The SF10 family of laser altimeters was designed by people on this forum. Requests for new features and numerous emails about performance and applications has lead to the development of a compact, light weight, rugged design that can be used in many UAV applications.
We've produce three different versions, each with the same features but having different measuring ranges and representing three broad categories of application - close to the ground, intermediate flight operations and maximum legal altitude. The picture below gives an idea of where we see the different products being used:
We've matched the cost of available technology to the different operating requirements of small and medium scale UAVs, and the table below shows how we've managed the trade-off between price and performance:
Model Laser Detector Maximum range Price
SF10/C High power High performance APD >120m High
SF10/B High power Standard APD >55m Medium
SF10/A Low power Standard APD >25m Low
In all models of the SF10 we've kept the energy of the laser pulses very low, making them Class1M - safe for human eyes, and because we believe in high reliability, all models have narrow band optical filters to cut out background sunlight.
Other standard features on all models include:
- USB port for entering configuration settings
- I2C bus with configurable address
- Serial port with configurable baud rate
- Analog output with configurable ranges
- Offset trim to match airframe
The team at LightWare would like to thank the hundreds of customers who have contributed to our ongoing effort to improve laser technology for UAS applications. We're having fun, I hope you are too!
L.D.
Comments
Tridge has flown the SF02's (also made by lightware) on his airplane and he also used it during his OBC win last week. He says good things about these sensors.
That's a cool question. The accuracy can only be verified against targets that have a known distance. Additionally, accuracy can also be checked against targets having known reflective properties. The combination of range and reflectivity create a distinct "signature" for every type of target, natural or human made.
It's possible to measure real world targets and compare their signature with those of calibration targets. If there is a close match between the two, then you can be certain that the distance measurement is also closely matched.
I grabbed the picture below from the production file of an SF10/A that's just been tested. The scale along the x-axis is a measure of the reflectivity of a bunch of different targets [arbitrary units, non-linear scale] and the y-axis is the error [cm] in the measurement associated with each particular type of target.
When a real-world target is measured, the 32-bit ARM processor in the SF10/A examines both the range and signal strength to make sure that the readings are within its calibration limits. If the target is outside these limits, then the reading is rejected and shows up as a lost signal. Otherwise its range can be determined to within the errors shown in the graph.
How was accuracy and range determined for real world applications as discussed above? How do you know the height of the aircraft when ideally the laser should be more precise and accurate than barometer or GPS (even RTK GPS)?
Alexey - We hope to have snow tests confirmed soon and we will do water tests when we're next testing one of our full scale aircraft units from a helicopter - don't have a fixed date yet.
Andreas - We labelled them in the order they were first sold even though the "B" was actually the first one we developed! Someone from marketing will come and change the names no doubt ;)
Out of curiosity, going from low to high price & range, why are they labelled C, A, B as opposed to, say, C, B, A or something more sequential?
We have same experience with Hokuyo lidars. With maximum range about 30 meters in case of wet surfaces real range is reduced to 10-15 meters.
Do you plan to test range of your altimeters over water or snow?
Hey Alex, we've tested other products with similar optics over snow and ice successfully but the signal strength is reduced over water, so we recommend using the longer range, more powerful lasers if reliable reading is critical over water.
Brilliant work, the size and cost of laser altimiters has come down significantly in the last few years thanks to companies like yours. Otherwise we'd still be paying $10k for a 1kg laser altimiter from Riegl.
lightware.co.za
Where to buy? :)
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