Radiometric Thermal Imaging: How It Works and When You Need It

Not all thermal cameras are the same. Consumer thermal cameras (like those built into some phones) show relative heat patterns. Radiometric thermal cameras record the actual temperature at every pixel. This distinction matters for inspection work.

Radiometric vs Non-Radiometric

A non-radiometric thermal image shows that one area is warmer than another. It produces a colour-mapped image where red means warm and blue means cool. But it does not tell you the actual temperature. You cannot measure a 15-degree differential or compare readings across different images.

A radiometric thermal image stores a temperature value for every pixel. The resulting file (typically a TIFF with embedded thermal data) can be analysed in software to extract precise temperatures, calculate differentials, draw temperature profiles across surfaces, and compare readings between inspections.

Why Precision Matters

For building inspection, knowing the actual temperature differential between a suspected moisture area and a dry area is essential for diagnosis. A 2-degree differential might be normal thermal bridging. A 5-degree differential indicates likely moisture. A 10-degree differential is almost certain water presence.

For solar panel inspection, the IEC TS 62446-3 standard classifies faults by temperature differential. A hotspot 10K above module mean temperature is Class 1 (monitor). Above 20K is Class 3 (urgent). Without radiometric data, these classifications cannot be made.

How Thermal Cameras Work

Thermal cameras detect infrared radiation emitted by all objects above absolute zero. The sensor is a microbolometer array, typically 640x512 or 320x256 pixels, sensitive to long-wave infrared (LWIR) radiation in the 7.5 to 13.5 micrometre wavelength band.

The camera converts the infrared signal to a temperature reading using calibration data and emissivity settings. Emissivity is a property of the surface material. Most building materials have emissivity between 0.85 and 0.95. Shiny metals have much lower emissivity (0.1 to 0.3), which can cause misleading readings if not accounted for.

Drone-Mounted Thermal Cameras

Professional inspection drones carry radiometric thermal cameras as dedicated payloads or dual-sensor gimbals. Common models include:

• DJI Zenmuse H30T: 640x512 radiometric thermal, 56mm lens, 40x zoom visible camera
• DJI Mavic 3 Thermal: 640x512 radiometric, suitable for rooftop and solar inspection
• FLIR Vue TZ20-R: dual-thermal radiometric, long-range zoom for tower and infrastructure

These cameras capture both visible and thermal images simultaneously, allowing easy cross-reference between what you see and what the heat signature shows.

When You Need Radiometric Thermal

• Building moisture detection: quantifying temperature differentials between wet and dry areas
• Solar panel inspection: IEC-compliant fault classification by delta-T
• Electrical inspection: identifying overloaded connections by measured temperature
• Insulation audit: calculating heat loss rates from measured surface temperatures
• Energy auditing: quantifying thermal performance of building envelope

When You Do Not Need It

Visual heat pattern detection (non-radiometric) is sufficient for:

• Search and rescue (finding people or animals by heat signature)
• Leak detection where presence/absence is enough (not severity)
• Quick screening where further investigation will follow

If the question is "is there a problem?" rather than "how bad is the problem?", non-radiometric may be adequate. But for professional inspection reports, radiometric data is the standard.

Interpreting Results

Thermal images require expert interpretation. Apparent hotspots can be caused by reflections, emissivity differences, solar loading, or HVAC exhaust. An experienced thermographer distinguishes genuine defects from artifacts. Always engage a qualified operator for inspection work, not just someone with a thermal camera.