How NETD of Thermal Imaging Cameras Is Measured

NETD (Noise Equivalent Temperature Difference, unit: mK / millikelvin) is defined as the target-background temperature difference that produces an output signal equal to the RMS temporal noise of the camera pixel, the core metric for thermal sensitivity. Standard measurement follows ASTM E1543, VDI/VDE 5585 industrial standards, relying on a precision temperature-controlled blackbody radiation source as uniform IR reference target.

1. Required Test Hardware

• High-stability surface blackbody (emissivity ≥0.98, temperature stability ≤10 mK RMS, adjustable precise temperature)
• Dark shielded test chamber (block ambient stray infrared radiation)
• Tested thermal camera (configured fixed integration time, frame rate, F-number per specification; complete NUC non-uniformity correction before testing)
• Frame-grabber / SDK to export raw pixel AD count data (unprocessed original digital signal)

2. One mainstream standard test method: Dual-temperature Responsivity & Temporal Noise Method

Step1: Configure camera parameters

• Uncooled LWIR microbolometer: Max integration time + standard fixed lens;
• Cooled MWIR detector: Set integration time to half-well dynamic range, lens removed for bare FPA testing.
• Complete 2-point non-uniformity correction first to eliminate fixed pattern noise (FPN).

Step2: Capture three groups of raw frame data

• Low temp T₁ (e.g., 20 °C): Collect ≥64 continuous frames, average all frames pixel-by-pixel → signal array S₁(AD counts at T₁)
• Mid fixed temp T₀ (e.g.,25 °C): Collect ≥128 sequential frames, take the standard deviation of each pixel’s values over all the frames, and place these standard deviations into an array which represents the temporal noise. (AD counts at σₙ)
• High temp T₂ (e.g.,30 °C): Collect ≥64 continuous frames, average frames → signal array S₂ (AD counts at T₂)

Step3: Calculate responsivity & final NETD

• Pixel responsivity: R= (S₂-S₁)/(T₂-T₁) ​​(counts/°C)
• Single-pixel NETD: NETD_pixel​= σₙ/​​​​R (Kelvin)
• Final camera NETD = average of all valid pixel NETD values (exclude dead/bad pixels), and multiplying by 1000 gives the figure of merit in milliKelvins (mK).

3. Critical test conditions affecting final NETD result

• Specified test temperature point (common: NETD @30°C ambient);
• Camera integration time, F/# aperture, frame rate;
• Ambient temperature & humidity inside test enclosure;
• Spectral band (LWIR 8–14μm / MWIR3–5μm).

4. Typical NETD benchmark values

• Uncooled consumer thermal camera: 40~80 mK
• High-grade uncooled industrial bolometer: <35 mK
• Cryogenically cooled photon detector: <20 mK

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