Wayman Baker (NOAA/NWS) opened the meeting, welcomed the participants to Oxnard, and reviewed the action items from the Summer meeting in Boulder.
Steve Mango (Integrated Program Office - IPO) discussed the progress being made on NPOESS (the 5 payload instruments have been down-selected, and the payload integrator is to be down-selected soon)and the continuing effort by the IPO to find a way to address the unfulfilled wind data requirement. He noted that the fourth METOP instrument (in the 2009 to 2013 time frame) will be fully converged with NPOESS. This may leave room on NPOESS for a new sensor. He indicated that the IPO is interested in integrating a Doppler Wind Lidar (DWL) developed by others on such an "NPOESS Lite" platform. Overall, the IPO will support a GTWS data buy as appropriate, as well as continuing to support activities such as the Lidar Working Group. Steve was asked was asked whether the IPO will provide raw data or data products; both will be available. As to why there was not a DWL on the NPOESS Airborne Sensor Testbed (NAST), Steve replied that there can be one, but someone (outside of the IPO) must take the initiative to develop it.
Bob Menzies spoke on behalf of Carol Raymond (NASA New Millennium Program - NMP). The Earth Science Program of NMP is moving forward with the E01 Land Imager mission, which is coordinated with Landsat and features the validation of nine breakthrough technologies. The E03 mission will be the Geostationary Interferometric Fourier-Transform Spectrometer (GIFTS), which will provide imaging, sounding, and chemistry capability over the Indian Ocean. The question of how NOAA (and others) would validate water vapor winds from GIFTS was raised; the answer is via assimilation at NCEP and the NASA, NOAA, NSF Joint Center for Satellite Data Assimilation (JCSDA). In the future, NMP will be looking to do more, less expensive missions focused on proving technology components. Workshops covering a number of technology areas are planned: (1) large deployable optics; (2) formation flying; (3) ultra-high data rates; and high-performance spectrometry.
The first of these workshops was held in January 2001 in Arlington, VA. In addition to optics for IR, visible, and UV systems, DIAL technology was covered. Several in the audience asked when summaries of these workshops would be made available. Bob indicated that they will be posted on the NMP Website after final approval and presentation to Ghassem Asrar.
Gert-Jan Marseille (KNMI) discussed on-going work using the LITE data set to gain insight for the design of the European DWL Atmospheric Dynamics Mission (ADM). The ADM demonstration mission, scheduled for 2006, will feature a single fixed line-of-sight (LOS) and is slated to provide 2 - 3 m/s horizontal LOS accuracy at horizontal and vertical resolutions of 50 km and 1 km , respectively. A double-edge filter Doppler detection is used and an accumulation charge-coupled device (CCD) detection chain. The 355 nm wavelength will be exploited to measure molecular backscatter and density, aerosol backscatter, and cloud optical depth. Simulations based on the LITE data set indicate that a 1.1 m telescope and 120 mJ pulse will be required. OSSEs using the same nature run as NCEP show that after proper quality control of simulated winds, the forecast is improved by about _ day after 4-5 days in the N. Hemisphere. More work will be done to review the assumption of uniform aerosol backscatter, cloud distributions and dynamics, and zero-wind biases, in order to make more realistic OSSEs.
Stephan Rahm (DLR) discussed the DLR's plans for simulation and validations studies to support ADM. The simulations are to consider solar elevation effects, the earth's gravity field orbital perturbations, vertical velocity, and beam degradation resulting turbulence. For validation, the use of a Falcon-20 aircraft is being proposed. A 2 micron system may be used for quality control comparisons. Comparisons of DWL observations with rawinsondes, wind profilers, and the German Weather Service model are also foreseen. In response to a question, Stephan said that for a 2003 ADM launch, a space-qualified laser transmitter is needed by 2003. Because of the high-risk nature of ADM, an airborne mission should be used to reduce risk and allow for technology improvement.
T. Itabe (NASDA) provided a status report on the DWL for the Japan Experiment Module (JEM) on the International Space Station.
