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Estimating methane (CH4) emission rates using quantitative CH4 retrievals from the Next Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) requires the use of wind speeds. Model wind speeds have limited temporal and spatial resolution, meteorological station wind data are of variable quality and are often not available near observed plumes, and the use of ultrasonic anemometers co-located with methane sources is impractical for AVIRIS-NG flight campaigns with daily coverage of thousands of square kilometers. Given these limitations, this study focused on the use of the Twin Otter Doppler Wind Lidar (TODWL) to measure near surface winds and provide coincident measurements to CH4 plumes observed with AVIRIS-NG. In a controlled release experiment, TODWL observed wind speed and direction agreed well with ultrasonic anemometer measurements and CH4 emission rates derived from TODWL observations were more accurate than those using the ultrasonic anemometer or model winds during periods of stable winds. During periods exhibiting rapid shifts in wind speed and direction, estimating emission rates proved more challenging irrespective of the use of model, ultrasonic anemometer, or TODWL wind data. Overall, TODWL was able to provide reasonably accurate wind measurements and emission rate estimates despite the variable wind conditions and excessive flight level turbulence which impacted near surface measurement density. TODWL observed winds were also used to constrain CH4 emissions at a refinery, landfill, wastewater facility, and dairy digester. At these sites, TODWL wind measurements agreed well with wind observations from nearby meteorological stations, and when combined with quantitative CH4 plume imagery, yielded emission rate estimates that were similar to those obtained using model winds. This study demonstrates the utility of combining TODWL and AVIRIS-NG CH4 measurements and emphasizes the potential benefits of integrating both instruments on a single aircraft for future deployments.

During October&ndash, November 2014 and May 2015, NASA sponsored and conducted a pair of airborne campaigns called Polar Winds to investigate atmospheric circulations, particularly in the boundary layer, over the Arctic using NASA&rsquo, s Doppler Aerosol WiNd (DAWN) lidar. A description of the campaigns, the DAWN instrument, wind retrieval methods and data processing is provided. During the campaigns, the DAWN instrument faced backscatter sensitivity issues in the low aerosol conditions that were fairly frequent in the 2&ndash, 6 km altitude range. However, when DAWN was able to make measurements, comparisons with dropsondes show good agreement and very low bias and supports the use of an airborne Doppler wind lidar such as DAWN that can provide profiles with high velocity precision, ~65 m vertical resolution and horizontal spacing as fine as 3&ndash, 7 km. Case study analyses of a Greenland tip jet, barrier winds and an upper level jet are presented and show how, despite sensitivity issues, DAWN data can be confidently used in diagnostic studies of dynamic features in the Arctic. Comparisons with both an operational and research Weather Research and Forecasting (WRF) model for these events also show the potential for utilization in model validation. The sensitivity issues of the DAWN laser have since been corrected.

Spatiotemporal variability in the convective boundary layer height zi over complex terrain is governed by numerous factors such as land surface processes, topography, and synoptic conditions. Observational datasets to evaluate weather forecast models that simulate this variability are sparse. This study aims to investigate the zi spatial variability (along a total leg length of 1800 km) around and over a steep isolated mountain (Granite Mountain) of horizontal and vertical dimensions of 8 and 0.9 km, respectively. An airborne Doppler lidar was deployed on seven flights during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) campaign conducted at Dugway Proving Ground (Utah) from 25 September to 24 October 2012. During the afternoon, an east–west zi gradient over the region with zi that was approximately 200 m higher on the eastern side than on the western side of Granite Mountain was observed. This gradient illustrates the impact of two different land surface properties on zi spatial variability, with a sparsely vegetated desert steppe region on the east and a dry, bare lake-bed desert with high subsurface soil moisture to the west of Granite Mountain. Additionally, the zi spatial variability was partly attributed to the impact of Granite Mountain on the downwind zi. Differences in zi were also observed by the radiosonde measurements in the afternoon but not in the morning as the zi variability in morning were modulated by the topography. The high-resolution lidar-derived zi measurements were used to estimate the entrainment zone thickness in the afternoon, with estimates ranging from 100 to 250 m.

