Search

The NAcA/Goddard Space Flight Center Scanning Raman Lidar has made measurements of water vapor and aerosols for almost ten years. Calibration of the water vapor data has typically been performed by comparison with another water vapor sensor such as radiosondes. We present a new method for water vapor calibration that only requires low clouds, and surface pressure and temperature measurements. A sensitivity study was performed and the cloud base algorithm agrees with the radiosonde calibration to within 10- 15%. Knowledge of the true atmospheric lapse rate is required to obtain more accurate cloud base temperatures. Analysis of water vapor and aerosol measurements made in the vicinity of Hurricane Bonnie are discussed.

We compare aerosol optical thickness (AOT) and precipitable water vapor (PWV) measurements derived from ground and airborne lidars and sun photometers during the Tropospheric Aerosol Radiative Forcing Observational Experiment. Such comparisons are important to verify the consistency between various remote sensing measurements before employing them in any assessment of the impact of aerosols on the global radiation balance. Total scattering ratio and extinction profiles measured by the ground-based NASA Goddard Space Flight Center scanning Raman lidar system, which operated from Wallops Island, Virginia (37.86 deg N, 75.51 deg W); are compared with those measured by the Lidar Atmospheric Sensing Experiment (LASE) airborne lidar system aboard the NASA ER-2 aircraft. Bias and root-mean-square differences indicate that these measurements generally agreed within about 10%. Aerosol extinction profiles and estimates of AOT are derived from both lidar measurements using a value for the aerosol extinction/backscattering ratio S(sub a) = 60 sr for the aerosol extinction/backscattering ratio, which was determined from the Raman lidar measurements. The lidar measurements of AOT are found to be generally within 25% of the AOT measured by the NASA Ames Airborne Tracking Sun Photometer (AATS-6). However, during certain periods the lidar and Sun photometer measurements of AOT differed significantly, possibly because of variations in the aerosol physical characteristics (e.g., size, composition) which affect S(sub a). Estimates of PWV, derived from water vapor mixing ratio profiles measured by LASE, are within 5-10% of PWV derived from the airborne Sun photometer. Aerosol extinction profiles measured by both lidars show that aerosols were generally concentrated in the lowest 2-3 km.

The NASA/GSFC Scanning Raman Lidar (SRL) was stationed on Andros Island in the Bahamas during August - September, 1998 as a part of the third Convection and Moisture Experiment (CAMEX-3) which focussed on hurricane development and tracking. During the period August 21 - 24, hurricane Bonnie passed near Andros Island and influenced the water vapor and cirrus cloud measurements acquired by the SRL. Two drying signatures related to the hurricane were recorded by the SRL (Scanning Raman Lidar) and other sensors. Cirrus cloud optical depths (at 351 nm) were also measured during this period. Optical depth values ranged from approximately 0.01 to 1.4. The influence of multiple scattering on these optical depth measurements was studied with the conclusion that the measured values of optical depth are less than the actual value by up to 20% . The UV/IR cirrus cloud optical depth ratio was estimated based on a comparison of lidar and GOES measurements. Simple radiative transfer model calculations compared with GOES satellite brightness temperatures indicate that satellite radiances are significantly affected by the presence of cirrus clouds if IR optical depths are approximately 0.02 or greater. This has implications for satellite cirrus detection requirements.

Aerosol backscattering and extinction profiles measured 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 during two nights in April 1994 are discussed. These profiles are shown to be consistent with the simultaneous aerosol size distribution measurements made by a PCASP (Passive Cavity Aerosol Spectrometer Probe) optical particle counter flown on the University of North Dakota Citation aircraft. We describe a technique which uses both lidar and PCASP measurements to derive the dependence of particle size on relative humidity, the aerosol real refractive index n, and estimate the effective single-scattering albedo Omega(sub 0). Values of n ranged between 1.4-1.5 (dry) and 1.37-1.47 (wet); Omega(sub 0) varied between 0.7 and 1.0. The single-scattering albedo derived from this technique is sensitive to the manner in which absorbing particles are represented in the aerosol mixture; representing the absorbing particles as an internal mixture rather than the external mixture assumed here results in generally higher values of Omega(sub 0). The lidar measurements indicate that the change in particle size with relative humidity as measured by the PCASP can be represented in the form discussed by Hattel with the exponent gamma = 0.3 + or - 0.05. The variations in aerosol optical and physical characteristics captured in the lidar and aircraft size distribution measurements are discussed in the context of the meteorological conditions observed during the experiment.

