Ultrasonic anemometry on Mars

Abstract

On Mars, we have yet to fully quantify and understand atmospheric turbulent transport (Banfield, JASA, 2016). The key required instrument is a wind sensor that can resolve horizontal and vertical winds, as well as the perturbations associated with turbulent eddies. On the surface, 10–20 Hz sampling and a sensitivity of 5 cm/s is required (McBean, 1972). Viking, Pathfinder, Curiosity, and Insight all used hot film or hot wire anemometers that can be confused by radiative heating and all have a response time of approximately 1 Hz. Sonic anemometry is an alternative high speed, high accuracy approach which uses differences in the acoustic phase delay to determine flow speed. Operation on Mars is challenging due to the low acoustic source strength and high attenuation in the thin (6–11 mbar) CO2 atmosphere, as well as large temperature variations (-100 °C to 20 °C). In this paper, we describe a three axis continuous wave piezoelectric anemometer with a high resolution and high precision analog phase detection circuit. Testing was in dry carbon dioxide between 2 and 20 mbar near 20 °C. At 6 mbar, we demonstrate resolution better than 10 cm/s, and accuracy of 3% at flow speeds up to 12 m/s. Low temperature testing is ongoing.