This study presents a verification and an analysis of wind profile data collected during Tropical Storm Erika (2015) by a Doppler Wind Lidar (DWL) instrument aboard a P3 Hurricane Hunter aircraft of the National Oceanic and Atmospheric Administration (NOAA). DWL-measured winds are compared to those from nearly collocated GPS dropsondes, and show good agreement in terms of both the wind magnitude and asymmetric distribution of the wind field. A comparison of the DWL-measured wind speeds versus dropsonde-measured wind speeds yields a reasonably good correlation (r2 = 0.95), with a root mean square error (RMSE) of 1.58 m s−1 and a bias of −0.023 m s−1. Our analysis shows that the DWL complements the existing P3 Doppler radar, in that it collects wind data in rain-free and low-rain regions where Doppler radar is limited for wind observations. The DWL observations also complement dropsonde measurements by significantly enlarging the sampling size and spatial coverage of the boundary layer winds. An analysis of the DWL wind data shows that the boundary layer of Erika was much deeper than that of a typical hurricane-strength storm. Streamline and vorticity analyses based on DWL wind observations explain why Erika maintained intensity in a sheared environment. This study suggests that DWL wind data are valuable for real-time intensity forecasts, basic understanding of the boundary layer structure and dynamics, and offshore wind energy applications under tropical cyclone conditions.

The Global Wind Observing Sounder (GWOS) concept, which has been developed as a hypothetical space-based hybrid wind lidar system by NASA in response to the 2007 National Research Council (NRC) decadal survey, is expected to provide global wind profile observations with high vertical resolution, precision, and accuracy when realized. The assimilation of Doppler wind lidar (DWL) observations anticipated from the GWOS is being conducted as a series of observing system simulation experiments (OSSEs) at the Joint Center for Satellite Data Assimilation (JCSDA). A companion paper (Riishøjgaard et al.) describes the simulation of this lidar wind data and evaluates the impact on global numerical weather prediction (NWP) of the baseline GWOS using a four-telescope configuration to provide independent line-of-sight wind speeds, while this paper sets out to assess the NWP impact of GWOS equipped with alternative paired configurations of telescopes. The National Centers for Environmental Prediction (NCEP) Gridpoint Statistical Interpolation (GSI) analysis system and the Global Forecast System (GFS) were used, at a resolution of T382 with 64 layers, as the assimilation system and the forecast model, respectively, in these lidar OSSEs. A set of 45-day assimilation and forecast experiments from 2 July to 15 August 2005 was set up and executed.In this OSSE study, a control simulation utilizing all of the data types assimilated in the operational GSI/GFS system was compared to three OSSE simulations that added lidar wind data from the different configurations of telescopes (one-, two-, and four-look configurations). First, the root-mean-square error (RMSE) of wind analysis is compared against the nature run. A significant reduction of the stratospheric RMSE of wind analyses is found for all latitudes when lidar wind profiles are used in the assimilation system. The forecast impacts of lidar data on the wind and mass forecasts are also presented. In addition, the anomaly correlations (AC) of geopotential height forecasts at 500 hPa were evaluated to compare the control and different GWOS telescope configuration experiments. The results show that the assimilation of lidar data from the GWOS (one, two, or four looks) can improve the NCEP GFS wind and mass field forecasts. The addition of the simulated lidar wind observations leads to a statistically significant increase in AC scores.

One of the most important applications of a space-based Doppler Wind Lidar (DWL) would be to improve atmospheric analyses and weather forecasting. Since the mid-1980s, Observing System Simulation Experiments (OSSEs) have been conducted to evaluate the potential impact of space-based DWL data on numerical weather prediction (NWP). All of these OSSEs have shown significant beneficial impact on global analyses and forecasts. In more recent years, a limited number of experiments have been conducted to evaluate the potential impact of DWL data on hurricane forecasting and also to begin to evaluate the impact of real airborne DWL observations. These latest studies suggest that DWL can complement existing hurricane observations effectively and have the potential to contribute to improved hurricane track and intensity forecasting.

This paper briefly presents a case for a global wind pathfinder mission using the proven coherent DWL technology as a component in a global wind observing strategy that also includes CMV/AMV, OVW, CYGNSS, near-future small sats, etc. The proposed lower energy per pulse/high PRF coherent DWL addresses the challenge of making precise measurements in the presence of clouds.

The three-dimensional global wind field is the most important remaining measurement needed to accurately assess the dynamics of the atmosphere. Wind information in the tropics, high latitudes, and stratosphere is particularly deficient. Furthermore, only a small fraction of the atmosphere is sampled in terms of wind profiles. This limits our ability to optimally specify initial conditions for numerical weather prediction (NWP) models and our understanding of several key climate change issues. Because of its extensive wind measurement heritage (since 1968) and especially the rapid recent technology advances, Doppler lidar has reached a level of maturity required for a space-based mission. The European Space Agency (ESA)'s Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) Doppler wind lidar (DWL), now scheduled for launch in 2015, will be a major milestone. This paper reviews the expected impact of DWL measurements on NWP and climate research, measurement concepts, and the recent advances in technology that ...