The JEM DWL is intended as a demonstration instrument also. It is to use 2 micron, coherent Doppler detection and feature two fixed telescopes directed fore and aft, with 0.4 m optics. Major issues to be worked include heat rejection, optimization of heterodyne efficiency, and the development of a 2 J, 10 Hz laser transmitter, in time for deployment in 2007. An airborne system is on the verge of preliminary flights in February, 2001, uing CTI 2 micron laser technology.
Bob Brown (University of Washington) discussed the role of DWLs in a scatterometer environment, beginning with the history of the scatterometers and the impact of the data they have provided. Bob reminded the audience how much of the impact was not anticipated or at least defined before the observations were available. Bob stated that satellite wind data are needed for the planetary boundary layer to complement the scatterometer near-surface data. Bob was asked whether scatterometer data are useful beyond speeds of 25 m/s. He replied that scatterometer retrieval tables have undergone intensive re-calibration, and that the model functions now extend to speeds as high as 65 m/s.
Dave Emmitt (Simpson Weather Associates - SWA) discussed the status of the NCEP bracketing Observing System Simulation Experiments (OSSEs) for several notional DWL concepts. Dave reported that preliminary results of the OSSEs will be prevented at the GTWS workshop in Greenbelt. He emphasized that a great deal of work has been done in recent months. The ECMWF nature run has been vetted and clouds adjusted, simulations of observations for current sensor systems are complete, and the "calibration" OSSE is nearly complete. Initial DWL assimilation experiments have been run, and are being checked for presentation at the end of the month. Dave also reviewed the bracketing OSSE strategy and how it is designed to provide an impact trade space for future, more technology-specific instrument concepts in the future.
John McGinley (NOAA Forecast Systems Laboratory) reported on the Regional DWL OSSEs, which are being coordinated with the global (NCEP) OSSE. The NCAR-Penn State MM5 was being used to provide the regional nature run, a non-trivial exercise requiring two weeks to get a 10-day run. John is encouraged by the results of initializing the boundaries of the model using the nature run versus using the actual observations. FSL is ready to start observation extraction and then assimilation, and hopes to finish the work by October. They still need to do statistics to make certain that using MM5 (instead of the Colorado State RAMS Model) is climatologically acceptable. Features do appear reasonable.
Barry Rye (NOAA/ETL) followed with a presentation on ETL's efforts to do DWL instrument modeling for the regional OSSEs being performed by FSL. ETL is providing satellite tracks to FSL. Taking the FSL nature run output, and ETL is developing a scattering and transmission model. Barry described coordination with several other studies designed to support the regional OSSEs, including cloud studies at Colorado State, University, DWL simulated observations from SWA, and Gary Spiers' efforts to model biases. He described ETL's standard instrument model, which is very reliable and has been adapted to run under Windows.
Ron Ticker (NASA HQ) spoke about NASA activities related to a Global Tropospheric Wind Sounder (GTWS) mission. He stated that there is great interest in winds at NASA in an number of Earth Science disciplines. He reviewed the results of the joint NASA/NOAA RFI on winds in FY99 and stated that there is private sector interest in a GTWS as a commercial data buy, and that it may be viable, but concern over the ability to meet the data requirements indicates that further government-industry dialog is needed. Ron described recent agency activities, including the establishment of a GTWS Executive Steering Committee (GEST) with representation from NOAA and NASA, the planning of a NASA/NOAA Science Definition Team for GTWS, and the upcoming GTWS Workshop in Greenbelt. In the event that a commercial data buy is attempted, the government must be prepared to be a smart buyer, develop a technology-neutral specification, and explore means to share cost and risk with other buyers. Ron was asked whether other buyers are essential to a GTWS; he replied that it depended on whether the cost to NASA and NOAA as a sole buyer was low enough. A number of questions followed, many concerned with whether or not NOAA and NASA and DoD wind requirements are in fact compatible. Ron indicated that the Workshop and the SDT are intended to address these issues.
