Michael T. Dehring

Molecular optical air data system (MOADS) prototype II

The Molecular Optical Air Data System (MOADS) is a compact instrument designed to measure aircraft airspeed as well as the density of the air surrounding the aircraft. Other air data products provided by the instrument include density altitude, angle of attack (AOA), angle of side-slip (AOS), and Mach number. MOADS is a direct-detection LIDAR that measures these air data products from fringe images derived from a Fabry-Perot etalon. Determination of airspeed and direction is achieved through three telescopes that view a fixed air volume ahead of the aircraft turbulent flow field. This method reduces the measurement error as compared to traditional measurements made from within this turbulent region. As a direct detection LIDAR instrument, MOADS is capable of collecting both molecular and aerosol LIDAR returns, which allows operation in clear air as well as in aerosol-filled atmospheric regions. A second prototype was designed, built and tested. This MOADS prototype has been validated in a laboratory wind tunnel. Presented here are the airflow velocity measurement results from ground testing and vibration test measurements.

Performance and comparison of 532-nm and 355-nm groundwinds lidars

GroundWinds 2nd Generation (2nd Gen.) New Hampshire (NH) and GroundWinds Hawaii (HI) are direct detection Doppler LIDAR instruments that operate at 532nm and 355nm, respectively. These ground based incoherent LIDARs utilize backscatter from Rayleigh and Mie scattering to measure Doppler shifts in the atmosphere. The NH and HI instruments routinely make wind measurements from 0.5 to 15 kilometers and achieve sub-meter per second accuracies in the lower troposphere. This paper will provide a brief review of each instrument, and detail the instruments performance and achievements in wind measurement.

Direct detection Doppler wind lidar: ground-based operation to space

Observing System Simulation Experiments (OSSE) conducted by organizations and reseachers around the world indicate that accurate global wind profiles observed by a spaceborne Doppler wind lidar (DWL) have the potential to significantly improve weather forecasting, hurricane tracking, and global climate studies. Accurate wind profiles from airborne and spaceborne platforms will also have national defense and homeland security applications. In this paper, we will first give a brief review of the history and status of Doppler wind lidar development. Then we will present some results from GroundWinds, a ground-based direct detection Doppler wind lidar (D3WL) technology development and demonstration testbed sponsored by the National Oceanic and Atmospheric Administration (NOAA). We will describe our plan for observing winds from 30 km looking down as part of the BalloonWinds program. We will then use GroundWinds as references to discuss the feasibility and requirements for a spaceborne D3WL in the context of an initial point design. We will discuss Raytheons internal research and development (IRAD) plan with the objective of developing a prototype space-qualified laser as an engineering model and risk reduction laser for a spaceborne Doppler wind lidar.

GroundWinds New Hampshire and the LIDARFest 2000 campaign

The GroundWinds New Hampshire instrument is a direct detection Doppler LIDAR system that utilizes backscatter signal from both Rayleigh and Mie scattering to measure Doppler shifts in the atmosphere from the ground. This system is the first of two planned systems that will be used to validate the technology and improve the design for other potential implementations. As a means to that end, a validation campaign was conducted in September 2000 to compare the GroundWinds measurements to that from four other systems. These were the GLOW instrument, the NOAA Mini MOPA system, and a Microwave sounder from the National Weather Service. This paper will review the design of the GroundWinds instrument, as well as summarize some of the preliminary GroundWinds results from the field experiment.

High-altitude balloon-based wind LIDAR demonstration: from near space to space

A near space, high-altitude balloon mission (BalloonWinds) is planned to demonstrate the performance of a direct detection wind LIDAR instrument. The program is a NOAA-funded initiative to demonstrate direct detection, fringe imaging Doppler Wind LIDAR (Light Detection and Ranging) technology. BalloonWinds will involve a series of high altitude missions (~30km), each lasting 8-10 hours, scheduled for launch in 2006 to validate wind LIDAR technology from a near space platform. With the promise of responsive, affordable launch vehicles and near space platforms, there is an opportunity to demonstrate launch-on-demand capability of low-cost instruments that can provide regional or global wind data. It has been well established that direct measurement of winds will improve weather forecasting accuracy and hurricane landfall prediction and would provide benefits to government agencies and the public at large. An overview of the BalloonWinds instrument design and near space flight plan is presented in this paper as well as a concept design for a low-cost, 6-12 month space mission. Instrument performance simulations are used to demonstrate the feasibility and effectiveness of the low-cost approach for global wind sounding compared to traditional mission concepts.

