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At least 109 records · Page 6

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NASA NTRS1974

Multiple target tracking and target attitude determination with a scanning laser radar

A scanning laser radar that can acquire and track single or multiple targets has recently been developed. Scan patterns have been designed for acquisition and tracking of one or more targets using a narrow laser beam. A synchronously scanned transmitter-receiver is used to acquire and track targets anywhere in a 376 x 376 element raster covering a 30 x 30 deg field. All scan patterns are electronically programmed, and the system automatically acquires and tracks the target or targets without the aid of an operator. The maximum tracking rate is 1.0 deg/sec (10.0 deg/sec) when used with a 1 kHz (10 kHz) scan rate. The estimated free space range against passive cooperative targets (corner cube reflectors) is 30 nautical miles. The laser radar has an accuracy of 10 cm (range) and 0.05 deg (angle). The developmental system is relatively small (1.5 cu ft), lightweight (60 lbs) and low-power-consuming (60 W).

Flom, T.↗

NASA NTRS1977

Optical scanning system for laser velocimeter

An optical system was developed to provide fast incremental scanning of a backscattered laser velocimeter focus point over a 36-cm distance. The system is used to measure flow velocities at 16 positions along its optical axis and to scan these 16 positions up to 30 times a second. Dwell time at each location is approximately 2 milliseconds. Sample volumes typically are 0.2 mm in diameter by 1.4 cm in length. The optical scanning system consists of a wheel containing plane parallel quartz windows of various thicknesses. The laser velocimeter beams are imaged to a primary focus within the dead airspace of an optical cell. The beams emerging from the cell pass through the windows of the scanning wheel. The refraction of the beams passing through the windows causes an apparent shift of the focus within the optical cell and hence in the test zone. Light scattered from the secondary focus within the test zone is concurrently collected and reimaged through the same optical path which originally projected the primary focus. The reimaged backscattered light containing the velocity information is then collected and focused onto a photomultiplier detector system to complete the scanned laser velocimeter optical system.

Rhodes, D. B.↗

NASA NTRS1977

Scanning and focusing mechanisms of METEOSAT radiometer

The scanning and focusing mechanisms settled onboard the METEOSAT Radiometer are described. A large camera which will take line by line pictures of the earth from a geostationary satellite in the same manner as a TV picture using both the spin of the spacecraft and the tilt of a telescope is included. The scanning mechanism provides the + or - 9 degrees tilt angle of the telescope through 2,500 elementary steps of 1.256 0.0001 radian. As the radiometer image quality is closely dependent on the characteristics of the scanning law, the mechanism is required to fulfill functional performances specifications particularly severe in terms of linearity of the scan curve, accuracy of each step as well as repeatability of the short-term scanning. The focusing mechanism allows + or - 12 millimeters shift of the telescope focus by step increments of 0.140 mm. The focus adjustment is achieved by moving a dihedral reflector according to a pure straight-line motion. The main requirements of each mechanism are summarized and their design and performances are described in detail.

Jouan, J.↗

NASA NTRS1980

Simple Cassegrain scanning system for infrared astronomy

To meet the need for a reliable, fast imaging system capable of being taken rapidly on and off the telescope, a simple, inexpensive, and compact Cassegrain reimaging system for scanning IR images was constructed. Using commercially available components without requiring close mechanical tolerances, the design solves the problem of beam stability pointed out by Koornneef and van Overbeeke (1976). For the moving-iron galvanometer scanner, it is noted that at the imaging frequency of 0.5 Hz, hysteresis in image plane motion was found to be less than 0.2 arc sec for a 64-arc sec scan, and the deviation from linearity with a triangular wave input was found to be less than 0.3 arc sec. This system and a scanning secondary were used to image Venus at 11.5 microns, and compared with the scanning secondary, the reimaging system did not appear to contribute any additional noise, considerably improved mechanical reliability, and eliminated cross-scan motion

Apt, J.↗

NASA NTRS1982

The design of the Galileo scan platform control

The design of the scan platform control for the Galileo spacecraft is described. Emphasis is given to the inertial pointing of the scan platform when the spacecraft is in the dual-spin configuration. The various methods of operation used in Galileo scan pointing are outlined. Important design considerations, such as spacecraft flexibility and the separation of the actuator and sensor by a flexible structure, are discussed. An explanation is given of the pointing requirements imposed on the scan platform control. Also given is a high level description of the relevant scan pointing algorithms. The performance of the design is demonstrated by means of a sample slew test case. The simulation program used in the test includes models of the flexibility of the stator structure, the friction in the clock and cone actuators, the gyro sensor characteristics, and the system time delays.

