A Martian sonic anemometer

We are developing an acoustic anemometer for use in the low pressure atmosphere of Mars. Acoustic anemometers have high sensitivity, high temporal resolution, and high accuracy, are insensitive to radiative heating and demand little power. In these ways they are superior to the anemometers previously flown to Mars. Accurate, well-calibrated anemometers are crucial for understanding the near-surface atmospheric environment (e.g., slope winds, convective cells, dust devils, and aeolian processes in general). Furthermore, the high time-resolution, high sensitivity, 3D wind resolving capability and well-defined, open sampling volume available from an acoustic anemometer allow it to resolve individual turbulent eddies, a first for Mars. This feature allows it to directly measure eddy fluxes, for example water vapor vertical fluxes between the surface and atmosphere when coupled with a fast hygrometer (e.g. a tunable diode laser, TDL). This ability to measure water vapor fluxes is viewed as a high priority science goal of Mars landers. We expect that the instrument designed in this program is a prime candidate to fly on any of the future planned Mars Scout landers or Mars Surveyor Landers. We have identified the difficulties in adapting earth acoustic anemometers for use on Mars, namely the acoustic attenuation of ultrasound in Mars' atmosphere, and acoustic impedance mismatch between typical acoustic transducers and the Martian atmosphere. We are in the process of testing 3 styles of cutting-edge capacitive transducers, with favorable acoustic impedance characteristics, in a simulated Martian atmosphere anechoic chamber. Initial testing shows that our instrument concept is feasible for use on Mars, and accuracies of better than 3-5cm/s and 0.1K are attainable.