A Backscattering LASER Nephelometer for in Situ Particle Detection

A laser backscattering nephelometer is designed to measure in-situ cloud microphysical characteristics. In-situ measurement by a probe will be a guidepost that tie the cloud-top view from remote sensing to the properties and processes below. In situ measurements of Saturn’s cloud properties and dynamics can provide ground truth to cloud models and global climate simulations. The nephelometer is based on the 1989 Galileo probe, with much lower size (1000 vs 5700 cm³), weight (1.7 vs 4.4 kg) and power (1.5 vs 11.3 Watts). The sensor detection system records intensities of backscattered light from two pulsed lasers operating at 1550 nm and 785 nm at 1.0 kHz frequencies. Using two wavelengths allows discrimination over a range of particle sizes. The construction and testing of an Engineering Development Unit (EDU) with flight-like parts, optics, and lasers is currently in progress. The system is suitable for a range of in-situ atmospheric missions, including descent probes and landers. The EDU includes both laser channels, full laser functionality, and on-board data processing. 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 balloon-ready instrument will consist of two COTS lasers, from Integrated Optics, an in-house designed circuit board for detecting scattered light and confirming proper laser operation, and an Arduino data collection to record data to SD card. The light from each laser will be split by a 70/30 beamsplitter cube, directing 70% of beam towards the atmosphere to conduct scattering measurements, and 30% to use as a reference source. It requires a 12V power supply capable of providing 1.5 W of power for a flight duration of up to two days. The instrument will collect data while passing through multiple cloud layers. The flight duration can be from several hours up to two days, benefitting from passage through a variety of cloud densities and altitudes.