Chodas, J. L.↗

NASA NTRS1982

Entropy, instrument scan, and pilot workload

Experimental results are presented from a set of experiments designed to explore the relationship between the performance, skill, and visual scanning behavior of pilots under varying levels of mental workload. Instrument fixations were recorded as groups of pilots with widely differing levels of skill simultaneously performed a continuous instrument flight task and a verbally presented loading task with four discrete levels. Pilot scanning patterns were found to be significantly affected by the level of mental workload in a manner that was dependent on skill. These scanning alterations were quantified by the methods of entropy and autocorrelation, where the former concerns visual scan path and the latter assesses the relations among scan periodicity, skill level and mental task periodicity.

Tole, J. R.↗

NASA NTRS1983

Summary of NASA Langley's pilot scan behavior research

The present investigation is concerned with the information acquired in a series of basic studies designed to obtain an understanding of the pilot's scanning behavior. In the studies, use was made of an oculometer system which operates by shining a beam of collimated infrared light at the subject's eyes. A number of oculometer software modifications have been made to make the oculometer user-friendly and versatile. Scanning is found to be a subconscious conditioned activity. The conditioned activity of scanning is different for each pilot. There are also slight variations between test runs for the same conditions for the same pilot. This indicates that scanning is situation dependent. Attention is given to the rate of information transfer, the possibility that scanning can be disrupted, the visual approach look-point, and workload sensitive measures.

Spady, A. A., Jr.↗

NASA NTRS1984

Design of the Galileo scan platform control

Design of the scan platform control for the Galileo spacecraft is presented. Emphasis is placed on the inertial pointing of the scan platform when the spacecraft is in the dual-spin configuration. The various methods of operation used for Galileo scan pointing are outlined. Major design considerations, such as spacecraft flexibility and separation of actuator and sensor by a flexible structure, are discussed. The pointing requirements imposed on the scan platform control are explained. A high-level description of the relevant scan pointing algorithms is included. The performance of the design is demonstrated by a sample slew test case.

Chodas, J. L.↗

NASA NTRS1985

Scan Angle and Detector Effects in Thematic Mapper Radiometry

The effects of scan angle and interdetector differences on thematic mapper radiometry were analyzed. The data set used for this study consisted of computer compatible tapes (CCT's) of raw data (CCT-BT), radiometrically corrected data (CCT-AT), and geometrically corrected data (CCT-PT) for two scenes, 40049-16262 (north central Iowa) and 40037-16031 (Arkansas). Radiometric corrections currently performed were found to improve overall consistency of data, but some residual stripping remains in the corrected data due to the quantization of signal values and other effects. A new type of banding was discovered which is related to the bi-directional scanning of TM. An initial empirical model was developed for correcting this effect in band 1, but should receive additional development. The scan angle effects observed corresponded to those expected based on atmospheric considerations and scene characteristics. Low frequency scan-to-scan noise was detected in band 1, band 7, and to a lesser extent in bands 2 and 3. The band 1 detectors which exhibited this noise showed strong correlation in their variation.

Metzler, M. D.↗

NASA NTRS1985

Visual information transfer. Part 1: Assessment of specific information needs. Part 2: Parameters of appropriate instrument scanning behavior

The present study explored eye scan behavior as a function of level of subject training. Oculometric (eye scan) measures were recorded from each of ten subjects during training trials on a CRT based flight simulation task. The task developed for the study incorporated subtasks representative of specific activities performed by pilots, but which could be performed at asymptotic levels within relatively short periods of training. Changes in eye scan behavior were examined as initially untrained subjects developed skill in the task. Eye scan predictors of performance on the task were found. Examination of eye scan in proximity to selected task events revealed differences in the distribution of looks at the instruments as a function of level of training.

Comstock, J. R., Jr.↗

NASA NTRS1984

Spacelab data analysis using the space plasma computer analysis network (SCAN) system

The Space-plasma Computer Analysis Network (SCAN) currently connects a large number of U.S. Spacelab investigators into a common computer network. Used primarily by plasma physics researchers at present, SCAN provides access to Spacelab investigators in other areas of space science, to Spacelab and non-Spacelab correlative data bases, and to large Class VI computational facilities for modeling. SCAN links computers together at remote institutions used by space researchers, utilizing commercially available software for computer-to-computer communications. Started by the NASA's Office of Space Science in mid 1980, SCAN presently contains ten system nodes located at major universities and space research laboratories, with fourteen new nodes projected for the near future. The Stanford University computer gateways allow SCAN users to connect onto the ARPANET and TELENET overseas networks.

Green, J. L.↗

NASA NTRS1985

Eye-scan behavior in a flight simulation task as a function of level of training

The present study explored eye-scan behavior as a function of level of subject training. Oculometric (eye-scan) measures were recorded from each of ten subjects during training trials on a CRT-based flight simulation task. The task developed for the study incorporated subtasks representative of specific activities performed by pilots, but which could be performed at asymptotic levels within relatively short periods of training. Changes in eye-scan behavior were examined as initially untrained subjects developed skill in the task. Eye-scan predictors of performance on the task were found. Examination of eye-scan in proximity to selected task events revealed differences in the distribution of looks at the instruments as a function of level of training.

