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an image of the area around the city of Angkor, Cambodia. The city houses an ancient complex of more than 60 temples dating back to the 9th century. The principal complex, Angkor Wat, is the bright square just left of the center of the image. It is surrounded by a reservoir that appears in this image as a thick black line. The larger bright square above Angkor Wat is another temple complex called Angkor Thom. Archeologists studying this image believe the blue-purple area slightly north of Angkor Thom may be previously undiscovered structures. In the lower right is a bright rectangle surrounded by a dark reservoir, which houses the temple complex Chau Srei Vibol. In its heyday, Angkor had a population of 1 million residents and was the spiritual center for the Khmer people until it was abandoned in the 15th century. The image was acquired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on the 15th orbit of the space shuttle Endeavour on September 30, 1994. The image shows an area approximately 55 kilometers by 85 kilometers (34 miles by 53 miles) that is centered at 13.43 degrees north latitude and 103.9 degrees east longitude. The colors in this image were obtained using the following radar channels: red represents the L-band (horizontally transmitted and received); green represents the L-band (horizontally transmitted and vertically received); blue represents the C-band (horizontally transmitted and vertically received). The body of water in the south-southwest corner is Tonle Sap, Cambodia's great central lake. The urban area at the lower left of the image is the present-day town of Siem Reap. The adjoining lines are both modern and ancient roads and the remains of Angkor's vast canal system that was used for both irrigation and transportation. The large black rectangles are ancient reservoirs. Today the Angkor complex is hidden beneath a dense rainforest canopy, making it difficult for researchers on the ground to study the ancient city. The SIR-C/X-SAR data are being used by archaeologists at the World Monuments Fund and the Royal Angkor Foundation to understand how the city grew, flourished and later fell into disuse over an 800-year period. The data are also being used to help reconstruct the vast system of hydrological works, canals and reservoirs, which have gone out of use over time. Research teams from more than 11 countries will be using this data to study the Angkor complex. P-45156Image Distortion E D C B A Ground Range Slant Range DistortionDistorted image Corrected image Slant-range distortion Slant-range distortion is the compression, to varying degrees, of an image in the direction of the sensor. It results from the timing and the spherical (circular) nature of the propagation of radar wavesFrom what direction was this image acquired? Distorted image Corrected image Slant-range distortionDistortion of the image b) Foreshortening The appearance of an object or surface as compressed when seen from a particular viewpoint. It is dependent on viewing angle and surface aspect and slopeDistortion of the imageDistortion of the image to theTbe distance of an object from the aircraft antenna is determined by the length of time required for the pulse of microwave energy traveling at the speed of light to reach the object and be reflected back to the antenna. Signals from houses 1 and 2 will arrive sooner than signals from the two houses farther away (3 and 4). In this example, the 10-7 second pulse length equates to 30 m. The resolution across track is equal to half the pulse length, in this case 15 m. Houses 1 and 2 will be resolved as distinct objects in the radar image. Houses 3 and 4, separated by less than half the radar pulse length will be perceived by the antenna as one broad object. Rr=(τc)/(2cosΘ) τ= pulse transmission duration c = speed of light Θ = angle of depression Shorter pulses have lower energy Range ResolutionSynthetic Aperture Radar A large antenna is “synthesized” using the travel path of the satellite to enable image resolution much greater than would be capable with a conventional radar antenna systemResolution θ"R L SLAR3.5 Radar scattering• Seasat: Launched by NASA 1978, last for a couple months, carried L-band (23.5 cm) active SAR at 800 km altitude. Resolution 25 m, swath width was 100 km. • RADARSAT: Launched by Canadian government in 1995 to monitor environmental changes. Orbit is at 798 km. Repeat time 24 days. Uses C-band (5.6 cm) SAR. It has many viewing angles. Resolution 10, 25, 30, 50, and 100 m (incident angle 10-60).Areal coverage 50x50 km to 500x500 km. 4. Radar platformsBeam Characteristics Beam Mode Beam Position Incidence Angle Range (deg) Resolution (m) Range x Azimuth Nominal Area (km) Fine F1N F1 F1F F2N F2 F2F F3N F3 F3F F4N F4 F4F F5N F5 F5F 36.4-39.5 36.8-39.9 37.2-40.3 38.9-41.8 39.3-42.1 39.5-42.5 41.1-43.7 41.5-44.0 41.8-44.3 43.2-45.5 43.5-45.8 43.8-46.1 45.0-47.3 45.3-47.5 45.6-47.8 9.1 x 8.4 8.7 x 8.4 8.4 x 8.4 8.1 x 8.4 7.8 x 8.4 50 X 50 Standard S1 S2 S3 S4 S5 S6 S7 19.4-26.8 24.1-30.9 31.0-37.0 33.6-39.4 36.4-41.9 41.7-46.5 44.7-49.2 26.0x27.0 22.0x27.0 27.6x27.0 25.7x27.0 24.2x27.0 22.1x27.0 20.1x27.0 110 X 100• Phased Array type L band Synthetic Aperture Radar on board Advanced Land Observing Satellite (ALOS). Objective is to detect changes in topography and geology. ALOS launched by JAXA 2006. Swath width 40-350 km, and resolution 7-100 m (depending on the incident angle) 4. Radar platforms4. Radar platforms • ESA ERS-1/2: Launched 1991 and 1995, SAR onboard, and scatterometer C-band , sun-synchronous orbit at 800 km. This view of Little Nicobar Island is part of a multitemporal composite of an ERS-1 SAR radar image acquired 21 December 1992 and ERS-2 image acquired 12 January 2005. The image is used to highlight the massive damage done to the west coasts of the Nicobar Islands during the December 2004 tsunami disaster, seen here in red. Source: ESAPALSAR color composite image of Jakarta, Indonesian Capital of images taken on Feb. 05, 2007 after the flood of Feb. 02, and before the flood on June 20, 2006. The blue colors shows the flooded areasThis RADARSAT image shows salvage operations for the Irving Whale oil spill off the coast of the Maritimes. The seven ships of the salvage operation are seen as very bright dots, and three small oil spills are readily identified by their dark tones.Images of different Radar sensors


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CU-Boulder GEOG 5093 - Image Distortion

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