GUIDELINES FOR THE APPLICATION OF THE ECAC RADAR SEPARATION(9)

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For a single radar station, the effect of correlated position errors, due to “partial loss of resolution”, is found to have the most crucial impact on the radar separation minimum. Correlated position errors, due to another source of radar problems called “multi-path” (distortion of the radar beam due to the characteristics of the terrain surrounding the radar site), has a very limited effect on the separation applied as it affects adjacent aircraft plots in the same way.
5.2.2 Mono / Multi radar data processing
Most radar chains contain, at centre level, a radar data processing system which includes some form of tracking. The type of tracking applied (mono-radar mosaic, multi-radar tracking based on different merging techniques of mono-radar tracks, real-multi radar tracking techniques based e.g. on so-called variable-update techniques, etc.) is of great importance because of the effect on the accuracy with which the overall radar system presents the aircraft positions to the controller.
The effect of random, correlated and systematic single radar errors on the track accuracy is, therefore, very much dependent on the type and complexity of the tracker (e.g. a logic to assess and eliminate systematic radar errors).
Even though more computing resources and communications links are required in the multi-environment and complicated algorithms are needed to reduce the misalignment errors, it is generally acknowledged that a number of the features which constitute a multi-radar environment render this system more attractive than the mono-environment.
The most widespread advantages are listed hereafter :
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Increased opportunity of detection (higher radar data update rate) in a defined interval of time reduces the probability of losing tracks and improves the following of manoeuvres.

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Improved quality of detected air picture.

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Improved combination technique is obtained when the individual target co-ordinated data are weighted according to their accuracy.

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Quality enhancement by redundancy in the domains of acquisition, distribution and processing of data.

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A properly designed multi-radar tracking system,  having sufficient overlapping radar coverage, can overcome resolution loss problems created by individual radars.

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Capability of reconfiguration in case of failure of some sensors leads to improved contingency planning.

The further development of the tracker together with the degree of radar redundancy (multi-radar coverage) will finally determine to what an extent a degradation in plot reliability and/or accuracy affects the accuracy of the track position. The track accuracy is simultaneously affected by the movements of the aircraft. Depending on the amount and changes of the aircraft Mode-of-Flight 1) (MOF) and the types of MOF’s, the visualised separation of aircraft may be affected.
5.2.3 Technical Summary
In modern radar chains the extent to which the visualised separation of aircraft represents their real separation is a function of:
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the radar plot reliability and accuracy 2)

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the performance characteristics of the RDPS

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the relative changes in the Mode-of-Flight of the aircraft being tracked.

In other words :
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A multi-radar environment compared to the mono environment improves the performance of the tracking system, due to a higher data renewed rate, which should result in better track accuracy.

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The multi-radar environment is, at least, equal or more accurate than the mono-radar environment.

Several different methodologies are used by States today that are all valid in proving that a radar or a group of radars can support the  application of 5NM radar separation minima. An example of a methodology that can be used for a mono-radar system can be found at Annex 1 Attachment A. Examples of methodologies that can be used for a multi-radar tracking system can be found at Attachment B and C.
　
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