Earth Observation Satellites

Earth observation satellites are satellite sensors (image or instruments) on board to observe the Earth in certain colors, or frequencies of light (red, green, blue, ultraviolet, infrared, etc.). These satellites differ by the type of image tools they carry, the spatial resolution, spectral characteristics and track width which these sensors can visualize the earth, the viewing angle of the imaging instruments to the ground, and the type of job that they to move the earth. The orbit of the satellite has an effect on the spatial resolution, the image surface, and the frequency with which the same area can be monitored.

To view weather conditions at large scale and with high frequency is useful when a satellite is in a geostationary orbit. In such a job can find a satellite continuously an entire continent, and recording intervals of 5 to 15 minutes. But as the track is very high (about 36,000 kilometers above the Earth) it is difficult to obtain a high spatial resolution. For applications such as the tracking of clouds over continents, however, a high spatial resolution required.

For applications requiring images with high spatial resolution of a very specific area is needed, such as keeping an eye on a glacial lake and the mapping of destroyed buildings after an earthquake, a sensor requires high resolution. Such a sensor is located on a satellite in a relatively low orbit, about 500-900 km above the earth and generally has a narrow track width, making it a time but can see a small area. In addition, it is not possible to continuously view the same area in such a job, because of the relative motion of the satellites relative to the Earth. Images of a particular area can only be obtained when the satellite flies over it.

Landsat was the first observation satellite from the United States, launched in 1972. SPOT is a European observation satellite, which is in orbit 830 kilometers high flying around the earth, and put a strip of 60 kilometers wide fixed. SPOT is able to observe the planet in 26 days. The MODIS sensor aboard the Terra and Aqua satellites with a lower resolution of 250 to 1000 meters has a web width of 2330 kilometers and can daily observe the earth.

Earth observation instruments can be classified in many ways. One of these formats is the distinction between passive and active sensor. The passive sensor only increases reflected sunlight and light emission from the earth and which captures this observation. An active sensor itself sends a signal, and captures the signal on an operation again when reflected and where it carries out. Passive sensors provide images similar to aerial photos. One of the possible results provide an optical image in red, green and blue to a normal color.

Of the various types of satellite images, these images of the highest resolution, but it is compared to traditional aerial photography still lower. At present, the ground resolution of this satellite 1.25 meters. The 1.25 meter is removed from the WorldView-3 satellite. The resolution depends on the satellite shoot. Commercial satellites generally have a higher resolution than satellites that provide freely accessible images. When panchromatic (black and white) images are made, the resolution is approximately three times higher than in optical images. The resolution of WorldView-3 panchromatic images is 30 cm, currently the highest resolution available with satellites. These satellite images are widely used for mutation detection.

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