What is the NETD sensitivity of infrared thermal imaging?
Every infrared thermal imaging product has a NETD indicator. What does it mean? It represents the detection sensitivity of the infrared detector and infrared module, which has a great impact on the performance of the infrared system.
NETD and MRTD, in simple terms, are the detection sensitivity of infrared detectors and infrared components. This is an important evaluation indicator unique to infrared thermal imaging devices and has a great influence on system performance. They look very similar, so do they mean the same thing?
Definition of NETD
NETD (Noise Equivalent Temperature Difference) is the "noise equivalent temperature difference", also known as thermal sensitivity. NETD is a measure of the temperature resolution of an infrared imaging system limited by the objective signal-to-noise ratio, and is an objective indicator for measuring temperature sensitivity.
NETD measurement
How can this parameter be obtained? We use an infrared imaging system to observe the standard test pattern (half-moon target). When the ratio of the peak signal to the root mean square noise voltage generated at the output end of the infrared imaging system is 1, the temperature difference between the target and the background is the NETD of the infrared device.
NETD is used to describe the minimum temperature difference detectable by an infrared thermal imager. It is one of the important indicators for measuring the performance of an infrared detector system. The smaller the NETD value, the higher the sensitivity. The importance of NETD is equivalent to the signal-to-noise ratio in the visible light field. It not only reflects the sensitivity of the infrared detector and the movement components, but also directly affects the main functional indicators of the infrared system such as target recognition and detection distance.
Limitations of NETD
Although the NETD parameter frequently appears in the parameter tables of infrared detectors and core components, it lacks the fact that it does not take into account the impact of human visual characteristics on sensitivity. In addition, NETD represents the temperature resolution of infrared devices for low-frequency scenes (uniform large targets) and cannot represent the temperature resolution performance when used to observe scenes with higher spatial frequencies.
Definition of MRTD
MRTD (Minimum Resolvable Temperature Difference) is the "minimum resolvable temperature difference". MRTD is an extremely important parameter for infrared systems to detect and locate thermal anomalies and detect targets.
MRTD measurement
MRTD measurement is based on subjective measurement. Four target patterns with different spatial frequencies and aspect ratios of 7:1 are placed in a uniform background. The temperature difference between the target and the background gradually increases from zero. When the observer can just distinguish the four patterns (with a probability of 50%), the temperature difference between the target and the background is called the minimum distinguishable temperature difference.
The significance of MRTD application
MRTD is a common test in the field of high-end infrared applications. The lower the value, the more sensitive the system is. This is actually a systematic comprehensive indicator. MRTD can be tested by both thermal imager manufacturers and thermal imager users.
MRTD is the most important parameter for comprehensively evaluating the performance of infrared imaging systems. We can use it to evaluate the probability of thermal imaging systems detecting, identifying and recognizing targets. Therefore, MRTD is also a common reference standard for many end users to select infrared thermal imaging components.
Limitations of MRTD
Because MRTD describes the spatial and temperature resolution of the infrared imaging system on a comprehensive level, MRTD is not only related to the spatial frequency of the target and the temperature difference of the ambient background, but also to the observer's vision and the quality and settings of the display device. It is a subjective measurement, and the test results will vary from person to person.
Similarities between NETD & MRTD
NETD and MRTD are both measures that describe the temperature resolution performance of infrared imaging systems. Theoretically, the smaller the NETD and MRTD values are, the more sensitive the thermal imaging system is to temperature differences. In actual imaging, when multiple targets are close together and have small temperature differences, they can be clearly distinguished on the infrared image.
Differences between NETD and MRTD
NETD is a relatively objective parameter, a measure of the temperature resolution of an infrared imaging system limited by the objective signal-to-noise ratio, and an objective indicator for measuring the temperature sensitivity of an infrared thermal imager or infrared detector and its infrared core module.
MRTD is a relatively subjective parameter, which comprehensively describes the spatial and temperature resolution capabilities of an infrared imaging system for a target when imaging in noise. It reflects both the temperature sensitivity and spatial resolution of a thermal imager, as well as the subjective factors of the observer, and is a comprehensive performance indicator of a system.