Effects of distance, target size, aspect, and reflectivity on LIDAR-Lite v3/v3HP returned signal strength

The device transmits a focused infrared beam that reflects off of a target, and a portion of that reflected signal returns to the receiver. The distance is calculated by taking the difference between the moment of signal transmission to the moment of signal reception. Successfully receiving a reflected signal is heavily influenced by several factors. These factors include:

• Target distance: The relationship of distance (D) to returned signal strength is an inverse square. So, with increase in distance, returned signal strength decreases by 1/D^2 or the square root of the distance. 

• Target size: The relationship of a target's Cross Section (C) to returned signal strength is an inverse power of four. The device transmits a focused near-infrared laser beam that spreads at a rate of approximately 0.5º as distance increases. Up to 1m it is approximately the size of the lens. Beyond 1m, the approximate beam spread in degrees can be estimated by dividing the distance by 100, or ~8 milliradians. When the beam overfills (is larger than) the target, the signal returned decreases by 1/C^4 or the fourth root of the target's cross section.

• Aspect: The aspect of the target, or its orientation to the sensor, affects the observable cross section and, therefore, the amount of returned signal decreases as the aspect of the target varies from the normal.

• Reflectivity: Reflectivity characteristics of the target's surface also affect the amount of returned signal. In this case, we concern ourselves with reflectivity of near infrared wavelengths (see Related Content).

In summary, a small target can be very difficult to detect if it is distant, poorly reflective, and its aspect is away from the normal. In such cases, the returned signal strength may be improved by attaching infrared reflectors to the target, increasing the size of the target, modifying its aspect, or reducing distance from the sensor.