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Thursday, July 14, 2011

Detecting Earthquakes with Satellite

As is known, that the earth is frequent natural disasters such as earthquakes. However, its appearance is very difficult to predict, earthquakes just come and destroy all affected areas. To detect the symptoms there had been an instrument called a seismograph. This tool detects vibrations around him, but still could not offset the seismograph was the time of appearance of sudden disaster. This makes scientists think in order to predict more accurately, when the occurrence of natural disasters. Then be made of a new technology to overcome these problems and this tool was first applied in America, when the Landers earthquake. Since then, new technologies have been widely used for various earthquakes around the world.
New technology to solve the problem called "Interferometric Synthetic Aperture Radar (InsAR)". InsAR This is a technique used in radar remote sensing and geodesy. Geodetic method uses two or more synthetic aperture radar (SAR) to generate an image map or digital elevation surface deformation, using a phase difference of the wave back to the satellite or aircraft. This technique can potentially measure centimeter-scale changes in deformation, over a span of time from day to day.

InsAr it will constantly emit radar waves from satellite radar and radar waves are recorded when received back by the sensor as a result reflected by the target on the surface of the earth.

Images obtained from satellite radar contained two important information. Information is power transmit beam in the form of phase and amplitude, which is influenced by the number of waves emitted and reflected back. At the time of the wave emitted performed phase measurements. In the images obtained from each pixel, will have two information. The intensity of the signal can be used to determine the characteristics of a material that reflects the wave, while the wave phase is used to determine whether there has been a movement (deformation) on the surface of the reflecting wave.

After transmitted through sensors, radar waves then reflected by the Earth's surface and received again by sensors. Wave reflection is referred to as the signal back. There are two parameters that affect the return signal, namely: system parameters and surface parameters.

In the system parameters that can affect the return signal is the wavelength, polarization, and turning angle. Meanwhile, the surface parameters associated with things like the condition of the surface of the imaged area covers the surface roughness, surface geometry, and the nature dielektrika. There are three possible result of interaction of radar waves emitted by the earth's surface that is scattered objects, the specular reflected, or reflected perfectly.

In this imaging, the radar will emit waves form a synthetic aperture radar (SAR). The concept is to utilize the frequency of radar signals along the spectrum, to distinguish the two spread in the beam antenna. A decisive factor in this process is the scouting radar, namely the phase as well as the amplitude of the received and stored for use in subsequent processes. In this case the phase should be stable in the period to send and receive signals. This leads to the impression created by long antennae are used, by combining information from different wave received.

SAR uses the principle Dopler. Wave propagation has a certain frequency and when a frequency is obtained by applying the principle Dopler, then the frequency is called frequency Dopler. Frequency differences that occur will lead to results different image for each object, without needing to use a long antenna. At the time the vehicle moves past the target while doing the imaging, then the object is recorded at specified intervals with a frequency that is different. The highest frequency that is the object that has a relatively nearby distance with the sensor.

InsAR imaging method can be applied to an aircraft or spacecraft vehicle satellite. On the plane rides used two antennas, at the same time and perform imaging with a single pass (singlepass), whereas the satellite vehicle used one antenna by performing imaging with passing more than once at different times (multipass). On the use of two antennas, based on the position of the antenna can be divided into two kinds, namely the transverse position of the aircraft (accross track) and the longitudinal plane (along track).

InsAR which is one of the SAR method is currently widely used for topographic mapping of land and ice surfaces, the study of geological structure and classification of rocks, ocean current and wave studies, study characteristics and movement of ice, the observation of deformation, deformation associated with volcanic eruptions and earthquakes .

Especially for the field of deformation, now InsAR be a promising alternative technologies in the study of deformation such as subsidence (land subsidence) and earthquake research. Use of InsAR in earthquake research develops, following the Landers earthquake in America, documented and well informed by the image deformation InsAR. This technology can also be utilized for military purposes .*** [ZULFI NUGRAHA | PIKIRAN RAKYAT 07072011]
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