Three-dimensional winds obtained with an airborne Doppler lidar are used to investigate the spatial structure of topographically driven flows in complex coastal terrain in Southern California. The airborne Doppler lidar collected four hours of data between the surface and 3000 m MSL along a 40-km segment of the Salinas Valley during the afternoon of 12 November 2007. The airborne lidar measurements, obtained at horizontal and vertical resolutions of approximately 1500 and 50 m, respectively, reveal a detailed spatial structure of the atmospheric flows within the valley and their associated aerosol features. Clear skies prevailed on the flight day with northwesterly synoptic flows around 10 m s−1. The data document a shallow sea breeze making a transition into an upvalley flow in the Salinas Valley that accelerates in the upvalley direction. Along with the acceleration of the upvalley wind, the lidar data indicate the presence of enhanced sinking motions. No return flows associated with the sea-breeze or upvalley flows are observed. While synoptic flows are aligned along the valley axis in the upvalley direction, lidar data indicate the presence of a northerly cross-valley flow around the height of the surrounding ridges. This flow intrudes into the valley atmosphere and induces, along with thermally driven slope flows on the sunlit valley sidewall, a cross-valley circulation that causes an asymmetric distribution of the aerosols. This study demonstrates the large potential of airborne Doppler lidar data in describing flows in complex terrain.

Airborne Doppler wind lidars are increasingly being used to measure winds in the lower atmosphere at higher spatial resolution than ever before. However, wind retrieval in the range gates closest to the earth’s surface remains problematic. When a laser beam from a nadir-pointing airborne Doppler wind lidar intercepts the ground, the return signal from the ground mixes with the windblown aerosol signal. As a result, winds in a layer adjacent to the surface are often unreliable and removed from wind profiles. This paper describes the problem in detail and discusses a two-step approach to improve near-surface wind retrievals. The two-step approach involves removing high-intensity ground returns and identifying and tracking aerosol radial velocities in the layer affected by ground interference. Using this approach, it is shown that additional range gates closer to the surface can be obtained, thereby further enhancing the potential of airborne Doppler lidar in atmospheric applications. The benefits of the two-step approach are demonstrated using measurements acquired over the Salinas Valley in central California. The additional range gates reveal details of the wind field that were previously not quantified with the original approach, such as a pronounced near-surface wind speed maximum.

Emerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain meteorology. To address scientific needs and help improve the prediction of mountain weather, the U.S. Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multi-institutional, and multinational group of researchers. The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements. The access to the Granite Mountain Atmospheric Sciences Testbed of the U.S. Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platforms, has provided an unprecedented opportunity to investigate phenomena of time scales from a few seconds to a few days, covering spatial extents of tens of kilometers down to millimeters. This article provides an overview of the MATERHORN and a glimpse at its initial findings. Orographic forcing creates a multitude of time-dependent submesoscale phenomena that contribute to the variability of mountain weather at mesoscale. The nexus of predictions by mesoscale model ensembles and observations are described, identifying opportunities for further improvements in mountain weather forecasting.

Through the use of observation operators, modern data assimilation systems have the capability to ingest observations of quantities that are not themselves model variables but are mathematically related to those variables. An example of this is the so-called line-of-sight (LOS) winds that a spaceborne Doppler wind lidar (DWL) instrument would provide. The model or data assimilation system ideally would need information about both components of the horizontal wind vectors, whereas the observations in this case would provide only the projection of the wind vector onto a given direction. The estimated or analyzed value is then calculated essentially as a weighted average of the observation itself and the model-simulated value of the observed quantity. To assess the expected impact of a DWL, it is important to examine the extent to which a meteorological analysis can be constrained by the LOS winds. The answer to this question depends on the fundamental character of the atmospheric flow fields that are analyzed, but, just as important, it also depends on the real and assumed error covariance characteristics of these fields. A single-level wind analysis system designed to explore these issues has been built at the NASA Data Assimilation Office. In this system, simulated wind observations can be evaluated in terms of their impact on the analysis quality under various assumptions about their spatial distribution and error characteristics and about the error covariance of the background fields. The basic design of the system and experimental results obtained with it are presented. The experiments were designed to illustrate how such a system may be used in the instrument concept definition phase.

