After our success with the Peersonic detector working in-flight (see our blog post here) we decided to push on and get some actual field testing done! This will be the first time we've attempted to use the UAV to record actual BATS!
The first thing to do was identify an area in which is likely to have some bats flying around and that we can fly the UAV at. Fortunately, our flying site in Oxfordshire has a lovely line of trees with woods and hedges at both ends which look quite promising.
During the day we set up a flight path which took us down the tree line, over a hedge at the end, looped round the wood then cut in towards the tree line again heading back towards us and past the wood at the end with a final turn taking us over a hedge and back to the starting point. The whole route took about 6 minutes 30 seconds to fly.
Although the description is all very well and good a picture of the route might be more useful:
We flew this a number of times to ensure we weren't too close to the trees or in danger at any point. To do this we used a FPV (first person view) set up on the plane in order to assist in distance perception to trees. It turned out that this was fairly crucial as during the first run we were a little close to the trees. After some minor changes to the flight path we repeated the route and were happy with it. We decided on an altitude of 15 m to make sure we'd have more than enough clearance for any objects. Here's the plane's view of the flight path:
On to the night flying!
With the route set, we were ready for the night flying with the detector. A bit of fiddling later and we'd set off on our first pass of the route. It's a strange feeling watching the lights of the plane sail off into the distance. It's great to see how stable the plane flies at night as well when the wind was a little lower.
After two passes we decided to take a walk up to the woods at the start of the tree line to see if we could find any bats using our other detector. Happily we noticed one or two commuting down a hedge line that connected to the woods.
A short re-route of the flight plan later and we had a flight running down the hedge line at an altitude of 8 m and 15 m horizontally from the hedge.
Have we recorded a bat?!
When looking through the sonogram, we noticed this:
Between 204300 and 204400 ms there's what looks like a 45 kHz bat call. The sound lasts for a duration of approx 7 ms and has a classic hockey stick appearance. It's also at bang on 45 kHz which ties in with a 45 pip.
There is however, a lot of ultrasonic interference from the motor/propeller and we want to be sure that this is a bat.
HERE'S THE LINK TO THE RECORDING:
If you have any experience we'd really appreciate your thoughts. The full .wav file is accessible via this link (right click - save as). Please feel free to download let us know what you think.
As always, we'd like to acknowledge Peter at Peersonic.co.uk for his constant support and providing the recording equipment that has been so useful in progressing this project.
Thanks, Tom & Tom