Advantages of shore based radar Remote Sensing
Synoptic coverage of (very) large areas (hundreds square km).
Equivalent with a multitude (thousands!) of point sensors: hence very cost-effective and much less logistic effort.
No disturbance of the wave field by large water piercing constructions (e.g. measuring poles).
Shore based installations are almost invulnerable; hence very reliable, also during storms.
Radar is an all-weather observation technique: thus shore based systems are very suitable for continuous (day and night) wave and current monitoring and also very suitable for capturing rare (e.g. storm) events.
Oceanographic applications of Microwave imaging radar
Shore based radar system primarily used for detecting and tracking ships at sea.
The rough sea surface also produces a radar echo; the so-called “sea clutter” (one man’s noise is sometimes another man’s signal….)
Microwave imaging radar can (also) be used for measuring waves, currents and water depths at sea.
History of shore based radar for oceanography in the Netherlands
Pioneering phase using photos of the PPI screen of a radar in Zeeland in the sixties by Rijkswaterstaat (Oudshoorn).
Fundamental and practical research at TNO (Paul de Loor) and TU Delft in the seventies and eighties.
Growing towards operational applications in the 21st century by the Dutch companies Tech5 and SeadarQ (Jan Kleijweg).
Signal processing with the Dutch SeadarQ system
SeadarQ is basically a software package operating on a PC, which is connected to the raw signal output (analog video, sync pulse, azimuth, north reset etc.) from the microwave radar.
Often data from an existing navigation radar can be used, but sometimes a separate radar has to be installed (much more effort).
A (short) reconnaissance survey is necessary.
Installation is relatively simple and takes a few days/weeks.
Current and depth information derived from the wave dispersion relationship
In case of an undisturbed (deep water, no current) wave situation the phase velocity (different at each frequency) of the waves is well-known.
The wave velocity calculated from the series of radar images deviates in practice from the undisturbed one due to the influence of currents (especially the short waves) and finite depth (mainly the long waves).
From the measured deviations the current and depth can both be estimated separately .
In fact the waves function as a kind of Lagrangian drifters or floats; carried along by the ambient current and retarded by the bottom.
VV short pulse (70 ns) Radar on Ameland lighthouse