Lidar and Mission Parameter Trade Study of Space-Based Coherent Wind Measurement Centered on NASA's 2006 GWOS Wind Mission Study Parameters

The global measurement of vertical profiles of horizontal vector winds has been highly desired for many years by NASA, NOAA and the Integrated Program Office (IPO) implementing the National Polar-orbiting Operational Environmental Satellite Systems (NPOESS). Recently the global wind mission was one of 15 missions recommended to NASA by the first ever NRC Earth Sciences Decadal Survey. Since before 1978, the most promising method to make this space-based measurement has been pulsed Doppler lidar. The favored technology and technique has evolved over the years from obtaining line-of-sight (LOS) wind profiles from a single laser shot using pulsed CO2 gas laser technology to the current plans to use both a coherent-detection and direct-detection pulsed Doppler wind lidar systems with each lidar employing multiple shot accumulation to produce an LOS wind profile. The idea of using two lidars (hybrid concept) entails coherent detection using the NASA LaRC-developed pulsed 2-micron solid state laser technology, and direct detection using pulsed Nd:YAG laser technology tripled in frequency to 355 nm wavelength

Parameter Trade Studies For Coherent Lidar Wind Measurements of Wind from Space

The design of an orbiting wind profiling lidar requires selection of dozens of lidar, measurement scenario, and mission geometry parameters; in addition to prediction of atmospheric parameters. Typical mission designs do not include a thorough trade optimization of all of these parameters. We report here the integration of a recently published parameterization of coherent lidar wind velocity measurement performance with an orbiting coherent wind lidar computer simulation; and the use of these combined tools to perform some preliminary parameter trades. We use the 2006 NASA Global Wind Observing Sounder mission design as the starting point for the trades

Computer Simulation of Global Profiles of Carbon Dioxide Using a Pulsed, 2-Micron, Coherent-Detection, Column-Content DIAL System

We present preliminary results of computer simulations of the error in measuring carbon dioxide mixing ratio profiles from earth orbit. The simulated sensor is a pulsed, 2-micron, coherent-detection lidar alternately operating on at least two wavelengths. The simulated geometry is a nadir viewing lidar measuring the column content signal. Atmospheric absorption is modeled using FASCODE3P software with the HITRAN 2004 absorption line data base. Lidar shot accumulation is employed up to the horizontal resolution limit. Horizontal resolutions of 50, 100, and 200 km are shown. Assuming a 400 km spacecraft orbit, the horizontal resolutions correspond to measurement times of about 7, 14, and 28 s. We simulate laser pulse-pair repetition frequencies from 1 Hz to 100 kHz. The range of shot accumulation is 7 to 2.8 million pulse-pairs. The resultant error is shown as a function of horizontal resolution, laser pulse-pair repetition frequency, and laser pulse energy. The effect of different on and off pulse energies is explored. The results are compared to simulation results of others and to demonstrated 2-micron operating points at NASA Langley

Design and Calibration of Autonomous Coherent Doppler Lidar for Space Missions

Developed a new algorithm for the simulation of three dimensional homogeneous turbulent velocity fields. For typical atmospheric conditions it is impossible to produce a simulated velocity field that simultaneously satisfy a given spatial correlation and the corresponding spatial spectrum because of spectral aliasing. The new algorithms produce a turbulent velocity field which has accurate spatial correlations which is required for performance predictions from space-based systems. Developed a new algorithm for extracting the spatial statistics of the atmospheric velocity field using coherent Doppler lidar. The performance of the algorithm was compared with past methods and the new algorithm produces useful results for space-based data, which was not possible before. Developed new methods for verification of the errors in ground-based and space-based Doppler lidar wind measurements. These new methods do not require independent in situ data. This is an important issue for the verification of space-based Doppler lidar measurements of the global wind field. The performance of the new algorithm was compared with past results for both space-based and ground-based operation. The new algorithm has the best performance and is the only algorithm that performed satisfactory for spacebased operation. The performance of coherent Doppler lidar for a space missions with various scanning geometries was determined using computer simulation which contained the effects of random instrumental velocity errors, wind shear, wind variability along the range-gate and from shot-to-shot, and random variations in atmospheric aerosol backscatter over the measurement volume. The bias in the velocity estimates was small and the accuracy in the is typically less than 0.5 m/s for high signal conditions. For a large number of shot per velocity estimate, the threshold signal level for acceptable estimates is proportional to the number of shots to the minus one half power. This agrees with previous results determined for ground-based measurements. The use of multi-element optical detectors for autonomous operation of coherent Doppler lidar was shown to be a very promising technique. Optimal detector geometries were determined by computer simulation of performance: for ground-based testing with a fixed calibration target and for space-based operation using the random surface returns. The effects of refractive turbulence on ground-based calibration of coherent Doppler lidar was determined by computer simulations and compared with theoretical predictions. New techniques were required to correctly predict performance for the focused beam geometry commonly used for verification of space-based operation. An improved velocity estimator was evaluated for space-based applications were signal shot measurements are used to produce vector wind measurements. This permits more accurate measurements when the signal level is not known a priori or not available from multiple shot measurements. The average Doppler lidar signal spectrum including the effects of velocity turbulence was derived and calculated. This permits new estimation algorithms for turbulence based on spectral estimates. In situ atmospheric measurements were conducted and analyzed using an instrumented kite-platform. This work helps provide the required in situ data for verification of Doppler lidar velocity statistics

