Interferometric Synthetic Aperture Radar
Interferometric Synthetic Aperture Radar ( InSAR ; German radar interferometry ) is a method of SAR - interferometry for the use of phase differences in the detection of the reception strengths of the signals coming back from the terrain with two antennas arranged next to each other.
overview
From these phase differences, complex arithmetic operations can be used to process object heights of the terrain topography and thus digital terrain models .
Areas of application for radar interferometry are the detection of changes in the earth's surface in the mm and cm range ( glaciers , volcanism, landslides, earthquakes, subsidence caused by mining, etc.) and the measurement of ocean currents .
Measurement method
Recordings can be made using aircraft-borne systems, here the distance between the antennas is a few decimeters. Greater distances are required when using satellite technology. During the shuttle mission STS-99 ( Shuttle Radar Topography Mission ) carried out in 2000 , a 60 m long boom was used to obtain interferometric SAR data. Large parts of the earth's surface were documented from a height of around 230 km during a single overflight. This method is therefore also known as “single-pass interferometry”.
The advantages of the methodology are:
- Generation of surface models
- High precision
- Cost effectiveness
- Simultaneous recording of large areas
In the case of InSAR, the corresponding phase values can also be compared from respectively corresponding image points of two SAR images recorded at different times. This enables you to measure distance differences of a fraction of a wavelength (cm). The trajectories are slightly offset, with only one antenna performing the recording. This “repeat pass method” has the disadvantage that intermittent changes that impair the surface roughness affect the radar echo and thus falsify the measurement recordings and the calculated terrain topographies. Influencing factors are, for example, wind conditions or rainfall.
technology
This technology achieved its breakthrough with the launches of the ERS-1 and ERS-2 ( European Remote Sensing Satellite ) satellites in 1991 and 1995, as well as the STS-99 mission in 2000. The latter has in recent years an almost global elevation model with a previously unattainable height geometric resolution. Other current radar systems are PALSAR on the Japanese satellite ALOS and ASAR on Envisat . The German satellite TerraSAR-X has been delivering SAR data since 2007 . Since 2010, its mission has been supplemented by the TanDEM-X satellite .
literature
- Bert M. Kampes: Radar interferometry - persistent scatterer technique. Springer, Dordrecht 2006, ISBN 978-1-4020-4576-9
- Ramon F. Hanssen: Radar interferometry - data interpretation and error analysis. Kluwer Acad. Publ., Dordrecht 2001, ISBN 0-7923-6945-9
- Gini Ketelaar: Satellite radar interferometry - subsidence monitoring techniques. Springer, Dordrecht 2009, ISBN 978-1-402-09427-9