The aerosol retrieval algorithms used by the Moderate-Resolution Imaging Spectroradiometer (MODIS) and Multi-Angle Imaging SpectroRadiometer (MISR) sensors on the Earth Observing Satellite (EOS) AM-1 platform operate by comparing measured radiances with tabulated radiances that have been computed for specific aerosol models. These aerosol models are based almost entirely on surface and/or column averaged measurements and so may not accurately represent the ambient aerosol properties. Therefore, to validate these EOS algorithms and to determine the effects of aerosols on the clear-sky radiative flux, we have begun to evaluate the vertical variability of ambient aerosol properties using the aerosol backscattering and extinction profiles measured by the Cloud and Radiation Testbed (CART) and NASA Goddard Space Flight Center (GSFC) Raman Lidars. Using the procedures developed for the GSFC Scanning Raman Lidar (SRL), we have developed and have begun to implement algorithms for the CART Raman Lidar to routinely provide profiles of aerosol extinction and backscattering during both nighttime and ,daytime operations. Aerosol backscattering and extinction profiles are computed for both lidar systems using data acquired during the 1996 and 1997 Water Vapor Intensive Operating Periods (IOPs). By integrating these aerosol extinction profiles, we derive measurements of aerosol optical thickness and compare these with coincident sun photometer measurements. We also use these measurements to measure the aerosol extinction/backscatter ratio S(sub a) (i.e. 'lidar ratio'). Furthermore, we use the simultaneous water vapor measurements acquired by these Raman lidars to investigate the effects of water vapor on aerosol optical properties.

Lidar backscattering profiles available from the LITE data set have been used to estimate the optical depths of the Saharan dust layer over West Africa and E. Atlantic regions, in the context of validating the 3-D conceptual model of the Saharan dust plume proposed by Karyampudi and Carlson. The aerosol extinction profiles and optical depths were retrieved from LITE using the Fernald et al. (1972) method. An extinction-to-backscattering ratio, S(sub a), of 25 was selected for optical depth calculations. The spatial analysis of total column and Saharan dust layer optical depths show higher optical depths over W. Africa that decrease westward over E. Atlantic. The higher optical depths over W. Africa, in general, are associated with heavy dust being raised from the surface in dust source regions. Rapid depletion of these heavy dust particles, perhaps due to sedimentation, appear to decrease the dust loading within the dust layer as the plume leaves the west African continent. Higher optical depths are generally confined to the southern edge of the dust layer, where the middle level jet appears to transport the heavy dust concentrations that tend to mix downward from vertical mixing associated with the strong vertical shears underneath the middle jet. Thus, LITE measurements although, in general, validate the Saharan dust plume conceptual model, show maximum values of optical depths near the southern edge of the dust plume over the E. Atlantic region instead of near the center of the dust plume as described in the conceptual model.

In presenting an overview of the cirrus clouds comprehensively studied by ground based and airborne sensors from Coffeyville, Kansas, during the 5-6 December 1992 First ISCCP Regional Experiment (FIRE) intensive field observation (IFO) case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions may have significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur based particles that became effective cloud forming nuclei in cirrus clouds. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded with the upper level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to approximately 600 L(exp. 1)), complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40 and -50 degrees C. Implications for volcanic-cirrus cloud climate effects and unusual (nonvolcanic) aerosol jet stream cirrus cloud formation are discussed.