Comstock, J. R., Jr.↗

NASA NTRS1987

AVIRIS scan drive design and performance

The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) images the ground with an instantaneous field of view (IFOV) of 1 mrad. The IFOV is scanned 30 deg from left to right to provide the cross-track dimension of the image, while the aircraft's motion provides the along-track dimension. The scanning frequency is 12 Hz, with a scan efficiency of 70 percent. The scan mirror has an effective diameter of 5.7 in, and its positional accuracy is a small fraction of a milliradian of the nominal position-time profile. Described are the design and performance of the scan drive mechanism. Tradeoffs among various approaches are discussed, and the reasons given for the selection of the cam drive.

Miller, D. C.↗

NASA NTRS1988

Large aperture scanning airborne lidar

A large aperture scanning airborne lidar facility is being developed to provide important new capabilities for airborne lidar sensor systems. The proposed scanning mechanism allows for a large aperture telescope (25 in. diameter) in front of an elliptical flat (25 x 36 in.) turning mirror positioned at a 45 degree angle with respect to the telescope optical axis. The lidar scanning capability will provide opportunities for acquiring new data sets for atmospheric, earth resources, and oceans communities. This completed facility will also make available the opportunity to acquire simulated EOS lidar data on a near global basis. The design and construction of this unique scanning mechanism presents exciting technological challenges of maintaining the turning mirror optical flatness during scanning while exposed to extreme temperatures, ambient pressures, aircraft vibrations, etc.

Smith, J.↗

NASA NTRS1988

AVIRIS scan drive design and performance

Miller, D. C.↗

NASA NTRS1989

Pointing a ground antenna at a spinning spacecraft using conical scan - Simulation results

The results are presented for an investigation of ground antenna pointing errors which are caused by fluctuations of the receiver AGC signal due to thermal noise and a spinning spacecraft. Transient responses and steady-state errors and losses are estimated using models of the digital Conscan (conical scan) loop, the FFT, and antenna characteristics. Simulation results are given for the on-going Voyager mission and for the upcoming Galileo mission, which includes a spinning spacecraft. The simulation predicts a 1 sigma pointing error of 0.5 to 2.0 mdeg for Voyager, assuming an AGC loop SNR of 35 to 30 dB with a scan period varying from 128 to 32 sec, respectively. This prediction is in agreement with the DSS 14 antenna Conscan performance of 1.7 mdeg for 32 sec scans as reported in earlier studies. The simulation of Galileo predicts 1 mdeg error with a 128 sec scan and 4 mdeg with a 32 sec scan under similar AGC conditions.

Mileant, Alexander↗

NASA NTRS1992

Rotating-unbalanced-mass devices and methods for scanning balloon-borne-experiments, free-flying spacecraft, and space shuttle/space station attached experiments

A method and apparatus for scanning balloon-borne experiments, free-flying spacecraft, or gimballed experiments mounted on a space shuttle or space station, makes use of one or more rotating unbalanced mass devices for selectively generating circular, line, or raster scan patterns for the experiment line of sight. An auxiliary control system may also be used in combination with the rotating unbalanced mass device, for target acquisition, keeping the scan centered on the target, or for producing complementary motion for raster scanning. The rotating unbalanced mass makes use of a mass associated with a drive shaft, such mass having a center of gravity which is displaced from the drive shaft rotation axis. The drive shaft is driven with a substantially constant angular velocity, thereby resulting in relatively low power requirements since no acceleration or deceleration of the mass is generally involved during steady state operations. The resulting centrifugal force of the rotating unbalanced mass is used to generate desired reaction forces on the experiment or spacecraft to create a desired scan pattern for the experiment line of sight.

Polites, Michael E.↗

NASA NTRS1990

Tropical Rainfall Measuring Mission (TRMM) project. VI - Spacecraft, scientific instruments, and launching rocket. Part 3 - The electrically Scanning Microwave Radiometer and the Special Sensor Microwave/Imager

The two microwave radiometers for TRMM are designed to measure thermal microwave radiation upwelling from the earth. The Electrically Scanning Microwave Radiometer (ESMR) scans from 50 deg to the left through nadir to 50 deg to the right in 78 steps with no moving mechanical parts in a band centered at 19.35 GHz. The TRMM concept uses the radar to develop a climatology of rain-layer thickness which can be used for the interpretation of the radiometer data over a swath wider than the radar. The ESMR data are useful for estimating rain intensity only over an ocean background. The Special Sensor Microwave/Imager (SSM/I), which scans conically with three dual polarized channels at 19, 37, and 85 GHz and a single polarized channel at 22 GHz, provides a wider range of rainfall intensities. The SSM/I spins about an axis parallel to the local spacecraft vector and 128 uniformly spaced samples of the 85 GHz data are taken on each scan over a 112-deg scan region simultaneously with 64 samples of the other frequencies.

Wilheit, Thomas T.↗