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Kavaya, Michael J.

Publications and source records attributed to Kavaya, Michael J..

90 records · Page 5
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NASA NTRS1999

Coherent Doppler Wind Lidar Technology for Space Based Wind Measurements Including SPARCLE

It has been over 30 years since coherent lidar systems first measured wind velocity, and over 20 years since the "ultimate application" of measuring Earth's winds from space was conceived. Coherent or heterodyne optical detection involves the combination (or mixing) of the returned optical field with a local oscillator (LO) laser's optical field on the optical detector. This detection technique yields the benefits of dramatically improved signal-to-noise ratios; insensitivity to detector noise, background light and multiply scattered light; reduction of the returned signal's dynamic range; and preservation of the optical signal spectrum for electronic and computer processing. (Note that lidar systems are also referred to as optical radar, laser radar, and LADAR systems.) Many individuals, agencies, and countries have pursued the goal of space-based wind measurements through technology development, experiments, field campaigns and studies.

Kavaya, Michael J.↗
NASA NTRS1999

Measuring Tropospheric Winds from Space Using a Coherent Doppler Lidar Technique

The global measurement of tropospheric wind profiles has been cited by the operational meteorological community as the most important missing element in the present and planned observing system. The most practical and economical method for obtaining this measurement is from low earth orbit, utilizing a Doppler lidar (laser radar) technique. Specifically, this paper will describe the coherent Doppler wind lidar (CDWL) technique, the design and progress of a current space flight project to fly such a system on the Space Shuttle, and plans for future flights of similar instruments. The SPARCLE (SPAce Readiness Coherent Lidar Experiment) is a Shuttle-based instrument whose flight is targeted for March, 2001. The objectives of SPARCLE are three-fold: Confirm that the coherent Doppler lidar technique can measure line-of-sight winds to within 1-2 m/s accuracy; Collect data to permit validation and improvement of instrument performance models to enable better design of future missions; and Collect wind and backscatter data for future mission optimization and for atmospheric studies. These objectives reflect the nature of the experiment and its program sponsor, NASA's New Millennium Program. The experiment is a technology validation mission whose primary purpose is to provide a space flight validation of this particular technology. (It should be noted that the CDWL technique has successfully been implemented from ground-based and aircraft-based platforms for a number of years.) Since the conduct of the SPARCLE mission is tied to future decisions on the choice of technology for free-flying, operational missions, the collection of data is intrinsically tied to the validation and improvement of instrument performance models that predict the sensitivity and accuracy of any particular present or future instrument system. The challenges unique to space flight for an instrument such as SPARCLE and follow-ons include: Obtaining the required lidar sensitivity from the long distance of orbit height to the lower atmosphere; Maintaining optical alignments after launch to orbit, and during operations in "microgravity"; Obtaining pointing knowledge of sufficient accuracy to remove the speed of the spacecraft (and the rotating Earth) from the measurements; Providing sufficient power (not a problem on the Shuttle) and cooling to the instrument. The paper will describe the status and challenges of the SPARCLE project, the value of obtaining wind data from orbit, and will present a roadmap to future instruments for scientific research and operational meteorology.

Miller, Timothy L.↗
NASA NTRS1999

Prospects of Measuring Atmospheric Winds with a 2-Micron Coherent Doppler Lidar from the International Space Station

The measurement of global winds in the troposphere is often cited as the most important single missing element of our present weather and climate observing system. The most promising technique for filling this gap is with space-based coherent Doppler lidar. A Space Shuttle mission (SPAce Readiness Coherent Lidar Experiment, SPARCLE) is being developed at NASA/MSFC (Huntsville, AL) that will provide the first space-based test of the technique, validating the ability to maintain the severe requirements on optical alignments during launch and space operations, and removing the Doppler shift of the spacecraft velocity and Earth's rotation. Continued development will include a scientific research mission in the mid-2000's, and an operational instrument around 2010. It is anticipated that the International Space Station will be a good candidate as a platform for the scientific research mission (as an attached payload). The need for and value of wind observations, the status and objectives of the SPARCLE mission, and detailed plans for the follow-on missions, including technology development, will be discussed.