The first Atmospheric Radiation Measurement (ARM) Remote Cloud Study (RCS) Intensive Operations Period (IOP) was held during April 1994 at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) site near Lamont, Oklahoma. This experiment was conducted to evaluate and calibrate state-of-the-art, ground based remote sensing instruments and to use the data acquired by these instruments to validate retrieval algorithms developed under the ARM program. These activities are part of an overall plan to assess general circulation model (GCM) parameterization research. Since radiation processes are one of the key areas included in this parameterization research, measurements of water vapor and aerosols are required because of the important roles these atmospheric constituents play in radiative transfer. Two instruments were deployed during this IOP to measure water vapor and aerosols and study their relationship. The NASA/Goddard Space Flight Center (GSFC) Scanning Raman Lidar (SRL) acquired water vapor and aerosol profile data during 15 nights of operations. The lidar acquired vertical profiles as well as nearly horizontal profiles directed near an instrumented 60 meter tower. Aerosol optical thickness, phase function, size distribution, and integrated water vapor were derived from measurements with a multiband automatic sun and sky scanning radiometer deployed at this site.

The NASA/Goddard Space Flight Center Scanning Raman Lidar (SRL) had a highly successful deployment at the Department of Energy Cloud and Radiation Testbed (CART) Site in Billings, OK during April, 1994 for the first Intensive Operation Period (IOP) hosted there. During the IOP, the SRL operated from just after sundown to just before sunrise for all declared evenings of operation. The lidar acquired more than 123 hours of data over 15 nights with less than 1 hour of data lost due to minor system malfunction. The SRL acquired data both on the vertical and in scanning mode toward an instrumented 60 m tower during various meteorological conditions such as an intense cold frontal passage on April 15 which is the focus of this presentation.

In presenting an overview of the cirus clouds comprehensively studied by ground-based and airborne sensors from Coffeyville, Kansas, during the 5-6 December 1992 Project First ISCCP Region Experiment (FIRE) Intensive Fields Observation (IFO) II case study period, evidence is provided that volcanic aerosols friom the June 1991 Pinatubo eruptions may have significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur-based particles that became effective cloud-forming nuclei in cirrus clouds. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded within the upper-level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol-enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to approximately 600/L), complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40 and -50 C. Implications for volcanic-cirrus cloud climate effects and usual (nonvolcanic aerosol) jet stream cirrus cloud formation are discussed.

Observations of upper tropospheric relative humidity obtained from Raman lidar and Cross-chain Loran Atmospheric Sounding System (CLASS) sonde instruments obtained during the First ISCCP Regional Experiment (FIRE) Cirrus-II field program are compared with satellite measurements from the GOES 6.7-micron channel. The 6.7-micron channel is sensitive to water vapor integrated over a broad layer in the upper troposphere (roughly 500-200 mbar). Instantaneous measurements of the upper tropospheric relative humidity from GOES are shown to agree to within roughly 6% of the nearest lidar observations and 9% of the nearest CLASS observations. The CLASS data exhibit a slight yet systematic dry bias in upper tropospheric humidity, a result which is consistent with previous radiosonde intercomparisons. Temporal stratification of the CLASS data indicates that the magnitude of the bias is dependent upon the time of day, suggesting a solar heating effect in the radiosonde sensor. Using CLASS profiles, the impact of vertical variability in relative humidity upon the GOES upper tropospheric humidity measurements is also examined. The upper tropospheric humidity inferred from the GOES 6.7-micron channel is demonstrated to agree to within roughly 5% of the relative humidity vertically averaged over the depth of atmosphere to which the 6.7-micron channel is sensitive. The results of this study encourage the use of satellite measurements in the 6.7-micron channel to quantitatively describe the distribution and temporal evolution of the upper tropospheric humidity field.