John Pereira (NOAA/NESDIS) reviewed NOAA's activities to investigate a GTWS, including on-going support for the University of New Hampshire's "GroundWinds" surface-based DWL development, and the partnership established with NASA, as described by Ron Ticker. The GroundWinds activities included a three-way DWL intercomparison campaign in New Hampshire in September 2000, some preliminary results of which were to be discussed at the Oxnard workshop. UNH and its partners are continuing with the development of a new surface-based DWL to be deployed at the NOAA site on Mauna Loa in Hawaii, and are preparing a design concept for a mobile surface DWL as well. Questions were directed at the concept of the space-based GTWS. For example would an RFP recognize a two-step process: (1) a prototype followed by (2) an operational instrument, or not the answer is that ANY GTWS must be useful, doable, and affordable. An extended discussion of technology, proposal evaluation/source selection, and payment schemes followed. It was pointed out that these matters could not be resolved in the context of the present meeting.
Bob Atlas (NASA/GSFC) announced the joint NASA/NOAA GTWS Science Requirements Workshop in Greenbelt, February 26- 28. Goals of the workshop are to lay the groundwork for quantifying NASA's science requirements for wind data, validating NOAA's operational requirements, reconciling the two for a single specification, and laying the framework for a GTWS data validation plan. The agenda, including invited plenary session presentations on climate, tropical and extra-tropical meteorology, chemistry, OSSEs, and validation strategy was reviewed. It was noted that the plenary session would be open to industry, academia, and government employees on a first-come, first-served basis, but that the "break-out" sessions would be confined to invitees only. A question arose as to whether new OSSEs could address science (atmospheric processes) as opposed to weather prediction alone. Bob indicated that new OSSEs are in fact being designed for that purpose.
Sammy Henderson (Coherent Technologies Inc. - CTI) discussed recent progress on eye-safe lidar development at CTI. Several systems take advantage of 2 micron wavelength, with applications varying from a wind/aerosol, high PRF (500 Hz) instrument used for airport wind scanning near Aspen, CO, to an airborne system developed with ONR and scheduled for May/June 2001 flight testing on a Twin Otter aircraft. In addition, CTI has provided to input for the sensor risk reduction on the Japanese JEM ISS. An agile PRF transmitter (at 1.5 microns) is being developed as a hard target detector for the USAF. In addition to Doppler instruments, CTI has a direct detection DIAL for C02 at two microns. In short, they have a number of systems demonstrated in the field and which are commercially available. They contend that they are ready to apply their expertise to future space missions. Sammy was asked why high PRF systems were used; he replied that doing so kept cost down, effectively trading sensitivity on a single shot for more easily achievable shot energy. Asked how soon a 2 J, 2-micron laser could be developed, Sammy estimated within two years - given a sufficient infusion of money.
Adam O'Shay (FSU) presented a paper on Global Wind Forecasts base with improved wind analysis via the FSU "Superensemble". The Superensemble (SE) is based on the assemblage of multiple-model training sets collected over an extended period. The approach involves analyzing the forecasting performance of all of the models over a variety of conditions and assigning weights accordingly. In this way, the SE gets the best out of all of the models, and outperforms most of them. The success of the SE resides in part on having the best characterization of the initial state, with the implication that having DWL observations to further improve the initial state could have substantial impact on forecasting skill. It was pointed out that the benefits of SE were shown at the 200 mb level. However, Adam confirmed that similar gain has been achieved at 850 mb.
U. Singh (NASA/LaRC) discussed the development solid-state 2-micron laser technology at LaRC. The efforts are intended to be multiply applicable and to produce in three years a laser suitable for Doppler and DIAL (CO2) detection. Conductive cooling is a big challenge, since 102 W of heat must be removed from a small, hard-to-access contact area. To minimize the heat removal challenge for DIAL, Upendra has demonstrated a Q-switched laser that generates 2 pulse-pair (two frequencies) from a single pumping action. Upendra was asked whether such double-pulses could be beneficial for Doppler wind sensing applications. He responded yes, if pulse separation of 200 microseconds or more can be achieved. It was also pointed out that a heterodyne detector for DIAL is not optimal due to speckle. Upendra indicated that he has a task to develop a 2-micron direct defection lidar for the DIAL application.
