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At least 1,711 records · Page 95

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NASA NTRS1978

A comparison of satellite sensor bands for vegetation monitoring

The first four Landsat-D thematic mapper sensor bands were evaluated and compared to the RBV and MSS sensors from Landsats-1, -2, and -3; Colvocoresses' proposed 'operational Landsat' three-band system; and the French SPOT three-band system by using simulation/integration techniques and in situ collected spectral reflectance data. Sensors were evaluated with regard to their ability to discriminate vegetation biomass, chlorophyll concentration, and leaf water content. The thematic mapper and SPOT bands were found to be superior in a spectral resolution context to the other three sensor systems for vegetational applications. Significant improvements are expected for most vegetational analyses from Landsat-D thematic mapper and SPOT imagery over MSS and RBV imagery.

Tucker, C. J.↗

NASA NTRS1979

Pioneer Venus Star Sensor

The design predictions and orbital performance verification of the solid state star scanner used in the Onboard Attitude Control of the Pioneer Venus Orbiter and Multiprobe are presented. The star sensor extended the scanner use to active despin control, and it differs from previous sensors in solid state detection, redundant electronics for reliability, larger field of view, and large dynamic spin range. The star scanner hardware and design performance based on the ability to predict all noise sources, signal magnitudes, and expected detection probability are discussed. In-flight data collected to verify sensor ground calibration are tabulated and plotted in predicted accuracy curves. It is concluded that the Pioneer Venus Star Sensor has demonstrated predictable star calibration in the range of .1 magnitude uncertainties and usable star catalogs of 100 stars with very high probabilities of detection, which were much better than expected and well within the mission requirements.

Gutshall, R. L.↗

NASA NTRS1978

Fiber optic sensors for military, industrial and commercial applications

Four examples of specific fiber optic sensor system designs, each of which demonstrates a different optical modulation format, are described. The birefrigent temperature transducer illustrates direct digital signal modulation. The temperature/pressure dependent semiconductor filter illustrates high-pass optical wavelength signal encoding. The coupled polarized-mode transducer shows how a solid-state sensor can produce narrow-bandpass optical wavelength signal encoding. The luminescent temperature sensor illustrates a way to construct a solid state sensor in order to produce pulse width modulation of an optical signal.

James, K. A.↗

NASA NTRS1980

AMTV headway sensor and safety design

A headway sensing system for an automated mixed traffic vehicle (AMTV) employing an array of optical proximity sensor elements is described, and its performance is presented in terms of object detection profiles. The problem of sensing in turns is explored experimentally and requirements for future turn sensors are discussed. A recommended headway sensor configuration, employing multiple source elements in the focal plane of one lens operating together with a similar detector unit, is described. Alternative concepts including laser radar, ultrasonic sensing, imaging techniques, and radar are compared to the present proximity sensor approach. Design concepts for an AMTV body which will minimize the probability of injury to pedestrians or passengers in the event of a collision are presented.

Johnston, A. R.↗

NASA NTRS1980

Electromagnetic sensors for general lightning application

Electromagnetic sensors for general lightning applications in measuring environment are discussed as well as system response to the environment. This includes electric and magnetic fields, surface current and charge densities, and currents on conductors. Many EMP sensors are directly applicable to lightning measurements, but there are some special cases of lightning measurements involving direct strikes which require special design considerations for the sensors. The sensors and instrumentation used by NMIMT in collecting data on lightning at South Baldy peak in central New Mexico during the 1978 and 1979 lightning seasons are also discussed. The Langmuir Laboratory facilities and details of the underground shielded instrumentation room and recording equipment are presented.

Baum, C. E.↗

NASA NTRS1978

A comparison between the first four thematic mapper reflective bands and other satellite sensor systems for vegetational monitoring

The first four Landsat-D thematic mapper sensors were evaluated and compared to the RBV and MSS sensors from Landsats-1, 2, and 3, Colvocoresses' proposed 'operational Landsat' three band system, and the French SPOT three band system using simulation/integration techniques and in situ collected spectral reflectance data. Sensors were evaluated by their ability to discriminate vegetation biomass, chlorophyll concentration, and leaf water content. The thematic mapper and SPOT bands were superior in a spectral resolution context to the other three sensor systems for vegetational applications. Significant improvements are expected for vegetational analyses from Landsat-D thematic mapper and SPOT imagery over MSS and RBV imagery.