Miller, Timothy L.↗
NASA NTRS1998

Tropospheric Wind Measurements From Space: The SPARCLE Mission And Beyond

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.

Kavaya, Michael J.↗
NASA NTRS1998

Tropospheric Wind Measurements from Space: The SPARCLE Mission and Beyond

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.

Kavaya, Michael J.↗
NASA NTRS1998

The SPAce Readiness Coherent Lidar Experiment (SPARCLE) Space Shuttle Mission

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.

Kavaya, Michael J.↗
NASA NTRS1996

Direct Global Measurements of Tropspheric Winds Employing a Simplified Coherent Laser Radar using Fully Scalable Technology and Technique

Innovative designs of a space-based laser remote sensing 'wind machine' are presented. These designs seek compatibility with the traditionally conflicting constraints of high scientific value and low total mission cost. Mission cost is reduced by moving to smaller, lighter, more off-the-shelf instrument designs which can be accommodated on smaller launch vehicles.

Kavaya, Michael J.↗
NASA NTRS1993

Coherent launch-site atmospheric wind sounder - Theory and experiment

The coherent launch-site atmospheric wind sounder (CLAWS) is a lidar atmospheric wind sensor designed to measure the winds above space launch facilities to an altitude of 20 km. In our development studies, lidar sensor requirements are defined, a system to meet those requirements is defined and built, and the concept is evaluated, with recommendations for the most feasible and cost-effective lidar system for use as an input to a guidance and control system for missile or spacecraft launches. The ability of CLAWS to meet NASA goals for increased safety and launch/mission flexibility is evaluated in a field test program at Kennedy Space Center (KSC) in which we investigate maximum detection range, refractive turbulence, and aerosol backscattering efficiency. The Nd:YAG coherent lidar operating at 1.06 micron with 1-J energy per pulse is able to make real-time measurements of the 3D wind field at KSC to an altitude of 26 km, in good agreement with our performance simulations. It also shows the height and thickness of the volcanic layer caused by the volcanic eruption of Mount Pinatubo in the Philippines.

Hawley, James G.↗
NASA NTRS1991

Coherent laser radar performance for general atmospheric refractive turbulence

A general theory for the signal-to-noise ratio (SNR) of a coherent detection laser radar is developed using the path-integral formulation (Fresnel approximation), which is valid for any typical path-integrated atmospheric refractive turbulence. The principal effects of refractive turbulence are discussed, and analytical expressions are presented for the case of untruncated Gaussians for the transmitted field, local oscillator field, and transmitter/receiver optics. The physical mechanisms that reduce heterodyne efficiency are identified.

Frehlich, Rod G.↗
NASA NTRS1991

Continuous wave coherent laser radar - Calculation of measurement location and volume

The SNR equation of a CW, monostatic, coherent laser radar system is examined for the case of a distributed aerosol target. General analytic equations are derived which explicitly describe the contribution to total SNR from each range interval along the optic axis, the range resolution of the measurement, and the atmospheric volume contributing to the measurement. Plots are presented showing the location in range and the volume of the laser radar measurement.

Kavaya, Michael J.↗
NASA NTRS1991

Coherent lidar airborne windshear sensor - Performance evaluation

As part of the NASA/FAA National Integrated Windshear Program, a measurable windshear hazard index has been defined that can be remotely sensed from an aircraft, to give the pilot information about the wind conditions along the flight path. A technology analysis and end-to-end performance simulation measuring signal-to-noise ratios and resulting wind velocity errors for competing coherent laser radar (lidar) systems have been carried out. The results show that a Ho:YAG lidar at a wavelength of 2.1 microns and a CO2 lidar at 10.6 microns can give the pilot information about the line-of-sight component of a windshear threat from his present position to a region extending 2-4 km in front of the aircraft. This constitutes a warning time of 20-40 s, even in conditions of moderately heavy precipitation.

Targ, Russell↗
NASA NTRS1991

Eye-safe coherent laser radar system at 2.1 microns using Tm,Ho:YAG lasers

An eye-safe pulsed coherent laser radar has been developed by using single-frequency Tm,Ho:YAG lasers and heterodyne detection. Returns from a mountainside located 145 km from the laser radar system and the measurement of wind velocity to ranges exceeding 20 km have been demonstrated with transmitted pulse energies of 22 mJ.

