Navigation Mode

At its' highest resolution, the RAS family of Radars produce a significant quantity of data. Navigation Mode is a simple way of distilling the whole of the radar’s field of view to a much smaller dataset, containing the range and bearing of the key objects within the view. The processing to distil the radar data down to these key points can be carried out inside the radar, which reduces the network bandwidth requirements. Alternatively, the source code for this functionality is available, which allows customers to implement this processing within their own specific environment.

The information below describes how the “Navigation Mode” output from a radar is derived from the radar’s view of the environment surrounding it.

This mode is a very simple approach to extracting features from the scene that the radar presents; it is ideally suited to extract features linked to solid, well-reflecting objects within the view of radar that do not have the COSEC² fill-in feature to the radar output beam.

The key parameters to configure the operation of this feature extraction process can be configured in a radar by Colossus message type 205 and the navigation mode output from the radar can be requested by Colossus message type 120. When this feature extraction method is appropriate, the network bandwidth utilisation for the radar’s connection is greatly reduced.

Alternatively, the source code for navigation mode feature extraction function is provided for both C++ and Python environments. This approach can be used to process the raw radar data within a customer’s complete control, and dynamic adjustment/adaptation of the key parameters is possible.

A much more robust, but computationally more intensive feature extraction method is CFAR - a “common form of adaptive algorithm used in radar systems to detect target returns against a background of noise, clutter and interference” (ISBN 0-201-19038-9).

There are various implementations of CFAR, and this approach to feature extraction is much more capable in high clutter environments, or radar scenes where a fixed thresholding approach across all ranges and azimuths is inappropriate.

The Navtech RAS family of radars support a CFAR “point cloud” output over an RDP connection - more details are available here. This function is available in radar firmware 3.1.0.325 and later

Examples

The following images demonstrate how reducing the value of “Threshold” for a given field of view from a RAS6 radar affects the distribution of data within the Navigation Mode output.

In the scenes below, the source raw radar data is shown on the left hand side and the resultant Navigation Mode output is shown on teh right hand side.

The radar is mounted around 1.5m above ground level, and has a view of a grassed area, a roadway and some roadside hedges.