R. A. Ferrare

Raman lidar system for the measurement of water vapor and aerosols in the Earth’s atmosphere

A nighttime operating Raman lidar system that is designed for the measurement of high vertical and temporal resolution profiles of the water vapor mixing ratio and the aerosol backscattering ratio is described. The theory of the measurements is presented. Particular attention is given to operational problems that have been solved during the development of the system. Data are presented from Sept. 1987 and described in their meteorological context.

Algorithm for atmospheric corrections of aircraft and satellite imagery

Abstract An algorithm is described for making fast atmospheric corrections. The required radiation parameters are stored in a lookup table. The procedure is to enter the lookup table with the measured radiance, wavelength, view and illumination directions, heights of observation and surface, and the aerosol and gaseous absorption optical thicknesses. The surface radiance, the irradiance incident on a surface, and surface reflectance are computed then. Alternately, the program will compute the upward radiances at specific altitudes for a given surface reflctance, view and illumination directions, and aerosol and gaseous absorption optical thicknesses.

Raman lidar measurements of aerosol extinction and backscattering: 1. Methods and comparisons

This paper examines the aerosol backscattering and extinction profiles measured at night by the NASA Goddard Space Flight Center Scanning Raman Lidar (SRL) during the remote cloud sensing (RCS) intensive operations period (IOP) at the Department of Energy Atmospheric Radiation Measurement (ARM) southern Great Plains (SGP) site in April 1994. These lidar data are used to derive aerosol profiles for altitudes between 0.015 and 5 km. Since this lidar detects Raman scattering from nitrogen and oxygen molecules as well as the elastic scattering from molecules and aerosols, it measures both aerosol backscattering and extinction simultaneously. The aerosol extinction/backscattering ratio varied between approximately 30 sr and 75 sr at 351 nm. Aerosol optical thicknesses derived by integrating the lidar profiles of aerosol extinction measured at night between 0.1 and 5 km are found to be about 10–40% lower than those measured by a Sun photometer during the day. This difference is attributed to the contribution by stratospheric aerosols not included in the lidar estimates as well as to diurnal differences in aerosol properties and concentrations. Aerosol profiles close to the surface were acquired by pointing the lidar nearly horizontally. Measurements of aerosol scattering from a tower-mounted nephelometer are found to be 40% lower than lidar measurements of aerosol extinction over a wide range of relative humidities even after accounting for the difference in wavelengths. The reasons for this difference are not clear but may be due to the inability of the nephelometer to accurately measure scattering by large particles.

Aerosol optical properties over the midcontinental United States

Solar and sky radiation measurements were analyzed to obtain aerosol properties such as the optical thickness and the size distribution. The measurements were conducted as part of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) during the second intensive field campaign (IFC) from June 25 to July 14, 1987, and the fifth IFC from July 25 to August 12, 1989, on the Konza Prairie near Manhattan, Kansas. Correlations with climatological and meteorological parameters show that during the period of observations in 1987, two types of air masses dominated the area: an air mass with low optical thickness and low temperature air associated with a northerly breeze, commonly referred to as the continental air, and an air mass with a higher optical thickness and higher temperature air associated with a southerly wind which we call “Gulf air.” The size distributions show a predominance of the larger size particles in Gulf air. Because of the presence of two contrasting air masses, correlations with parameters such as relative humidity, specific humidity, pressure, temperature, and North Star sky radiance reveal some interesting aspects. In 1989, clear distinctions between continental and Gulf air cannot be made; the reason for this will be discussed.

Raman Lidar and Sun Photometer Measurements of Aerosols and Water Vapor

NASA/GSFC Scanning Raman Lidar measurements of water vapor mixing ratio, relative humidity, aerosol backscattering and extinction are used to investigate relationships between aerosol optical properties and water vapor.

Observation of Anomalous Raman Scattering Associated with Clouds

During a field campaign in 1991, the NASA Goddard Space Flight Center Scanning Raman Lidar measured, in the water vapor channel, Raman scattering from a low-level cloud in excess of saturation. The excess scattering has been interpreted to be spontaneous Raman scattering by liquid water in the cloud droplets. A review of theoretical and laboratory studies indicate that the technique may provide a remote method to observe cloud liquid water.

Scanning Raman lidar to measure atmospheric water vapor and aerosols

Raman lidar is an effective tool for measuring the vertical and temporal evolution of atmospheric water vapor and aerosols. The NASA/GSFC Scanning Raman Lidar (SRL) has participated in several coordinated field campaigns since its first operation in 1991. The measurement capabilities of the SRC are discussed and representative data are presented. This lidar is based on a XeF excimer laser with an output wavelength of 351 nm. The pulsed laser beam is directed into the atmosphere using laser-hardened dichroic mirrors. The signals backscattered from the atmosphere are gathered by a 0.76 m diameter telescope and detected using photomultiplier tubes. A photon counting data acquisition system operating at 100 MHz records the return signals. Four return signals are measured: the backscatter at the laser wavelength due to Rayleigh and Mie scattering from molecules and particles and the Raman shifted returns due to molecular water vapor, nitrogen and oxygen. The system includes a large 1.1 m/spl times/0.8 m scan mirror which allows the full aperture of the telescope to be scanned from horizon to horizon in a single scan plane.

Recent lidar measurements of stratospheric ozone and temperature within the Network for the Detection of Stratospheric Change

The Goddard mobile lidar was deployed at Cannon Air Force Base near Clovis, New Mexico during the Spring of 1990. Measurements of stratospheric ozone and temperature were made over a period of six weeks. Data from the lidar system is compared with data from a balloon-borne, ultraviolet instrument launched from nearby Ft. Sumner, New Mexico. Along with several improvements to this instrument which are now underway, a second lidar dedicated to temperature and aerosol measurements is now being developed.