Surface Lidars - Group members are working with various data sets from surface-based lidars, including tropical clouds measured at MCTEX (an experiment in the Tiwi Islands off the north coast of Australia), mid-latitude clouds measured by a micro-pulse lidar at the Atmospheric Radiation Measurement (ARM) Program Southern Great Plains site near Ponca City, Oklahoma, and equatorial clouds measured by another micro-pulse lidar at the ARM Program Tropical West Pacific site at Manus Island, Papua New Guinea. We are primarily interested in obtaining physical properties (cloud base, top, structure) and optical properties (IR and visible emittance, optical depth, and depolarization ratio) of cirrus clouds in these locations. Measurements of these properties can be used to infer shape and size characteristics of the ice particles in these clouds.

Also see the Lidar/Radar combined section.

Airborne Lidars

Spaced Based Lidars - Group members are working with data from the Lidar In-space Technology Experiment (LITE), an experiment in which a lidar was operated from the Space Shuttle Endeavour in October 1994. Studies have focused on optical properties, cloud structure, and multiple scattering of lidar pulses. LITE is providing valuable experience in the planning of future space-based lidar missions. The lidar pulse extension phenomenon observed during the 1994 LITE mission may be understood in the context of photon multiple-scattering occurring within the scattering media. The simple ranging algorithm employed to locate targets in physical space is based on the assumption of two-way geometric travel distance (from the source, scattering off the target, and returning to the detector), and is insufficient for long-range operations. Due to hardware limitations, ground eye-safety, and signal to noise requirements, the necessary lidar beam/detector geometries lend themselves to significant multiple scattering effects when applied to orbit ranges. These effects manifest themselves in the observed lidar pulse stretching, which is an unknown function of both the optical properties of the scattering medium (\emph{eg}, cloud extinction and scattering phase function properties) and the instrument optics. If it is possible to numerically identify fundamental pulse stretching behaviors in terms of these driving cloud parameters, their retrievals via inversion techniques may be possible.

Develop groundbased remote sensing techniques to determine ice cloud optical properties and microphysics.

Determine cloud optical depth at one wavelength band each in the infrared and visible solar spectrum in order that radiative fluxes and radiation divergence in a cloudy atmosphere can be calculated.

Calculate optical depth and emittance in atmospheric IR window (10.86 µm)

• Measure IR zenith radiance continuously (Note: fast, accurate narrow-beam radiometers have been developed for this project, supported by ARM.)
• Obtain cloud height and structure from lidar backscatter
• Correct for water vapor absorption and emission using sonde and microwave radiometer data.

Determine visible backscatter profiles from 532 nm lidar

• Correct cloud backscatter for effects of aerosol and molecular scatter
• Obtain backscatter to extinction ratio from integrated attenuated backscatter-emittance relation when cloud is optically thick
• Calculate visible optical depth, considering effects of multiple scattering

Use visible extinction/IR absorption ratio to calculate IR radiance from modeled cloud backscatter profile, iterating until agreement with measured values

Fit of integrated attenuated backscatter vs. emittance curve gives backscatter to extinction ratio k and an additional value of the visible extinction/IR absorption ratio a, giving information on cloud microphysics and effective particle size.

TOVS/HIRS The Tiros Operational Vertical Sounder (TOVS) / High resolution Infrared Radiation Sounder (HIRS)

SSMT/2 - Special Sensor Microwave/ Water Vapor Sounder

SSMI