Laser Range Gating

Laser Range-Gated Imaging for Imaging at Long Ranges and Through Obscurants (Fog, Smoke, Mist, Haze, Rain)

Range-gated imaging permits imaging at long ranges while minimizing the effect of obscurants (fog, rain, or smoke) in the atmosphere. In range-gated imaging, a pulsed laser is used to illuminate the scene while the reflected light is detected by a camera with a short exposure time referred to as a gate. The gate is delayed so imaging occurs at a particular range, thus the image is only from the reflection of objects at that range.

The diagram below explains the range gated imaging technique, where a gated SWIR camera and a pulsed laser are used to detect the distance to an object.

Long-range identification is critical for military operations for target identification and friend-versus-foe determination (Identification Friend or Foe - IFF). To overcome the lack of photons available at night, illuminators can be very useful, allowing the user to light up the target. Using illuminators in continuous-wave (CW) mode can blind the imaging system when obscurants such as dust, smoke, or fog are present, due to the backscattered light. The range-gated imaging system removes these reflections and allows imaging at the desired range only. The key to safe range-gated imaging is to employ laser sources in the SWIR band. These sources, such as popular 1550 nm lasers, are eye-safe, reducing potential harm to either combatants or noncombatants on the battlefield. InGaAs SWIR imagers are the ideal sensors choice. InGaAs also allows for an all solid state solution - solid state lasers instead of gas lasers - minimizing long term maintenance and cost.

In the image below, on the left is an example of "Close-range" identification range gated imagery and on the right is an example of "Long-range" identification range gated imagery.

Many SWIR camera capabilities are considered sensitive. If you would like to learn more about SWIR capabilities for the military, you can register at a special web site, You must be a US Government employee or a USG contractor and be a US Citizen to access this site.