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Radar (or laser) altimeter for DJI drones

Alexey Dobrovolskiy

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Joined
Dec 1, 2018
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Many sensors, especially geophysical, like georadars, magnetometers, metal detectors, echo sounders - require flights with constant distance over ground - sometimes at very low altitude.

That can be useful even for cameras if you need to get images with more or less the same GSD - or don't have precise DEM for the flight over rough terrain. Or you use simple software without the possibility to import DEM data :).

We at SPH Engineering (UgCS) started working with geophysical sensors approx 3 years ago and very quickly stuck with the inability of DJI drones to use an external altimeter to measure the distance to the surface and keep constant AGL. Tricky question why they did that only for Agras series of drones, but this useful feature is not available on m600/m600 pro - the workhorse of the industry to carry heavy sensors - on newer drones too.

So we were had to implement our own terrain-following system for DJI drones. It works with any drone with DJI onboard SDK support (M600/M600Pro, M210/M210V2, any drones with A3 - and will be available for M300 soon).

A couple of samples how it works in real life -

Alexey Dobrovolskiy on LinkedIn: #drones #dronetechnology #gpr | 25 comments

or


How it works.

Internally it is quite complex - radar altimeter, onboard computer, and a lot of software. Imagine how many drones crashes we had while debugging and tuning all that stuff :).

Radar altimeter connected to our onboard computer (called SkyHub). SkyHub connected to the DJI autopilot or drone using API port. When operator on the ground activates terrain following mode, SkyHub takes control over the drone, and uses waypoint coordinates from mission loaded to autopilot, and data from the radar altimeter to drive the drone along the planned route with specified altitude.

Below is a photo of a typical set of equipment before shipment to the customer (it is set with echosounder marked by 1). 2 - set of cables, 3 - SkyHub, and 4 - altimeter, all with mountings for m600 pro.

ECT400 set - with marks.jpg


Standard question - why we use radar altimeters instead of the popular and not very expensive (and very precise) laser range finders. Initially, we used laser devices, but very soon we (and unfortunately our customers around the world) found that laser altimeters have many environmental restrictions. Our customers in Peru and Papua New Guinea were able to work only in the morning or evening - small laser devices are not powerful enough to work under the very bright sun. They not work well over water and fresh ice. They are absolutely useless in fog and under rain/snow. So finally we switched to radar altimeters.

The only drawback of radar altimeters that we use - limited range comparing with laser range finders. Our radar altimeter has a maximum distance up to 50m, popular small laser devices have distance up to a couple of hundreds of meters. So our system still supports laser altimeters for the customers who need terrain-following but on higher altitudes.

At the end one more video of flight with radar altimeter over water -

Good luck, fly low :), and stay safe!
 

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