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BRIEF HISTORY OF SAR

(SAR) was created by Carl Wiley at Goodyear Aircraft Company in, Arizona, in 1951. From that time forward, as the company became Goodyear Aerospace Corporation, and finally Lockheed Martin Corporation, the Arizona employees past and present played a long and storied role in numerous SAR firsts. These include the original SAR patent (known as Simultaneous Doppler Buildup), the first demonstration SAR and flight test, the first operational SAR system, the first operational SAR data link, the first 5-foot resolution operational SAR system, the first 1-foot resolution SAR system, and the first large scale SAR digital processor.

Fig 1, Carl Wiley

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FOLLOW BRIEF HISTORY

The company has installed and flown over five hundred SAR systems on more than thirty different types of aircraft for numerous countries worldwide. This company designed and manufactured all of the evolving high-performance SAR systems for the U. S. Air Force SR-71 "Blackbird" spy plane throughout its entire working history, spanning for more than twenty-nine years.

Recent SAR accomplishments include long-range standoff high-performance SAR systems, smaller high-resolution podded SAR systems for fighter aircraft, and foliage penetration (FOPEN) SAR. The company is currently developing the high-performance SAR/MTI (Moving Target Indication) radar for the Army Aerial Common Sensor (ACS) system.

Fig 2, Blackbird spy plane

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WORKING MECHANISM

Synthetic Aperture Radar (SAR) is an active sensor that transmits microwave signals and then receives the returned signals back, which are backscattered from the Earth’s surface. SAR calculates distances between the sensor and the point on the Earth’s surface where the signal is backscattered. This distance is a slant range that can be projected on the ground representing the ground range. The direction of the flight can be referred to as along-track or azimuth direction, and the direction perpendicular to the flight path is the across-track or range direction. The angle between the direction the antenna is pointing and the nadir is the look angle.

Fig 3, Showing the mechanism of SAR

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FOLLOW WORKING MECHANISM

The angle between the radar beam center and the normal to the local topography is the incidence angle. Both angles are sometimes used synonymously, which is only valid if the SAR’s geometry is simplified neglecting the Earth’s curvature and the local topography.

Because the look angle of the sensor significantly affects the behavior of the backscatter, it is one of the main parameters determining the viewing geometry and the incidence angle of the backscattered signal. Depending on the characteristics of the illuminated terrain, areas of layover and shadow may occur in the imagery.

Fig 4, Showing the SAR working

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USAGE

SAR can provide extra information to analyze and respond to climate change, ecosystem loss, natural catastrophes, and other environmental phenomena that pose a threat to national and global security. Here are a few instances of how SAR might be utilized for such things:

Agriculture. Surface roughness differences are a result of field ploughing, soil tillage, and crop harvesting.

Floods. Surface reflection differences can aid in the identification of significant flooding, minor flooding, metropolitan areas, and permanent bodies of water.

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FOLLOW USAGE

Land displacements, such as sinking ground caused by the extraction of subterranean natural resources, can be shown by differences in measurements over time.

There is snow on the ground. By discriminating between wet snow, dry snow, and snow-free locations, differences in surface reflection can assist forecast snowmelt.

Wildfires. Penetration through dense smoke can help estimate vegetation loss and provide more accurate and timely information about the scope of a forest fire.

Wetlands. Where land is covered by shallow water, penetration through wetland areas might disclose flooded plants.