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Drones are complex technologically advanced devices and even though they are relatively easy to control where virtually anyone can use one how they get to that point can be confusing and difficult to understand. With the continued advancements in the technology that is on drones it can be quite amazing what they are capable of.
One of these things that drones do amazingly well is hold steady at a certain height as well as tell you how high that they are. Knowing how high a drone is off the ground is vitally important since you are only supposed to fly them at a maximum height (400 feet in the USA). So, how do drones actually know how high they are?
Drones are able to determine their height based on GPS as well as a barometer and altimeter. These three things separately or combined will give you the altitude that you see on your drone’s readout.
The way each drone operates is slightly different and can vary from manufacturer to manufacturer so some drones might only use a barometer while others solely rely on the GPS. It is important to remember that even if the drone says that it is a certain distance above the ground it is your job to ensure that is correct as you will be the one that gets into trouble for flying your drone too high even if the readout shows one height and then rapidly changes to another because of the changing terrain below.
How do drones measure altitude?
Altitude and distance above the ground are two seperate things. According to the FAA you must keep your drone less than 400 feet above ground level but that doesn’t mean that is your altitude at the time of the flight.
Drones will measure the actual altitude using a barometer. This will allow them to determine the barometric altitude which is the height above sea level that the drone is flying at.
However, just because the altitude is a certain height that doesn’t mean that is how high your drone is actually at above the surface. In most every place in the USA your drone will be at a positive attitude before ever leaving the ground if you measure using a barometer. What that means is the altitude is not an accurate measurement of how high your drone actually is.
It is also important to know that just because a drone has a height of 400ft ATO (at take off) that also doesn’t mean that you aren’t violating the FAA’s rules. That is because if you take off from the top of the hill and then the height above take off is 400 feet but your drone is now above a valley you could actually be 500+ feet above the surface which is in violation of the FAA rules!
As a drone pilot it is up to you to ensure that you are following all of the rules that the FAA puts into place so knowing which numbers to look at is important.
Can you hear a drone at 400 feet?
There are no two ways about it, drones are noisy. This is true no matter if you are flying in the middle of the city or in the quiet countryside. Whether you can hear a drone or not depends a lot on whether you are actually in a quiet location or not.
How loud a drone is and whether you can hear it when it is at a height of 400 feet varies from drone to drone and from location to location. If you are already in the middle of a busy city you certainly could not hear it but if you are at a quiet place with a super loud drone then you would definitely be able to.
The smaller and more quiet the drone is the less likely you are to hear it at 400 feet. For example the DJI Phantom is much louder than the Mavic Pro is at all heights but it is especially noticeable at 400 feet. The smaller Mavic is virtually impossible to hear at 400 feet while the Phantom you can certainly hear.
No matter which drone you are using at 400 feet the sound will be virtually impossible to pick up if you are inside a city while flying over open fields will allow you to pick up the noise much easier.
If you are worried about your drone being too loud then you will want to opt for a smaller drone (such as the Mavic Air found here) but in general at 400 feet you really don’t have to worry about being “too
loud”.
How far away can you hear a drone?
As in the previous question the results will vary depending on your location and which drone you are using. The quieter the drone is that you are starting off with the quieter it will be when you are flying it further away.
Another variable with how far away the drone can be heard is how high you are off the ground. If you are 400 feet off the ground then you can be much closer in distance than if you are 5 feet off the ground.
For most drones if you are a few hundred feet in the air you will start to not be able to discern the drone sounds from the surrounding sounds when you are 500-700 feet away from it. This will vary based on the drone model and the ambient noise level as well.
If you were in a completely silent location with no road noise at all you might still be able to pick up the faint sounds of your drone even at 1,000ft+ away but that would be rare. Also how you are using your drone will affect its sound levels as well as a hovering drone will be much quieter than a drone that is moving around.
These are all super general answers since the answer really varies based on terrain, drone model, ambient noise, your hearing, etc. but the 500-700 feet at a drone height of 100-200 feet is a relatively close answer for most drones and most people.
Conclusion
How high a drone is flying as well as how loud they are when they are flying that high or far away can all be difficult things to accurately judge. When it comes to drone height it is always better to err on the side of caution.
If you take off from a valley and never go higher than 400 feet above your take off height then you will be sure that you never exceed the 400ft threshold that has been put in place by the FAA. However, if you go to the peak of the highest mountain all it would take was you flying a few hundred feet away and you could easily be well above the 400 feet limit.