense operations and coastal infrastructure management (polders, harbors), as well as ecosystem preservation programs, require a better understanding and a regular monitoring of the coast line evolution" (Polidori, 2009, p.627). From an environmental perspective, the use of remote sensing does not disturb the local population, or the flora or fauna, yet presents an environmental snapshot of the area that can be analyzed, so recommendations can be made as to how to improve the balance between inhabitants and the natural world.

The benefits and limitations of using remote sensing in coastal environments

The majority of current multispectral sensors have rows of multiple detectors. Each row is able to view one type of light. Each detector can view one pixel. An aircraft or satellite carrying the entire sensor moves and records the amount of light being reflected, which creates a digital image based upon the image presented by the detectors. The advantages of using such a digital image (an image made up of numbers) is that researchers "can define objectively the spectral characteristics of different habitats and process the images using computers….By empirically relating such spectra to known types of habitat at known positions during field survey, a computer can be used to classify all pixels in an image, creating a habitat map" (Edwards 2009). However, some pixels called mixtels cannot capture the habitat image perfectly. These images will look like mixtures of light. This is due to current problems with low spatial resolution digital images where individual pixels may cover two or more habitat types. (Edwards 2009).

In general, remote sensing is a highly flexible technology, and can be used in sensing the needs of specific habitats or a general area. "Some remote sensing studies may be highly focused on specific surface features and, therefore, not concerned with mapping all habitats in an area" (Mumby 2009). Regardless, "it is sensible to extend the scope of the mapping exercise to include those habitats which most strongly resemble the habitat of interest…By incorporating those habitats which are most likely to create misclassifications and errors in the habitat maps, the accuracy of the mapping objective can be determined" (Mumby 2009). Comparing the images of known habitat areas, to see if the images are distinct, lends greater credence to the portrait generated of the area as a whole. Sensors can be used to map both geomorphological zones and more broadly-defined ecological habitats.

Properly executed, with the use of 'control' groupings and 'ground-truthing,' the technology can be highly effective. "The number of ground-truthing sites required per habitat is difficult to quantify and depends on the size of the area and distribution (i.e. complexity) of habitats: smaller study areas and areas of relatively uniform habitat (e.g. sand banks) require less ground-truthing. For example, 10 sites per habitat may be acceptable for a single bay whereas 30 may be required to map an entire coastline. However, whereas ground-truthing requirements may vary, it is imperative that an adequate number of sites are visited for accuracy assessment -- ideally at least 50 independent sites per habitat" (Mumby, Green, Edwards & Clark 2009). Adequate ground-truthing can increase accuracy as high as 75%-100%.