Flying over water, possible sensor error

[Shaw10]

While flying over a river at a height of 6m, the mini started to increase in height on it's own. I had to down stick to fight it. This resulted in the opposite and I had to up stick to keep it from losing height. It was never less than 5m above the water. Could the downward sensor be confused with the running water underneath?

 

[DanMan32]

Probably. Although the range finder (distance) is infrared so you'd think it would go through the water and read low.

 

[est73]

I’ve seen the same effect over a river but I figured it was caused by the haze coming off the water.

 

[DanMan32]

I’ve seen the same effect over a river but I figured it was caused by the haze coming off the water.

Very likely it was the haze/mist in your case.

 

[WithTheBirds]

You can take your pick of guesses here as to what ultimately confused the downward sensors. From the manual a transparent, reflective or moving surface below the mini is likely to result in unpredictable behaviour. There are several options with a river it would seem.

 

[Piranha]

We must ask DJI to give as an option to switch off downward sensors in fly app

 

[lilewis]

I can understand the haze issue, but how about just over water in general - on a non foggy morning/day.

If there's a problem with the sensors too close to the water, might there be a formula to determine what altitude over the water this should no longer be a problem? I assume 100 ft is probably ok but at what height does the risk end?

 

[FoxhallGH]

There are a lot of reports of Mavic's having problems with maintaining altitude when over water. Bottom line is that you don't trust it to keep altitude ... My Mavic Pro likes to drift down toward the water all the time and requires constant monitoring ... I believe that it gets worse the closer you get, due to the ripples blown on the surface by the down-thrust from the prop's.

 

[DJake_2000]

There are a lot of reports of Mavic's having problems with maintaining altitude when over water. Bottom line is that you don't trust it to keep altitude ... My Mavic Pro likes to drift down toward the water all the time and requires constant monitoring ... I believe that it gets worse the closer you get, due to the ripples blown on the surface by the down-thrust from the prop's.

Noticed similar altitude-shedding behaviour when cruising over a calm ocean a week ago. I was flying at around 3 - 5 meters over the surface and doing a banking turn, when the drone started descending quite rapidly. Bailed out with full throttle at 1,5 meters and had a similar issue later during the day, just yawing slowly higher up.

It was a bit alarming, but since there's even a mention in the manuals about possible issues with the sensors when flying over water, it's solely on me for not keeping an eye on the height. Most of the time the drone held altitude perfectly though.

 

[Louis08]

This has also been reported for the Tello, btw. And it is mentioned in the specs:

• Operating Environment: Non-reflective, discernable surfaces

might there be a formula to determine what altitude over the water this should no longer be a problem?

I'd look at the tech specs and say that anything above ~30ft should be safe (that's the range of the downward sensor)

More info on the topic is (surprise, surprise) in the user manual on page 16.....

 

[WithTheBirds]

This has also been reported for the Tello, btw. And it is mentioned in the specs:

• Operating Environment: Non-reflective, discernable surfaces

I'd look at the tech specs and say that anything above ~30ft should be safe (that's the range of the downward sensor)

More info on the topic is (surprise, surprise) in the user manual on page 16.....

Also of interest in the specs is that, for the downward sensors, diffuse reflectivity or +20% is specified. It is well known that water is a very good IR light absorber. We should expect the mini has no hope of measuring the distance to the bottom over a body of water and probably thinks it has over 30ft (or whatever the ranging distance is) of clear distance below it over water, even if it is much closer to the surface (absence of returned IR to perform a measurement). This might be the simple explanation why altitude might suddenly change flying over water, bottom sensor ranging is lost and the flight controller switched to the barometer derived value.

 

[sar104]

While flying over a river at a height of 6m, the mini started to increase in height on it's own. I had to down stick to fight it. This resulted in the opposite and I had to up stick to keep it from losing height. It was never less than 5m above the water. Could the downward sensor be confused with the running water underneath?

If you want to skip all the guesswork, the flight log would show exactly what the sensor was reading.

 

[lilewis]

This has also been reported for the Tello, btw. And it is mentioned in the specs:

• Operating Environment: Non-reflective, discernable surfaces

I'd look at the tech specs and say that anything above ~30ft should be safe (that's the range of the downward sensor)

More info on the topic is (surprise, surprise) in the user manual on page 16.....

Thank you!

 

[DanMan32]

I started thinking about this.
I've only xperienced VPS over land on my M2 to cause the AC to go up if it's too close to the ground as the ground rises. I've never seen it go down when the ground goes down. I've tested this over my driveway which slopes maybe 3 feet over 10ft if I recall correctly.

I'll have to compare this with the Mini.

 

[SpitFire]

Just confirming what every body has said about flying higher then 10 feet over water. If for some reason you have to fly that low over water, is good to be able to see the Mavic with your eyes. The Mavic can some times descend a bit when flying that low over water. Its tough to tell exactly how close the bird is to the water when watching the live view. Some have turned off the "Visual Navigation settings" in Advanced settings "Landing Protection" settings to prevent a forced landing from being initiated. I have flown over water all the time. Have been staying at least 30 feet above water surface and there is no need to do anything with the sensors.
Always need to keep your eye on the Bird, very important to have it in your line of sight.

 

[changkh]

Hi, I am new here and is interested to get a Mini too. This is one of the questions I have in mind.
If there is GPS signal, doesn't the Mini uses that to maintain altitude instead of the VPS?

 

[Louis08]

If there is GPS signal, doesn't the Mini uses that to maintain altitude instead of the VPS?

Wouldn't that question be worth a seperate thread? It has almost no connection to flying over water and might be of more general interest.....

I assume GPS doesn't overrule VPS - and I wouldn't be surprised if height over/under takeoff point wasn't measured barometrically anyway, at most assisted by VPS readings....

 

[DanMan32]

Actually it's a relevant question since altitude is at issue here.

A barometer is used for altitude along with VPS.