A Laser Nephelometer for detection of in-situ particles in planetary atmospheres

Abstract:

The NASA Ames nephelometer experiment characterizes the makeup of planetary clouds. Current cloud measurements, based on satellite imagery or ceilometry, provide low resolution data about the edges of cloud layers. Nephelometry yields microphysical data about particle size, shape, and concentration from a cloud’s interior. This new nephelometer design is an improvement over the one that flew on the 1989 Galileo probe, also built at Ames, with much lower size (1000 vs 5700 cm³), weight (1.7 vs 4.4 kg) and power (1.5 vs 11.3 Watts). Improvements in lasers, circuitry, data collection, and power sources have allowed a greatly reduced footprint and there have been advances in our understanding of gaseous planets and cloud structures. The nephelometer requires a single backscatter detector for each of its two lasers, in contrast to the Galileo Nephelometer, that required light in a range of angles, across an arc of ~180 degrees to make measurements. This simplified design is possible due to improvements in detector sensitivity and data analysis techniques. The smaller form factor allows us to fly on more opportunities in threshold environments and planetary atmospheres. The sensor detection system records intensities of backscattered light from two pulsed lasers operating at 1550nm and 785nm. These lasers benefit from the telecom industry’s investments in compact laser technology, providing high output for low input power. The arrangement of two lasers allows for a smaller instrument, rather than the large diode arc used by the Galileo nephelometer. Our prototype (Figure 1) has measured intensities of scattered light, yielding particle size and density based on Mie and dynamic light scattering. A balloon flight is planned for early next year, which will prove the hardware operation in planetary atmosphere conditions (i.e. low temperature, partial pressure). This would give access to multiple cloud layers and atmospheric conditions, validating detection of aerosol particles in multiple depths of field, particle sizes and densities, with the desired resolution and accuracy. The instrument’s feasibility has been demonstrated in the lab and is currently at technology readiness level (TRL) 4. Validation by balloon flight will result in a TRL 5 instrument, meaning it has been demonstrated in a relevant environment.