Interferometric Synthetic Aperture Radar (InSAR) is a monitoring technique which uses radar imagery to measure ground movement. The radar images are acquired using satellites which emit an electromagnetic beam that is subsequently backscattered from the Earth’s surface and received by the sensor on the satellite. The phase of the signal received by the satellite is related to the distance between the satellite and the ground. By comparing the phase of one radar image with another, we can determine whether the ground has moved away from or towards the satellite between those images. Combining multiple radar images, we can produce a time history of movements to calculate mm/yr precision!
InSAR measures movement in one direction, the satellite line-of-sight. The primary source of SatSense’s data, the Sentinel-1 mission, flies in a polar orbit and looks to its right. When the satellite flies from north to the south, the look angle is towards the west and this is known as the descending orbit. The opposite occurs for the ascending pass such that the satellite look angle is to the east. As the Earth spins beneath the orbiting satellite, the same part of the Earth can be imaged by the satellite in both ascending and descending passes. By combining data from these two passes, we can estimate the vertical and horizontal components of the observed motion.