Interferometric Synthetic Aperture Radar
Interferometric Synthetic Aperture Radar ( InSAR ) ( German: radar interferometry ) is a methodology of SAR interferometry for the use of phase differences in the detection of the received levels of the returning signals from the grounds with two adjacent antennas.
From these phase differences of the terrain topography and thus digital terrain models can be processed by complex operations object heights.
Applications of radar interferometry, the detection of changes in the earth's surface in the mm and cm range (glaciers, volcanoes, landslides, earthquakes, mining -related cuts, etc.) and the measurement of ocean currents.
Recordings can be performed by means of air -borne systems, where the distance between the antennas is a few decimeters. With the use of satellite technology, greater distances are required. When carried out in 2000 shuttle mission STS -99 ( Shuttle Radar Topography Mission ), a 60 m long boom was used to obtain interferometric SAR data. Large parts of the earth's surface about 230 km altitude have been documented in single overflight. This process is therefore referred to as " single-pass interferometry ".
The advantages of the methodology are:
- Generation of surface models
- High precision
- Simultaneous recording of large areas
In InSAR the corresponding phase values can also be compared addition, each corresponding image points of two recorded at different times SAR images. This one is in a position to measure differences in distance from a fraction of a wavelength ( cm). Here, the trajectories are slightly offset, with only one antenna is recording. This " Repeat - pass " method has the disadvantage that between temporal changes that affect the surface roughness influence the radar echo and thereby falsify the recordings and the computed terrain topography. Influencing factors are, for example, wind conditions or rainfall.
The breakthrough was achieved by this technique with the launch of ERS- 1 and ERS -2 ( European Remote Sensing Satellite ) in 1991 and 1995 and the STS -99 mission in 2000. Latter has in recent years an almost global digital elevation model with unprecedented large geometric resolution delivered. More current radar systems are PALSAR on ALOS and the Japanese satellite Envisat ASAR on. Since 2007, the German satellite TerraSAR- X will provide SAR data. Since 2010, its mission is complemented by the satellite TanDEM -X.