How to achieve full range with your LRF

A Practical Integration Checklist for reliable Range Performance

During integration you may find that the LRF does not achieve the range performance specified in the datasheet. The checklist below highlights the most common root causes and practical checks to quickly identify and resolve them.

1. Check Alignment of LRF to Line of Sight

Correct alignment of the LRF module to the system line of sight (e.g. camera or sight axis) is critical to achieving the specified performance. If the LRF beam is not properly co aligned with the camera crosshairs (system line of sight), the laser energy may partially or completely miss the intended target, reducing effective range and hit probability. In a military context, misalignment can lead to ranging the background instead of the actual threat, resulting in incorrect distances for fire control solutions and inaccurate target coordinates. This is especially critical for small moving targets such as drones: even a small angular offset to the line if sight can cause the narrow laser beam to miss the drone as it moves, so no reliable range is measured although the drone is clearly visible in the camera image. Boresight stability should be ensured not only at the start, but also throughout the whole lifetime, with periodic checks for proper alignment. The optional coaxial pointer inside the Ultisense fiberlaser modules simplifies alignment checks and supports long-term boresight stability. 

More about that here: Accurate laser alignment with Coaxial Pointer

2. Verify Range-Limiting Software Settings

Ultisense LRF modules offer configurable software functions such as range gate and range focus that allow to intentionally limit measurements to specific distance windows. If a range gate or a range focus is activated the module ignores valid targets outside that defined distance window, giving the impression of not properly measuring. Always verify which functions are enabled during measuring.

3. Confirm Correct Power Supply and Laser Activation

Ensure that the LRF is powered according to the specified voltage and current requirements. Undervoltage can prevent the laser from emitting at the designed energy level, which is required to achieve full range performance.

4. Ensure that Tx and Rx lenses are Not obstructed

Partial obscuration of either the transmitter or receiver apertures by housing structures, mounts or other system elements will reduce the laser output. Even small mechanical overlaps or misaligned buffers can reduce the range performance by either limiting the transmitted energy or the received signal.

5. Check for Crosstalk at the Front Window

One of the most common causes of performance errors is crosstalk – but once detected it can usually be eliminated with minor adaptations in the host system.

Crosstalk occurs when part of the transmitted (Tx) laser beam is reflected by the system’s front window directly back into the receiver (Rx). Instead of detecting a true target reflection from outside the host system, the LRF detects an internal reflection and calculates a false distance. This can manifest as incorrect ranges, or as ranges that appear even when no physical target has reflected the beam.

Detecting Crosstalk: The Blue Sky Test

An easy way to check for crosstalk is to measure with the LRF into a clear blue sky where no solid target is present. Under normal conditions, the LRF beam will not be reflected by any target, so no valid distance can be detected and a specific error message should be returned. If, instead of an error message, a distance is displayed when measuring into the sky, this strongly indicates that the front window is reflecting the transmitter beam back into the receiver, causing crosstalk with erroneous measurements.

If crosstalk is detected, consider the following measures:

Check Front window glass and coatings

Verify that the glass and coatings used for the front window are highly transparent for 1550 nm wavelength. (If you additionally use a pointer, also transmission for 830/850nm pointer wavelength also needs to be considered.) The surface should be optically flat and uniform to avoid unintended reflections. Any coating designed for other wavelengths may influence the transmission for 1550 nm and should be tested before integration.

Check Front window angle

A perpendicular (90°) angle of the window relative to the optical axis of the LRF is not recommended because it might reflect a portion of the beam directly back towards the receiver. To avoid this, a slight tilt of 5-10° of the front window is recommended so that any transmitter reflection is redirected away from the Rx aperture.

Check Mechanical separation / buffering between Tx and Rx

To additionally reduce internal reflections between the transmitter and receiver channels it is recommended to use a mechanical buffer between Tx and Rx. This buffer helps to block direct reflections from Tx to Rx that might otherwise create erroneous distance measurements.

6. Account for Atmospheric Conditions and Target Properties

Also consider atmospheric conditions and target properties, as they have a strong impact on the range performance. Fog, mist, dust, smoke, and salt water spray in maritime environments attenuate the 1550 nm laser beam and therefore reduce the effective range. Measuring towards the sun is likewise challenging, because the LRF may have difficulty distinguishing between direct sunlight and a true target reflection. Target size, shape, and reflectivity also influence performance: small targets offer a smaller area for beam reflection and therefore return less energy, also dark targets reflect less energy than bright targets; both conditions lead to reduced range performance. In addition, the object’s shape (flat, round, etc.) determines whether the reflection is scattered or focused, which further affects the amount of energy returned to the receiver.
It is worth carefully reading the LRF datasheets, where visibility, target size, and target reflectivity are usually specified in detail. To achieve similar performance to the datasheet values, it is necessary to reproduce similar environmental conditions and target characteristics in the tests.

Summary

Full range performance depends not only on the Ultisense LRF module itself, but also on several system level parameters that can be optimized during integration. Before integration, it is worth to systematically check alignment, software configuration, front window crosstalk, mechanical apertures, environmental conditions, and power supply quality to fully exploit the range performance of a LRF module.