UN EXPECTED

the video of the final project is in the final slide

A S YNTHETIC A PERTURE R ADAR ( SAR ), OR SAR,

• is a mostly airborne or spaceborne coherent radar system that uses a platform's flight path to electronically simulate an antenna or a very large aperture, which generates high-resolution imaged remote sensing. Over time, individual transmit/receive cycles (PRT's) are completed with data from each cycle stored electronically. Signal processing uses the size and phases of the signals received via successive pulses of synthetic aperture elements. After a certain number of cycles, the stored data is recombined (taking into account the Doppler effects inherent in the different transmitter to target geometry in each subsequent cycle) to create a high-resolution image of the terrain over which it is hovered.

HOW DOES IT WORK

• The detailed description of the operation theory of Synthetic Aperture Radar (SAR) is complex and beyond the scope of this site. Instead, this page is intended to give the reader an intuitive sense of how Synthetic Aperture Radar (SAR) works. (Click here for a more detailed explanation of Synthetic Aperture Radar (SAR).) Consider an airborne synthetic aperture radar image perpendicular to the aircraft's speed as shown in the figure below. A synthetic aperture radar (SAR) typically produces a two-dimensional (2-D) image. One of the dimensions of the image is called the range (or cross path) and is a measure of the "line-of-sight" distance from the radar to the target. Range and resolution are measured in a synthetic aperture radar (SAR) in the same way as most other radars: the range is determined by measuring the time from transmitting the pulse to receiving the echo from the target, and in the simplest synthetic aperture radar (SAR), the range resolution is determined from During the transmitted pulse width, i.e. narrow pulses give accurate band resolution.

HOW DOES IT WORK

• The other dimension is called the azimuth (or along the path) and is perpendicular to the scale. The ability of the synthetic aperture radar (SAR) to produce a relatively accurate azimuth resolution distinguishes it from other radars. For accurate azimuth resolution, a physically large antenna is required to focus transmitted and received energy into a sharp beam. The sharpness of the beam determines the accuracy of the azimuth. Similarly, optical systems, such as telescopes, require large apertures (mirrors or lenses similar to a radar antenna) for accurate imaging resolution. Because the frequency of the synthetic aperture radar (SAR) is much lower than that of optical systems, the accuracy of the moderately synthetic aperture radar (SAR) requires an antenna too large to be practically carried by an airborne platform: antenna lengths of several hundreds are often of meters are required. However, airborne radar can collect data while flying at this distance, then process the data as if it came from an actual long antenna. The distance traveled by the aircraft in the installation of the antenna is known as the compositional aperture. The narrow synthetic beamwidth results from the relatively long synthetic aperture, which produces a finer resolution than is possible from a smaller physical antenna.

HOW DOES IT WORK

• The achievement of accurate azimuth resolution can also be described from the point of view of Doppler processing. The location of the target along the flight path determines the Doppler frequency of its echoes: targets in front of the aircraft produce positive Doppler displacement, while targets behind the aircraft produce negative displacement. As the aircraft flies a distance (synthetic aperture), the echo is resolved into a number of Doppler frequencies. The target Doppler frequency determines the azimuth position. While this section attempts to provide an intuitive understanding, synthetic aperture radars (SARs) are not as simple as described above. Sending short pulses to provide range accuracy is generally impractical. Typically, longer pulses are transmitted with wide bandwidth modulation, which complicates band processing but reduces the maximum power requirements on the transmitter. For moderate azimuth accuracy, the target range for each location on the synthetic aperture varies along the synthetic aperture. The energy reflected from the target must be "mathematically focused" to compensate for the scope dependence through the aperture before the image is formed. In addition, for micro-precision systems

the video of the project