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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 consider considering the overall improvement in performance and futures future versions of this feature will include more intelligent classification to correctly distinguish between small and large objects.

How to Configure Debris Detection

To enable the debris detection:

1. Navigate to the Debris settings:
   1. Radar -> Tracker Settings -> Debris tab.
   2. Select Use Debris Channel.
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2. Once enabled, the next step is to draw the debris detection area. This area can be specific to this radar or a larger area that can be used by several radars.

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   The debris area is completely independent of the normal tracking area (i.e. the carriageways). This enables you to define the debris detection system to operate in specific areas . In addition this also allows you to exclude areas of detection which may cause the debris detection specific problems and can be safely excluded without compromising the overall performance of the system. Like with normal tracking areas, you can create one or more for debris, per radar.

3. Once the debris detection area has been created, you can add the area and tracking parameters to the tracker configuration:
   1. Enter Edit mode.
   2. Select the "+" key beside the Tracking Areas list.
   3. Select your debris area and the Debris Default tracking parameters.
   4. Select Save when complete.
      
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4. The default configuration is now complete.

Default Configuration Overview

The default configuration has been designed around detecting debris with a radar cross section of 15cm² out to 150m. This should work for most environments. However if you are encountering problems with false alarms, then you can consider altering the following settings:

Threshold Delta

(Tracker->Debris->Threshold)

Default value: 16

This threshold works in exactly the same way as for normal processing, but it only applies to the debris channel. The threshold output is always levels above, therefore there are the normal area dependent threshold settings in the Debris Default tracking parameters, however we would encourage you to only use this global threshold setting. If you increase this value, you will desensitise the detection, decreasing the value will increase sensitivity and therefore increase the likelihood of nuisance alarms.

Full Window Size

(Tracker->Debris->Scan to Scan Integration)

Default value: 16

This provides the total number of scans used to examine a signal to establish whether we think it is debris. In the worst case this may lead to a 4 second delay in detecting debris, but as discussed in the introduction, this process is essential to detect small targets with any level of confidence. Increasing this window size will delay detection and potentially reduce false alarms. The disadvantage of delaying detection is that more of the target will become absorbed into the clutter map and therefore become harder to detect over time.

This settings is linked to the Recent Window Size and the Hit Counts - they should all be considered when making changes to the configuration.

The process will be looking for the Full Hit Count Threshold being exceeded within this window. For example with a Full Window Size of 16 and a Full Hit Count Threshold of 10, we expecting our debris signal to appear above threshold 10 times out of 16 scans.

Recent Window Size

(Tracker->Debris->Scan to Scan Integration)

Default value: 6

This window provides the total number of scan to analyse within the last n of the Full Window Size. This allows us to specify a level of confidence that indicates the same signal we saw at the beginning of the full window is still there by the end of the full window scan period.

For example if the Full Windows Size is 16 and the Recent Window Size is 6 then this means use the last 6 scans (i.e. 11 - 16) of the full window as the recent window.

 Within this recent window we look for a further hit threshold using the Recent Hit Count Threshold. This has to be exceeded along with the Full Hit Count Threshold for the detection to be considered genuine debris.

Increasing this value will typically indicate you expect more threshold hits over a larger proportion of the full window scan. Decreasing this value indicates you are focusing on hits at the very end of the scan period.

Full Hit Count Threshold

(Tracker->Debris->Scan to Scan Integration)

Default value: 10

This is the total number of times we are expecting the threshold to be exceeded within the specified full window size. So if our Full Window Size is 16 and our full hit count is 10, then we need to see a total of 10 hits in 16 scans to consider the target as debris.

Recent Hit Count Threshold

(Tracker->Debris->Scan to Scan Integration)

Default value: 3

This is the total number of times we are expecting the threshold to be exceeded within the specified recent window size. So if our Recent Window Size is 6 and our recent hit count is 3, then we need to see a total of 3 hits in last 6 scans to consider the target as debris.