What is phase unwrapping in SAR interferometry?
Phase unwrapping is the key problem in building the elevation map of a scene from interferometric synthetic aperture radar (SAR) system data. Phase unwrapping consists in the reconstruction of the phase difference of the radiation received by two SAR systems as a function of the azimuth and slant range coordinates.
What is phase unwrapping insar?
Phase unwrapping is the process of restoring the correct multiple of 2π to each point of the interferometric phase image. For a well-behaved smooth phase field all the unwrapped phase differences between adjacent interferogram samples lie between -π and +π. When this is true, phase unwrapping is straightforward.
What is a interferogram?
: a photographic record made by an apparatus for recording optical interference phenomena.
Why is there an unwrap phase?
Unwrapped phase lets you designate a point (x-axis) value about which phase values are to be unwrapped. This would typically be a well-known point in a measurement such as the passband of a band pass filter.
What is InSAR used for?
InSAR (Interferometric Synthetic Aperture Radar) is a technique for mapping ground deformation using radar images of the Earth’s surface that are collected from orbiting satellites. Unlike visible or infrared light, radar waves penetrate most weather clouds and are equally effective in darkness.
How does a LIGO interferometer work?
Gravitational waves cause space itself to stretch in one direction and simultaneously compress in a perpendicular direction. In LIGO, this causes one arm of the interferometer to get longer while the other gets shorter, then vice versa, back and forth as long as the wave is passing.
What is NPL interferometer?
The NPL Gauge Block Interferometer was designed to measure the length of gauge blocks, length bars and Hoke gauges up to 300 mm in length. Up to 12 gauges can be wrung to a platen which is then placed in the instrument and measured after a suitable thermal settling period.
How does unwrap work?
Description. Q = unwrap( P ) unwraps the radian phase angles in a vector P . Whenever the jump between consecutive angles is greater than or equal to π radians, unwrap shifts the angles by adding multiples of ±2π until the jump is less than π. If P is a matrix, unwrap operates columnwise.
What unwrapped data?
Data is sent wrapped to save transmission costs. Unwrapped data is sent with one segment of record per line.
What is SAR and InSAR?
Interferometric Synthetic Aperture Radar (InSAR) is an effective way to measure changes in land surface altitude. Synthetic Aperture Radar (SAR) imagery is produced by reflecting radar signals off a target area and measuring the two-way travel time back to the satellite.
What is the difference between SAR and InSAR?
A SAR signal contains amplitude and phase information. Interferometric SAR (InSAR) exploits the phase difference between two complex radar SAR observations of the same area, taken from slightly different sensor positions, and extracts distance information about the Earth’s terrain.
How does LIGO detect gravitational waves?
When a gravitational wave passes by Earth, it squeezes and stretches space. LIGO can detect this squeezing and stretching. Each LIGO observatory has two “arms” that are each more than 2 miles (4 kilometers) long. The observatory uses lasers, mirrors, and extremely sensitive instruments to detect these tiny changes.