The German Tank Problem & Navigating by Scent

Overview & Synopsis

A robot searching for the source of an odor must eventually answer a deceptively hard question: have I arrived? Near the source, concentration gradients flatten, turbulence makes the signal intermittent, and a small robot often lacks the positional accuracy to map the plume. Here, we describe a lightweight remedy inspired by a World War II statistics conundrum: the German tank problem. To approximate enemy armament production, Allied analysts developed an estimator based on serial numbers from captured tanks. Analogously, we use the same procedure over sampled chemical sensor readings from a robot to create estimates for the peak concentration of an odor plume, and therefore the odor's source. Treating each sensor reading as an observation, our unbiased estimator needs only a running maximum and a sample counter. An exact confidence bound turns both numbers into a principled rule that the robot or UAV can use to determine whether to keep searching for the plume source or land. We derive the estimator and its bound, demonstrate its sample efficiency, and examine its robustness even when its assumptions fail. Finally, we summarize the estimator's role as the termination criterion for olfactory navigation.