Pulsed Lidar Performance/Technical Maturity Assessment

This report describes the results of investigations performed by the Georgia Tech Research Institute (GTRI) and the National Center for Atmospheric Research (NCAR) under a task entitled 'Pulsed Lidar Performance/Technical Maturity Assessment' funded by the Crew Systems Branch of the Airborne Systems Competency at the NASA Langley Research Center. The investigations included two tasks, 1.1(a) and 1.1(b). The Tasks discussed in this report are in support of the NASA Virtual Airspace Modeling and Simulation (VAMS) program and are designed to evaluate a pulsed lidar that will be required for active wake vortex avoidance solutions. The Coherent Technologies, Inc. (CTI) WindTracer LIDAR is an eye-safe, 2-micron, coherent, pulsed Doppler lidar with wake tracking capability. The actual performance of the WindTracer system was to be quantified. In addition, the sensor performance has been assessed and modeled, and the models have been included in simulation efforts. The WindTracer LIDAR was purchased by the Federal Aviation Administration (FAA) for use in near-term field data collection efforts as part of a joint NASA/FAA wake vortex research program. In the joint research program, a minimum common wake and weather data collection platform will be defined. NASA Langley will use the field data to support wake model development and operational concept investigation in support of the VAMS project, where the ultimate goal is to improve airport capacity and safety. Task 1.1(a), performed by NCAR in Boulder, Colorado to analyze the lidar system to determine its performance and capabilities based on results from simulated lidar data with analytic wake vortex models provided by NASA, which were then compared to the vendor's claims for the operational specifications of the lidar. Task 1.1(a) is described in Section 3, including the vortex model, lidar parameters and simulations, and results for both detection and tracking of wake vortices generated by Boeing 737s and 747s. Task 1.1(b) was performed by GTRI in Atlanta, Georgia and is described in Section 4. Task 1.1(b) includes a description of the St. Louis Airport (STL) field test being conducted by the Volpe National Transportation Systems Center, and it also addresses the development of a test plan to validate simulation studies conducted as part of Task 1.1(a). Section 4.2 provides a description of the Volpe STL field tests, and Section 4.3 describes 3 possible ways to validate the WindTracer lidar simulations performed in Task 1.1(a)

Potential Pitfalls Related to Space-Based Lidar Remote Sensing of the Earth with an Emphasis on Wind Measurement

A collection of issues is discussed that are potential pitfalls, if handled incorrectly, for earth-orbiting lidar remote sensing instruments. These issues arise due to the long target ranges, high lidar-to-target relative velocities, low signal levels, use of laser scanners, and other unique aspects of using lasers in earth orbit. Consequences of misunderstanding these topics range from minor inconvenience to improper calibration to total failure. We will focus on wind measurement using coherent detection Doppler lidar, but many of the potential pitfalls apply also to noncoherent lidar wind measurement, and to measurement of parameters other than wind. Each area will be identified as to its applicability

A Space-Based Point Design for Global Coherent Doppler Wind Lidar Profiling Matched to the Recent NASA/NOAA Draft Science Requirements

An end-to-end point design, including lidar, orbit, scanning, atmospheric, and data processing parameters, for space-based global profiling of atmospheric wind will be presented. The point design attempts to match the recent NASA/NOAA draft science requirements for wind measurement