Martian Sonic Anemometer Overview

1. Capabilities: • 3-D winds • Fast response (10-100 Hz) • High sensitivity, precision and accuracy (~5cm/s) • Robust against measurement contamination • Accurate Temperature sensor as well (~0.3K) • Current Maturity: • TRL 5 (Transducers 6) • Funding History: • PIDDP (2002-2005) • PIDDP (2008-present) • Participants: • Cornell (Banfield), Ball (Dissly), Microacoustic Instruments, Boulder Systems Design Martian Sonic Anemometer Overview Mars Wind Tunnel Denmark, June 2012

2. Robust Wind & Air Temperature Measurements • Aeolian Processes • Boundary Layer Meteorology • Validation for Mars mesoscale models • EDL Safety, Robotic & Human Surface Operational Safety • 3-D, Fast-Response Measurements • Directly measure eddies and eddy perturbations • This yields surface-atmosphere fluxes • Momentum • Heat • Water vapor (if coupled with TLS hygrometer) • Sonic Anemometer was proposed for MSL as part of the meteorology/surface-atmosphere exchange investigation MWX. Rated Cat 1. Sonic Anemometer Science Motivation

3. Fast Response Wind Measurements more fully match seismometer bandwidth Robust wind measurement to assess possibility of wind contamination of seismometry VBB measures up to 10Hz, SP to 100 Hz. Sonic measures at >10Hz (to ~100Hz). Use wind spectrum to verify siesmometry spectrum isn’t contaminated. Sonic Anemometer Benefits to InSight

4. Based on Gold-Standard Terrestrial Scientific Anemometers Sonic time-of-flight in opposite directions 3-D Winds from 3 orthogonal axes Temperature from speed of sound Sonic Anemometer Principle of Operation Terrestrial 3-D sonic anemometer on which our instrument is based

5. Difficult to make sound on Mars • Air density ~1%. Acoustic impedance mismatch • Use very special transducers (broadband & low acoustic impedance) • Much lower signal strengths • Use Radar technique: Pulse Compression Challenges at Mars

6. Transducers have evolved to much smaller packages, lower voltage, higher performance. Thermal tolerance tested well. 90 sol test from -60C to 0C. Flawless performance. 2 excursions to -135C (CO2 frost point) Flawless performance. Development History • Testing/Calibration in Danish Martian Wind Tunnel. • Excellent performance at 10 mbar. • Error bars ~ 5cm/s • Wind-shadowing effect evident (calibrate-able) • Identified 8° cross-flow in wind tunnel

7. JPL ASTRA PHAETON Project (Stratospheric Balloon Mars Simulator) Flew both sonic anemometer (1-D) and Hot Wire Anemometer • Very turbulent except @ float • Good results for both wind and temperature to ~100k’ • Cross-talk above 100k’ contaminated results. • Easy fix available. Development History

8. This sequence for each direction on each axis • 6mS repeat cycle • Pulse Compression is a time-domain convolution, but is done in frequency domain as a multiplication • Yields accurate travel time for each axis, each direction. These yield 3-D wind and temperature Operations Concept • Data Volume: 3-D winds & Temperature (four 2-byte values) @ ~20Hz = 160 Byte/s • InSightSeis: PTW data budget already allows for ~20% duty cycle for this in high rate winds alone (3.2Mbits/Sol)

9. Martian Sonic Anemometer: Signal Timing 0 1 2 3 4 5 6 Time (mS) Noisy X-axis #1 Noisy Send Receive Noisy Noisy X-axis #2 Receive Send Noisy Noisy Noisy Noisy Y-axis #1 Noisy Noisy Noisy Receive Noisy Send Receive Noisy Noisy Noisy Y-axis #2 Noisy Send Z-axis #1 Noisy Receive Noisy Noisy Noisy Send Z-axis #2 Noisy Noisy Noisy Noisy Send Receive