The investigators are developing a system tool that utilizes both pre-flight information and continuous real-time knowledge and description of the state of the atmosphere and atmospheric energetics by an Airborne Doppler Wind Lidar (ADWL) to provide the autonomous guidance for detailed and adaptive flight path planning by UAS and small manned aircraft. This flight planning and control has the potential to reduce mission dependence upon preflight assumptions, extend flight duration and endurance, enable long periods of quiet operations and allow for the optimum self-routing of the aircraft. The ADWL wind data is used in real-time to detect atmospheric energy features such as thermals, waves, wind shear and others. These detected features are then used with an onboard, weather model driven flight control model to adaptively plan a flight path that optimizes energy harvesting with frequent updates on local changes in the opportunities and atmospheric flow characteristics. We have named this package AEORA for the Atmospheric Energy Opportunity Ranking Algorithm (AEORA).

A simulation testbed has been developed to demonstrate and assess space-based wind measuring systems to reduce mission costs, extend mission life, and enable better data collection through impact studies, system trades, and the participation in Observing System Simulation Experiments (OSSEs). The numerical testbed is intended to determine the potential impact of proposed space-based and sub-orbital wind observing systems on analyses and forecasts. This paper presents the testbed used for evaluating two recent proposed space-based wind measuring concepts.

An airborne Doppler Wind Lidar has been used in several atmospheric boundary layer field experiments over the past decade. These experiments have taken place in California (Salinas Valley and the Monterey Peninsula), Arizona (Yuma Proving Grounds), and Utah (Dugway Proving Grounds). A primary objective of these field experiments was to compare model predicted winds in mountainous areas with wind observations obtained from the lidar measurements. To accomplish this, there is a basic challenge to determine when a comparison is valid in space and time. Here we have introduced the case for combining 12 pint step stare scans (conical) with near nadir stares to better represent the vertical air motions in complex terrain. We have also described a new scanning pattern that allows for LOS intersections for desired altitudes such as a ridge line or a valley floor.

Observing System Simulation Experiments (OSSEs) are an important tool for evaluating the potential impact of proposed new observing systems, as well as for evaluating trade-offs in observing system design, and in developing and assessing improved methodology for assimilating new observations. Detailed OSSEs have been conducted at NASA/ GSFC and NOAA/AOML in collaboration with Simpson Weather Associates and operational data assimilation centers over the last three decades. These OSSEs determined correctly the quantitative potential for several proposed satellite observing systems to improve weather analysis and prediction prior to their launch, evaluated trade-offs in orbits, coverage and accuracy for space-based wind lidars, and were used in the development of the methodology that led to the first beneficial impacts of satellite surface winds on numerical weather prediction. In this paper, we summarize early applications of global OSSEs to hurricane track forecasting and new experiments, using both global and regional models, that are aimed at both track and intensity forecasting.

The deployment of a space-based Doppler lidar would provide information that is fundamental to advancing the understanding and prediction of weather and climate. This paper reviews the concepts of wind measurement by Doppler lidar, highlights the results of some observing system simulation experiments with lidar winds, and discusses the important advances in earth system science anticipated with lidar winds. Observing system simulation experiments, conducted using two different general circulation models, have shown (1) that there is a significant improvement in the forecast accuracy over the Southern Hemisphere and tropical oceans resulting from the assimilation of simulated satellite wind data, and (2) that wind data are significantly more effective than temperature or moisture data in controlling analysis error. Because accurate wind observations are currently almost entirely unavailable for the vast majority of tropical cyclones worldwide, lidar winds have the potential to substan- tially improve tropical cyclone forecasts. Similarly, to improve water vapor flux divergence calculations, a direct measure of the ageostrophic wind is needed since the present level of uncer- tainty cannot be reduced with better temperature and moisture soundings alone.

[1] Observing System Simulation Experiments (OSSEs) are a powerful tool used to assess the potential impact on numerical weather prediction skill of planned or hypothetical future observing systems. Over the past several years an international Joint OSSE collaboration has emerged centered on the use of NASA's and NOAA's data assimilation systems. A Nature Run provided by the European Centre for Medium Range Weather Forecasts (ECMWF) has undergone extensive validation, and a set of simulated reference observations have been subjected to a set of calibration experiments. One of the first candidate observing systems assessed by this system is a wind lidar based on the Global Wind Observing Sounder (GWOS) concept developed by NASA in response to the National Research Council (NRC) Decadal Survey. A set of 45-day assimilation and forecast experiments has been set up and executed. The experiments were done using the NCEP operational forecast system, and the results show that wind lidar observations are likely to provide a significant increase in forecast skill even when used in a modern, radiance-based assimilation system.

