Let’s take a closer look at the components of the Aeroscope.
Directly below Mothra, at the 25 meter line mark, goes the Tethersonde. This instrument includes an anemometer, or wind meter. It transmits data in real time to a receiver attached to a computer at ground level. This allows us to see how high the aerostat is flying, and monitor conditions aloft like wind speed and direction. It also records temperature, relative humidity, and pressure every two seconds.
The main component of the Aeroscope is the array. We attach it far enough below Mothra to avoid noise from her kite wings. The array is made of rigid carbon-fiber arms attached to a custom fabricated hub. A tiny ultrasonic recording device called a Vesper sits at the end of each arm, and one at the hub. When a bat flies by the array, the Vespers record its echolocation calls. By carefully measuring the distance between the Vespers, we can estimate the amount of time needed for sound to travel to each one. Then we use that to triangulate the position of the bat in three-dimensional space at each echolocation call. Also mounted on the hub of the array are a night-vision camera, an environmental sensor, and an electronic metronome. We use the metronome to align the Vesper audio recordings precisely in order to determine the bat’s position.
Another important component is the insect net. I made this net myself based on specifications of nets used in many insect migration studies. Who knew that a sewing machine can be a critical scientific research tool! It’s big, because insects are widely dispersed at high altitudes, measuring a meter wide at the opening. We plan to use a remote control device to keep the net closed except when it is at the planned deployment altitude, but we’re still working on that part. I’ll share more about that adventure in a future post, but you can see a successful remote opening at the end of our video.
Finally, we attach additional environmental sensors, or Thermochrons, at different points along the tether line. That lets us detect changes in temperature or humidity at different altitudes. You might be surprised to hear that at night, it’s often warmer aloft than it is at ground level! For safety, we attach flashing lights at regular intervals along the line to make the Aeroscope visible to pilots flying in the area at night. This probably contributes to reports of UFOs in the area! We have special permission from the FAA to fly Mothra at our field site, and we file alerts to pilots (NOTAMs) every day we fly.