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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Windshear detection - Airborne system perspective

Functional requirements for airborne windshear detection and warning are discussed based on performance criteria of remote sensor devices such as Doppler radar, Doppler laser radar, and infrared radiometric techniques. These types of sensors are considered able to detect hazardous windshear conditions and provide adequate warning time for the flight crew to escape the encounter. Radar simulation and analysis show that windshear from microbursts can be detected. The Doppler systems can provide line-of-sight information from a region extending 2-4 km in front of the aircraft. The temperature drop associated with the formation of windshear can be measured by an airborne infrared radiometer which compares emission from CO2 in the immediate neighborhood of the aircraft to the emissions from CO2 in the air 4-5 km away. It is suggested that an integration of airborne sensor and ground derived data can support microburst avoidance.

Bowles, Roland L.↗
NASA NTRS1990

Windshear detection and avoidance - Airborne systems survey

Functional requirements for airborne windshear detection and warning systems are discussed in terms of the threat posed to civil aircraft operations. A preliminary set of performance criteria for predictive windshear detection and warning systems is defined. Candidate airborne remote sensor technologies based on microwave Doppler radar, Doppler laser radar (lidar), and infrared radiometric techniques are discussed in the context of overall system requirements, and the performance of each sensor is assessed for representative microburst environments and ground clutter conditions. Preliminary simulation results demonstrate that all three sensors show potential for detecting windshear, and provide adequate warning time to allow flight crews to avoid the affected area or escape from the encounter. Radar simulation and analysis show that by using bin-to-bin automatic gain control, clutter filtering, limited detection range, and suitable antenna tilt management, windshear from wet microbursts can be accurately detected. Although a performance improvement can be obtained at higher radar frequency, the baseline X-band system also detected the presence of windshear hazard for a dry microburst. Simulation results of end-to-end performance for competing coherent lidar systems are presented.

Bowles, Roland L.↗
NASA NTRS1997

Analysis of Technology for Compact Coherent Lidar

In view of the recent advances in the area of solid state and semiconductor lasers has created new possibilities for the development of compact and reliable coherent lidars for a wide range of applications. These applications include: Automated Rendezvous and Capture, wind shear and clear air turbulence detection, aircraft wake vortex detection, and automobile collision avoidance. The work performed by the UAH personnel under this Delivery Order, concentrated on design and analyses of a compact coherent lidar system capable of measuring range and velocity of hard targets, and providing air mass velocity data. The following is the scope of this work. a. Investigate various laser sources and optical signal detection configurations in support of a compact and lightweight coherent laser radar to be developed for precision range and velocity measurements of hard and fuzzy targets. Through interaction with MSFC engineers, the most suitable laser source and signal detection technique that can provide a reliable compact and lightweight laser radar design will be selected. b. Analyze and specify the coherent laser radar system configuration and assist with its optical and electronic design efforts. Develop a system design including its optical layout design. Specify all optical components and provide the general requirements of the electronic subsystems including laser beam modulator and demodulator drivers, detector electronic interface, and the signal processor. c. Perform a thorough performance analysis to predict the system measurement range and accuracy. This analysis will utilize various coherent laser radar sensitivity formulations and different target models.

Amzajerdian, Farzin↗
NASA NTRS1995

Comparison of Retracking Algorithms Using Airborne Radar and Laser Altimeter Measurements of the Greenland Ice Sheet

This paper compares four continental ice sheet radar altimeter retracking algorithms using airborne radar and laser altimeter data taken over the Greenland ice sheet in 1991. The refurbished Advanced Application Flight Experiment (AAFE) airborne radar altimeter has a large range window and stores the entire return waveform during flight. Once the return waveforms are retracked, or post-processed to obtain the most accurate altitude measurement possible, they are compared with the high-precision Airborne Oceanographic Lidar (AOL) altimeter measurements. The AAFE waveforms show evidence of varying degrees of both surface and volume scattering from different regions of the Greenland ice sheet. The AOL laser altimeter, however, obtains a return only from the surface of the ice sheet. Retracking altimeter waveforms with a surface scattering model results in a good correlation with the laser measurements in the wet and dry-snow zones, but in the percolation region of the ice sheet, the deviation between the two data sets is large due to the effects of subsurface and volume scattering. The Martin et al model results in a lower bias than the surface scattering model, but still shows an increase in the noise level in the percolation zone. Using an Offset Center of Gravity algorithm to retrack altimeter waveforms results in measurements that are only slightly affected by subsurface and volume scattering and, despite a higher bias, this algorithm works well in all regions of the ice sheet. A cubic spline provides retracked altitudes that agree with AOL measurements over all regions of Greenland. This method is not sensitive to changes in the scattering mechanisms of the ice sheet and it has the lowest noise level and bias of all the retracking methods presented.