The long-term goal is to analyze and, if necessary, reprocess the shipboard HRDL (High Resolution Doppler Lidar) data taken during the DYNAMO field campaign in order to make comparisons with existing airborne DWL measurements (TODWL) and to conduct investigations into the utilization of the data for studying atmospheric features and phenomenon during various conditions. One of the main objectives of our research was to see if what was learned from the TODWL (CIRPAS) and P3DWL (NRL) experience regarding rain in the field of view of Doppler Wind Lidar (DWL) data could be applied to the shipboard HRDL observations taken during DYNAMO. A second objective was to use the HRDL data and the W band radar data taken aboard the USS Revelle to investigate vertical motions within physically thick (optically thin) cirrus layers. During our evaluation of the HRDL data we have added a third objective which is to investigate dry convection rolls (Organized Large Eddies, OLE) from the perspective of a ship-borne DWL for comparison with that obtained from an airborne DWL during TODWL flights in April 2007 near Monterey, CA. This additional research objective is tightly associated with the research we are doing under another ONR DRI, the Unified Physical Parameterization for Extended Forecasts DRI, where the EDMF flux parameterization is being evaluated for its use in numerical models for seasonal predictions.

The first ever extensive study of tropical cyclones using Doppler Wind Lidars (DWL) was conducted in 2008 within the THORPEX Pacific Asian Regional Campaign. More than 100 hours of DWL profiles were obtained with an average spacing of 3km. These wind profiles along with dropsonde temperature, moisture and wind profiles are being used to study the genesis and evolution of tropical cyclones. Initial investigations are focused upon the impact the DWL profiles have on numerical weather prediction.

Obtaining accurate wind observations from an airborne Doppler lidar requires very precise pointing knowledge of the laser beam. A .1 degree pointing knowledge error can result in a .2 m/s velocity error along the line-of-sight. One option is to exercise great care in aligning the laser beam with the aircraft axes and then acquiring precise information from an onboard navigation system for aircraft attitude. A pointing knowledge approach using surface returns developed for a space mission has been adapted to the CIRPAS Twin Otter's Doppler wind lidar and has been demonstrated during a series of field experiments. RMSEs less than .05 m/s have been achieved for the three components of the wind in vertical profiles (50 m resolution) representing a few 100 meters of flight path. This approach negates the need for precise physical alignment and allows for continuous up dating of attitude corrections due to aircraft flexure, air stream loading of the scanner or any drift in the Inertial Navigation System. Examples of soundings and algorithm validation are presented along with applications where the vertical velocity data are evaluated for their realism.

Using a combination of two modest sized coherent and direct detection Doppler lidars may offer significant advantages over the single detection method approaches. All space-based Doppler wind lidar proposed missions to date have been based upon a single detection scheme, either coherent (WINDSAT, LAWS, SPARCLE, JEM/CDL) or direct (Zephyr, ALADIN, ADM) detection. A hybrid detection wind lidar has been proposed and is undergoing a feasibility study. The hybrid wind lidar is currently being baselined for an airborne test bed and is funded for a weather forecasting impact evaluations at NOAA and NASA.

In the 1970’s a government study was conducted to assess the technological feasibility of obtaining wind profiles from space using a Doppler lidar. In the 80’s, NASA considered developing a Doppler wind lidar but put plans on hold as the projected costs rose. In the 90’s, global wind observations remained a unmet need and a series of model experiments (Observing System Simulation Experiments) were conducted to perform instrument trades and general weather forecast impact assessments. This paper reports on some recent results of OSSEs at NOAA’s NCEP (National Center for Environmental Prediction) and NASA’s DAO (Data Assimilation Office).

Observing system simulation experiments (OSSE's) provide an effective means to evaluate the potential impact of a proposed observing system, as well as to determine tradeoffs in their design, and to evaluate data assimilation methodology. Great care must be taken to ensure realism of the OSSE's, and in the interpretation of OSSE results. All of the OSSE's that have been conducted to date have demonstrated tremendous potential for space-based wind profile data to improve atmospheric analyses, forecasts, and research. This has been true for differing data assimilation systems, analysis methodology, and model resolutions. OSSE's clearly show much greater potential for observations of the complete wind profile than for single-level wind data or observations of the boundary layer alone.

