DRI: Thermal Distance Ratings Explained (Johnson Military Criteria for Detection, Recognition, Identification)
Detection, Recognition, and Identification (DRI) are a set of standards developed by Army Night Vision Laboratory in the 1950s to compare the performance of thermal infrared cameras. This model, also referred to as the Johnson criteria, has become the universal standard for measuring thermal cameras.
Most clients will likely want more detail than what a DRI rating stipulates, since DRI ratings are not only based on military standards (designed for trained operators who know exactly what they’re looking for) and rarely translate to real-world conditions. This is why people who are not familiar with DRI standards are often disappointed with a thermal camera’s performance at the specified ranges that they read on brochures and marketing material. Infiniti Optics rates our cameras using DRI as required by the industry, but we also attempt to educate our customers on what those ratings mean and communicate what they can more accurately expect for performance. Please see more info in our DRI whitepaper below.
What is DRI?
DRI is a universally accepted set of standards that attempts to provide a means of measuring the distance at which a thermal sensor can produce an image of a specific target. These standards were initially developed by the US Army in the 1950s and unfortunately have not been updated much to account for newer technology with larger theoretical ranges that are less likely to be achieved in the real world.
The model is based on a 50% probability of achieving the following objectives, under ideal conditions. Please read each definition as they may not match what you would expect from reading the terms alone.
Detection refers to the distance at which a target initially appears in the image. This “target” is something out of the ordinary that is warmer or cooler than the ambient environment. Specifically, it will be visible on at least two pixels, so there will not be enough information to confirm what the target is at this distance, just that something is there.
Contrary to what might be expected, recognition does not mean that you can recognize an individual. Recognition refers to the distance at which you can determine an object’s class (is it human, animal or vehicle).
Identification refers to the distance at which you can differentiate between objects within a class. For example, identifying the type of vehicle (truck, SUV, or car) or whether the human is a soldier or civilian.
Note that these distance measurements are based on a 50% probability and do not take any atmospheric conditions into consideration. Weather is almost never ideal so in real use these distances are almost always shorter than specified.
An outdated specification
So the terms detection, recognition, and identification can be misleading, especially to end users who do not have a military or electro-optics background. To make matters worse, the original 1950s specifications were based on old sensors and screen display technologies. The increasing resolution of thermal sensors has shrunk the size of the DRI areas in relation to the overall field of view to tiny specks of white on the screen.
For example, our high-res uncooled thermal sensors have a resolution of 1280×1024, which is over 1.3 million pixels. Human “detection” only requires the target to be visible on 3–4 of those pixels. This is an extraordinarily small portion of the screen that can easily go unnoticed by the human eye.
Even when magnified, the amount of detail visible at the DRI distances is not as high as one might expect, as seen in the chart below.
Another often overlooked aspect is that these ratings are based on “ideal conditions” which rarely happen in the real world. In reality, the average application will get 25% less than the rated distance and in extreme conditions can be 90% less.
We wrote this white paper in an effort to explain the rating systems we use while also giving end users an idea of the actual performance they can expect from their thermal and visible/NIR cameras. That said, this information just scratches the surface of the many considerations that go into building long-range surveillance cameras.
In addition to thermal, Infiniti also offers active IR illumination, color/visible imaging, SWIR, and other sensors such as LRF, Radar and more. We do not limit our customers to any one technology; rather we custom build solutions that typically use multiple sensors depending on the project.
There are also many additional aspects to consider when building a camera system, such as cooled vs uncooled thermal, size and weight, stabilization, connection and control, environmental and ingress protection, international trade regulations and more; all of which need to be considered alongside budget and availability.
At Infiniti we excel at designing customized systems to suit your specific needs. We can examine your situational requirements, location conditions and project budget and recommend the best system (or systems) available within that budget. We are also experienced in configuring multi-camera systems complete with multichannel recording, wired or wireless networking, access control, radar integration and more.
Contact us today for our expert advice on the ideal solution for you.
Below is another resource on DRI standards and how they are measured, as well as our brochure for our available thermal camera modules.