Technology
Passive Coherent Location (Passive Radar)
Passive radar as one observation layer in a multi-source system.
What it observes
It observes airspace from the reflections of signals that other transmitters already send. A direct path and a reflected path are compared, and the difference tells where something may be.
The principle
A public-safe diagram of the mechanism, drawn without real values.
The diagram shows a reference path and a surveillance path between a transmitter, a receiver and an object, with a conceptual line of equal delay. It is a geometry of paths, not a sweep, and carries no map and no real position.
Where it sits in the chain
It is one of the sources in the first band. Its timed observations pass through time alignment and then join the other sources in correlation and fusion; it never stands alone.
What it does to the data
A delay and a shift between the direct and the reflected signal become a candidate observation: a place on a line of equal delay, with a stated confidence. Further sources are needed to narrow it.
How it shows up in the data
- Confidence
- Uncertainty band
| Time (relative) | Confidence | Uncertainty band |
|---|---|---|
| 1 | 40 | 26 - 54 |
| 2 | 42 | 28 - 56 |
| 3 | 45 | 33 - 57 |
| 4 | 60 | 52 - 68 |
| 5 | 63 | 56 - 70 |
| 6 | 66 | 60 - 72 |
| 7 | 68 | 62 - 74 |
| 8 | 52 | 40 - 64 |
| 9 | 50 | 38 - 62 |
| 10 | 54 | 44 - 64 |
| 11 | 58 | 49 - 67 |
| 12 | 60 | 52 - 68 |
Strengths / Constraints
Strengths
- It uses signals already in the air, so it adds no emitter of its own.
- It can watch a wide area continuously from a fixed receiver.
- Its geometry is explicit, so what it can and cannot say is stated by the geometry itself.
Constraints
- One transmitter and one receiver give a line, not a point; the candidate observation needs other sources to narrow it.
- It depends on the transmitters that happen to be present and on their continued operation.
- Objects close to the direct path, or low to the ground, are harder to separate from the direct signal.
Environmental dependencies
Terrain, buildings, weather and the choice of transmitters change which paths exist and how clean they are. The page states the conditions and gives no range.
Limitations
- Source availability: the technology relies on transmitters it does not control, so the picture changes when they change.
- Line of sight: paths blocked by terrain or buildings give no observation, and silence there is not emptiness.
- Environment and confidence: clutter and the surroundings change how clean a path is, so confidence varies from moment to moment.
- Validation scope and integration: the technology is a design at the evidence level of its projects, and its value depends on joining the other sources; no range or accuracy is stated.
Evidence and validation
This page claims nothing above the level of the projects it rests on.
- Passive Coherent Location (PCL) RadarEvidence level: E1 · Architecture Defined
- Critical Infrastructure Airspace ProtectionEvidence level: E0 · Concept
- Bird & Wildlife Radar IntelligenceEvidence level: E0 · Concept
- Distributed Passive Radar NetworkEvidence level: E0 · Concept
- City / Regional Low-Altitude Airspace NetworkEvidence level: E0 · Concept
- Near-Ground Airspace Intelligence NetworkEvidence level: E0 · Concept
Projects behind this
- Passive Coherent Location (PCL) RadarAirspace awareness from signals already moving through the environment.
- Critical Infrastructure Airspace ProtectionPersistent awareness for the airspace around infrastructure that cannot afford blind assumptions.
- Bird & Wildlife Radar IntelligenceUnderstand movement patterns in low-altitude airspace, not just individual detections.
- Distributed Passive Radar NetworkMany quiet observers. One evidence-aware regional state.
- City / Regional Low-Altitude Airspace NetworkBuild a regional airspace picture from observations that were never complete on their own.
- Near-Ground Airspace Intelligence NetworkBuild a coherent airspace state where terrain, structures and clutter make every observation harder to interpret.