Professor Bill Mullarkey Managing Director dB Research Limited and Research Fellow Denbridge Marine Limited

SeaHawk A patented, applied-mathematical technique for improving target detection and resolution.

Some Radar Basics The first task is to illuminate the target scene with energy and store the resulting echo returns on a B Plane Antenna Signal processing Radio Tx and Rx Scan Converter r B Plane Display

B Plane Bearing Range

Pulse Repetition Period Pulse Radar amplitude treturn Pulse Repetition Period Tx Rx (not to scale) time Pulse Radar

Radar performance The quality of a radar is defined by two metrics: The ability to resolve as separate, targets that are close together in range and bearing; and The ability to detect weak targets.

The first is determined by receiver bandwidth and pulse length for range; and the antenna characteristics for bearing The second is by the ratio of the echo’s energy to the receiver’s inherent noise.

It is expensive to reduce receiver noise so the only practical way to improve target detection is to illuminate the target scene with as much energy as possible.

Energy Not Peak Power Think in terms of Joules not Watts

Deconvolution Many will be familiar with blind and other forms of deconvolution that attempt to remove the sensor’s influence on the collection of data. It has been long established that all introduce artefacts. SeaHawk is a deconvolution process that does not do so.

Introduces false positive peaks Decovulution requires a kernel and can either be done in one go with a long kernel or a shorter one can be applied iteratively. The next slide has a changed y axis to show how those peaks get worse at each convolution

Note the false targets

Again, we can change the y axis

SeaHawk determines where the artifacts at each iteration must lie and clips them before they can cause trouble. It loses about 5% of the signal energy but does not introduce artifacts.

The Buoys are plastic and it was a dry day, so the only reflections have to come from the small holes the buoys make in the water.

The first is with SH switched off . The second with it on. The next two slides show images from a first generation SeaHawk enabled Raymarine radar, which used a 6ft open array antenna. The first is with SH switched off . The second with it on. Seahawk doubles the effective antenna size, to12ft .

So how does SeaHawk work? To understand how we need to think in the frequency domain not the time one. The polar diagram of an antenna is the impulse response of a low pass filter. Importantly, whilst that filter attenuates some frequencies beyond its -3dB, so called “cut off”, it does not eliminate them.

Imagine a HiFi system that has a graphic equalizer.

It is that easy. SeaHawk enhances the azimuthal frequencies to give the response of an antenna twice the size of the original. The next slide shows the frequency response of a 6ft and what would be that of a 12ft antenna, if a leisure –marine vessel could carry such a thing.

That slide showed: the natural azimuthal bandwidth of a 6 ft antenna (Blue Trace); the natural azimuthal bandwidth of a 12 ft antenna (Red Trace) ; the SeaHawk filter (Green Trace) ; and the overall SeaHawk-enhanced frequency response (Black Trace) .

Notice how the SeaHawk enhanced bandwidth matches that of the 12 ft antenna, with a little gain.

A long devolution kernel can be factorized into smaller ones that are used iteratively. If those kernels share the property of having only one positive region, then all artifacts must be negative going.

The SeaHawk Kernel

The key is to discard the negative regions at each iteration.

Five iterations of the SeaHawk kernel

It gets better Target detection depends upon the energy that illuminates the scene. The broad beamwidth antenna illuminates every target with twice as many pulses as would an antenna of twice the size. That corresponds to twice the energy less a 5% loss from the SeaHawk algorithm.

So what next? The first generation Seahawk was designed against tight timescales with the need to get a Raymarine SeaHawk enabled Digital Radar to market as quickly as possible. Since then there has been the opportunity to revisit the design and make some significant improvements. The next two slides are a taster.