Michael Kavaya (NASA/LaRC) reported on a software package for displaying satellite sampling over the Earth for virtually any orbit and scanning configuration; the tool is suitable for any sensor, active or passive, is geometrically correct, gives two and three dimensional views, and produces time-evolving coverage movies with relative ease. Michael played a sample video showing the coverage that might be achieved by a DWL in 833 km and 400 km orbits. He maintains that in addition to allowing clearer visualization of potential missions, the tool could be used for planning and executing cal-val activities involving surface-based sensors. Michael was asked whether clouds could be included. He replied that at this level, he envisions the tool as an aid in communicating with decision makers, not as a replacement for all science. Along those lines, it was suggested that a more complete narrative script might be needed to lead managers through the video.
Geary Schwemmer (NSA/GSFC) and Tom Wilkerson (Utah State University) unveiled a new, non-Doppler scanning lidar technique for making wind profiles. Geary provided the hardware in the form of his HARLIE lidar, and Tom developed an algorithm for wind retrieval that exploits simple aerosol backscatter as a tracer and tracks its motion on successive 45-degree conical scans. The system is simple, low energy, and effective at low altitudes. In tests it has shown agreement with rawinsonde winds. It also can use clouds (as high as 14 km so far) as a target and produce winds that agree with the GOES cloud track winds. There is a trade-off between how fast the system is scanned and how long the backscatter signal must be integrated. Tom and Geary foresee a role for this type of system as a cal-val platform for future space-based DWL.
Dave Emmitt (SWA) discussed work on an IPO-funded calibration-validation planning exercise for space-based DWL. Although Dave and the IPO are interested in pre-selection, pre-launch validation activities, the thrust of this work is towards the post-launch phase. Dave envisions three major components: (1) instrument performance models; (2) OSSEs and Observing System Experiments (OSEs) with real data; and (3) intercomparisons with surface and airborne DWL and with other wind observations as opportunities permit. Dave believes airborne DWL will give the most relevant comparisons, but that they will be hard to achieve and beset by sampling issues. While "comparisons of opportunity." including rawinsondes, ACARS, and wind profiler data will be plentiful, they may be less directly comparable.
Dave Emmitt continued by describing specific plans for an IPO-supported Airborne DWL cal-val plan. It is intended that an airborne DWL will allow signal processing issues critical to space-based DWL product generation and utilization to be investigated quantitatively. Although looking for deployment on the (NAST) in the future, initial mission plans call for installation on a Twin Otter aircraft. A field experiment is planned for May 21 - June 8, 2001, based from Monterrey, CA.; Focus issues will be surface returns from oceans, rivers, and their discrimination from near-surface dust and aerosol returns, effects of rolls in the PBL on representativeness. Flights are to cover coastal transects, and vegetation returns will also be sought.
Michael Kavaya reported on work to apply coherent Doppler lidar to measure river surface velocity as input to river discharge estimates by the USGS. The work complements NASA's interest in hydrology, and may be applicable to calibrating ocean surface returns from a space-based DWL. Michael noted that in 30 years of Doppler lidar, very little data have been accumulated pointing the lidar at the water surface. Therefore, a small 2 micron lidar was taken to the banks of the Tennessee River and operated. Initial results were ambiguous, however. The long minimum range constraint resulted in too shallow a depression below the horizontal. Even after efforts to decrease the minimum range, increase depression, and suppress the pulse tail, results to date remain uncertain. Michael is hoping that subsequent experiments will define the "knee" of the backscatter versus angle curve.
Dave Emmitt continued with a status report on the IPO-funded Hybrid DWL Study. The results of OSSEs and OSEs and the capabilities of and impact from current wind observations (scatterometers, rawinsondes, ACARS, GOES, etc.) is used as a starting point for defining the role to be filled by a DWL. However, the study also considers, in a rudimentary way at least, whether part of that role can be filled by emerging platforms, such as balloon constellations equipped with dropsondes, unmanned aircraft, and the GIFTS. A baseline hybrid with direct and heterodyne capabilities was described, and targeted capabilities (required above that anticipated from other systems) for the hybrid DWL was outlined.