Tucker, C. J.↗

NASA NTRS1980

Triple redundant hydrogen sensor with in situ calibration

To meet sensing and calibration needs, an in situ calibration technique was developed. It is based on electrolytic generation of a hydrogen/air atmosphere within a hydrogen sensor. The hydrogen is generated from water vapor in the air, and being electrical in nature, the in situ calibration can be performed completely automatically in remote locations. Triply redundant sensor elements are integrated within a single, compact housing, and digital logic provides inter-sensor comparisons to warn of and identify malfunctioning sensor elements. An evaluation of this concept is presented.

Lantz, J. B.↗

NASA NTRS1981

Development of a Shuttle Infrared Telescope Facility /SIRTF/ fine guidance sensor

Fine guidance technology development for the Shuttle Infrared Telescope Facility (SIRTF) centers upon the use of a single multiple-star-tracking sensor to provide the position information necessary to produce three-axis attitude control signals for precision payload pointing. The effort described in this paper is concerned with the development of a fine guidance sensor that employs a high-density charge-coupled imaging device for producing position information signals by using star fields. Multiple star position information produces three-axis position error signals that are used to update inertial reference gyros. The sensor employs advanced position interpolation algorithms to enhance field-of-view resolution and to correct for optical aberrations inherent in spatially chopped star images resulting from the telescope's movable secondary mirror. Operation of the sensor is under the control of a high-performance microcomputer that provides both autonomy and flexibility in a guidance application.

Salomon, P. M.↗

NASA NTRS1982

An aircraft sensor fault tolerant system

The design of a sensor fault tolerant system which uses analytical redundancy for the Terminal Configured Vehicle (TCV) research aircraft in a Microwave Landing System (MLS) environment was studied. The fault tolerant system provides reliable estimates for aircraft position, velocity, and attitude in the presence of possible failures in navigation aid instruments and onboard sensors. The estimates, provided by the fault tolerant system, are used by the automated guidance and control system to land the aircraft along a prescribed path. Sensor failures are identified by utilizing the analytic relationship between the various sensor outputs arising from the aircraft equations of motion.

Caglayan, A. K.↗

NASA NTRS1982

Evaluation of SMART sensor displays for multidimensional precision control of Space Shuttle remote manipulator

An enhanced proximity sensor and display system was developed at the Jet Propulsion Laboratory (JPL) and tested on the full scale Space Shuttle Remote Manipulator at the Johnson Space Center (JSC) Manipulator Development Facility (MDF). The sensor system, integrated with a four-claw end effector, measures range error up to 6 inches, and pitch and yaw alignment errors within + or 15 deg., and displays error data on both graphic and numeric displays. The errors are referenced to the end effector control axes through appropriate data processing by a dedicated microcomputer acting on the sensor data in real time. Both display boxes contain a green lamp which indicates whether the combination of range, pitch and yaw errors will assure a successful grapple. More than 200 test runs were completed in early 1980 by three operators at JSC for grasping static and capturing slowly moving targets. The tests have indicated that the use of graphic/numeric displays of proximity sensor information improves precision control of grasp/capture range by more than a factor of two for both static and dynamic grapple conditions.

Bejczy, A. K.↗

NASA NTRS1982

Optical tip clearance sensor for aircraft engine controls

Aircraft gas turbine performance and efficiency are related to airfoil tip clearance. The possibility has been considered to obtain optimum performance and efficiency by reducing clearance to a safe minimum with the aid of a closed-loop tip clearance control system, which utilizes a tip clearance sensor. The use of optical sensing methods appears to represent a potential solution to the tip clearance measurement problem. Principles of sensor operation are discussed along with dimensional considerations and diffraction limitations. A description is presented of the study of the feasibility of a certain sensor, taking into account the test rig system, the optical components, and the mounting tube. Attention is also given to the operation of the feasibility-study sensor, performance estimations, the optical fiber bundle, light beam refraction, and aspects of aircraft engine implementation.

