The 2D-S (Stereo) Probe: Design and Preliminary Tests of a New Airborne, High-Speed, High-Resolution Particle Imaging Probe

Abstract

The design, laboratory calibrations, and flight tests of a new optical imaging instrument, the two-dimensional stereo (2D-S) probe, are presented. Two orthogonal laser beams cross in the middle of the sample volume. Custom, high-speed, 128-photodiode linear arrays and electronics produce shadowgraph images with true 10-μm pixel resolution at aircraft speeds up to 250 m s−1. An overlap region is defined by the two laser beams, improving the sample volume boundaries and sizing of small (<∼100 μm) particles, compared to conventional optical array probes. The stereo views of particles in the overlap region can also improve determination of three-dimensional properties of some particles. Data collected by three research aircraft are examined and discussed. The 2D-S sees fine details of ice crystals and small water drops coexisting in mixed-phase cloud. Measurements in warm cumuli collected by the NCAR C-130 during the Rain in Cumulus over the Ocean (RICO) project provide a test bed to compare the 2D-S with 2D cloud (2D-C) and 260X probes. The 2D-S sees thousands of cloud drops <∼150 μm when the 2D-C and 260X probes see few or none. The data suggest that particle images and size distributions ranging from 25 to ∼150 μm and collected at airspeeds >100 m s−1 by the 2D-C and 260X probes are probably (erroneously) generated from out-of-focus particles. Development of the 2D-S is in its infancy, and much work needs to be done to quantify its performance and generate software to analyze data.

Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014

“…A three-view cloud particle imager (3V-CPI) provided images and habits of liquid and ice-phase hydrometeors in the 10 to 1280 µm size range. This instrument is the combination of a two-dimensional stereoscopic (2D-S; Lawson et al, 2006) laser shadow imaging probe and of a high-frame-rate cloud particle imager (CPI model 2) probe. The 2D-S component of the 3V-CPI instrument was used to analyze particle imagery in order to produce information on the concentration, size and phase of cloud particles.…”

Ice hydrometeor profile retrieval algorithm for high-frequency microwave radiometers: application to the CoSSIR instrument during TC4

“…The in situ ice particle size distributions are obtained from the two-dimensional stereo (2D-S) probe that flew on the DC-8 and WB-57 aircraft and the precipitation imaging probe (PIP) that flew on the DC-8. The 2D-S probe has true 10 µm pixel resolution with 128 photodiode linear arrays and fast electronics (Lawson et al, 2006). The 2D-S has horizontal and vertical channels, though only the horizontal channel is used for the DC-8 probe and the vertical channel for the WB-57 probe.…”

Aerosols that form subvisible cirrus at the tropical tropopause

“…These careful laboratory measurements led to a revision of the JLH data originally submitted to the CR-AVE data archive, to be presented in a future publication. SVC ice crystal size distributions and ice water content were measured using the Cloud Aerosol and Precipitation Spectrometer (CAPS, d=0.5-1550 µm) (Baumgardner et al, 2001) and the 2D-S two-dimensional stereo optical probe (5-1400 µm) (Lawson et al, 2006).…”