NETD is Noise Equivalent Temperature Difference; basically this noise in the images you are looking at

Simply put this is how well (at a defined set of parameters) the thermal sensor can discern between 2 temperatures.

It is measured in Millikelvin (mK). Typically from 30mK to 50mK. The smaller the figure the better the sensor can discern small temperature differences, a Lower Figure will generally result in a better image, with better contrast

PARD TA Thermals are 25mk which is considered the new standard

Excellent NETD is a fundamental that must be present. One other big item to watch out for is the F number of the Lens, often cheaper and smaller lenses are used such as F1.2, this means there will be a loss of 20% so that 35mK sensor is really 42mK

The end result will also be affected by the quality of lens, F Number, The programming of the Core and the environmental conditions.

This is a image showing a lower NETD on the left, vs that of the right – you can see far more definition in the image on the left.

The ability to differentiate between objects is critical to allowing the camera to produce the best images.

This is a retaining wall, its cold and damp, no sun on it and yet it looks very much like a photo