I'm calling bs on this one.
It has a barometer to sense altitude.
This is 100% not BS - I concur with the other Posters mentioning the IR sensors.
I have just returned from a session where I wanted to get some shots of the Sunrise, which I realised over the whole valley would look spectacular. Everything seemed fine in the first few moments - it had 10 sats at launch, so GPS/Home point launch was possible. And where I was I was confident I could see light blue sky above me.
I ascended to around...Ummm well actually I don't even know how many metres up, because I was watching the Spark itself (keeping line of site.) - Then I heard the beeping and the voice saying "Landing"...WTF??!
Next thing I look down and on the screen I see the X to cancel the landing, and looking at the Height reference it said 0.5m - but also with No vision in the background - just grey - I looked back up, and the Drone was gone...But I could still hear it...and it didn't seem to be getting closer. The Fog had closed in around it (as some mentioned the Fog of course, does play havoc with audio as well...so the pitch and volume was changing...I was a bit worried it was still gaining altitude or drifting...) - something I noticed even before I looked at the phone screen was that it appear to be Yawing without my control...It was time to take immediate action.
So I cancelled the Landing process - still it showed 0.5m of the ground...I was pulling back on the Throttle, and thought I could hear it coming down - but I couldn't see it, and the alarm kicked in again and she said she was landing...But no drone...
This process I continued a few times, flicking back and forth from Sports mode and pulling back on the throttle. Then I could see it, it hadn't changed location which was good - just guessing a thicker bank of fog had rolled past. But still not descending...So kept pulling back and resetting the auto-land...I had to do this about 8-9 times, each time it came down a little further.
What I realise later on was how lucky the sensors did not get completely wet to the point where they considered ground level reached and switched off the engines. But contrary to the "BS" notion - I have strong faith in the evidence that as soon as I had reached a certain Saturation layer the onboard CPU ignores Barometer (which in cold and fog is likely a bit messed up anyway.) - and also any height it gets from GPS (not sure if these units rely on GPS height.) - subsequently the CPU says - I am 0.5m from the ground - which automatically puts it in Landing mode, I've seen this in normal flying conditions, just cruising around, go too low and it will perform a Landing cycle!
It has made me curious (but not enough to test potentially losing a drone or breaking laws.) - to see if I had have 1. kept ascending would it punch through and discover it's real height (but then how would I get it down?!?!) ...2. Would it have eventually landed as a part of a Constant "landing cycle" where it's 0.5m does not get achieved, but it descends very slowly from 20m - I fear in that time period the unit would likely get soaked from such a long period in the precipitate. Attached is an image of the drone from no more than 2-3 minutes in the Pea-soup.
