Mavic Minis find it very difficult to gauge height over water.

[John Gowland]

The downward sensors of all drones need some sort of pattern to judge how high they are. On surfaces with no pattern like water they find it very difficult. More sophisticated drones such as the later Phantoms or Mavics can cope with difficulty. The Mavic Mini finds it more difficult than most. Be very careful of flying your Mavic Mini over surfaces with little pattern such as water. Once in water, it is very rare for drones to fly again.

 

[RichR]

It does state in the manual not to fly low over reflective surfaces such as water in the manual. If you're above visual sensor range then it's not an issue.

 

[bagger07]

The downward sensors of all drones need some sort of pattern to judge how high they are. On surfaces with no pattern like water they find it very difficult. More sophisticated drones such as the later Phantoms or Mavics can cope with difficulty. The Mavic Mini finds it more difficult than most. Be very careful of flying your Mavic Mini over surfaces with little pattern such as water. Once in water, it is very rare for drones to fly again.

take a look at my post

MM take a swim

this is my first drone only 2 weeks old and a few flight. yesterday in the backyard i practice my skill and pass over my inground pool maybe 2 feet over .i don,t know what happen but the only thing i remember is the word LANDING.and yes the MM sink in 4 feet for about 2 minutes i run...

mavicpilots.com

 

[EyesWideShut]

It does state in the manual not to fly low over reflective surfaces such as water in the manual. If you're above visual sensor range then it's not an issue.

A few questions:
I can see that reflective surfaces like water/snow at low levels might confuse the downward camera sensor but what actual happens? Does it go into a landing mode?
It appears in the reports I've read that the control sticks have no affect. Can't the landing be aborted and control be regained or is it happening too close to the surface for the pilot to have a chance to react?

 

[John Gowland]

As I indicated the more sophisticated drones do a far better job. I have hovered at around 7 inches with a Mavic 2 zoom and it is solid. The sensors are good enough to detect the tiniest of movements on water. You simply can't put top grade sensors in a tiny low-cost drone like the MM. I have had a Phantom 3 go down from around 3 feet. But this has never happened with a M2 or a Phantom 4 Pro v2. Even this dunking is pretty unusual, I have flown the MM quite close to the water but would never try it even a foot or 2 feet from the water, you can see it is not coping very well. Why it the MM dropped from this height, I don’t know, you would have to collate all the data and look at some hardware activity to be sure. This is not to say you should not fly over water, just that you should know what your bird is capable of. This MM a few days before flew out to an island over a kilometre with no issues, but it flew at about 6 feet high at its lowest.
If you are going to fly with any risk at all, have good insurance, including “DJI care”. For what it is, I think the MM an awesome drone, it really is amazing tech, given its size and cost.
This looks about 15 inches?

But this Mavic 2 Zoom never moved more than an inch, and for much longer than this short video.

 

[Sallee]

well.. MM and other much,but really much more expensive drones should NOT compare!
Its just the way it is, and solution is that if u want to hover above CALM water dont go below 5 meters, as i see it, below 5m sensors are beging to take over positioning from GPS.. the more u go down the more prox sensor taking over from gps.. thats how i understend how MM works, somebody correct me if i misinterpret manual
EDIT: also, i think problem here is when its hovering above water, if u are flying it should NOT be problem even if u are below 1m, but if u stop then there is a fair chance that MM can execute landing procedure

 

[scro]

There are 2 downward facing sensors on the MM and they can be confused in 2 different ways:

• Optical flow sensor - this is for horizontal positioning and works in a similar way to an optical mouse. It's a camera that detects panning movement. If there is no texture or detail for it to detect then it gets confused. Also if that texture is moving then it can confuse it (eg ripples moving on water, lots of leaves blowing across the ground, grass waving in the wind). I've tried holding a cushion under the MM when indoors and then had it "follow" the cushion around the room without touching the sticks. This has a reliable range of 10m, and can work up to 30m. I have a Tello that relies on VPS only for position hold and it can fly reliably up to 30m high above the terrain underneath it. The MM has one sensor whereas larger Mavics have 2. This gives a stereoscopic view, and hence can provide a 3D view of the terrain underneath the drone. This is why they are more reliable when in close proximity to water.
• IR proximity sensor. This gives a value for distance to ground by sending out an IR beam and measuring what is reflected back to the drone. Water can alternate between appearing transparent and fully reflective for the IR beam and this confuses the distance it measures - ie it sometimes sees down into the water and thinks it's further from the surface than it is, and sometimes it gets a strong reflection that makes it think it's closer than it actually is. It may be that the optical flow camera also detects the IR beam and can estimate height from the size of the IR spot. (Edit: that wouldn't work as the size of spot the camera sees would stay constant regardless of distance? )

 

[John Gowland]

This is DJI's take on flying over water.

"The prospect of flying over water can be a scary one for most drone pilots. Water environments are often filled with potential hazards such as boats, waves, high winds, and even birds. Although DJI does not encourage flying over water, professional aerial photographers and videographers will sometimes have to do precisely that. Therefore, this article offers constructive advice on what you can do before and during your over-water flight to ensure safety."
How to Fly Safely Over Water - DJI Guides

I fly over water 2 or 3 times a week, it's fun and generally safe. With some drones I fly very close to water, Mavic Air (1), Mavic Pro (1 and 2) Phantom 4 Pro (2.0)

and

With the 4 Phantoms and the Mavics (not mini) you can safely get pretty close to water with extra vigilance.

Like anything you need to practice a lot to get to know your and the drone’s capability.
This dunking was the only dunking I have had apart from a P4P V2.0 when it was hit by an unexpected high wave. In both cases DJI care replaced them without charge.
I suspect this MM dunking was very unusual even for a MM.
But the lesson is to be extra careful with a MM over water or other reflective volatile surface. A more important lesson is to have good insurance. Both DJI Care and your own personal insurance as a backup. I have never been out of pocket, so to speak. When we use the word safe it is only in reference to the drone. Never take any risk around people or property.