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.
An attempt is made here to evaluate the skill of forecast during boreal summer monsoon regime over the Indian region using the Observation Simulation System Experiment (OSSE) with Doppler Wind LIDAR (DWL) onboard International Space Station (ISS), assimilated in the initial condition. Through various techniques such as pattern correlation, root mean square error etc, we found that there is some positive impact of assimilating the DWL data on the forecast particularly at the lower tropospheric level. Impact on lowering the RMSE is seen for wind fields in the 850 and 500 hPa over Indian domain but not much impact is seen over larger domain. The moisture field and cloud also show marginal impact due to assimilation of DWL. This indicates that possibly due to lower spatial resolution of DWL data and more data gap over Indian and surrounding oceanic region, the impact on forecast is less. However, it shows the promise that monsoon being a convectively coupled system; increase in spatial data by DWL may better resolve the low level wind and subsequently the low level shear which is important for convection trigger in boundary layer.
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.
KEYWORDS: LIDAR, Data modeling, Satellites, Atmospheric modeling, Meteorological satellites, Systems modeling, 3D modeling, Computer simulations, Environmental sensing, Data centers
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.
An initialization method using airborne Doppler wind lidar data was developed and evaluated for a mass-consistent
diagnostic wind model over complex terrain. The wind profiles were retrieved from the airborne lidar using a
conical scanning scheme and a signal processing algorithm specifically designed for the airborne lidar system. An
objective data analysis method in complex terrain was then applied to those wind profiles to produce a threedimensional
wind field for model initialization. The model results using the lidar data initialization were compared
with independent surface weather observational data and profiles from a microwave radar wind profiler. For the
complex terrain in the Salinas valley, the model evaluation with a limited number of observations indicated that the
diagnostic wind model with airborne Doppler lidar data produced a reasonably good wind field in moderate to
strong wind conditions. However, caution must be stressed for weak wind conditions in which the flow is thermally
driven as the mass-consistent diagnostic wind model is not equipped to handle such cases.
During the GEOSS era, a Doppler wind lidar (DWL) described in this paper will be able to measure
directly the 3-dimensional wind field. These observations can be used synergistically with traditional
imagers, passive radiometers and active scatterometers to improve significantly the weather and climate
missions.
Synergisms being explored include laser height assignment and layer wind calibration for Cloud Motion
Vectors (CMVs) and Water Vapor Motion Vectors (WVMVs), and the adjudication of directional
ambiguities in Ocean Vector Winds (OVW) retrievals. These synergistic links will be incorporated into
adaptive targeting schemes being evaluated within Observing System Simulation Experiments designed
to explore ways to optimize the utility of the DWL observations.
Early concepts to globally measure vertical profiles of vector horizontal wind from space planned on an orbit height of
525 km, a single pulsed coherent Doppler lidar system to cover the full troposphere, and a continuously rotating
telescope/scanner that mandated a vertical line of sight wind profile from each laser shot. Under these conditions system
studies found that laser pulse energies of approximately 20 J at 10 Hz pulse repetition rate with a rotating telescope
diameter of approximately 1.5 m was required. Further requirements to use solid state laser technology and an eyesafe
wavelength led to the relatively new 2-micron solid state laser. With demonstrated pulse energies near 20 mJ at 5 Hz,
and no demonstration of a rotating telescope maintaining diffraction limited performance in space, the technology gap
between requirements and demonstration was formidable. Fortunately the involved scientists and engineers set out to
reduce the gap, and through a combination of clever ideas and technology advances over the last 15 years, they have
succeeded. This paper will detail the gap reducing factors and will present the current status.
The current Earth observing capability depends primarily on spacecraft missions and ground-based networks to provide the critical on-going observations necessary for improved understanding of the Earth system. Aircraft missions play an important role in process studies but are limited to relatively short-duration flights. Suborbital observations have contributed to global environmental knowledge by providing in-depth, high-resolution observations that space-based and in-situ systems are challenged to provide; however, the limitations of aerial platforms - e.g., limited observing envelope, restrictions associated with crew safety and high cost of operations have restricted the suborbital program to a supporting role. For over a decade, it has been recognized that autonomous aerial observations could potentially be important. Advances in several technologies now enable autonomous aerial observation systems (AAOS) that can provide fundamentally new observational capability for Earth science and applications and thus lead scientists and engineers to rethink how suborbital assets can best contribute to Earth system science. Properly developed and integrated, these technologies will enable new Earth science and operational mission scenarios with long term persistence, higher-spatial and higher-temporal resolution at lower cost than space or ground based approaches. This paper presents the results of a science driven, systems oriented study of broad Earth science measurement needs. These needs identify aerial mission scenarios that complement and extend the current Earth Observing System. These aerial missions are analogous to space missions in their complexity and potential for providing significant data sets for Earth scientists. Mission classes are identified and presented based on science driven measurement needs in atmospheric, ocean and land studies. Also presented is a nominal concept of operations for an AAOS: an innovative set of suborbital assets that complements and augments current and planned space-based observing systems.
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).
Planning is in progress to launch a much improved temperature and moisture sounder called GIFTS- Geosynchronous Imaging Fourier Transform Spectrometer. The IPO of the NPOESS had developed an Airborne Sounder Test bed, NAST, to simulate GIFTS data products. The IPO has also developed an airborne Doppler wind lidar (Twin Otter Doppler Wind Lidar - TODWL) to provide accurate wind profiles over the oceans to enable evaluation of the GIFTS and other space-based wind observing systems. This presentation reports on the first in a series of TODWL under flights of the NAST flown on NASA’s ER-2.
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 different 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.
