Frequently asked questions

Light detection and ranging, or LiDAR, refers to the use of laser light to determine the distance to an object (topographic LiDAR) or to remotely detect a gas or cloud (atmospheric LiDAR).

Back in the day, when only defense contractors were doing this stuff, laser detection and ranging (ladar) referred to the ranging of ‘hard targets’ (i.e. solid objects) and light detection and ranging (LiDAR) referred to the ranging of ‘soft targets’ (i.e. clouds and gases). However, these days, no one really uses the term ladar and LiDAR is widely used for the measurement of hard and soft targets.

Conventional direct detect LiDAR measures the time it takes for pulses of laser light (i.e. amplitude modulation) to travel to and from a target. With knowledge of the speed of light, one can determine the distance to the object. FMCW LiDAR uses frequency modulation (instead of amplitude modulation) and coherent detection to determine distance. Advantages of FMCW LiDAR compared to conventional direct detect LiDAR include the ability to achieve better range resolution, better measurement dynamic range, shot noise limited detection, and velocity sensitivity.

Gas Mapping LiDAR™ is an active remote sensor.

Passive remote sensors typically utilize either a temperature difference between the gas and background (e.g. thermal infrared cameras) or absorbed sunlight that bounces off the ground (e.g. solar infrared cameras) to measure integrated gas concentration. Active remote sensors measure integrated gas concentration by absorption of laser light emitted from the sensor.
 

A primary disadvantage of passive remote sensors is that they rely on the environment (namely temperature or sunlight) for their measurement. So passive remote sensors struggle with cloud cover, during the night, with shadows, for certain background temperature ranges or albedo (e.g. black-top vs concrete), etc. These limitations can lead to unacceptable levels of unreliability. Also, Gas Mapping LiDAR™ is typically 100 times more sensitive than airborne passive remote sensors.

For pulsed LiDAR systems, as lasers shine on an area of focus, the emitted light waves bounce off surrounding objects such as trees, raindrops, or even single molecules. The amount of time it takes for the bounced light to returned to the sensor is measured to calculate the distance. The location is then plotted using a GPS. This process is repeated millions of times per second, creating a real-time 3D image of the environment.

For continuous wave LiDAR systems, the fact that each gas absorbs a specific frequency of laser light, is used todetermine the concentration of a gas by comparing the returning light from a laser pulse that is absorbed by a gas to a laser pulse that is not absorbed by the gas.

Bridger Photonics makes use of continuous-wave LiDAR to measure both solid surfaces and gases.