Mike Hardesty (NOAA/ETL) discussed ETL's development plans for an airborne 2-micron DWL designed for atmospheric science research. The lidar is to be based on a high-resolution surface instrument, capable, for example, of observing waves in the stable lower atmosphere. As an evolutionary step, the ground-based lidar is now set for installation on a ship. For this purpose, three-dimensional motion compensation using differential GPS is being applied, and (more flexible) frequency locking loops are being used.
Jim Ryan (University of New Hampshire - UNH) opened the session on UNH's GroundWinds Intercomparison Campaign with an overview talk. Jim emphasized that the campaign from September 19 - 29 at North Conway, NH, was foremost intended as a maiden voyage for the DWL built for UNH by Michigan Aerospace Corporation (MAC) and intended first to demonstrate the wind-sensing capability of the instrument; science was a secondary consideration, to be pursued when opportunity arose and without interfering with the primary goal. Jim described the variety of hardware brought to the scene for the campaign, including NOAA/ET's mini-MOPA DWL to measure winds in the lower atmosphere, NASA/GSFC's GLOW DWL to provide coverage in the upper troposphere, a Doppler radar wind profiler, and locally launched GPS radiosondes, as well automated surface meteorological instrumentation. The planning and execution of the campaign required participation not only by UNH and MAC but from the Mount Washington Observatory, NOAA/ETL, NASA Goddard, and NOAA/NESDIS, which had funded the GroundWinds development. Jim noted the hard work and cooperation by all parties to overcome a number of start-up problems and collect a substantial set of observations during calm and active conditions, with and without clouds, during day and night.
Paul Hays (MAC) followed with a description of the design of the GroundWinds DWL and its performance during the September intercomparison campaign. GroundWinds-New Hampshire (GWNH) is a two channel, Fabry-Perot instrument building on the heritage of the High Resolution Doppler Imager (HRDI) on UARS. However, GWNH was designed to take advantage of a patented off-axis coupled etalon interferometer and photon recycling to increase system efficiency by a factor of about 10 over what would traditionally be expected from a fringe imaging direct detection DWL of comparable power-aperture product. In addition, GroundWinds makes use of the Circle-to-Line Imaging Optic (CLIO) to collapse circular fringes onto a linear pattern suitable for collection/integration on a streaking CCD chip. Paul showed a number of favorable comparisons of GWNH horizontal projected LOS profiles and radiosonde data, noting that locking the molecular channel zero to that of the aerosol appears to cause a ripple to propagate into the molecular data. Finally, Paul mentioned that GWNH is now being operated remotely from Ann Arbor, and that its successor, GW-Hawaii, will feature a more compact optical train and will operate at 355 nm instead of the 532 nm wavelength used for GWNH.
Numerous questions followed. Paul indicated that MAC fabricated its own interferometers, that there are no current plans for an aircraft mission inasmuch as there is no funding for one, and that the time resolution of GWNH is about 1 minute. Asked whether the technique of GW is compatible with any size of collection mirror, he replied yes, in principle, al long as the area*angle product of the system is conserved.
Bruce Gentry (NASA/GSFC) discussed how the Goddard Lidar Observatory for Winds (GLOW), a van-based direct detection DWL operating at 355 nm was prepared and brought to NH for the GroundWinds campaign. He reviewed GLOW's capability as a modular technology testbed, its heritage with ZEPHYR, and the fundamentals of using the double edge filter for Doppler determination. For the GW campaign, Bruce was able to locate a solar backscatter rejection filter, which though not optimally sized for GLOW, enabled daytime wind measurements to be made. Bruce displayed preliminary LOS winds from GLOW for September 25, 2000. Bumps due to cirrus can be detected in the returns. Bruce was asked whether photon efficiency for GLOW has been calculated. He replied that he is investigating this. Another question concerned whether photon recycling, such as that used for GWNH, could be applied to double-edge filter instruments. Bruce answered that it could be, with an increase in SNR by the square root of 2.
