4.3 Parametric subspace decomposition methods.4 Existing spectral estimation approaches.Īs of 2010, airborne systems provide resolutions of about 10 cm, ultra-wideband systems provide resolutions of a few millimeters, and experimental terahertz SAR has provided sub-millimeter resolution in the laboratory. This process forms the synthetic antenna aperture and allows the creation of higher-resolution images than would otherwise be possible with a given physical antenna. Signal processing of the successive recorded radar echoes allows the combining of the recordings from these multiple antenna positions. As the SAR device on board the aircraft or spacecraft moves, the antenna location relative to the target changes with time. The pulses are transmitted and the echoes received using a single beam-forming antenna, with wavelengths of a meter down to several millimeters. To create a SAR image, successive pulses of radio waves are transmitted to "illuminate" a target scene, and the echo of each pulse is received and recorded.
For a fixed antenna size and orientation, objects which are further away remain illuminated longer - therefore SAR has the property of creating larger synthetic apertures for more distant objects, which results in a consistent spatial resolution over a range of viewing distances.
Typically, the larger the aperture, the higher the image resolution will be, regardless of whether the aperture is physical (a large antenna) or synthetic (a moving antenna) – this allows SAR to create high-resolution images with comparatively small physical antennas. The distance the SAR device travels over a target during the period when the target scene is illuminated creates the large synthetic antenna aperture (the size of the antenna). SAR is typically mounted on a moving platform, such as an aircraft or spacecraft, and has its origins in an advanced form of side looking airborne radar (SLAR). SAR uses the motion of the radar antenna over a target region to provide finer spatial resolution than conventional stationary beam-scanning radars. Synthetic-aperture radar ( SAR) is a form of radar that is used to create two-dimensional images or three-dimensional reconstructions of objects, such as landscapes. Lava flows at the summit crater appear in shades of green and brown, while vegetation zones appear as areas of purple, green and yellow on the volcano's flanks. The city of Santa Cruz de Tenerife is visible as the purple and white area on the lower right edge of the island. that could be used as a replacement to repair.This radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. For example, if you did repairs, you could look up the word repair and find related words like fix, correct, improve, mend, etc. When creating a new name, you could use a thesaurus to find related words that may relate to your business. For example, repeating the same word throughout your writing can become repetitive to a reader, and you could use a thesaurus to get a synonym of the word.Ī thesaurus can also be used for someone creating a business name or registering a domain. Why would someone need a thesaurus on a computer?Ī thesaurus is used on a computer while writing an e-mail, letter, or paper to find an alternative meaning for words. Looking up the word "computer" in a dictionary would define the word like what is found on our computer definition. For example, looking up the word "computer" in a thesaurus may give words like PC, CPU, calculator, abacus, and laptop that could be used in place of the word computer. On the other hand, a dictionary explains the definition of a word. dictionaryĪ thesaurus is used to group different words with the same meaning ( synonyms) and similar words. Online thesaurus services include and the Merriam-Webster Thesaurus. For example, searching for "hope" may return synonyms like "achievement," "faith," "ambition," and "optimism."
Understand syn software#
A thesaurus is a book, software program, or online service that provides alternative or similar words to a word. Users using Microsoft Word can open a thesaurus by highlighting the word they want to look up and pressing the shortcut key Shift+F7.Ģ. A thesaurus is a software tool included with some word processors that provides synonyms for selected words on command. A thesaurus may refer to any of the following:ġ.
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