Radiometric thermal imagery records a calibrated temperature value for every pixel, so any point in the image can be measured after the flight. Non-radiometric thermal imagery records only the visual result of a temperature pattern: a picture with a colour ramp, with no retained value behind the colours. Both look like a thermal image. Only one of them supports a measurement.
Why the distinction matters
A non-radiometric camera applies its colour palette at capture time, scaled to whatever was in frame, and discards the underlying values. That is fine for finding something: a hot cell in a solar string or a wet patch of roof insulation still shows up as a bright area. What you cannot do afterwards is say how hot it was, compare it against another image taken on another day, or state a temperature difference against an adjacent reference area.
A radiometric file keeps the per-pixel data. In analysis software you can place a spot measurement anywhere in the frame, draw a region and read its maximum, set your own palette and range after the fact, and compute the delta between a suspect area and a healthy one. That delta, rather than the colour, is what inspection standards and warranty claims are usually built on.
Where it changes the deliverable
- Solar inspections. Fault classification depends on the temperature difference between an affected cell, module or string and the surrounding healthy modules. A severity threshold cannot be applied to a picture. See solar farm drone thermal inspection.
- Roof and building envelope. Moisture in insulation is identified by a thermal contrast that has to be quantified and trended, which is the subject of thermal versus visual imagery on a roof inspection.
- Electrical and mechanical assets. A loose connection or an overloaded component is assessed by its rise over a reference, under load, not by whether it looks bright.
- Repeat monitoring. Comparing this quarter against last quarter requires retained values. Two non-radiometric images auto-scaled to different ranges are not comparable even when the asset has not changed.
What radiometric does not give you
A calibrated value is not a guaranteed absolute temperature. Accuracy still depends on emissivity settings for the material, reflected apparent temperature, atmospheric conditions, viewing angle and distance, and on the camera being within its calibration period. In practice the relative difference between two areas in the same frame is far more dependable than an absolute reading, and good thermal reporting leans on the delta for that reason.
Conditions still govern whether a thermal survey is interpretable at all. Irradiance, wind and time of day decide that before the sensor type matters, which our article on the conditions that make or break a thermal inspection goes through.
How UAV Imaging flies it
The thermal sensor in the Zenmuse H20T payload on the Matrice 300 RTK is radiometric, so every thermal job here retains per-pixel values and the raw radiometric files are part of the deliverable rather than just the rendered images. If a report quotes a temperature or a delta, the file behind it can be reopened and checked.
When you are reviewing someone's thermal quote, the question to ask is whether the raw radiometric imagery is included in the deliverable. If the answer is a set of JPEGs with a colour ramp, the report's numbers cannot be verified.