| Assessing atmospheric water vapor measurements to the level of accuracy required for improving atmospheric radiation parameterizations has been difficult to achieve. This thesis describes how a new sensor, the NASA/GSFC Scanning Raman Lidar (SRL), is used to improve assessments of water vapor measurements. Water vapor profiles measured at night by this lidar during two field experiments are compared with those measured by radiosondes, dew point hygrometers, a microwave radiometer, sun photometers, and the LASE lidar. During the first experiment, the SRL data show differences in water vapor mixing ratio and precipitable water vapor measurements as high as 10-15%; during the second, the SRL data reveal: (1) 10-15% differences in the Vaisala and VIZ radiosonde water vapor mixing ratio profiles below two kilometers, and (2) agreement within 5% between the SRL, dew point hygrometers, and LASE. These comparisons show that, by measuring water vapor to within about 5%, the SRL can be used to evaluate point, profile, and integrated water vapor measurements.; Since this lidar detects Raman scattering from nitrogen and oxygen as well as the elastic scattering from molecules and aerosols, it measures both aerosol backscattering and extinction simultaneously with water vapor in the same scattering volume. Therefore, this instrument is well suited to study the interaction between water vapor and aerosols. 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 lidar profiles of aerosol backscattering and extinction compare well with those derived from aerosol size distribution measurements made by a PCASP (Passive Cavity Aerosol Spectrometer Probe) optical particle counter. Using both measurements, the change in particle size with relative humidity, the aerosol real refractive index n, and the single scattering albedo {dollar}rmomegasb{lcub}o{rcub}{dollar} are derived and are shown to vary with time and altitude. Values of n ranged between 1.4-1.5 (dry) and 1.37-1.47 (wet); {dollar}rmomegasb{lcub}o{rcub}{dollar} varied between 0.7-1.0. The SRL data show the ratio of aerosol extinction at 80% relative humidity to that at 60% relative humidity varies between 1.7 to 2.1. |
