Project · Sensing & Perception

Passive Coherent Location (PCL) Radar

Airspace awareness from signals already moving through the environment.

Evidence levelE1Architecture Defined

Bistatic geometry explorer

Interactive view

Data status: Illustrative

An illuminator, a receiver and an object on a blank plane. Drag the object, use the sliders or pick a geometry, and watch the surveillance path, the iso-delay ellipse and the Doppler lines follow. Nothing sweeps.

Reference pathSurveillance pathIso-delay ellipse

Object, acrossObject, down

Delay excess, in baselines: 0.33
Bistatic angle, degrees: 98
Path while the object moves right: Almost constant
Geometry for observation: Favourable

The plane is blank on purpose: no map, no coordinates and no frequency. The Doppler lines show one illustrative motion.

Passive radar signal lab

The real cross-ambiguity computation, on a synthetic scene.

Data status: Synthetic data

A synthetic broadcast signal and one echo of it go through a cross-ambiguity computation. The result is a range-Doppler map. Place the echo and watch the peak follow it along delay and Doppler; raise the noise to see the peak stand out of the floor.

Click or drag on the map to place the echo. Delay runs left to right and Doppler runs bottom to top.

Echo delayEcho Doppler

NoiseLowMediumHigh

Add a second echo

Strongest cell (delay / Doppler): ...
Peak above the floor: ...
Computed in: ...

Normalised units: delay in samples, Doppler in cycles per sample. There is no real frequency, waveform standard or site.

The scene is synthetic and seeded, so it is the same every time.

Why this exists

Active radar emits, so it is conspicuous, needs a licence and is costly to site. Illuminators of opportunity already exist in the environment, but the coverage they give is conditional, and that can be shown honestly only if the geometry is shown.

What it takes in

Each input adds something and leaves something unproven.

Reference pathA copy of an existing broadcast illuminator, taken from a path that does not include the object. No broadcast is named or described here.
Surveillance pathEchoes of the same illuminator arriving from the airspace, compared with the reference.
GeometryWhere the illuminator, the receiver and the object stand relative to each other, which decides what an echo can say.

Source presence: Data table
Item	Value
Source A	Contributes
Source B	Context only
Source C	Not yet available

Source presence RD03Data status: IllustrativeEvidence level: E0 · ConceptQuestion answered: Which sources contribute to this state?Three source markers connect to one state and carry a text status each. A source being present does not mean it is trusted; the label says what it contributes.Limitation: Sources are generic and their positions are not geographic.

How it works

Three steps, in the order the state is formed.

Takes a reference path from an existing broadcast illuminator.
Compares it with surveillance-path echoes, by delay and Doppler, at the level of principle only.
Emits spatial observations whose confidence depends on geometry into the fusion engine.

Passive and bistatic: the system adds no transmitter.
Conditional coverage is shown as conditional, not hidden.
It is never drawn as a rotating sweep, because nothing in it rotates.
It is not cheap radar. It is a different set of trade-offs.

Where it sits in the architecture

Passive coherent location is a spatial source at the start of the chain. It turns the geometry of existing signals into observations whose confidence depends on where the illuminator, receiver and object stand, and hands them to fusion in the core platform.

Read the architecture

Data flow: Data table
Stage	Value
1	Sources
2	Model
3	Policy
4	Interface
5	Consumer
6	Audit

Data flow CH13Data status: IllustrativeEvidence level: E0 · ConceptQuestion answered: How does data flow through the architecture?A pipeline of six stages, from sources to audit, shows how data moves through the model, the policy and the interface to the consumer, with a record kept at the end.Limitation: A conceptual flow. It does not describe a deployed system.

Evidence and assurance

What has been shown, to which level, and what has not.

Evidence ladder

E0 · Concept reached
E1 · Architecture Defined reached
E2 not reached
E3 not reached
E4 not reached
E5 not reached

