What is InSAR?
Interferometric Synthetic Aperture Radar (InSAR for short), detects and measures displacement over time. The technology is based on the comparison of multiple radar (SAR) image pairs. InSAR specialists create interferograms when they compare the phase information of two SAR images; i.e. an interferogram represents the difference in phase between two images, calculated for each pixel. This difference in the wavelength’s phase denotes the amount of displacement that took place between the image acquisition dates. InSAR specialists have to do advanced processing techniques to remove contaminant signals such as atmosphere. And ultimately, the displacement results are presented visually over optical satellite imagery so that clients can easily interpret what locations are moving, by how much, when.
The use of radar to detect the velocity of a moving object is commonly used in many well known applications: by the military to detect the speed of an approaching aircraft, in baseball to measure the speed of the pitcher’s fastball, and by law enforcement to determine whether your car is speeding. InSAR is not significantly different. Only our radar waves travel more than 1000km roundtrip through space and the earth’s atmosphere.
Unlike optical satellite images, radar can penetrate through clouds and can work equally effective at night, leading to 98% image acquisition reliability. There are currently five radar satellite constellations orbiting Earth. Each satellite has its own unique set of specifications in terms of orbit frequency, resolution, operational flexibility, and image cost. 3vG is satellite independent; we choose the best data source for each project based on the area of interest and our client’s overall monitoring objectives.
Benefits of using InSAR:
High Precision: ability to detect 1 – 2 mm of displacement per year
Large Area Coverage: images (areas of analysis) that are 1500+ km² each
Dense Data Coverage: typically generate tens of millions of data points per area of interest
Remote Sensing: no ground instruments or in-person inspections required
Full Site Monitoring: often detects displacement in areas of unknown risk
Measurement Frequency: updated displacement measurements after each satellite revisit (typically every 2 – 12 days)
|Satellite||Band||Precision||Vegetation||Resolution||Image Foot Print (LxW)||Revisit Time (days)|
|TerraSAR-X (TSX)||X||1 – 2 mm||Poor||3 m||50km x 30km||4 – 11|
|Cosmo (CSK)||X||1 – 3 mm||Poor||3 m||40km x 40km||4 – 16|
|Sentinel||C||3 – 5 mm||Moderate||20 m||110km x 250km||6-12|
|Radarsat-2||C||3 – 5 mm||Moderate||3 m||20km x 20km||24|
|ALOS-2||L||1 – 2 cm||Excellent||3 m||55km x 70km||14|