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Information obtainable from SAR includes backscattering coefficients, which exemplifies the strength of microwave irradiation emitted from the antenna and returned after scattering on the surface of targeted substances. Analysis of the backscattering coefficients enables to estimate, volume of water contained in soil, volume of biomass in forests, conditions of waves in the ocean and so on
• Analysis of Geology and Topography
• Analysis of Forests
• Analysis of Oceans
• Analysis of Soil Moisture
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| Example of SAR Backscattering Image(Mt. Fuji) |
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Analysis of Geology and Topography |
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JERS-1/SAR Image of Mt. Morgan
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The backscatter strength observed by SAR is strongly influenced by the soil moisture and surface roughness, and the difference in the surface roughness is sometimes useful in discerning objects on the surface of the earth. As the micro-wave length used by SAR is within the range of 1 centimeter to 1 meter, the discernible undulation of surface roughness of the object is on the order of several millimeters to several tens of centimeters. For this reason, backscatter strength observed by SAR is useful in distinguishing rock types based on the surface roughness.
In the image of the Mt. Morgan (Australia) observed by JERS-1/SAR, the rough surface areas have strong backscatter strength and consequently, the areas are shown brighter than other areas. Darker areas have weak backscattering strength and show smooth surface against micro waves.
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Example Image of Lineament Extracted from JERS-1/SAR
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The linear topographic features on the surface of the earth reflecting the underground fractures (namely all the cracks in the strata such as faults and joint) are called “Lineament”. As SAR images have strong contrast than optical images, topography is clearly shown. In the lineament pictures extracted from the JERS-1/SAR images, the lineament corresponds to linear topographical features. Although extraction by way of lineament has such a problem that reading criteria differ from person to person, this method has been tried to discover promising areas of oil, natural gas field and metal deposits.
In the exploration of oil, natural gas and mineral resources, remote sensing data including SAR images have been utilized in the early stage of exploration as an effective means to comprehensively understand geological and topographical information. Likewise, topography is an important information in the environment assessment and monitoring during exploitation of mineral resources and in disaster prevention, and thus, remote sensing data including SAR images have been widely utilized in these areas, too.
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Analysis of Forests |
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Since SAR observation is free from the obstructions of clouds and rain, it befits tropical rainforest areas where bad weather conditions dominate. Also, SAR data provides potentially important information with its characteristic scatter measurement of inner forest, in contrast to observation by optic sensor.
Backscatter is affected by complex factors such as forest elevation, inclination of land surface, water content of vegetations and soil, as well as the size and form of trunks, branches and leaves. For this reason, forest model based software is generally used to calculate the trend of backscatter. Also, there is an attempt to estimate formula based on the comparison of backscattering coefficient and the actually measured volume of vegetation, as long as the target forest area is homogeneous.
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Analysis of Oceans |
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| An example of ocean observation by SAR |
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The ripples of ocean mainly affect backscatter of SAR. As ripples on the surface of ocean increase, backscatter gets stronger. Analysis of backscatter strength of SAR data over ocean leads to understand the condition of ocean surface, which reflects various phenomena occurring in the ocean.
For example, when a part of the ocean surface is covered by spilled oil, the area generates fewer ripples than the surrounding area, and the backscatter appears weaker over the area.By using this phenomenon, it is used for an exploration of the subsea oilfield by detecting natural oil slick that gushes out from bottom of the sea, an oil outflow accident of the tanker, and an environmental monitoring of other oil pollutions etc.Likewise, the junction line between two sea currents, known as a rich fishing ground, has coarse surface due to the clash of currents and drifting substances gathered by the currents, both of which contribute to strengthen backscatter. Also, a wave behind a sailing ship reduces generation of ripples, causing weaker backscatter, indicating the possibility of extracting traces of ships from SAR data.
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Analysis of Soil Moisture |
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There is a great difference between specific inductive capacities of soil and water. As the amount of water contained in soil becomes greater, specific inductive capacity of the whole soil increases in proportion, and as a result, backscatter strength increases. In this way, analysis of backscatter strength leads to estimate the amount of water content in target land area.
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