Sensors

This chapter covers the theory of operation for sensor systems integrated into the DRONECOM tactical display. All contact data presented on the map display — tracks, threat warnings, classifications — originates from the sensor suite. Operators must understand sensor capabilities, limitations, and the tradeoffs involved in emission management to effectively employ the system.

How Detection Works

Every sensor follows the same fundamental process:

1. Energy propagates — either emitted by the sensor (active) or by the target (passive)
2. Signal attenuates with distance — strength decreases as a function of range
3. Detection occurs when the received signal exceeds the sensor’s sensitivity threshold

The critical distinction is between active and passive sensors:

• Passive detection of natural emissions (IR, visual, passive sonar hearing engine noise) — the sensor listens for energy the target produces naturally: thermal signatures, visible light, machinery vibration. Signal strength falls off with the square of distance (1/R²). This is the shortest-range mode but produces no emissions from the receiving platform.

• Active detection (radar, active sonar) — the sensor emits its own signal and listens for the return echo. The signal makes a round trip, so strength falls off with the fourth power of distance (1/R⁴). Longer range than passive detection of natural emissions, but the transmission itself is detectable by hostile platforms.

• Passive detection of active emissions (RWR hearing a hostile radar, passive sonar hearing a hostile sonar ping) — the sensor detects the powerful transmission of a hostile active sensor. The signal is strong and travels only the one-way path (1/R²), giving this mode the longest detection range of the three. A warning receiver will detect a hostile radar at significantly greater range than that radar can detect a return echo. This asymmetry is the foundation of the active-vs-passive tradeoff covered in the next section.

Active vs Passive — The Core Tradeoff

The central operational tension is situational awareness vs emission security.

When radar is active, detection ranges exceed those of any passive sensor. However, every hostile platform equipped with a Radar Warning Receiver (RWR) will detect those emissions — and because RWR operates on the one-way signal path (1/R²), an RWR can detect a radar transmission from significantly greater range than that radar can detect a return echo.

Operating in passive mode eliminates RWR exposure but limits detection to shorter-range passive sensors — IR, visual, and passive sonar. Coverage is reduced accordingly.

Every engagement involves this decision: activate sensors to establish the tactical picture, or maintain emission security and rely on passive detection.

The Electromagnetic Domain

Four sensor types operate in the electromagnetic spectrum — above the water surface.

Radar — Active. Emits radio energy, detects returns. Provides the longest detection ranges available. Subject to Doppler notching and ground clutter effects (see Advanced Effects). At sufficient signal strength, radar can resolve contact affiliation via IFF (Identification Friend or Foe).

RWR (Radar Warning Receiver) — Passive. Detects hostile radar emissions, providing bearing to the transmitting platform. As a passive sensor, RWR is always operational — EMCON settings have no effect on it.

IR (Infrared) — Passive. Detects thermal emissions — engine heat, exhaust plumes. Shorter range than radar but produces no emissions. Provides detection without revealing the receiving platform’s position.

Visual — Passive. Detects visible-spectrum signatures. The shortest-range electromagnetic sensor. Produces no emissions.

flowchart LR
    R["Own Radar\n(Active)"]:::friendly -- "Emission 1/R²" --> RWR["Hostile RWR\n(Passive)"]:::hostile
    R -. "Echo return 1/R⁴" .-> T["Hostile\nPlatform"]:::hostile
    T -- "Thermal 1/R²" --> I["Own IR\n(Passive)"]:::friendly
    T -- "Visible 1/R²" --> V["Own Visual\n(Passive)"]:::friendly

    classDef friendly fill:#0a2e1a,stroke:#22c55e,color:#22c55e
    classDef hostile fill:#2e0a0a,stroke:#ef4444,color:#ef4444

Note: Radar emissions detected by a hostile RWR travel the one-way path only — the RWR detects at greater range than the radar can detect a return echo. IR and visual sensors operate independently, detecting the target’s own thermal and visible signatures without producing emissions.

The Acoustic Domain

Two sensor types operate underwater. Electromagnetic sensors cannot penetrate the water surface, so subsurface platforms rely entirely on acoustic detection.

Active Sonar — Emits acoustic pings and listens for echoes. Fourth-power signal falloff, same as radar. The ping itself is detectable by hostile passive sonar — the same tradeoff as radar and RWR, applied to the subsurface domain.

Passive Sonar — Listens for engine noise, machinery vibration, and active sonar pings from other platforms. Square-law falloff. Produces no emissions — the subsurface equivalent of passive electromagnetic operation.

Medium Boundaries

The water surface is an absolute boundary for sensor propagation:

• Electromagnetic sensors (radar, RWR, IR, visual) cannot propagate through water. A submerged platform is undetectable by radar regardless of range.
• Acoustic sensors (active and passive sonar) cannot propagate through air. An airborne platform is undetectable by sonar.

This creates two distinct operational domains. A submarine operating silently below the surface exists in a separate detection environment from the air picture above. Maintaining awareness across both domains requires assets in each.

Reading Your Contacts

When sensors detect a target, it appears on the tactical display with the following data:

Track Code — A unique identifier assigned on initial detection (e.g., “T-001”). The track code persists even if the contact is temporarily lost and re-acquired — it is the contact’s permanent identity for the duration of the engagement.