In November to December 1991, a substantial number of remote sensors and in situ instruments were operated together in Coffeyville, Kansas, during the climate experiment First ISCCP Regional Experiment Phase 2 (FIRE 2). Includede in the suite of instruments were (1) the NOAA Environmental Technology Laboratory (ETL) three-channel microwave radiometer, (2) the NASA GSFC Raman lidar, (3) ETL radio acoustic sounding system (RASS), and (4) frequent, research-quality radiosondes. The Raman lidar operated only at night and the focus of this portion of the experiment concentrated on clear conditions. The lidar data, together with frequent radiosondes and measurements of temperature profiles (every 15 min) by RASS allowed profiles of temperature and absolute humidity to be estimated every minute. We compared 20 min measurements of brightness temperature (T(sub b) with calculations of T(sub b) that were based on the Liebe and Layton (1987) and Liebe et al. (1993) microwave propagation models, as well as the Waters (1976) model. The comparisons showed the best agreement at 20.6 GHz with the Waters model, with the Liebe et al. (1993) model being best at 31.65 GHz. The results at 90 GHz gave about equal success with the Liebe and Layton (1987) and Liebe et al. (1993) models. Comparisons of precipitable water vapor derived independently from the two instruments also showed excellent agreement, even for averages as short as 2 min. The rms difference between Raman and radiometric determinations of precipitable water vapor was 0.03 cm which is roughly 2%. The experiments clearly demonstrate the potential of simultaneous operation of radiometers and Raman lidars for fundamental physical studies of water vapor.

Raman lidar is a leading candidate for providing the detailed space- and time-resolved measurements of water vapor needed by a variety of atmospheric studies. Simultaneous measurements of atmospheric water vapor are described using two collocated Raman lidar systems. These lidar systems, developed at the NASA/Goddard Space Flight Center and Sandia National Laboratories, acquired approximately 12 hours of simultaneous water vapor data during three nights in November 1992 while the systems were collocated at the Goddard Space Flight Center. Although these lidar systems differ substantially in their design, measured water vapor profiles agreeed within 0.15 g/kg between altitudes of 1 and 5 km. Comparisons with coincident radiosondes showed all instruments agreed within 0.2 g/kg in this same altitude range. Both lidars also clearly showed the advection of water vapor in the middle troposphere and the pronounced increase in water vapor in the nocturnal boundary layer that occurred during one night.

In presenting an overview of the cirrus clouds comprehensively studied by ground-based and airborne sensors from Coffeyville, KS, during the 5-6 Dec. 1992 Project FIRE (First International Satellite Cloud Climatology Project Regional Experiment) IFO II case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur-based particles that became effective cirrus cloud-forming nuclei. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded within the upper level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol-enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to approximately 600 l(sup -1), small but complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40 to -50 C. Implications for volcanic-cirrus cloud climate effects, and usual (non-volcanic aerosol) jet stream cirrus cloud formation are discussed.

The Lidar In-Space Technology Experiment (LITE) is being developed by NASA/Langley Research Center for a series of flights on the space shuttle beginning in 1994. Employing a three-wavelength Nd:YAG laser and a 1-m-diameter telescope, the system is a test-bed for the development of technology required for future operational spaceborne lidars. The system has been designed to observe clouds, tropospheric and stratospheric aerosols, characteristics of the planetary boundary layer, and stratospheric density and temperature perturbations with much greater resolution than is available from current orbiting sensors. In addition to providing unique datasets on these phenomena, the data obtained will be useful in improving retrieval algorithms currently in use. Observations of clouds and the planetary boundary layer will aid in the development of global climate model (GCM) parameterizations. This article briefly describes the LITE program and discusses the types of scientific investigations planned for the first flight.

Raman lidar measurements over southeastern Kansas of stratospheric aerosols produced by the June 1991 eruptions of Mt. Pinatubo were made on 10 nights during November and December 1991. Both aerosol backscattering and extinction profiles were derived simultaneously from the lidar data since this system detects Raman scattering from nitrogen and oxygen as well as the backscattered light from aerosols and molecules. Aerosols scattering ratios greater than 3(at 351 nm) were measured on several nights. Peak aerosol concentrations were located between 19-22 km and varied significantly from night to night. Aerosol extinction/backscatter ratios computed from the lidar data and averaged over the altitude region of enhanced aerosol scattering between 15-25 km varied between 18-28 sr. Mie computations show these values to be consistent with scattering by aerosol particles with mode radii between 0.3 to 0.5 micron and that the ratios would increase to 40-65 sr at 694 nm. Aerosol optical thicknesses derived from the lidar extinction measurements at 351 nm varied between 0.04 and 0.06.

