A Dual-Wavelength In Situ Cloud Lidar with Very Large Sample Volume

Measurements of cloud properties ¿ including volumetric extinction coefficient, cloud optical depth, liquid water content and effective cloud drop radius ¿ are critical parameters for determining the impact of clouds on radiative forcing, a major factor in climate change. Because clouds cover about two-thirds of the globe, retrievals of cloud microphysical properties from remote measurements onboard satellites provide the only viable methodology for determining the integrative effect that clouds have on radiative forcing. However, uncertainties in the inversion algorithms used to remotely determine cloud properties are often significant, requiring in situ cloud measurements by research aircraft to improve and refine the retrievals. This project will develop a dual-wavelength in situ lidar that is capable of measuring volumetric cloud extinction, cloud boundaries, optical depth, effective cloud drop radius, and liquid water content over scales of 106 to 109 m3 ¿ several orders of magnitude greater than conventional cloud particle probes. The novel instrument measures the time of return of photons from laser pulses of two different wavelengths: one that is slightly absorbed and one that is not absorbed by water drops in clouds. Signals from off-axis photodetectors will be analyzed to determine microphysical properties of water clouds. The dual-wavelength in situ cloud lidar will be designed primarily for measurements of stratocumulus and stratus clouds, which are significant contributors to climate change, especially in Polar Regions. Commercial Applications and other Benefits as described by the awardee: A dual-wavelength in situ cloud lidar should be useful as a tool to quantify the effects of stratus clouds on global climate change. Also, aviation could benefit in a number of ways: (1) at uncontrolled airports, the instrument could warn incoming aircraft of low clouds and fog, which are visually undetectable at night; (2) the lidar could provide information on liquid water content and cloud boundaries, information that is critical for inflight icing precautions; (3) installed in small UAV¿s flying off costal areas, the instrument could provide information on the breakup of marine stratocumulus, potentially reducing flight delays and cancellations; and (4) the quantification of cloud properties and boundaries around aircraft carriers would provide valuable information to landing aircraft.