NTDS Class — Platform classification based on sensor data and signature analysis. Examples: Air , Surface , Subsurface , Command Ship , Missile , Torpedo . See Symbology for the full reference.

Affiliation — At long range, contacts are classified as Unknown . As signal strength increases within IFF identification range, affiliation resolves to Friendly , Hostile . Allied platforms share contact data via datalink — if an allied sensor identifies a contact, that identification propagates to your display.

Detection Mode — Indicates how the contact was most recently detected:

• Active return — your active sensor (radar or sonar) illuminated the target and received an echo
• Active emission — you detected the target’s own active sensor emissions (their radar or sonar)
• Passive — you detected the target’s natural emissions (thermal, visible, acoustic)

Contact Lifecycle

Contacts progress through three states:

• Active — Currently held by at least one sensor. Position updates continuously.
• Lost — All sensors have lost the contact. Last known position is displayed, decaying over time.
• Expired — The contact has been lost beyond the stale timeout and is removed from the display.

A lost contact can be re-acquired if any sensor regains detection before expiry.

stateDiagram-v2
    direction LR
    [*] --> Active : New detection
    Active --> Lost : All sensors lose contact
    Lost --> Active : Re-acquired
    Lost --> Expired : Stale timeout
    Expired --> [*]

    classDef success fill:#0a2e1a,stroke:#22c55e,color:#22c55e
    classDef warning fill:#2e2a0a,stroke:#eab308,color:#eab308
    classDef error fill:#2e0a0a,stroke:#ef4444,color:#ef4444

    class Active success
    class Lost warning
    class Expired error

EMCON: Emission Control

EMCON (Emission Control) is the primary tool for managing the active-vs-passive tradeoff at the platform level.

Active — All active sensors enabled. Maximum detection capability. The platform is emitting and detectable by hostile passive sensors.

Passive — All active sensors silenced. Detection limited to passive sensors only. The platform produces no sensor emissions.

Per-sensor toggle — Fine-grained control: radar can be silenced while active sonar remains operational, or vice versa. Only active sensors can be toggled — passive sensors (RWR, passive sonar, IR, visual) are always operational.

EMCON is set per-platform. Setting the carrier to Passive disables its radar but has no effect on embarked or deployed assets — each platform manages its own emission state independently.

The Horizon

Earth’s curvature limits the effective range of electromagnetic sensors. A sensor can only detect targets above its geometric horizon — beyond that distance, the curvature of the earth blocks the line of sight.

All EM sensors — radar, RWR, IR, and visual — are subject to horizon limitations. Sonar propagation follows different physical principles and is not horizon-limited.

Three factors determine horizon range:

Sensor altitude — Higher altitude extends the horizon. An airborne sensor platform can detect beyond the horizon that limits a surface-mounted radar. This is a primary motivation for deploying airborne surveillance assets — they extend the detection horizon significantly.

Mast height — Surface platform sensors are mounted on masts above the waterline. Greater mast height extends the sensor horizon. The AN/SPY-310 ship radar has a 15m mast height, giving it a horizon of approximately 17 km against a sea-level target.

Target altitude — Horizon range depends on both the sensor height and the target height. Two high-altitude platforms can maintain mutual detection at ranges far exceeding what a surface platform achieves against a sea-skimming target.

Approximate horizon ranges for representative altitudes:

Advanced Effects

Three effects modify radar detection performance. Understanding these effects is essential for effective sensor employment and tactical positioning.

Low-Altitude Clutter

Targets operating at low altitude are more difficult to detect — radar returns from the terrain or sea surface below contaminate the target echo. Below a ceiling altitude, detection capability is progressively degraded. Above the ceiling, the target is in clear air.

Sea-skimming missiles and low-altitude platforms exploit low-altitude clutter to reduce their radar detectability. Detection may not occur until the target has closed to short range.

Look-Down Clutter

Look-down clutter is similar to low-altitude clutter, but instead of a fixed ceiling altitude, the clutter region is defined by the earth’s horizon. When radar looks below the geometric horizon — the point where the line of sight meets the curvature of the earth — terrain returns compete with target returns. Attenuation increases linearly with the depression angle below the horizon, reaching maximum degradation (approximately 20 dB for the AN/SPY-310) at 10° below the horizon. Beyond that angle, attenuation remains at maximum.

Higher-altitude sensor platforms have their geometric horizon further below horizontal, providing more clear sky before clutter effects begin. This partially offsets clutter degradation for elevated sensor positions.

Doppler Notching

Radar uses Doppler shift — the frequency change caused by relative motion — to separate moving targets from stationary background returns. A target with significant radial velocity relative to the radar has maximum Doppler separation and is readily detected. A target moving perpendicular to the radar’s line of sight has near-zero Doppler shift and can be masked by clutter.

Aircraft can exploit this by maneuvering to minimize their radial velocity relative to a threat radar — a technique known as “notching.” The effect is transient, as the relative geometry changes continuously, but it can degrade detection during critical phases of an approach.

Sensor Reference

For complete sensor specifications, see the Platform Reference.