Mike Hardesty (NOAA/ETL) reviewed the design of ETL's 10 micron heterodyne detection mini-MOPA DWL and its role in the GWNH campaign. The mini-MOPA is a low-power, high PRF instrument, very precise but limited in sensitivity. It provided a direct basis for intercomparison with the GWNH aerosol channel at lower altitudes during the campaign. Mike noted that once all instruments were up and operational, winds were measured under almost every condition except haze. Both GWNH and the mini-MOPA detected clouds in the aerosol channels, and winds were found to be eminently measurable! Mike noticed offsets between the GW and MOPA winds, and investigated the spectra of the velocity time series for GWNH. Finding similar spectral behavior in the high and low signal cases, he is inclined to conclude that variation is in the instrument. Mike was asked about the effects of the complex terrain and turbulence on the intercomparison. It was acknowledged that these were factors and present a challenge to separating atmospheric variability from instrument uncertainty. He pointed out that while this could be better addressed by observations over flat terrain, the campaign at North Conway still offers one of the most direct and extensive DWL intercomparison data sets to date, from which much can be learned as the data are re-processed and studied in detail.
Jim Yoe (NOAA/NESDIS) and Rama Mundakkara (CIRA) presented some preliminary intercomparisons from the campaign. Because Mike Hardesty had already considered the lower atmosphere, aerosol-based winds, and because the radar wind profiler did not provide extensive height coverage, they focused on the performance of GWNH, GLOW and rawinsondes from ~6 km (below which GLOW was gated off to avoid saturation) - ~12 km (above which the GWNH signal was often too weak to be useful). Since the two DWLs were directed at the same azimuth and elevation, comparisons were made of a single horizontal component at 1 km height intervals, averaging 10 one-minute LOS velocity estimates. The rawinsonde wind observations were projected onto the same horizontal component as a function of height. General agreement was found between GLOW and GWNH for the 10-minute averaged winds, and with the rawinsondes as well, allowing for balloon drift and time of ascent. It was noted that there is considerable variability in the 1-minute wind estimates from which the averaged values were derived. An extended discussion followed on this issue. Jim pointed out that the results are preliminary, and that the one-minute, 1 km LOS data are subject to re-processing, and that they have not been considered in terms of signal power, nor has a complete statistical intercomparison been undertaken yet. He emphasized that the preliminary indications are that the campaign was a significant success in terms of generating such an extensive and varied set of observations.
Tom Wilkerson (USU) introduced another non-Doppler wind vector observation technique, "HOLO" which would use HARLIE (or a similar scanning lidar) and a video camera to track clouds. Winds at ranges of 0.5 - 15 km may be extracted, with precision of the order of 0.5 - 2 m/s, and an anticipated dynamic range of up to 40 m/s horizontal wind speed.
Kerry Nock (Global Aerospace Corporation) made a novel presentation on an alternative method to obtaining global wind observations by using a global constellation of stratospheric balloons. The "StratoSat" concept would use long-lived, steerable balloons to provide global coverage. Wind observations could be had either by dropsondes or by installing remote sensors such as DWL on the balloons. Kerry noted that StratoSat has been supported by NASA Advanced Concepts program, and that in February, 2001 an ultra-long lived (100 days) balloon capable of carrying a 1500 kg payload is being launched from Alice Springs, Australia. This could provide significant heritage for StratoSat. Kerry expressed the opinion that StratoSat could function as a cal-val platform for space-based DWL, or could compete to be the primary global wind sensing capability. He also envisions StratoSat contributing to ozone and climate monitoring and hazard detection. A lively discussion followed, during which data up/down linking, flight termination and payload recovery, and political considerations (such as flying balloons over various sovereign nations) were considered.
The minutes were recorded by Jim Yoe of the NOAA/NESDIS Office of Research and Applications.