Henderson, Sammy W.↗
NASA NTRS1991

Theory of CW lidar aerosol backscatter measurements and development of a 2.1 microns solid-state pulsed laser radar for aerosol backscatter profiling

The performance and calibration of a focused, continuous wave, coherent detection CO2 lidar operated for the measurement of atmospheric backscatter coefficient, B(m), was examined. This instrument functions by transmitting infrared (10 micron) light into the atmosphere and collecting the light which is scattered in the rearward direction. Two distinct modes of operation were considered. In volume mode, the scattered light energy from many aerosols is detected simultaneously, whereas in the single particle mode (SPM), the scattered light energy from a single aerosol is detected. The analysis considered possible sources of error for each of these two cases, and also considered the conditions where each technique would have superior performance. The analysis showed that, within reasonable assumptions, the value of B(m) could be accurately measured by either the VM or the SPM method. The understanding of the theory developed during the analysis was also applied to a pulsed CO2 lidar. Preliminary results of field testing of a solid state 2 micron lidar using a CW oscillator is included.

Kavaya, Michael J.↗
NASA NTRS1990

Pulsed coherent solid-state 1.06-micron and 2.1-micron laser radar systems for remote velocity measurement

A low average power, pulsed, solid-state, 1.06-micron coherent laser radar (CLR) for range and velocity measurements of atmospheric and hard targets has been developed. The system has been operating at a field test site near Boulder, CO since September, 1988. Measurements have been taken on moving targets such as atmospheric aerosol particles, belt sanders, spinning disks, and various stationary targets. The field measurements have shown that this system exhibits excellent velocity measurement performance. A fast-tuning CW Nd:YAG oscillator has also been developed which has a frequency tuning range of greater than 30 GHz (which spans a target radial velocity range of over 16 km/s) and a tuning speed greater than 30 GHz/ms.

Henderson, Sammy W.↗
NASA NTRS1988

Optical properties of Southern Hemisphere aerosols: Report of the joint CSIRO/NASA study

This study was made in support of the LAWS and GLOBE programs, which aim to design a suitable Doppler lidar system for measuring global winds from a satellite. Observations were taken from 5 deg S to 45 deg S along and off the E and SE Australian coast, thus obtaining representative samples over a large latitude range. Observations were made between 0 and 6 km altitude of aerosol physical and chemical properties in situ from the CSIRO F-27 aircraft; of lidar backscatter coefficients at 10.6 micron wavelength from the F-27 aircraft; of lidar backscatter profiles at 0.694 microns at Sale, SE Australia; and of lidar backscatter profiles at 0.532 microns at Cowley Beach, NE Australia. Both calculations and observations in the free troposphere gave a backscatter coefficient of 1-2 x 10 to the -11/m/sr at 10.6 microns, although the accuracies of the instruments were marginal at this level. Equivalent figures were 2-8 x 10 to the -9/m/sr (aerosol) and 9 x 10 to the -9 to 2 x 10 to the -8/m/sr (lidar) at 0.694 microns wavelength at Sale; and 3.7 x 10 to the -9/m/sr (aerosol) and 10 to the -8 to 10 to the -7/m/sr (lidar) at 0.532 microns wavelength at Cowley Beach. The measured backscatter coefficients at 0.694 and 0.532 microns were consistently higher than the values calculated from aerosol size distributions by factors of typically 2 to 10.

Gras, John L.↗
NASA NTRS1987

Polarization effects on hard target calibration of lidar systems

The theory of hard target calibration of lidar backscatter data, including laboratory measurements of the pertinent target reflectance parameters, is extended to include the effects of polarization of the transmitted and received laser radiation. The bidirectional reflectance-distribution function model of reflectance is expanded to a 4 x 4 matrix allowing Mueller matrix and Stokes vector calculus to be employed. Target reflectance parameters for calibration of lidar backscatter data are derived for various lidar system polarization configurations from integrating sphere and monostatic reflectometer measurements. It is found that correct modeling of polarization effects is mandatory for accurate calibration of hard target reflectance parameters and, therefore, for accurate calibration of lidar backscatter data.

Kavaya, Michael J.↗