Water vapor is one of the most important constituents of the earth's atmosphere. It has a major impact on both atmospheric dynamics and radiative transfer. From a dynamic standpoint, the distribution of water vapor with height determines convective stability which is the major indicator of destructive storm development. Also, water vapor stored in the planetary boundary layer acts as the fuel to intensify severe weather. In regards to radiative transfer, water vapor is the most active IR molecule in the atmosphere. It is more effective in absorbing and emitting IR radiation than either carbon dioxide or methane, and thus plays an important role in global change. The main objective of FIRE (First ISSCCP (International Satellite Cloud Climatology Project) Regional Experiment) was to study the development and radiative characteristics of cirrus clouds. The SPECTRE (Spectral Radiation Experiment) project was designed to acquire the necessary atmospheric observations to compare radiative measurements with radiative transfer theory, with special emphasis on understanding the water vapor spectral continuum. The FIRE/SPECTRE field campaign was conducted during Nov. - Dec. 1991 in Coffeyville, Kansas. A complete understanding of water vapor, its distribution with height, and its temporal variation was important for both experiments.

Because of the importance of atmospheric water vapor variance, we have analyzed data from the NASA/Goddard Raman lidar to obtain temporal scales of water vapor mixing ratio as a function of altitude over observation periods extending to 12 hours. The ground-based lidar measures water vapor mixing ration from near the earth's surface to an altitude of 9-10 km. Moisture profiles are acquired once every minute with 75 m vertical resolution. Data at each 75 meter altitude level can be displayed as a function of time from the beginning to the end of an observation period. These time sequences have been spectrally analyzed using a fast Fourier transform technique. An example of such a temporal spectrum obtained between 00:22 and 10:29 UT on December 6, 1991 is shown in the figure. The curve shown on the figure represents the spectral average of data from 11 height levels centered on an altitude of 1 km (1 plus or minus .375 km). The spectra shows a decrease in energy density with frequency which generally follows a -5/3 power law over the spectral interval 3x10 (exp -5) to 4x10 (exp -3) Hz. The flattening of the spectrum for frequencies greater than 6x10 (exp -3) Hz is most likely a measure of instrumental noise. Spectra like that shown in the figure are calculated for other altitudes and show changes in spectral features with height. Spectral analysis versus height have been performed for several observation periods which demonstrate changes in water vapor mixing ratio spectral character from one observation period to the next. The combination of these temporal spectra with independent measurements of winds aloft provide an opportunity to infer spatial scales of moisture variance.

The Boundary Layer Lidar System (BLLS), together with the gustprobe system onboard the NASA Electra has acquired a unique data set which, for the first time, clearly depicts a gravity wave above a convectively driven planetary boundary layer (PBL). In addition, we believe that the data show the development of a trapped gravity wave over a period of about an hour. If this is the case, it would certainly be the first time that such a process has been seen in the atmosphere. We also conclude that the gravity wave, while being initiated by the convection in the PBL, ultimately acts to organize and control scales in the PBL.

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.

The NASA/GSFC Crustal Dynamics Project microwave water vapor radiometer (J03) is evaluated in terms of measurements of the integrated precipitable water vapor content of a particular column of the troposphere. The measurements were taken during the Atmospheric Moisture Intercomparison Study (ATMIS) held at Wallops Island (Virginia) during April 1989. Water vapor sensing instruments used during ATMIS, included radiometers, radiosondes, and the NASA/GSFC Raman lidar. Comparisons between water vapor measurements by the radiometer and the lidar yielded a correlation coefficient of 0.998 and rms differences for three nights of -0.2 +/- 0.2 mm (April 11-12), -0.8 +/- 0.5 mm (April 16-17), and -0.4 +/- 0.3 mm (April 17-18). The integrated precipitable water vapor measurements for these three nights were approximately 5, 10 and 21 mm, respectively. This study shows that the radiometer provides accurate continuous measurements of the water vapor integrated through the depth of the atmosphere.

