NETd

NETD stands for Noise Equivalent Temperature Difference. It is a metric used in infrared thermography and thermal imaging to describe the smallest temperature difference that a detector can reliably resolve under specified conditions.

NETD is defined as the temperature difference that would produce a signal equal to the rms noise of the imaging system. It is typically specified in millikelvin (mK) and indicates the thermal sensitivity: lower NETD implies that the system can detect smaller temperature differences. NETD depends on the detector type (cooled vs uncooled), the optical system, and the readout electronics, as well as testing parameters such as integration time, bandwidth, emissivity of the target, scene temperature, and ambient conditions. It is not a property of the detector alone but of the whole imaging chain.

NETD is commonly contrasted with MRTD (minimum resolvable temperature difference), which incorporates both radiometric sensitivity and spatial resolution. While NETD measures sensitivity, MRTD measures the smallest temperature difference that can be resolved at a given image detail.

Typical NETD values vary widely: cooled infrared detectors can reach tens of millikelvin, while uncooled microbolometer cameras commonly range from tens to hundreds of millikelvin, with consumer devices often around 100–300 mK. Higher-end scientific instruments may achieve lower NETD.

NETD is used to characterize and compare thermal cameras for applications such as building diagnostics, electrical and mechanical inspection, industrial process monitoring, and security and surveillance.