The radar satellite sends out a sinusoidal radar signal to the Earth and measures the reflection. This reflection has two components:
- The amplitude: the strength of the reflection. This is visually interpretable.
- The phase: the fraction of a full sinusoidal wave cycle at the moment the signal is received by the satellite. This looks random.
Both components are essential for InSAR measurements, but using the phase makes them so accurate.
The radar satellite measures the phase values of all the objects in the area it flies over. After the satellite has passed over that same area for the second time, we can compare the phase values. When a certain object moves (e.g. the house in the image below), the satellite signal’s travel distance changes, resulting in a phase difference between the two satellite acquisitions. Because we now accurately know the phase difference, we can compare it to the length of a full wave cycle in order to determine the deformation with high precision. This is called InSAR.
Because the house is subsiding, the satellite signal has to travel a longer distance in the second acquisition. This results in a phase difference that can be accurately translated into a deformation value.
The InSAR technique is useful for comparing two images, but its real strength lies in deformation time series. With up to 60 observations per year, minute deformation dynamics can be monitored over areas as large as a country or as small as an individual building. Next to that, by using InSAR time series we can better model disturbances and thereby increase the measurement precision.
InSAR data is new and different and requires a different view than conventional measurements techniques. Consulting support is therefore included in every contract. Allow us to help you apply our data to your business case.