Two cold-air outbreaks were studied during the Genesis of Atlantic Lows Experiment. A lidar system was operated to observe the boundary layer evolution and the development of clouds. On the first day (January 30, 1986) boundary layer rise was less than 50 percent of the value for the second day (March 2, 1986). On the first day only a thin broken cloud cover formed, while on the second day a thick solid cloud deck formed - although the average moisture content was 60 percent of that on the first day. A trajectory slab model was employed to simulate the evolution of the layer over the ocean near the east Atlantic shore. The model allows for vertical gradients in conservative variables under neutrally buoyant conditions. The primary effect of these assumptions, which are based on observed thermodynamic profiles, is to reduce cloudiness to be more in line with observations. Boundary-layer depth was reasonably well predicted as was sensible and latent heat flux.

The Raman lidar observations of a weak gravity current and an internal bore associated with a thunderstorm gust front are presented. These observations have been complemented by conventional surface meteorologial analyses, special radiosonde data, spectral and bandpass filter analysis of barograph data, and infrared satellite imagery. Results obtained reveal the time-space continuity and dynamic nature of two boundary-layer disturbances seen in the lidar data. A comparison of the lidar display with the rawinsonde data makes it possible to determine the thermal fields associated with these disturbances at high temporal resolution (2 min) and an altitude of 6 km. The airflow associated with the disturbances was inferred by synthesizing the lidar and rawinsonde data. One of the two disturbances represents a dissipating outflow boundary (gust front) and can be characterized as a gravity current. The second disturbance represents an internal bore propagating ahead of the gravity current on a surface-based stable layer, which acted as a waveguide. The lidar revealed a mean bore depth of 1.9 km, observed and calculated speeds were in good agreement (about + or - 20 percent).

Several major NASA research efforts in lidar remote sensing are reviewed, with attention given to hardware and key sensor issues along with results and expectations. The discussion covers temperature and pressure measurements, measurements methods and instrumentation, pressure data, wind field measurements, atmospheric backscatter measurement, aerosol and cloud measurements, and water vapor measurement. Consideration is also given to the applicability of lidar measurements to problems of operational weather analysis and forecasting, climate studies, mesoscale and severe storm analysis and forecastig, and studies of atmosphere/surface interface.

We describe preliminary results from a comprehensive computer model developed to guide optimization of a Raman lidar system for measuring daytime profiles of atmospheric water vapor, emphasizing an ultraviolet, solar-blind approach.

The objective of this research was to obtain high resolution measurements of the height of the Marine Atmospheric Boundary Layer (MABL) during cold air outbreaks using an Airborne Lidar System. The research was coordinated with other investigators participating in the Genesis of Atlantic Lows Experiment (GALE). An objective computerized scheme was developed to obtain the Boundary Layer Height from the Lidar Data. The algorithm was used on each of the four flight days producing a high resolution data set of the MABL height over the GALE experiment area. Plots of the retrieved MABL height as well as tabular data summaries are presented.

A large aperture scanning airborne lidar facility is being developed to provide important new capabilities for airborne lidar sensor systems. The proposed scanning mechanism allows for a large aperture telescope (25 in. diameter) in front of an elliptical flat (25 x 36 in.) turning mirror positioned at a 45 degree angle with respect to the telescope optical axis. The lidar scanning capability will provide opportunities for acquiring new data sets for atmospheric, earth resources, and oceans communities. This completed facility will also make available the opportunity to acquire simulated EOS lidar data on a near global basis. The design and construction of this unique scanning mechanism presents exciting technological challenges of maintaining the turning mirror optical flatness during scanning while exposed to extreme temperatures, ambient pressures, aircraft vibrations, etc.

Data are presented on the planetary boundary layer (PBL) over the ocean acquired with an airborne downward-looking lidar during the Frontal Air-Sea Interaction Experiment (FASINEX) with the purpose of studying the impact of an ocean front on air-sea interactions. No changes in the PBL structure were detected by lidar. Lidar data were then used along with other readily available remotely-sensed data and a one-dimensional boundary-layer-growth model to infer the mean PBL moisture and temperature structure and to estimate the surface fluxes of heat and moisture.

