Track Anomaly Detection Using Log-Likelihood and MAD Thresholding

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Solution Overview

Problem

Existing methods for detecting track anomalies, particularly in maritime AIS tracks, require significant computational resources and are not suitable for real-time use, especially on embedded systems with limited computing power, and often necessitate adjusting detection thresholds based on track duration.

Innovation Solution

A method utilizing a neural network trained on historical tracks to calculate average log-likelihood values, followed by a Median Absolute Deviation (MAD) score calculation, allowing for real-time anomaly detection with a fixed threshold independent of track duration, reducing computational requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If GeoTrackNet method is used for anomaly detection, then detection accuracy is improved, but computational resource consumption increases significantly

Engineering Contradiction:
Improveanomaly detection accuracyVSAvoidcomputational resource consumption
Core Design Contradiction:
Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent segments the anomaly detection process into two distinct phases: an offline training phase where the neural network is trained on historical data, and an online inference phase where the trained model is applied to new tracks. This segmentation allows computationally intensive operations to be performed offline, reducing real-time resource consumption while maintaining detection accuracy.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent performs preliminary training of the neural network offline using historical track data before deployment. The trained model parameters are stored and reused during online operation, eliminating the need to perform heavy computational training during real-time anomaly detection, thus reducing online computational resource consumption.

Inventive Principle:
Principle #10Preliminary action

2Measurement precision

If GeoTrackNet method is used for anomaly detection, then detection accuracy is improved, but processing time increases making real-time use impossible

Engineering Contradiction:
Improveanomaly detection accuracyVSAvoidprocessing time
Core Design Contradiction:
Measurement precisionVSLoss of time

Solution Approach 1:

The patent divides the detection process into offline training (time-consuming but performed once) and online inference (fast and repeated). This segmentation enables real-time processing during online operation while achieving high accuracy through the preliminary offline training phase.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The neural network is trained in advance offline, so that during online operation, only lightweight inference is required. This preliminary action eliminates the need for time-consuming training during real-time detection, enabling real-time processing while maintaining high detection accuracy.

Inventive Principle:
Principle #10Preliminary action

3Measurement precision

If detection threshold is adjusted according to track duration, then detection accuracy is improved, but system complexity increases due to frequent threshold modification

Engineering Contradiction:
Improvedetection accuracyVSAvoidthreshold management complexity
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent transforms the detection threshold from a variable that changes frequently with track duration into a fixed value derived from statistical parameters (mean and standard deviation of log-likelihood scores). This parameter transformation simplifies threshold management while maintaining detection accuracy across different track durations.

Inventive Principle:
Principle #35Parameter changes

Solution Approach 2:

The system automatically computes the detection threshold using statistical properties of the trained model's output on validation data. This self-service approach eliminates the need for manual threshold adjustment and complex threshold management, reducing system complexity while adapting to different track characteristics.

Inventive Principle:
Principle #25Self-service

4Measurement precision

If GeoTrackNet method is used, then anomaly detection capability is improved, but resource constraints of embedded systems make it unsuitable

Engineering Contradiction:
Improveanomaly detection capabilityVSAvoidresource requirements
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments computational tasks between offline training (performed on powerful systems) and online inference (performed on embedded systems). This segmentation enables deployment on resource-constrained embedded devices by moving heavy computational burden to the offline phase.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The neural network is trained in advance on powerful systems, and only the trained model parameters are deployed to embedded systems. This preliminary action reduces the resource requirements of embedded systems during online operation, making anomaly detection feasible on devices with limited computational resources.

Inventive Principle:
Principle #10Preliminary action

Data Source

PatentEP4579524B1Track abnormality detection method and related device
Publication Date: 2026.04.22 THALES SA
  • EP4579524B1 patent drawingFigure 1
  • EP4579524B1 patent drawingFigure 2
  • EP4579524B1 patent drawingFigure 3

AI summary

This method (100) comprises, in configuration, the steps of: training a neural network (110) on training tracks to predict a log-likelihood value of a data of a track; calculating (120) an average log-likelihood value for validation tracks and calculating (125) a median; calculating (130) a score on the average log-likelihood value of test tracks with respect to the median and calculating (135) a statistical coefficient; defining (140) an abnormality threshold from the median and the statistical coefficient.The method comprising, in inference, the steps of: acquiring (150) at least one track of interest; processing (160) the track of interest by: calculating a mean log-likelihood value of the track of interest, calculating a score of the mean log-likelihood value of the track of interest relative to the median; and comparing the score of the mean log-likelihood value of the track of interest to the abnormality threshold, the track of interest being "abnormal" when the score of the mean log-likelihood value of the track of interest is greater than the abnormality threshold, and "normal" otherwise.