Ferraro, Ellen J.↗
NASA NTRS2012

Comparison of Surface Elevation Changes of the Greenland and Antarctic Ice Sheets from Radar and Laser Altimetry

A primary purpose of satellite altimeter measurements is determination of the mass balances of the Greenland and Antarctic ice sheets and changes with time by measurement of changes in the surface elevations. Since the early 1990's, important measurements for this purpose have been made by radar altimeters on ERS-l and 2, Envisat, and CryoSat and a laser altimeter on ICESat. One principal factor limiting direct comparisons between radar and laser measurements is the variable penetration depth of the radar signal and the corresponding location of the effective depth of the radar-measured elevation beneath the surface, in contrast to the laser-measured surface elevation. Although the radar penetration depth varies significantly both spatially and temporally, empirical corrections have been developed to account for this effect. Another limiting factor in direct comparisons is caused by differences in the size of the laser and radar footprints and their respective horizontal locations on the surface. Nevertheless, derived changes in elevation, dHldt, and time-series of elevation, H(t), have been shown to be comparable. For comparisons at different times, corrections for elevation changes caused by variations in the rate offrrn compaction have also been developed. Comparisons between the H(t) and the average dH/dt at some specific locations, such as the Vostok region of East Antarctic, show good agreement among results from ERS-l and 2, Envisat, and ICESat. However, Greenland maps of dHidt from Envisat and ICESat for the same time periods (2003-2008) show some areas of significant differences as well as areas of good agreement. Possible causes of residual differences are investigated and described.

Zwally, H. Jay↗
NASA NTRS2011

LIDAR Metrology for Prescription Characterization and Alignment of Large Mirrors

We describe the use of LIDAR, or "laser radar," (LR) as a fast, accurate, and non-contact tool for the measurement of the radius of curvature (RoC) of large mirrors. We report the results of a demonstration of this concept using a commercial laser radar system. We measured the RoC of a 1.4m x 1m spherical mirror with a nominal RoC of 4.6 m with a manufacturing tolerance of 4600mm +/- 6mm. The prescription of the mirror is related to its role as ground support equipment used in the test of part of the James Webb Space Telescope (JWST). The RoC of such a large mirror is not easily measured without contacting the surface. From a position near the center of curvature of the mirror, the LIDAR scanned the mirror surface, sampling it with 1 point per 3.5 sq cm. The measurement consisted of 3983 points and lasted only a few minutes. The laser radar uses the LIDAR signal to provide range, and encoder information from angular azimuth and elevation rotation stages provide the spherical coordinates of a given point. A best-fit to a sphere of the measured points was performed. The resulting RoC was within 20 ppm of the nominal RoC, also showing good agreement with the results of a laser tracker-based, contact metrology. This paper also discusses parameters such as test alignment, scan density, and optical surface type, as well as future possible application for full prescription characterization of aspherical mirrors, including radius, conic, off-axis distance, and aperture.

Eegholm, B.↗
NASA NTRS1966

Radio electronics

Low noise amplifiers, laser radar optics, gas lasers and holography, and microminiaturized solid state devices for radio electronics

LIDAR↗
NASA NTRS2017

Optical Testing Using Portable Laser Coordinate Measuring Instruments

High precision, portable coordinate measuring instruments (CMI) such as laser radars (LR) and laser trackers (LT) have been used for optical system alignment and integration. The LRs ability to perform a non-contact scan of surfaces was previously utilized to characterize large spherical and aspheric mirrors. In this paper, we explore the use of a CMI as an accurate, fast, robust, and non-contact tool for prescription characterization of powered optical surfaces. Using Nikons MV-224350 LR and Leicas Absolute Tracker AT401402 instruments, proof of concept measurements were performed to characterize a variety of optical components by measuring the actual and apparent, or equivalently the direct and through (DT), coordinates of calibrated metrology targets. Custom macros in metrology software and other data reduction code were developed to compute surface-ray intercepts and surface slopes from the DT shots. The calculated data is fit to an aspheric surface formula to obtain the optimum prescription. The results were compared to the nominal parameters and were crosschecked using LR scans or other approaches. We discuss potential applications across the fields of optical component fabrication and system alignment and testing.