A Raman lidar system was used to measure the temperature profile of the upper troposphere and lower stratosphere. The system consists of a tripled Nd-YAG laser and a 1.5 meter diameter telescope. Two photomultipliers are used at the output of the telescope to allow for measurements at both the laser wavelength and at the Raman shifted wavelength due to atmospheric nitrogen. The signal from the photomultipliers is recorded as photon counts in 1 microsec bins. The results of a number of laser shots are summed together to provide atmospheric returns which have acceptable signal to noise characteristics. Measurements of the Raman nitrogen return were acquired up to an altitude in excess of 20 km. Temperature profiles were retrieved from the attenuation corrected Raman nitrogen return assuming the atmosphere to be in hydrostatic equilibrium and using the ideal gas law. Retrieved temperature profiles are shown compared with independent temperature measurements.

The structure of the Planetary Boundary Layer (PBL) was measured, using an airborne lidar, over the Atlantic Ocean during several intensive observation periods of the Genesis of Atlantic Lows Experiment (GALE). Primary emphasis is on the understanding of the convective structure within the PBL during cold air outbreaks. Cold outbreaks generally occur in between the development of coastal storms; and behind a cold front sweeping down from Canada out across the Atlantic. As the cold dry air moves over the relatively warm ocean, it is heated and moistened. The transfer of latent and sensible heat during these events accounts for most of the heat transfer between the ocean and atmosphere during winter. Moistening of the PBL during these eventsis believed to be an important factor in determining the strength of development of the storm system which follows. In general, the more PBL moisture available as latent heat the higher the probability the storm will intensify. The major mechanism for vertical mixing of heat and mositure within the PBL is cellular convection. Knowlede of the organization and structure of the convection is important for understanding the process.

As part of MASEX and GALE a number of research flights were carried out over the Marine Boundary Layer (MBL) during periods when extremely cold and dry continental air was flowing out over the warm coastal waters at the east coast of the U.S. Such periods, which are named cold air outbreaks are characterized by massive warming and moistening of the MBL resulting in rapid entrainment conditions. As the MBL deepens as a function of fetch over the ocean, clouds develop. The line of cloud formation typically follows the coast line closely as has been observed many times from satellite imagery. The backscatter data from the NASA Goddard airborne lidar, which was used to measure the depth of the MBL in great detail, is ideally suited to verify parametrized models of boundary layer growth rate. The data indicates that the deepening MBL gradually develops clouds at its top. Those clouds form an integral part of the MBL and exercise an important influence on the energy cycle within the MBL. It is suggested that the rapid entrainment observed during overcast conditions represent an increase in efficiency of conversion of available turbulence kinetic energy into entrainment energy.

The application of an airborne downward-looking lidar to the study of organized cellular convection in the planetary boundary layer (PBL) over the ocean is described. The lidar consisted of a frequency doubled Nd-YAG 530 mm-wavelength laser whose axis was aligned colinearly with the optical axis of an all-reflecting 40 mm-diameter Newtonian telescope. The airborne lidar provided a unique observation of both microscale and mesoscale variations of the PBL top. The lidar data, presented as constant backscatter isopleth soundings, provide a visual indication of the presence of vertically organized convection cells. Comparisons of the lidar-derived PBL structure with both a conceptual model of the PBL and laboratory simulations of Deardorf et al. (1980) of a developing convective PBL showed that the observations are consistent with a model of mixing in the PBL, which involves a field of organized updrafts separated by downdrafts.

Comparison of lidar and in situ measurements of stratospheric aerosol profiles obtained by backscattered ruby laser light and by direct in situ sampling over Laramie, Wyoming, on two nights in mid-September 1972. The lidar backscattering and the particle number density profiles correlated well. Based on these initial comparative experiments, the ground-based lidar coupled with temperature soundings appears to be a possible method for determining the relative aerosol profile under given stratospheric loading conditions.

Laser optical radar measurement of atmospheric Raman backscattering by nitrogen, oxygen, and water vapor