SF 11 Laser altimeter, an useful tool for agriculture purpose

Last year I was searching how to fly at safe low altitude to take the higher resolution photos that possible, to identify weeds and insects in crops and trying to know if a laser altimeter can do the task, first I bought a Lidar lite but looks unstable over rought terrain perhaps bad installed or configured and no more support to ask, but, in the way, Laserdeveloper offer me to test the SF11 and send me one, I was little nervous because I'm not have much electronic knowledge, I couldn't make Lidar work yet, and SF11 looks more professional with PC connection and configuration capable, but results an RTF tool, very easy to install, Pixhawk configuration I use as instructions said, I use serial connection  http://ardupilot.org/copter/docs/common-lightware-sf10-lidar.html?h... and SF11 configuration I don't change nothing but have many things for different tasks, standard ones looks nice for me.

It have an intuitive software to test with the pc too, you plug to USB with provided cable, open the program and look readings, I them took a ruler and measured the SF11 with the floor and looks near perfect :O ; many rainy days them (I'm in winter :( ) I did a first little fly with strong wind, the wind hit the copter but altitude didn't change, a better day I can fly more to test and take this video flying over a rought terrain; I'm going to test over different crops with different stages, and different slopes to see what happend. 

Thank's to Laser developer to give me the opportunity to test this great altimeter :D

Now I test the SF11 over dry corn and, as Laserdeveloper explain here: http://diydrones.com/group/agricultural-uavs/forum/topics/testing-s... the laser reads the floor instead dry plants so, no issues when little spaces between plants appears, wind isn't a complication too.

3 Nov: Now time to fly wheat, searching for insects and diseases, windy, as always, is present
https://www.youtube.com/watch?v=M2o7SXrW6KU
It's curious to compare sonar altimeter with Baro

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MR60
Comment by Hugues on July 16, 2016 at 2:32pm

Nice application. I assume you did not use auto mode as I understood lidar is not yet used in auto mode in current release?

Comment by Cala on July 16, 2016 at 4:49pm

Thank's Hugues, Auto works in 3.4 beta release I understand https://www.youtube.com/watch?v=MNibVWClmmE

but it's a bug to solve in auto mode  https://github.com/ArduPilot/ardupilot/pull/4455

so I'm waiting a new release to move this copter; in the way, I test with Pos hold to learn the limits of laser altimeter with less risk.

It's impressive how the pilot compensate the Laser readings when change the angle :O ,I remember your alliens driving the copter and laught alone :D . I read some people uses a servo to compensate angle, it's actually not necessary with this altimeter or newer releases.

Comment by Cala on July 16, 2016 at 5:00pm

Sorry, I confuse, this is the video with laser altimeter  https://www.youtube.com/watch?v=_ir6KK48oEA

Comment by Robert Hoermann on July 17, 2016 at 6:44am

Cool, we will soon follow up with the same Lidar as an sweeping forward looking distance control unit.

Comment by Cala on July 17, 2016 at 6:52am

Nice, please share your experiences to see how it's work.

Comment by Laser Developer on July 17, 2016 at 11:44pm

Wow! Very nice tests Cala, thank you. Seeing how the SF11 performs in real-world conditions is the best way for us to make improvements and advance the science of laser altimetry.

For those people unfamiliar with lasers altimeters, you may be surprised to see how well the SF11 works over uneven surfaces and moving grass. This is a consequence of the physics that permits scattered reflections from steeply angled surfaces which is why our eyes are able to see these surfaces using scattered sunlight.

The short wavelength of light ensures that most natural surfaces scatter light in all directions providing a very consistent signal back to the optical detector of the SF11. The rule of physics that is at work here is that any surface that has microscopic features that are larger than the wavelength being used will produce scattering. Since light has a very short wavelength, most surface meet this criteria, especially those of plants and soil.

Another advantage of using laser light in agricultural applications is that the strength of the return signal is surprisingly high. This is because of the infra-red properties of chlorophyl that make plant matter reflective at the specific wavelength that the SF11 uses.

For other non-contact technologies, the laws of physics make it very hard for them to work under these same conditions. For example, ultrasonic devices operate at a much longer wavelength (using sound) and the energy of their beam is easily deflected away by the flat surfaces of the leaves or simply absorbed by the sound dampening structure of the plant as a whole.

Comment by Nadia Nilsen on July 18, 2016 at 1:28am

Thank you Cala. Impressive low flight.

@Robert, let us know if you need any assistance.

Comment by Cala on July 18, 2016 at 2:10pm

Thank's Laser, to better explain how this tool works, at the begining I couldn't understand how can perform so well,  I expected that was going to jump up and down with every little leaf :O , as I have new videos I share here :D

Nadia is who give me great support about the SF11, thank's Nadia.

Comment by saTxRxasis on August 25, 2016 at 7:10pm

Your quad really stay at low altitude, what a great success! I really adored with your work.

So I assumed you use Pixhawk and I have silly question. Can I do the same with APM 2.6 on f/w 3.2.1? I know that this fc is obsolote but if it can't, what feature that naught in f/w 3.2.1 which can drive SF11?

Comment by Laser Developer on August 25, 2016 at 10:33pm

@Cala - More "real world" performance testing of the SF11/C showing some very important results. My favorite part is the high altitude test near the end ;).

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