Khreishi, M.↗
NASA NTRS2017

Optical Testing Using Portable Laser Coordinate Measuring Instruments

High precision, portable coordinate measuring instruments (CMI) such as laser radars (LR) and laser trackers (LT) have been used for optical system alignment and integration. The LR's ability to perform a non-contact scan of surfaces was previously utilized to characterize large spherical and aspheric mirrors. In this paper, we explore the use of a CMI as an accurate, fast, robust, and non-contact tool for prescription characterization of powered optical surfaces. Using Nikon's MV-224/350 LR and Leica's Absolute Tracker AT401/402 instruments, proof of concept measurements were performed to characterize a variety of optical components by measuring the actual and apparent, or equivalently the "direct and through" (D&T), coordinates of calibrated metrology targets. Custom macros in metrology software and other data reduction code were developed to compute surface-ray intercepts and surface slopes from the D&T shots. The calculated data is fit to an aspheric surface formula to obtain the optimum prescription. The results were compared to the nominal parameters and were crosschecked using LR scans or other approaches. We discuss potential applications across the fields of optical component fabrication and system alignment and testing.

Khreishi, Manal↗
NASA NTRS1993

Determining the 3-D structure and motion of objects using a scanning laser range sensor

In order for the EVAHR robot to autonomously track and grasp objects, its vision system must be able to determine the 3-D structure and motion of an object from a sequence of sensory images. This task is accomplished by the use of a laser radar range sensor which provides dense range maps of the scene. Unfortunately, the currently available laser radar range cameras use a sequential scanning approach which complicates image analysis. Although many algorithms have been developed for recognizing objects from range images, none are suited for use with single beam, scanning, time-of-flight sensors because all previous algorithms assume instantaneous acquisition of the entire image. This assumption is invalid since the EVAHR robot is equipped with a sequential scanning laser range sensor. If an object is moving while being imaged by the device, the apparent structure of the object can be significantly distorted due to the significant non-zero delay time between sampling each image pixel. If an estimate of the motion of the object can be determined, this distortion can be eliminated; but, this leads to the motion-structure paradox - most existing algorithms for 3-D motion estimation use the structure of objects to parameterize their motions. The goal of this research is to design a rigid-body motion recovery technique which overcomes this limitation. The method being developed is an iterative, linear, feature-based approach which uses the non-zero image acquisition time constraint to accurately recover the motion parameters from the distorted structure of the 3-D range maps. Once the motion parameters are determined, the structural distortion in the range images is corrected.

Nandhakumar, N.↗
NASA NTRS1992

Trial of a slant visual range measuring device

Each year, fog at airports renders some landing operations either difficult or impossible. The visibility that a pilot of a landing aircraft can expect is in that case the most important information. It could happen that the visibility versus the altitude is constantly decreasing or increasing. However, it is not possible to distinguish this with the existing sensors at an airport. If the visibility is decreasing with the altitude, one has the worst case - ground fog. The standard visibility sensor, the transmissometer, determines only the horizontal visual range, which will be underestimated in comparison with the real visibility a pilot has on his landing approach. Described here is a new technique to measure the slant visual range, making use of a slant scanning device - an eye-safe laser radar. A comparison with commercial visibility sensors shows that it is possible to measure visibilities with the slant looking laser radar in the range from 50 meters up to 2000 meters and even distinguish inhomogenities like ground fog.

Streicher, J.↗
NASA NTRS2018

Applying the SOFIA Coordinate System to the HIRMES Instrument

The High-resolution Mid-infrared Spectrometer (HIRMES) will be in-flight aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) in late 2019, which will allow for observations of the structure and evolution of protoplanetary disks. SOFIA has a different coordinate system from the system being used to build HIRMES and needs to be defined and applied to HIRMES. This is necessary because the first mirror, which is aiming the incoming light onto the slit wheel by allowing for tip and tilt adjustments, cannot rotate. Thus, the SOFIA coordinate system allows for this additional degree of freedom and allows for the slit wheel to be in line with the telescope. Using a laser radar, multiple measurements around the instrument were taken of tooling balls, which quantified an uncertainty with the measurements. Also, a laser radar was used to scan the entirety of the instrument. The center of the front flange was determined using the measurements and scans of the instrument, which was used to determine the origin of the SOFIA coordinate system and its uncertainty. By knowing the center of the front flange, an off-center, rotated coordinate system was created, matching the mechanics' schematics for the system. Going forward, this coordinate system will allow for continued alignment of the instrument in preparation for flight and for accurate measurements when aboard SOFIA.

