The “Flight of the Bumblebee” by Hough Transform of Doppler Radar Images

In this paper, we monitor the potential pollination productivity of a commercial bumblebee colony by counting daily bumblebee flights. A unique and orderly, rather than chaotic, flight pattern of bumblebees in front of a commercial colony was observed with a low-power, 24 GHz Doppler radar. The Doppler return from a departing bumblebee appears as an approximately straight line in a Doppler-Time-Image (DTI), corresponding to a constant acceleration. The line becomes a point when transformed into Hough space. A parametric description of that point allowed us to identify and count departing bumblebees while rejecting arriving bumblebees and other environmental effects. The technique was validated by simulation and daily counts of foraging bumblebees in the summers of 2021 and 2024. When leaving the colony, we discovered that foraging bumblebees accelerate at an unexpectedly high and constant rate of 9.8 m/sec², This acceleration appeared to be independent of temperature or time of day.