John G. DeVore — Visidyne, Inc.
Joe Kristl — Visidyne, Inc.
Saul Rappaport — Massachusetts Institute of Technology - Dept of Physics
Category
Instruments
Description
The circles and error bars show profiles of the azimuthally averaged aureole radiance around the star Capella for a broad range of cirrus optical depths on the evening of December 16, 2011. The dashed curves show fits to a sum of three functions representing the instrument point spread function (PSF), cirrus ice crystal diffraction (Stellar Aureole), and city shine scattered from the Boston, Massachusetts area (Background).
While climate change monitoring has improved significantly from routine, ground-based, sun photometer measurements of aerosols made at AERONET sites worldwide, the impacts of cirrus clouds remain much less certain because they occur high in the atmosphere and are more difficult to measure. We report on a Phase I SBIR project to retrieve microphysical properties of cirrus ice crystals using stellar aureole imaging. We have demonstrated that (1) we have clearly measured aureole profiles; (2) we can follow the aureole profiles out to about ~1/4 degree from stars (~1/2 degree from Jupiter); (3) the aureoles from cirrus have very distinctive profiles, being flat out to a critical angle, followed by a steep power-law decline with a slope of ~ -3; (4) the profiles are well modeled using gamma size distributions; and (5) the critical angle in the profiles is ~0.12 degrees, (6) indicating that the particle size distribution extends out to at least several hundred microns (based on particle averaged projected area).
