How Far Can a Thermal PTZ Camera Detect a Person? DRI Range Tables for 384x288 and 640x512 Cores

Engineering reference · Fengtaida Product Management · Theoretical values under the Johnson criteria — verify against your RFQ datasheet

Direct Answer

A 12 µm uncooled thermal PTZ camera with a 50 mm lens can theoretically detect a standing person at about 1,000 m, recognise a person versus an animal at about 260 m, and identify silhouette-level detail at about 130 m under the Johnson criteria (50 % probability, no atmospheric loss). Doubling focal length doubles every range. Sensor resolution (384×288 vs 640×512) changes field of view, not range. Real-world distances are shorter and depend on atmosphere, target-to-background temperature difference and humidity.

What DRI Means — and What It Does Not

Standard targets used across the industry (NATO STANAG 4347 convention): person 1.8 m × 0.5 m (critical dimension 0.5 m); vehicle 2.3 m × 2.3 m.

DRI Range Table — 12 µm Uncooled Core, 50 % Probability, No Atmospheric Loss

All values in metres, theoretical geometric limit (D = Detection, R = Recognition, I = Identification). Derate 20–40 % for typical outdoor conditions; more in fog, rain, or when the target is thermally similar to its background.

The point most datasheets leave out

At the same pixel pitch, 640×512 does not see farther than 384×288 — it sees 1.67× wider at the same focal length. Choose 640×512 when one preset must cover a wide sector or you want to keep context while zoomed; choose a longer lens when you need range.

Why Real Range Is Shorter Than the Table

1. Atmospheric transmission — water vapour and aerosols absorb 8–14 µm radiation; a 50 mm lens rated ~1 km in the table may deliver 600–800 m detection in humid coastal air.
2. ΔT (target vs background) — a person at dawn after a cold night is far easier than mid-afternoon in summer when ground temperature approaches body temperature.
3. NETD — a core with ≤40 mK resolves lower ΔT than a ≤60 mK core; the table assumes sufficient contrast. Request NETD in the datasheet.
4. Probability level — the Johnson 50 % figure means half of trained observers succeed; for operational planning many integrators specify 90 %, which roughly halves the range.
5. Motion and platform — pan/tilt stability and image stabilisation affect effective resolution at long focal lengths.

How to Choose — Six Engineering Steps for a Thermal PTZ Specification

1. Define the task per zone: detection-only (alarm), recognition (classify), or identification (needs optical). Map each perimeter segment to a level.
2. Set the required range per level from the site drawing — camera post to fence line, shoreline or outer buffer.
3. Pick focal length from the table that meets the recognition range, not detection — detection ranges look impressive but trigger alarms you cannot classify.
4. Choose resolution by coverage: 640×512 when one preset must cover a wide sector; 384×288 when cost matters and sectors are narrow.
5. Specify NETD and frame rate (≤50 mK; 25/30 Hz for tracking moving targets — note export-control frame-rate limits in some regions).
6. Pair with an optical channel sized to the identification range, plus laser or white-light illumination if night identification is required.

Reading the Table for a Fengtaida Configuration

Fengtaida speed domes and positioning systems (IR6, IRS, IRS2, IRW2 housings) offer the thermal channel as a configured module. The model code states the thermal configuration explicitly (see the "About Model Name" page of the IRW2D/IRS2D datasheet):

So a quotation for …T635 means a 640×512 core with a 35 mm lens — read the 640×512 / 35 mm row above (theoretical person detection ≈ 730 m, recognition ≈ 180 m). A …T325 means 384×288 with 25 mm — read the 384×288 / 25 mm row. This lets you check any Fengtaida quotation against the DRI table before ordering.

Pixel pitch, NETD and frame rate are not stated in the published datasheet; request them in your RFQ (see checklist). The table assumes 12 µm pitch; if the quoted core uses 17 µm, multiply ranges by 12/17 ≈ 0.7.

RFQ Checklist (copy into your tender)

• Thermal core: resolution, pixel pitch, spectral band, NETD, frame rate
• Thermal lens: focal length (fixed or continuous zoom range), F-number, athermalised yes/no
• Stated DRI ranges with: target size, probability level, atmospheric assumption
• Optical channel: sensor size, zoom ratio, focal range, low-light sensitivity
• Illumination: type, stated range and the criterion used
• Environmental: IP rating (IEC 60529), operating temperature (IEC 60068-2-1/-2), salt spray (ASTM B117), wind load
• Integration: ONVIF profile(s), radiometric output if temperature measurement is required

Quote Red Flags

• A single "detection range" with no target size or criterion stated
• DRI ranges identical across different focal lengths (copy-paste datasheets)
• "Identify a person at 2 km" claimed for a thermal-only camera
• Resolution marketed as range ("640 sees twice as far")
• No NETD figure anywhere in the datasheet

Related Reading

• Border Security: Long-Range PTZ Surveillance Deployment
• Marine & Port: Ruggedized PTZ Surveillance Deployment
• Anti-Drone: Counter-UAS Surveillance Deployment
• IRW2D Thermal EO/IR PTZ Dome Camera

Sources

• Johnson, J. (1958). Analysis of Image Forming Systems. U.S. Army Engineer Research and Development Laboratories.
• NATO STANAG 4347 — standard target definitions for thermal imager assessment.
• IEC 60529 (IP code); IEC 60068-2-1/-2 (cold / dry heat); ASTM B117 (salt spray).
• Fengtaida IRW2D / IRS2D datasheet (PDF): model-code page for thermal configuration codes.