Sensor ETM

September 3, 2012
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The data detected for the sensor are transmitted in the form of electromagnetic radiation reflected or emitted by the surface of the object. On account of the biggest efficiency and versatility that these detectors have to register the REM in different intervals of wave length, the sensory imageadores have great capacity to generate, simultaneously, a great one I number of images in different parts of the specter. The imageador is an instrument that at every moment catches the reflected or emitted electromagnetic energy of small samples of an area of the terrestrial surface, converting it through the detectors, in an electric sensor. All the sensory imageadores, the exception of the radars, are constituted of three systems: an optic system, an electronic and a system of register of data (or output unit), that they are grouped in an only aeroporttil unit. The digital image is a quantizada representation of the corresponding values of reflectance to each element of imageada unitria area in the land for the sensor.

The digital values are only entire or discrete values, that if associate with each pixel, representing the integrated reflectance of different objects inside of that unitria area of imageamento. Pixels can be dimensionados by two attributes: vpela space position, that is, space coordinates that pixel occupies in image; vpelo value of radincia of pixel. As the space coordinates of pixel it is a cartesian system, the digital image has the representation in the matrical form. The indices of the lines and columns of the matrix of the image identify coordinates x, y of each pixel and the value of f of each element in the matrix identifies the reflectance that is express in the image for ash levels. The histograma is a simple form to examine in the digital image its distribution statistics of each ash level in terms numbers of it of pixel. Generally it has a gaussiano behavior, therefore it can be represented by the statistical parameters of average and variance. The average is related with the value of ash level, and the variance, as measured, of the one idea of as the contrast of the levels of ash in the image, or its reflectances. However, the histograma of the image does not contain no information on the space distribution of the ash levels of the image.

One of the great advantages of a multispectral sensor is possibility of if constructing images colored through monitorial standard RGB. Standard RGB is an additive system of three colors R+G+B. To form a colorful composition she is necessary that three identical images of the object are overlapped, represented each one for its respective intensities of colors red-green-blue. Of the intersection, it adds, or combination, of three spots of light, results the calls secondary colors, for example: Red + Green = Yellow? Red + Blue = Magneta? Green + Blue = Cyan the area of intersection between the three primary colors results in the white. The image of the study area was gotten from Sensor ETM of LANDSAT 5, that it is imageador multispectral of the type of sweeps

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