Project assurance panel

Mission and context: Observe low airspace from signals already present, without a transmitter of our own and without implying coverage that the geometry cannot support.
Primary contribution: Spatial observations built from the reference and surveillance paths, each carrying a confidence that depends on geometry.
Decision value: Lets a reviewer see where passive observation can and cannot support a claim. It does not say what an object is.
Evidence status: Evidence level: E1 · Architecture Defined A frozen architecture specification exists. No prototype, test result or deployment is claimed.
Next validation step: Specify the geometry-dependent confidence model, then check it in simulation against synthetic scenes such as those in the signal lab, and record the outcome.
Behaviour when degraded: When the illuminator is unavailable or the geometry is unfavourable, observations carry a wider band or are not produced, and the state says that coverage is absent there. It does not guess.
Role in integration: Supplies spatial observations to fusion and its geometry state to system monitoring. It depends on illuminators that it does not control.
Human review: A person reviews any state in which a passive observation contributes to an action, and reads the geometry that produced it.
Public-safe limitation: No illuminator, frequency, range or site is named. The explorer and the signal lab use invented scenes in normalised units.
Open unknowns: How coverage varies across real illuminators and terrain, how often an illuminator is unavailable and how confidence should be scored are not yet known.

When inputs degrade

When the illuminator is unavailable or the geometry is unfavourable, observations carry a wider band or are not produced, and the state says that coverage is absent there. It does not guess.

Normal
Degraded
Unavailable

System health over time: Data table
Time (relative)	Component 1	Component 2	Component 3
1	Normal	Normal	Normal
2	Normal	Normal	Normal
3	Normal	Normal	Normal
4	Normal	Normal	Unavailable
5	Normal	Normal	Unavailable
6	Normal	Degraded	Normal
7	Normal	Degraded	Normal
8	Degraded	Normal	Normal
9	Degraded	Normal	Degraded
10	Normal	Normal	Normal
11	Normal	Normal	Normal
12	Normal	Normal	Normal

System health over time CH07Data status: Synthetic dataEvidence level: E0 · ConceptQuestion answered: How has system health changed?Three bands, one for each of three example components, show normal, degraded and unavailable periods as different fills and patterns, so state never depends on colour alone.Limitation: Periods are invented and say nothing about any real component.

Where it applies

An environment where emitting is undesirable
Why it matters here
Active radar is conspicuous and needs spectrum of its own.
What it contributes
Spatial observation from signals that are already there.
What it does not replace
Active sensors where the site requires them.
A region with several illuminators and several receivers
Why it matters here
More geometry gives more places where an echo is informative.
What it contributes
Observations whose confidence follows geometry, ready to be combined.
What it does not replace
A coverage commitment. Coverage stays conditional.

Role in the data flow

Supplies spatial observations to fusion and its geometry state to system monitoring. It depends on illuminators that it does not control.

Validation path

Specify the geometry-dependent confidence model, then check it in simulation against synthetic scenes such as those in the signal lab, and record the outcome.

Validation by stage: Data table
Item	Defined	Prototype	Integrated	Field
Module A	Done	In progress	Not started	Not started
Module B	Done	Not started	Not started	Not started
Module C	In progress	Not started	Not started	Not started

Validation by stage CH15Data status: IllustrativeEvidence level: E0 · ConceptQuestion answered: What is the validation status per stage?A grid of three example modules against four validation stages marks each cell as done, in progress or not started. Most cells are still open, as expected at this point.Limitation: Modules and statuses are placeholders and do not report real validation.

Limitations

Coverage is conditional. It depends on which illuminators exist, where the receiver stands and where the object is, and it is not stated as a range.
Objects close to the line between illuminator and receiver are hard to separate from the direct signal, so the geometry can be weak exactly where an object is.
The signal lab and the explorer use invented scenes in normalised units. They show a principle, not the performance of a system.
The evidence is a written specification. No measured result supports a claim about detection or accuracy.

Related projects

Each link says why the two belong together.

Capabilities

Multi-Source ObservationObserve through more than one source.

Solutions

Technology

Passive Coherent Location (Passive Radar)Passive radar as one observation layer in a multi-source system.

One passive node, or a network of them

Two projects that share a method and answer different questions.

One passive node, or a network of them
Aspect	Passive Coherent Location (PCL) Radar	Distributed Passive Radar Network
What it gives	Spatial observations from one receiver, with confidence that depends on geometry.	A regional state built from many receivers, with the overlap between them kept visible.
How it weakens	Where the geometry is poor, observations widen or are not produced.	A node that drops out lowers the regional state in steps, and the claim wording steps down first.
What it does not do	Cover a region, or survive the loss of its only receiver.	Remove the conditions of passive geometry from each node.

Next step

Discuss PCL for Your Environment

Evidence ladder

Project assurance panel

An environment where emitting is undesirable

A region with several illuminators and several receivers

Capabilities

Solutions

Technology