Dual Wavelength In-Situ Cloud Lidar

The Department of Energy is seeking instruments for the in situ measurement of cloud properties. In particular, large sample volumes are needed to fill the gaps in the spatial scale between current in situ measurements (cubic centimeters) and remote sensing retrievals of cloud properties (tens of cubic meters to thousands of cubic meters). These instruments are critical for a better understanding of the ¿cloud feedback¿ problem. Existing in situ cloud lidar, which uses a photomultiplier tube, has obstacles that prevent placement on aerial measurements platforms: limited dynamic range, insensitivity to near infrared, the need for high laser power, and bulky size. To overcome these limitations, this project will develop a compact, dual-wavelength, in situ cloud lidar, based a on unique coherent heterodyne detection approach. This approach uses a silicon detector for visible measurements and an InGaAs detector with wavelength division multiplexing for near IR measurements. These measurements include volume average extinction, cloud thickness, effective radius, and liquid water content. The resulting lidar will offer large field of view, large dynamic range, high sensitivity, low power, compact size, light weight, and fast vertical profiling. In particular, sample volumes will range from cubic meters to hundreds of cubic meters. In Phase I, a proof-of-concept laboratory breadboard will be designed and built. The design will be based on computer simulations to validate key performance parameters, such as sensitivity, accuracy, dynamic range, sample volume, vertical resolution, and temporal resolution. The resulting product will be a compact lidar instrument to be placed on aerial measurement platforms. Commercial Applications and other Benefits as described by the awardee: A lidar product with large sample volumes should be immediately applicable to in situ cloud measurement, supporting a strategy of sustainable and pollution-free energy development. Biomedical applications should include coherent, computer tomographic imaging systems for measurements in scattering tissues. Another application would be in the communication industry, to increase the detection sensitivity of terrestrial fiber communications.