Using radar reflectors to correct water level measurements

We have long been aware that water levels are rising. Water level developments in Danish waters are closely monitored by DMI (the Danish Meteorological Institute), the Coastal Directorate and a number of ports and municipalities, which operate a network of online gauges that record water level data on an ongoing basis. This data is processed by DMI, who are responsible for advance warnings of extreme tidal levels, such as in connection with storm surges.

Reliably measuring water levels is therefore important, such as when authorities need to issue warnings about extreme tidal flooding scenarios, which can have a major impact on how citizens and communities are able to best protect themselves from harm to people, animals, buildings and infrastructure.

The positioning of water level gauges can cause imprecise measurements

Currently, the elevation of water level gauges is typically quality assured every three years. They are, however, often positioned in unstable areas, such as coastal areas that are prone to subsidence, which causes the elevation of the water level gauge to sink.

When recording water level movements, some of the movement recorded might therefore be due to the water level gauge having sunk. There is therefore a need to be able to differentiate between the rise in water level and local water level gauge subsidence.

This can be performed using satellite measurements, which is where the radar reflector comes into play.

Satellite data about ground motion is used to correct water level gauge measurements

Colleagues from Geopartner Inspections, the Coastal Directorate and Kynde & Toft are reflected in the newly installed radar reflector of Thyborøn Harbour’s water level gauge. Photo KDI

By using a radar reflector, Geopartner Inspections can collect data from satellites every six days. This data can be used to calculate ground subsidence with millimetre accuracy. Connecting a radar reflector to a water level gauge therefore makes it possible to continuously make adjustment corrections for how much the water level gauge is affected by subsidence. This enables an accurate water level measurement to be obtained.

If very up-to-date data is required, the calculations can be performed in real time. This means that the calculation of settlement rate is updated each time a new satellite observation becomes available.

Water level statistics require reliable water level measurements

Reliable water level measurements are a component in the preparation of water level statistics, which are calculated by the Coastal Directorate every five years. These are used in connection with the definition of storm surges, which is of great importance, for example, when determining compensation.

Water level statistics are of course also used in connection with activities in coastal areas and should therefore be expected to become of even greater importance and attention in coming years.

Ports should have their own water level gauges for flood simulations

Geopartner Inspections therefore recommends that ports that do not yet have their own water level gauge should consider the advantages of acquiring one to ensure the best possible data basis to produce the best possible quality storm surge warnings for use in accurate simulations of flood scenarios.

We generally see an increasing use of reflectors due to the need to achieve monitoring that is closer to real time. The use of radar reflectors ensures up-to-date, accurate data that can be collected in a way that is cost-effective. This is crucial to future large-scale investments to protect life, land and property.

Contact us for more information on radar reflectors and satellite data

Karsten Vognsen
Mobil +45 5151 7351
Niels Henrik Broge
Mobil +45 4131 8534