The littoral
zone is an area of economic and environmental importance. It is also one in which all
oceanographic parameters can vary quite dramatically in short time and space scales.
Similarly it presents problems for long term autonomous moorings of instrument packages
due to high volumes of shipping, fishing and leisure craft. Surface current monitoring
Radar systems have proven to be an essential tool in monitoring coastal flows around the
world.
These systems are deployed from on-shore stations. They provide high spatial
resolution data (100-1000m) over long stretches of coastal waters and at typical repeat
cycles of 20 minutes. The speed and direction of currents from the integrated surface are
determined through the use of high frequency radio waves. At an operational frequency of
27MHz, a working range of 35km is achieved. This provides a cell resolution of 1km and up
to 700 data points every 20 minutes. In order to produce orthogonal u,v components of
velocity, two systems are required. These would be at two distinct locations illuminating
the same sea area. Surface current Radar systems will operate in all but the most extreme
sea states and require minimal supervision. They provide a cost effective way of
collecting large volumes of spatially and temporally rich data in the littoral zone, and
have proven to be accurate. The nature of data collected by Surface Current Radar systems
makes them ideal for use in validating circulation models or for providing initial
conditions for such models.
The Principle
Surface current Radar operates by measuring the speed of sea waves
of a particular length which includes any motion due to current. The radio wave interacts
with sea waves of precisely half it’s wavelength. During normal operations it will
detect both the advancing and receding waves which appear as Bragg peaks on the power
spectrum of the reflected signal. As the natural speed due to gravity of a sea
wave is known, the difference between the theoretical position of the Bragg peak (in zero
current conditions) and its actual position can be used as a measure of the speed of the
current. In practice measurements obtained from a single radar only give the component of
the motion which is either directly towards or away from the site. Values from two sites
are needed to calculate both the speed and direction of the current at a point. This data
is mapped out by the system on a grid.
The littoral
zone is an area of economic and environmental importance. It is also one in which all
oceanographic parameters can vary quite dramatically in short time and space scales.
Similarly it presents problems for long term autonomous moorings of instrument packages
due to high volumes of shipping, fishing and leisure craft. Surface current monitoring
Radar systems have proven to be an essential tool in monitoring coastal flows around the
world.
These systems are deployed from on-shore stations. They provide high spatial
resolution data (100-1000m) over long stretches of coastal waters and at typical repeat
cycles of 20 minutes. The speed and direction of currents from the integrated surface are
determined through the use of high frequency radio waves. At an operational frequency of
27MHz, a working range of 35km is achieved. This provides a cell resolution of 1km and up
to 700 data points
every 20 minutes. In order to produce orthogonal u,v components of
velocity, two systems are required. These would be at two distinct locations illuminating
the same sea area. Surface current Radar systems will operate in all but the most extreme
sea states and require minimal supervision. They provide a cost effective way of
collecting large volumes of spatially and temporally rich data in the littoral zone, and
have proven to be accurate. The nature of data collected by Surface Current Radar systems
makes them ideal for use in validating circulation models or for providing initial
conditions for such models.
Surface current Radar operates by measuring the speed of sea waves
of a particular length which includes any motion due to current. The radio wave interacts
with sea waves of precisely half it’s wavelength. During normal operations it will
detect both the advancing and receding waves which appear as Bragg peaks on the power
spectrum of the reflected signal. As the natural
speed due to gravity of a sea
wave is known, the difference between the theoretical position of the Bragg peak (in zero
current conditions) and its actual position can be used as a measure of the speed of the
current. In practice measurements obtained from a single radar only give the component of
the motion which is either directly towards or away from the site. Values from two sites
are needed to calculate both the speed and direction of the current at a point. This data
is mapped out by the system on a grid. 