Space-based global wind observations are a potential application of Doppler lidars. While the use of Doppler lidars to measure winds has existed for several decades, the availability of airborne systems is relatively recent. Ground based Doppler wind lidars (DWL) have provided much experience in interpreting return signals and validating performance models. However, spacebased operations present a very different perspective on the atmosphere. For that reason, airborne lidars are critical in the development of signal processing algorithms and performance model validation for both future space-based as well as sub-orbital instruments. As a component of a program to develop a calibration/validation strategy for all space-based wind observing systems, an airborne coherent 2 micron DWL was flown early in 2002. The primary purpose of those flights was to investigate the surface returns from water. This paper summarizes those missions and offers several examples of the findings.

As Doppler lidars designed for environmental remote sensing move from ground-based platforms to airborne and space-based platforms, issues related to processing surface and near-surface returns are of increasing interest. In the case of Doppler wind lidars, the surface returns can be useful in calibrating the velocity estimates along the associated lines-of-sight, assuming the surface is not moving relative the Earth's frame of reference. This assumption may not hold for water surfaces and in that case, the Doppler signal might be useful in estimating surface currents (rivers and oceans). Whether the water returns are used for calibrating wind lidars or making water current measurements, the confounders of accurate observations include waves and the independent motions of overlying aerosols in the layer adjacent to the surface (LAS). As part of a program to develop calibration/validation techniques for space-based Doppler wind lidars, a series of laboratory and airborne experiments are being executed. At NASA/MSFC a water slide has been constructed and used with a 2μm coherent lidar to study the signal from water surfaces having varying velocities, roughnesses and turbidities. The angle of the water slide to the lidar beam can also be varied to test the theoretical function of signal return vs. angle of incidence. Results of those experiments have provided input to the design and execution of a set of airborne 2μm coherent lidar experiments conducted in February and March 2002 out of Monterey, CA. The airborne system (funded by the US Navy and the Integrated Program Office of the NPOESS) collected data to be used to develop signal processing algorithms that can discriminate between the water surface motions and the velocity of the wind blown aerosols that are combined in the signal from just one range gate. This paper will report on both sets of experiments.

Through the use of observation operators, modern data assimilation systems can ingest observations of quantities that are not themselves model variables, but are mathematically related to those variables. An example of this are the LOS (line of sight) winds that Doppler wind lidars provide. The model - or data assimilation system - needs information about both components of the horizontal wind vectors, whereas the individual observations in this case only provide the projection of the wind vector onto a given direction. In order to assess the expected impact of such an observing system, it is important to examine the extent to which a meteorological analysis can be constrained by the LOS winds. A single-level wind analysis system designed to explore these issues has been built at the NASA Data Assimilation Office. In this system, simulated wind observations can be evaluated in terms of their impact on the analysis quality under various assumptions about their spatial and angular distributions as well as the observation error characteristics. The basic design of the system will be presented along with experimental results obtained with it. In particular, the value of measuring LOS winds along two different directions for a given location will be discussed.

A major component of the hydrologic cycle is river discharge. Within the continental USA, the USGS operates nearly 7000 streamgaging stations. For much of the rest of the world major river discharge is poorly, sparsely or not monitored at all. In preparation for a shuttle demonstration of coherent Doppler lidar wind observing, it was determined that the assumption of a zero velocity for the surface return was probably not valid for a large fraction ofthe globe. Ocean currents, river currents, blowing sand or dust near the surface, or even swaying trees violate that assumption. However, what appeared as a confounder for shot to shot velocity calibration may actually be useful information to oceanographers and those involved with river flow. This paper describes the current status of efforts to determine both the usefulness of an observation of the river surface velocity and the feasibility of obtaining such information from a space-based Doppler lidar.

NASA recently approved a mission to fly a Doppler Wind Lidar on a US Space Shuttle. SPARCLE, managed by Marshall Space Flight Center in Huntsville, AL, is targeted for launch in March 2001. This mission is viewed as a necessary demonstration of a solid state lidar using coherent detection before committing resources to a 3-5 year research or operational mission. While, to many, this shuttle mission is seen as the first step in a series leading to a fully operational wind observing system, to others, it is a chance to validate predictions of performance based upon theoretical models, analyses of airborne and ground-based data and sophisticated observing system simulation experiments. The SPARCLE instrument is a 100 mJ, 6 Hz, diode pumped 2 micron laser with a .25 m telescope using heterodyne mixing in a fiber and an InGaAs detector. A 25 cm silicon wedge scanner will be used in step-stare modes with dwells ranging from 60 seconds to .5 seconds. Pointing knowledge is achieved with a dedicated GPS/INS mounted close to the lidar. NASA's hitchhiker program is providing the instrument enclosures and mission logistics support. An on- board data system in sized to record 80 Gbytes of raw signal from two 400 MHz A/D converters. On-board signal processing will be used to control the frequency of the Master Oscillator. SPARCLE is predicted to have a singleshot backscatter sensitivity near 5 by 10-6 m-1 sr-1. To achieve higher sensitivity, shot accumulation will be employed. Ground-based, 2 micron DWLs have been used to assess the benefits of shot accumulation. Airborne programs like MACAWS have provided good data st for evaluating various sampling strategies and signal processing algorithms. Using these real data to calibrate out simulation models, we can describe when and how well SPARCLE is expected to perform.

