Axine Labs
Free / commercial imagery

Sub-Pixel Target Anomaly Detection

Anomalies below the size of a pixel: artificial coatings, camouflage materials and low fill-fraction objects.

Anomaly detection against a locally estimated background, for man-made materials smaller than a pixel.

Sub-Pixel Target Anomaly Detection
In view

Sub-pixel anomaly response over mixed ground, where a target occupies part of a pixel rather than all of it.

WHAT IT FINDS

What it detects.

MaterialTypical settingWhat can confuse it
Man-Made Materials & Camouflage FabricsTactical terrain, infrastructure security, and border surveillance zonesDense natural canopy shadowing and bright specular reflections

METHOD

How it works.

Calibrated reflectance goes in, and every pixel is fitted against a public reference library.

01Step 1

Background covariance estimation

Local and scene-wide background covariance are computed across the contiguous channels. How well this works depends on how many distinct materials the background already contains.

02Step 2

Reed-Xiaoli anomaly detection

Measures how far each pixel sits from its surrounding background in spectral distance, with the false alarm rate held constant rather than the threshold.

03Step 3

Constrained energy minimisation

A filter that passes a chosen target signature at unit gain while suppressing everything else. It needs a signature to look for, which is the difference between this and plain anomaly detection.

04Step 4

Abundance and coordinates

Surviving pixels carry an estimated abundance and a location, and each export records the confidence attached to it.

SPECIFICATIONS

What you get, and what it runs on.

Values deliveredDetector response and estimated abundance, floating point
OutputSub-pixel anomaly layer
TurnaroundQuoted with the order once this moves out of development
Formats
GeoJSON Target AlertsCloud-Optimized GeoTIFF (COG)Provenance record (detector version, background window, scene ids)

Conditions it needs

Sun angle limit:55°
Cloud cover limit:5%
Vegetation cover limit:50%

Method and checks are documented in Axine Applied Spectroscopy Technical Whitepaper · Series 6.

Read the paper

Scope

Exploratory. Detection degrades as the background gets more varied and as the target fills less of a pixel.