Navy nominates radar study

Joris Derksen is a student in uniform; he studies at the TU Delft faculty of electrical engineering, mathematics and computer science as well as at the faculty of military science of the Royal Netherlands Naval College in Den Helder.

His study into the limitations of radar systems (called Microwave Ray Tracing, or MIRAT for short) is nominated, along with two competitors, for the Royal Navy Van Hengel-Spengler prize for the best operational innovation by young students.

Light, as we have learned, travels in straight lines. But no such luck with microwaves used in radar (radio detection and ranging). Since radar is in use, its operators are accustomed with fluke effects as seeing ships that are beyond the horizon, or missing incoming aircraft although they may be less than 10 kilometres away.

The surprising ways that microwaves propagate, refract, scatter and diverge cannot be helped much. It’s the law of physics at work and the chance of detection will depend on transmission power, frequency and pulse length as well as on earth surface roughness, temperature and humidity – to name a few parameters.

Various models have been developed to predict radar performance to assist radar operators in coping with varying circumstances. One of the systems in use called CARPET works with ray tracing and is developed by TNO. Another one, called AREPS, is better in modelling atmospheric effects but is calculation-heavy. Both systems calculate the probability of detection as a function of atmosphere and environment.

Derksen combined elements of both models in his own ray-tracing model called MIRAT. By limiting ray-tracing to a simplified horizontally stratified atmosphere, MIRAT allows for a non-uniform atmosphere to be modelled without posing excessive computational demands.

 

MIRAT

MIRAT

MIRAT

In contrast to the other programmes, MIRAT does not calculate a point’s probability of detection, but it merely maps the outgoing microwaves.

MIRAT’s outcome is a simple diagram that tells the radar operator where the microwaves go. In the example, there is ‘ducting’ in the lower atmosphere (less than 50 metres). The repeated reflection of the microwaves may extend beyond the horizon, which not only means an advance warning, but also the risk of being detected from behind the horizon by enemy ship’s electronic warfare systems.

Another risky feature are shadow zones; it allows airplanes to fly undetected in a considerable height range.

Derksen (26) would like to continue his research on the effects of a non-uniform atmosphere for the Royal Navy.

LTZE3 Joris Derksen, Microwave Ray Tracing, Modelling the propagation of microwaves through a non-uniform atmosphere near the earth’s surface, Supervisor KTZE Dr. F. Bolderheij, March 2012