As we plan for a future space-based wind lidar, there are several data product issues that are only resolvable with airborne downward scanning lidars. The US Navy has developed an airborne coherent Doppler lidar that allow us to perform a number of experiments to address some of these issues. During field programs in 2002 and 2003, flights over the ocean near Monterey, California revealed the frequent existence of organized circulations that contained correlations between the aerosol backscatter and the variations in the wind field. This paper discusses the instrument and some of the data that were collected in the presence of organized large eddies in the marine boundary layer.
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.
Vast amounts of energy and chemical constituents are moved about within ocean and river currents. IN the case of deep ocean currents, some reasonable estimates of this transport can be derived from models and sea surface altimetry data. River flows can be estimated form river channel models and indirectly form stage/discharge relationships. However, much of what we know with some measure of accuracy about river and ocean current si derived form in situ measurements. Current meters are the usual choice for obtaining direct observations of the current profiles with depth. Obtaining such profiles using some form of remote sensing is a technological challenge. Surface currents, on the other hand, are more attractive targets for non-contact monitoring. However, useful relationships between the surface motion and the deeper motions are problematic with confounders including wind stress and/or density stratification. In spite of these impediments, there may indeed be some useful information derivable from observations limited to the surface motions of the oceans or rivers, particularly if observations can be obtained with high spatial and temporal density. This paper looks at the possibility of measuring surface currents using airborne and space-based Doppler lidars.
Global observations oftropospheric wind profiles represent a significant potential for advancing weather research and operational forecasting. Space-based Doppler lidar is considered to be one ofthe best candidates for providing vertical wind profiles over the entire globe. The traditional issues of accuracy, spatial resolution and global coverage are currently being formulated within the context of modem 4-D data assimilation. However, this is being done without the benefit of space heritage for active Doppler lidars in space. Considerable resources are being directed at developing "roadmaps" that will guide investments in the technologies that will eventually deliver the data products usable by tomorrow's ever more demanding numerical models. Coherent detection and direct detection offer two very different lidar approaches to making wind observations. In some quarters, the issue is which system to choose over the other. However, given that the two detection techniques have complimentary attributes, it may be more cost effective to employ both. This paper describes the merits of a Wind Observing Satellite using Hybrid (WOSIH) Doppler lidar technologies which would involve (1) a conically scanned 2 micron coherent Doppler lidar for cloud and PBL aerosol wind observations and (2) a 4 point conical-step-stare direct detection tripled YAG (.355?m for obtaining mid and upper tropospheric winds from the Rayleigh returns.
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.
The U.S. Air Force seeks reliable wind measurements in the vicinity of clouds from the perspective of a satellite platform or high altitude aircraft. These wind observations may be used as input to tactical decision aids or assimilated into weather forecast models. There is also interest in making direct wind measurements below clouds by sampling through optically thin gaps. Ground-based and airborne-based lidars have demonstrated the ability to make direct measurements of horizontal winds based on determination of the wind-induced Doppler shift in the backscatter signal. To develop an optimal design concept for space-based lidar platforms, a simulation model has been developed to address questions of optimum laser wavelength, pulse length, minimum power, scanning strategies, optimal signal processing and wind computation algorithms. This paper presents an operational simulation model, the Defense Lidar Simulation Model (DLSM), for space- based/airborne coherent and incoherent Doppler lidar wind sounders that produces simulated Doppler lidar winds using either global or mesoscale atomospheric model wind fields.
Direct-detection lidar has been demonstrated to be useful in locating probable sources of aerosol pollutants, and to some extent characterizing their density in a qualitative manner. Lidar has been less successful in producing quantitative maps of aerosol pollutants because it does not directly measure the quantity of interest. We describe a CO2 lidar which has been used to measure airborne coal dust and propose its use in combination with a dispersion model to produce quantitative information.
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.
NASA's New Millennium Program selected a Doppler Wind Lidar (DWL) using heterodyne detection for the EO-2 mission scheduled for launch in 2001. The Space Readiness of Coherent Lidar Experiment (SPARCLE) will involve a 100mj, pulsed 2 micron laser and a 25 cm wedge scanner. This mission represents the first time a DWL will have flown in space to make tropospheric wind measurements. In addition to demonstrating that the technology can operate in a space environment, the SPARCLE will also provide data sets that are critical to the validation of system performance models and the selection of optimal scanning patterns required for future data products. Extensive computer simulations have been conducted for SPARCLE and some of the follow-on mission concepts that would lead to a fully operational instrument. Global weather forecasting models have been used to provide realistic representations of cloud, water vapor, winds and their effects on DWL data product accuracy and coverage. Results from these simulation efforts indicate that a Coherent DWL can be built and operated to provide virtually full tropospheric coverage, clouds permitting.
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.
NASA's New Millennium Program selected a Doppler Wind Lidar (DWL) using heterodyne detection for the EO-2 mission scheduled for launch in 2001. The SPAce Readiness of Coherent Lidar Experiment (SPARCLE) will involve a 100 mj, pulsed 2 micron laser and a 25 cm wedge scanner. This mission represents the first time a DWL will have flown in space to make tropospheric wind measurements. In addition to demonstrating that the technology can operate in a space environment, the SPARCLE will also provide data sets that are critical to the validation of system performance models and the selection of optimal scanning patterns required for future data products. Extensive computer simulations have been conducted for SPARCLE and some of the follow-on mission concepts that would lead to a fully operational instrument. Global weather forecasting models have been used to provide realistic representations of cloud, water vapor, winds and their effects on DWL data product accuracy and coverage. Results from these simulation efforts indicate that a Coherent DWL can be built and operated to provide virtually full tropospheric coverage, clouds permitting.
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