DRI: Thermal Distance Ratings Explained Johnson Military Criteria for Detection, Recognition, Identification
DRI stands for Detection, Recognition and Identification also known as Johnson Criteria developed by Army Night Vision Laboratory in the 1950's to define the performance of FLIR infrared thermal cameras used for surveillince. While DRI is a miltiary stnadard most clients want more detail (Pixels on Target) than DRI rating s stipulates which is why many clients who buy thermal cameras solely based on their rated performance which are rearley refelct real world condtions. This why people who are not fmailari with DRI miltiary standards are often dissapointed with a thermal cameras perofrmance at the specifed ranges they read on brochures and marketing material. A basic version of DRI based on pixels counts. Detection is 1x2 pixels for (1 line pair) recognition is 3x2 pxiels (3 line pairs) and identifcation is 6x2 pixels (6 line pairs) with a 50% probability in ideal condtions.
Infiniti Optics uses multiple mehtods of rating our cameras which includes DRI as required by the industy. While we use DRI like many others we find DRI to be both outdated and misleading especially to end users who do not have a military or electro-optics background.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 to tiny specks of white on the screen that makes detection hard even for trinaed operators in good conditions.
For example, our standard uncooled thermal sensors have a resolution of 640×480, which is over 300,000 pixels. Human “detection” only requires the target to be visible on 3–4 of those pixels to be of the target which works out to be only .00098% of the screen. This is an extraordinarily small portion of the screen that can easily go unnoticed by the human eye. In fact, if this page were the size of your video feed, the area required for a human detection rating would be equivalent to the size of this rectangle: This area becomes even smaller when you consider HD sensors, which have resolutions over four times larger at 1280×1024 (over 1.3 million pixels). 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.
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
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.
Pixels on Target (PPM)
Used by many manufacturers as a simpler alternative to NVThermIP, this method is done by calculating the number of pixels needed across the critical dimension of the target and then converting that value to the
required pixels per meter. The sensor and lens measurements then allow us to easily calculate the pixels per meter performance of the camera across a full range of distances and calculate the distance where each level of detail
is achieved. At Infiniti, we calculate the critical dimension by using the square root of the target height multiplied by its width, resulting in a critical dimension measurement for a human at 0.95m and a military vehicle at 2.2m. To fully understand how we do our ratings please see our white papers DRI VS DORI and for a very technical explanation on thermal see DRS thermal DRI explanation.
Infiniti optics custom builds all types of EO/IR solutions and can offer them as open frame modules (lens and sensor attached) or as complete integrated PTZ cameras with Visible and SWIR sensors for ultra long-range imaging required by a host of military and defense applications.