For over 20 years researchers have been investigating the feasibility of profiling tropospheric vector wind velocity from space with a pulsed Doppler lidar. Efforts have included theoretical development, system and mission studies, technology development, and ground-based and airborne measurements. Now NASA plans to take the next logical step towards enabling operational global tropospheric wind profiles by demonstrating horizontal wind measurements from the Space Shuttle in early 2001 using a coherent Doppler wind lidar system.

Both single-agency and multi-agency efforts are currently underway to put a Doppler lidar wind sounder into space within the next decade. Justification for this ambitious project rests mainly in the universally recognized need to provide direct measurements of the winds as input to both climate studies and forecast models. Expectations of success are based heavily upon ground-based observations as well as a few airborne observations. While the space-based observations will be taken at 5-10 Hz providing samples with a spatial separation of 50 to 70 kilometers within the earth's atmosphere, both the ground-based and airborne observations have been acquired primarily at 20 to 100 hertz providing a shot density of many samples per square meter resolution. Furthermore, many of the wind velocity estimates derived from these ground-based and airborne instruments have been acquired by using a poly-pulse pair technique involving 20 to sometimes 100 pulses. Currently there is very little in the way of data that is acquired in a single shot mode and processed to achieve resolution, both in space and time, that will approximate that which is achievable with a space-based system.

A space-based Doppler Lidar Atmospheric Wind Sounder (LAWS) has been proposed by NASA as a facility instrument for the NASA Earth Observing System. Simpson Weather Associates, Inc. has developed LAWS Simulation Models (LSM) that are coupled with Global Circulation Models (GCM) to evaluate the potential impact of global wind observations on the basic understanding of the earth’s atmosphere and on the predictive skills of current forecast models (GCM and regional scale). This paper uses the LSM to examine the three dimensional distribution of LAWS’ observations over the globe. Such a study must consider the effects of atmospheric aerosols, molecular attenuation of the lidar signal, opaque clouds, and the presence of thin cirrus clouds.

Tropospheric wind field is a primary atmospheric variable, the knowledge of which is required at a global scale for operational meteorology and climatology studies. With the present state-of-the-art technology a spaceborne Doppler coherent lidar is foreseen to fullfil the requirements on sampling and wind speed accuracy. An initial feasability study has been conducted at NOAA in the late 70's proposing a viable concept for a laser remote sensor instrument WINDSAT. In the late 80's NASA and ESA started two studies on wind Doppler lidar so-called LAWS and ALADIN respectively to be launched either on a polar or a low inclinaison orbit depending on the scientific objectives and instrument performances dictated by the overall technology : lidar and platform. In these two studies a conical scanning mode provides the horizontal coverage at the earth surface. In a separate way restricting at first the scientific objectives to the climatology of the tropics CNES in France started a feasability study for a low inclinaison mission so-called BEST which includes among others a wind Doppler lidar. A new instrumental concept is proposed for BEST which is a multi-fixed line-of-sight configuration relaxing the constraints on lag-angle compensation and laser technology. So, a comparison of the two scanning modes has to be made keeping in mind the applications in order to show what can be acomplished with an increasing instrumental complexity. The various subjects to be covered by a comparison analysis are : horizontal coverage, cloud obstruction, sampling at various time scales, representativeness and wind speed accuracy, but also the data assimilation methods. Such a study is conducted for BEST and ALADIN by LMD and DMN following a step by step approach with an increasing complexity and completeness.

The concept of using a Doppler lidar to measure winds from space was first seriously posed by the Defense Meteorological Satellite Program Office (DMSP) of the USAF in the late 70's. NOAA, under contract to the USAF, conducted a feasibility study for a lidar system they called WINDSAT (Huffaker et al., 1980, 1984). Their conclusions were that given sufficient power (~ 10-20 J) winds could be measured throughout the troposphere and would provide global profiles of accuracy and density similar to those provided by the U.S. network of rawinsondes. The projected platform requirements and lidar development costs were significant and exceeded the existing resources available to the DMSP.