Doppler Winds Lidar Technology Development and Demonstration

High resolution (both spatial and temporal) and accurate tropospheric wind profiling from spaceborne platforms has been one of the most wanted capability by both DOD and civilian user communities to support weather forecasting, national defense and homeland security applications. This capability is still only a dream after decades of research and development due to a variety of reasons. With the recent rapid advancement of diode-pumped solid-state lasers and advanced detectors, space-based Doppler winds lidar missions are much more feasible and promising than ever before. In this paper, we will first discuss the strong needs for space- based Doppler winds lidar. We will then present a brief overview of the GroundWinds and BalloonWinds projects in Section II and III, which are intended as direct detection Doppler wind lidar (D3WL) technology development and demonstration test-bed sponsored by the National Oceanic and Atmospheric Administration (NOAA). In Section IV, we will discuss the design and fabrication of a high energy laser transmitter prototype for space-based Doppler winds lidar supported by Raytheons internal research and development (IRAD) program. This laser transmitter prototype is intended to enhance the technology readiness level (TRL) and reduce the risk of future space-based Doppler winds lidar development.

GroundWinds balloon fringe-imaging Doppler lidar mission concept and instrument performance

Over the past few years, the GroundWinds program has produced two operational, ground based, multi-order fringe imaging direct detection Doppler wind LIDARs. The two existing instruments are located in Bartlett, NH and Mauna Loa, HI and operate at a wavelength of 532 nm and 355 nm, respectively. Both systems employ Fabry-Perot etalons as the wavelength resolving element and are capable of detecting Doppler shifts in both Aerosol and Molecular backscatter from 0.25 km to 18 km. Patented technologies demonstrated and developed through this program, such as Photon-Recycling (U.S. patent #6,163,380) and the Circle To Line Optic (U.S. Patent #4,893,003), will be incorporated into the next generation interferometer design and flown on a high altitude (30km) balloon. The opportunity to view the entire troposphere from a downward looking high altitude platform will serve as an empirical reference point for scaling to space. This paper will discuss the BalloonWinds mission concept and top-level specifications of the instrument subsystems. Additionally, this paper will report on the testing and progress of the instrument build and present performance projections based on the as built system.

Low-cost mission architecture for global tropospheric wind measurements

Tropospheric wind measurements are of great meteorological and tactical value, but are presently not available on a global basis. The primary obstacle to a space-based Doppler wind LIDAR mission capable of obtaining these measurements has been the cost and risk associated with flying high power lasers and large telescopes in low-earth orbit. This paper presents an alternative approach that would result in a low-cost, low-risk responsive approach to deploying a global tropospheric wind measurement system.

Instrument specifications and performance prediction for 2005 high altitude (30 km) balloon demonstration of GroundWinds fringe imaging Doppler lidar

The GroundWinds direct detection Doppler wind LIDARs located in NH and HI are operational, ground based, multi-order fringe imaging systems capable of detecting Doppler shifts in both Aerosol and Molecular backscatter from 0.25 km to 18 km. The technology developed through these GroundWinds programs will be incorporated and flown on a high altitude (30km) balloon in 2005. The demonstration of GroundWinds Fabry-Perot based incoherent LIDAR technology from a high altitude, downward looking platform to measure winds throughout the entire troposphere and boundary layer will be a significant milestone toward the validation of this technology. Key questions will be answered about the phenomenology of direct detection LIDAR, especially its effectiveness in the optically thick boundary layer. The extensive characterization of the 532nm GroundWinds NH and 355nm GroundWinds HI LIDARs serve as excellent reference points from which performance estimates and technology requirements can be determined to ensure a successful balloon mission. This paper will describe the baseline BalloonWinds instrument specifications; including etalon specifications, system component transmissions, transmit/receive specifications, required laser power, and detector characteristics. This paper will also present performance estimates based on model simulations that employ the baseline system specifications.

Spaceflight-qualified tunable cryogenic infrared Fabry-Perot etalon

Though a Phase I and II NASA SBIR initiative Michigan Aerospace Corp. has demonstrated a spaceflight qualified, tunable infrared Fabry Perot etalon. The design included use of single crystal ferroelectric actuators for tuning the etalon gap. The operational wavelength range of this etalon was designed for 10-14μm and utilized Zinc-Selenide for the plate substrate with a plate reflectivity of 0.8. At a temperature of 193 K and 0.4 milli-torr, the etalon achieved a finesse of 11.8, a bandpass of 1.23 nm and had a free-spectral range of 14.2 nm at the test wavelength of 10.013 μm. At this temperature, the etalon was tunable over ~8.5 free-spectral ranges, or 45 μm in gap spacing. Testing concluded that the etalon will retain 57% of its total dynamic range at a temperature of 75 K compared to its dynamic range at room temperature. The design was qualified for a Delta-II launch vehicle vibration specification.