Wraback, Elizabeth↗
NASA NTRS1993

CSI flight experiment projects of the Naval Research Laboratory

The Naval Research Laboratory (NRL) is involved in an active program of CSI flight experiments. The first CSI flight experiment of the Naval Research Laboratory, the Low Power Atmospheric Compensation Experiment (LACE) dynamics experiment, has successfully measured vibrations of an orbiting satellite with a ground-based laser radar. The observations, made on January 7, 8 and 10, 1991, represent the first ever measurements of this type. In the tests, a narrowband heterodyne CO2 laser radar, operating at a wavelength of 10.6 microns, detected vibration induced differential-Doppler signatures of the LACE satellite. Power spectral densities of forced oscillations and modal frequencies and damping rates of free-damped vibrations were obtained and compared with finite element structural models of the LACE system. Another manifested flight experiment is the Advanced Controls Technology Experiment (ACTEX) designed to demonstrate active and passive damping with piezo-electric (PZT) sensors and actuators. This experiment was developed under the management of the Air Force Phillips Laboratory with integration of the experiment at NRL. It is to ride as a secondary, or 'piggyback,' experiment on a future Navy satellite.

Fisher, Shalom↗
NASA NTRS1991

Future technologies for lidar/DIAL remote sensing

Several technology needs for future space-based lidar/DIAL applications are outlined in connection with Mission to Planet Earth. First, approved laser radar missions included in Mission to Planet Earth are outlined with emphasis on engineering developments at the NASA Langley Research Center. The current status of solid-state laser materials is then presented with particular reference to those materials that will lead to the development of a 2-micron technology for a variety of wind sensing applications. Finally, recommendations are given for accelerated technology development which will lead to laser radar experiments from space to improve scientific understanding of atmospheric chemistry and dynamics, the greenhouse effect, and improvements in measurements of meteorological parameters.

Allario, Frank↗
NASA NTRS1985

The WINDSAT concept for measuring the global wind field

The Wave Propagation Laboratory of the National Oceanic and Atmospheric Administration's (NOAA) Environmental Research Laboratories has investigated the feasibility of measuring the global wind field by using an infrared coherent laser radar under a joint program with the U.S. Air Force Space Division Defense Meteorological Satellite Program (DMSP). These studies considered both the analytical and hardware feasibility of a spaceborne global wind measuring coherent laser radar (WINDSAT). Objectives and requirements of the Air Force Defense Meteorological Satellite Program were used in the study. The vertical distributions of the horizontal wind field were required throughout the troposphere with 300 km square horizontal and 1 km vertical resolution with a measurements accuracy of 1 m/s. Complete global coverage was required. The lidar system performance should also be scalable to operational satellite conditions. The analytical studies were performed for both a 300 km altitude Space Shuttle orbit and an operational polar orbit of 800 km altitude (Huffaker, 1978; Huffaker et al., 1980). A hardware definition study was performed for a Space Shuttle demonstration test flight (Lockheed Missiles and Space Co., 1981). Studies have also been conducted to determine the feasibility of mounting a WINDSAT payload on an Advanced TIROS-N spacecraft (RCA Corporation, 1983).

Huffaker, R. Milton↗
NASA NTRS1985

Lasers in space

Hinkley and Herring (1984) have considered the differences between active (laser) and passive remote sensing from space. The conclusion was reached that spaceborne lasers will eventually complement passive sensors in providing information on the distributions of key atmospheric species and meteorological parameters. Precise information can also be obtained of ice sheet and crustal dynamics for geological and mapping applications. NASA initiated recently an airborne measurement program directed toward some of these objectives. The program employs optical radar (laser radar) systems onboard the NASA advanced ER-2 high-flying aircraft. The results of the experiments are to provide important information with respect to the potential utility of spaceborne laser remote sensing. A study indicated that a spaceborne pulsed carbon dioxide laser could measure tropospheric winds. Attention is also given to measurements of atmospheric gases by spaceborne lasers, solid-state lasers for spaceborne remote sensing, and laser communication in space.

Hinkley, E. D.↗
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.↗