A space-based Doppler Lidar Atmospheric Wind Sounder (LAWS) has been proposed by NASA as a facility instrument for the NASA Earth Observing System. A LAWS Simulation Model (LSM) has been developed to assess the impact of a spaced-based Doppler lidar wind profiler on global and regional features. Hardware feasibility and data studies are ongoing.1,2,3 The uniqueness of global Lidar wind measurements from space raises many fundamental questions that may impact the design of such a system. The distribution of aerosols that provide backscatter, the molecular attenuation that reduces signal strength, the effects of wind shear and turbulence that effect measurement accuracy, and the presence of thin cirrus clouds that can enhance the performance are all issues that must be considered.

Data from a wide variety of measurement platforms are integrated to analyze a GATE cloud cluster and its environment. Lower tropospheric mass and moisture fluxes are computed on several scales using rawinsonde, aircraft, radar and satellite data from 18 September 1974. Lower tropospheric mass and moisture budget analyses are combined with GATE tethered-balloon measurements of cloud properties at cloud base to diagnose active cloud and turbulent fluxes in three areas of different scale ranging from 2.3-34.8 × 1010 m 2 (1.8-28.2° latitude)2. The significant convection was concentrated in the region of strongest and deepest low-level convergence and highest conditional instability. Observed layer clouds were well correlated with levels of synoptic-scale divergence. Despite large differences in low-level convergence and echo-area coverage, all three regions exhibited similar vertical eddy moisture fluxes at cloud base. Increased area coverage by precipitating clouds was found to be associated with in...

This paper examines the computation of surface-level vertical fluxes of total energy in a moist atmosphere. A flux equation is derived which includes the enthalpy of water, the temperature dependence of the latent heat of condensation and variable moisture composition of air. The complete formulation requires keeping track of liquid water fluxes. However, if this is not possible, then the total energy flux is best approximated by neglecting the enthalpy of all net fluxes of water substance. An important finding is that sensible heat fluxes derived using a moist specific heat at constant pressure are not compatible with usual formulations of latent heat unless the net vapor flux is neglected.

Simultaneous observations at up to six levels through a depth of 1100 m from a tethered balloon and instrumented ship's boom of 49 gust fronts associated with convective clouds are used to describe the mean and the detailed characteristics of tropical oceanic cumuli outflow at the surface and in the boundary layer. The changes in temperature and velocity of the maritime tropical gust front are about 50%; of the changes observed in mid-latitude convective outflows. Vertical velocities at the gust front ⩾l m s-1 are continuous through the lower 500 m for time periods up to 8 min implying vertical displacements of at least 500 m entirely sufficient at the observed humidities (q >- 15 g kg-1) to initiate new cloud growth. Horizontal and vertical vorticity in the order of 10-3 s-1 to 10-2 s-1 is observed at the gust front.

The potential impact of mesoscale patterns of winds, clouds and aerosols upon satellite based lidar estimates of the global winds are discussed with examples taken from a NASA simulation study.

A space-based CO2 Doppler lidar is being considered by NASA, NOAA, DOD, and European groups to obtain direct measurements of the winds in the cloud free regions of the troposphere by measuring the Doppler shift in the backscattered energy from aerosols in motion. Workshops and panel meetings have addressed the needs of the user community and the desired measurement accuracies (NASA, 1985). Early feasibility studies by NOAA and NASA presented a generally optimistic outlook for obtaining useful wind measurements (Huffaker, et al., 1980). Current efforts are now in progress to assess the accuracies in more detail and to evaluate the impact that such global measurements will have on predictive atmospheric models (Emmitt, 1987).

The prospect of obtaining directly measured winds on a global scale has raised questions about the expected quality of the lidar wind measurements and the potential for biases due to sampling patterns and line-of-sight impediments. Extensive computer simulations are ongoing to address these and other issues. One source of measurement bias is found in regions of the atmosphere where gradients in both lidar backscatter and the winds occur together. The potential biases that result are identified and their magnitudes estimated.

This paper is a companion paper to another conference paper entitled "Assessment of error sources for one component wind measurements with a space-based Doppler lidar" by Emmitt and Bilbro. In that paper the proposed lidar system is described and errors associated with the radial component measurement of the winds discussed. In this paper we focus upon the errors that arise out of combining these one-component observations into estimates of the total wind vector. These errors are of a totally different nature and have serious implications to the inclusion of lidar observed winds into numerical models.

The onset of a low level jet and downslope winds is described with wind measurements taken with NASA/MSFC's Doppler Lidar during the 1982 JAWS in Denver, Colorado.