Safe distance above water

[Delenot]

I have heard of, and recently experienced, water surfaces adversely effecting the downward facing sensors on the mini. What is the minimum safe distance to be above water so that these sensors are not getting confused? Another way to ask this i guess is, what is the maximum range of the bottom sensors?

 

[jigsaw]

Very good question. I would also like to know. I was flying over a lake this past Friday and I stayed at least 10 feet above the water.

 

[CarstenB]

I have heard of, and recently experienced, water surfaces adversely effecting the downward facing sensors on the mini. What is the minimum safe distance to be above water so that these sensors are not getting confused? Another way to ask this i guess is, what is the maximum range of the bottom sensors?

according to the manual, the VPS operating range is 0.5-30m above ground. DJI recommends to fly at least 2m above water.

How to Fly Safely Over Water - DJI Guides

Check out these essential tips for keeping your drone safe while flying over water.

store.dji.com

 

[C.W.]

A lot of people that fly over water will cover the sensors with opaque tape like electrical tape so the sensors won’t try and land on water

 

[BokiFly]

I am also interested in this.

So problem with flight low over water is that Mini could determine that we want to land, so it can initiate landing?
Like in this interested topic from yesterday?

While we are on this, what Mini uses to maintain height? What sensors? Does he uses GPS to determine altitude?

 

[scro]

While we are on this, what Mini uses to maintain height? What sensors? Does he uses GPS to determine altitude?

The mini has a pressure sensor (barometer) built in, and uses this as its primary means to determine its height, with air pressure dropping nearly linearly with height for typical drone flying altitudes. The app gives height relative to takeoff point. this way it gives an accurate number without needing to know the current atmospheric pressure. In the EXIF data for photos there's an absolute height recorded too. This is approximately height above sea level, but without any correction due to atmospheric pressure. It can be 100s of meters off true height above sea level.

When in close proximity (approx <10m? - open to correction on this!) to the ground it also uses an IR proximity detector. This is one of the 2 sensors that can get confused by water as the water is partly transparent and partly reflective to the IR beam emitted from the drone. Since it doesn't get a reliable reflection it can allow the drone to get much closer to the water than 0.5m without it realising, or fool the drone into thinking it's much closer than what it is, and potentially initiate a landing. Taping over the sensor stops all signals from the IR sensor including these erroneous ones.

 

[BokiFly]

It's more clear now. Thank you.

I thought that if a drone is on certain height over water and I don't touch left stick up or down (but only forward and left-right) that it will maintain height, as it is very precise with that in normal flight. I was hoping that it will work that way over water too, but it seems that it is not the case from the reasons that you described (there is a warning about that in manual also).

I suppose that there is no precise info about minimal recommended height over water (with or without taping over the bottom sensors). But I see that @CarstenB wrote "DJI recommends to fly at least 2m above water". Is that from the manual? If it is then I miss that information.

Here is some video with Mini in FPV mode over water.

 

[Simone L]

A lot of people that fly over water will cover the sensors with opaque tape like electrical tape so the sensors won’t try and land on water

Could you just turn off sensors when flying over water?

 

[scro]

Could you just turn off sensors when flying over water?

There's no official option to switch them off on the Mini, hence the tape

 

[Fun Flyer]

Could you just turn off sensors when flying over water?

Hi Simone L. There is no way to turn off the sensors on the MM. That is why some people cover the sensors with tape.

Edit: scro beat me to it with an answer.?

 

[Simone L]

There's no official option to switch them off on the Mini, hence the tape

Doh. I fly a mavic 2 pro and I think there is a mode where the sensors can be switched off...Sport?? New to flying so still lots to learn.;-)

 

[scro]

I have never used an MP2, but from others' comments I understand that it has that as an option (without needing tape).

 

[SpitFire]

I fly over water all the time, find that keeping at least 30 feet high above the surface of the water. Find that no need to do anything different, no need to turn off sensors. Flying over water, important to keep your eye on altitude, VLOS very important if flying lower then 30 feet.

 

[Dronernator]

I have heard of, and recently experienced, water surfaces adversely effecting the downward facing sensors on the mini. What is the minimum safe distance to be above water so that these sensors are not getting confused? Another way to ask this i guess is, what is the maximum range of the bottom sensors?

I try not to go any lower than 2 metres but usually much higher. I was out at weekend hovering over a river, about 2mtr above, and the mini was slowly dropping & rising. It was a slow moving river so no waves, etc that would make the sensors think it was over a moving surface. I took it up a bit higher and it stayed perfectly still.

 

[Deleted member 103366]

Not that it answers "how low above water is safe" but would not one way of testing the range of the sensors etc. be to take off on a significant slope and go high, well over the 30m. Then, staying well above 30m AGL, fly either up slope or down slope until lthe ground directly beneath the drone is either significantly higher or significantly lower than the home point. Then descend vertically at maximum speed and see where, AG, the drone starts to automatically slow its descent. I presume the drone does not know the height of the ground relative to the take off point so it must be measuring or be attempting to measure it's height AGL during the descent if not the entire flight .
I can't test this myself here, sorry.

 

[scro]

The ground proximity sensor will start sensing the ground approaching some time before it starts to slow the descent, so it wouldn't categorically prove where the sensor starts providing a valid reading to the control firmware. From my experience it is around 1m or less from the ground that it really slows down, although I am probably not giving it anywhere near full stick.

Any volunteers to try flying their drone into the ground??

 

[CarstenB]

I suppose that there is no precise info about minimal recommended height over water (with or without taping over the bottom sensors). But I see that @CarstenB wrote "DJI recommends to fly at least 2m above water". Is that from the manual? If it is then I miss that information.

it's not mentioned in the manual but in the "How to fly safely over water" DJI guide which i have linked in my post. The manual is quite valuable but the DJI website also has answers to many questions posted here.

 

[djharrisx]

Any volunteers to try flying their drone into the ground??

Quite unintentionally I managed to put PhiliusFoggg's plan into practice (sort of!) yesterday. After my unfortunate experience referred to by BokiFly at #5, thankfully I was able to react straight away to the "Landing" warning, so no ill-effects.

Still, worth being aware of, so I've knocked the relevant footage together.

Also, given how this topic began, there's some low flying over the River Trent at the end. Personally, I think the golden rule is to descend very gently over water and be ready to push the left stick forward in the blink of an eye.

AirdataUAV log here

 

[BokiFly]

That was really low over water, cool

 

[Deleted member 113929]

according to the manual, the VPS operating range is 0.5-30m above ground. DJI recommends to fly at least 2m above water.

How to Fly Safely Over Water - DJI Guides

Check out these essential tips for keeping your drone safe while flying over water.

store.dji.com

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