Introduction

This section covers the function and process of debris detection, and links to the debris configuration options.

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Overview

The debris detection system utilises a dedicated processing channel within the Radar Tracker. This channel is highly optimised to look for small, stationary objects which have appeared within the detection range of the radar. The system comes with a well-defined setup of default parameters which are designed to work with the CTS radar.

Debris Detection Processing

The debris processing is quite different from the normal tracking approach. It is optimised for stationary targets. The key processes to support this are:

• Long Term Clutter Map: In normal tracking, the clutter map (long term average) has to update reasonably fast. This is to ensure normal clutter, such as trees and long grass, does not generate any false alarms. This works well with moving targets, such as normal traffic, however the downside is that tracks will be absorbed into the clutter map when they become stationary. This can happen in a matter of seconds which means stationary objects, such as debris, can be missed. By having a much slower updating clutter map, stationary targets are observed for longer and the chances of seeing small, static objects are much improved. This approach does increase the probability of false alarms however we use the second key process, multi-scan analysis, to focus on just the targets we want to detect.

• Multi-Scan Analysis: This process differs from the typical radar processing because it looks at data over several scans. Essentially it looks for signals which are greater than the specified signal threshold over a number of rotations. Depending on how many times it see a target exceed the threshold, the process will generate an artificial signal based on the total number of detections. This provides a high level of confidence that the object being examined is in fact a genuine piece of debris. The process does delay the creation of the track but typically this is only by a few seconds.

• Classification: The debris channel is configured to always report any target as debris. This sounds logical, but also consider that any stationary object, from small to large, could be reported as debris. This would include stopped vehicles or people standing still. This is a minor disadvantage considering the overall improvement in performance and future versions of this feature will include more intelligent classification to correctly distinguish between small and large objects.

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Debris Configuration

Global Debris Channel settings are explained here: Debris (Tracker Settings) , whilst the Highways Debris Tracking Parameter configuration is covered here: Tracking Parameters.

Configuration requires only the use of Standard Processes: Creating and Editing Entities.

Vehicle to Debris Correlation

Vehicle to Debris Correlation is the process of re-classifying a new debris track to stopped vehicle track, if a slow moving vehicle track was lost in close proximity to the new debris track. Given the debris channel reports any target as a debris track, stationary vehicle tracks and debris tracks need to be differentiated between. In the graph and diagram below, the Vehicle to Debris Correlation process is illustrated:

1. A slow-moving vehicle track meets the minimum number of track sightings and travels under the maximum speed required for correlation. 

2. After nine sightings, the track is lost.

3. Within the Expire Period, e.g. 3 seconds, a debris track is created on a similar trajectory to the previously lost vehicle track.

4. The area around the track, defined by the Check Distance (m), is searched for vehicle tracks lost in the last 3 seconds (the Expire Period).

5. The previously lost vehicle track's history is discovered, and the system recognises the new debris track is instead probably that vehicle track - now stopped. The stationary target is re-classified from a debris track to a vehicle track. 

    

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The configuration options for Vehicle to Debris Correlation are under the Topology tab:

Enabled: Select to enable Vehicle to Debris Correlation.

Minimum Seen Count (hits): Minimum number of consecutive sightings a vehicle track is required to accumulate before being lost to be correlated to a debris track.

Maximum Speed (m/s): Maximum speed the vehicle track can be travelling at to be correlated to a debris track.

Check Distance (m): The radius of the area around a new debris track that is searched for lost vehicle tracks to be correlated.

Expire Period (s): How long the track history of a lost vehicle track is maintained for potential correlation to a debris track before being culled. 

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