Patented radar reflectors are used to continuously capture satellite data about local ground motion and use it to predict future uplifting or subsiding ground elevation.
These predictions can be linked to data about rising sea levels due to climate change as experienced worldwide in recent years, the long-term impact of which is now the object of increasing focus. Although rising water levels and ground motion progress at an almost unnoticeable rate, we should expect to see major changes for many years to come.
Society will have to make large investments to protect assets and prevent the worst consequences. Decisions made in this regard depend upon a valid data basis and well-founded future prognoses, as investments will be spread over many years and need to be as effective and future-proofed as possible.
Using radar reflection to calculate ground motion
Radar satellites operate by transmitting a radar pulse that is reflected by the Earth’s surface. The satellite then measures the reflection of the transmitted radar pulse. The method whereby the radar pulse is reflected is used to characterise the surface. Variations in the measured reflection shown in two radar images contain information about how the surface has moved in the interval between the recording of the two radar images. This technique is called InSAR and can also be used in the form of longer temporal sequences of images, from which more robust surface motion patterns can be derived.
Radar reflectors assure a strong signal
The advantage of putting up a radar reflector (to capture and reflect satellite signals) is that it ensures a strong signal that can be easily identified on radar images. The precise origin of the signal is also known. If the movements of the radar reflector are known (e.g. from repeated measurements over time using levelling), this information can be used to calibrate calculations for all other natural radar reflective objects that are present throughout the entire sequence of satellite images. Natural reflectors include kerb stones, road signs, lampposts, large slabs, steps and various other stone, concrete or metal objects which are characterised by flat surfaces and right angles.
Geopartner therefore considers the use of radar reflectors as a natural extension of the part of the surveying business that focuses on levelling-based elevation measurement and the ongoing development of elevation measurements.
Using radar reflectors
Setting up radar reflectors can produce a more robust basis for the calibration of satellite calculations of the movement of permanent objects on the surface, even if this is not an entirely uncomplicated process and requires specialist expertise to interpret the calculated movements.
The benefits of setting up radar reflectors
- makes it easier to closely monitor surface ground motion in almost real time
- supplements and minimises the need for costly levelling, such as when using water level gauges etc.
- can be used as a fixed point for best possible local GNSS measurement
- can be used as a dynamic fixed elevation point
- can be used to monitor movements of critical buildings and infrastructure
Radar reflectors are already in use in a number of sectors:
- Underground storage (Download Energinet customer case)
- Municipalities & public authorities
- Other consulting
Different types of radar reflectors for different purposes
Geopartner has developed different reflectors which are all in production.
- The “muse” type reflector is a double trihedral reflector that transmits a signal in both ascending and descending satellite tracks. This type of reflector is suitable for positioning in stable areas, where there is a need to collect ground motion information at a well-defined point.
- Tri-hedral reflector is smaller than the muse type reflector and reflect only signals from either ascending or descending satellite tracks. A special foundation system can be selected to ensure minimal disruption on location, fx for installation on dikes.