Poppel, G. L.↗

NASA NTRS1982

In-flight estimation of spacecraft attitude sensor accuracies and alignments

A simple estimator is developed for determining in flight the accuracies of vector attitude sensors. The estimator is unbiased and independent of the configuration of the sensors. In addition, the estimator requires neither an a priori estimate of sensor accuracies nor an estimate of the spacecraft attitude. A covariance analysis of the estimator is given. Data from the Magsat mission is analyzed as a example. A simple algorithm for estimating attitude sensor misalignments, which is independent of any knowledge of the spacecraft attitude, is also presented. This misalignment estimator is applied to in-flight data from the Solar Maximum Mission.

Schuster, M. D.↗

NASA NTRS1980

Analytical design of multispectral sensors

An optimal design based on the criterion of minimum mean square representation error using the Karhunen-Loeve expansion was developed to represent the spectral response functions from a stratum based upon a stochastic process scene model. From the overall pattern recognition system perspective, the effect of the representation accuracy on a typical performance criterion (the probability of correct classification) is investigated. The optimum sensor design provides a standard against which practical (suboptimum) operational sensors can be compared. An example design is provided and its performance is illustrated. Although developed primarily for the purpose of sensor design, the procedure has potential for making important contributions to scene understanding. Spectral channels which have narrow bandwidths relative to current sensor systems may be necessary to provide adequate spectral representation and improved classification performance.

Wiersma, D. J.↗

NASA NTRS1983

Sensor failure detection for jet engines

Revisions to the advanced sensor failure detection, isolation, and accommodation (DIA) algorithm, developed under the sensor failure detection system program were studied to eliminate the steady state errors due to estimation filter biases. Three algorithm revisions were formulated and one revision for detailed evaluation was chosen. The selected version modifies the DIA algorithm to feedback the actual sensor outputs to the integral portion of the control for the nofailure case. In case of a failure, the estimates of the failed sensor output is fed back to the integral portion. The estimator outputs are fed back to the linear regulator portion of the control all the time. The revised algorithm is evaluated and compared to the baseline algorithm developed previously.

Beattie, E. C.↗

NASA NTRS1983

Balloon-borne pressure sensor performance evaluation utilizing tracking radars

The pressure sensors on balloon-borne sondes relate the sonde measurements to height above the Earth's surface through the hypsometric equation. It is crucial that sondes used to explore the vertical structure of the atmosphere do not contribute significant height errors to their measurements of atmospheric constituent concentrations and properties. A series of radiosonde flights was conducted. In most cases, each flight consisted of two sondes attached to a single balloon and each flight was tracked by a highly accurate C-band radar. For the first 19 radiosonde flights, the standard aneroid cell baroswitch assembly used was the pressure sensor. The last 26 radiosondes were equipped with a premium grade aneroid cell baroswitch assembly sensor and with a hypsometer. It is shown that both aneroid cell baroswitch sensors become increasingly inaccurate with altitude. The hypsometer radar differences are not strongly dependent upon altitude and it is found that the standard deviation of the differences at 35 km is 0.179 km.

Norcross, G. A.↗

NASA NTRS1982

Validation of aerosol measurements by the satellite sensors SAM II and Sage

A global data base on stratospheric aerosols has been obtained with the aid of the sensors SAM II and SAGE since the satellites carrying the sensors were launched in October 1978 and Feburary 1979, respectively. Several major comparative experiments have been conducted to acquire correlative data for validating the extinction profiles measured by these satellite sensors. The present investigation has the objective to present results from the first two of these experiments, which were conducted at Sondrestorm, Greenland, in November 1978, and at Poker Flat, Alaska, in July 1979. In both experiments, extinction profiles derived from the correlative sensors (dustsonde, lidar, filter, wire impactor) agreed, to within their respective uncertainties, with the extinction profiles measured by SAM II and SAGE (which in turn agreed with each other).

Russell, P. B.↗

NASA NTRS1983

Evaluation of a total energy-rate sensor on a transport airplane

A sensor that measures the rate of change of total energy of an airplane with respect to the airstream has been evaluated. The sensor consists of two cylindrical probes located on the fuselage of a transport airplane, an in line acoustic filter, and a pressure sensing altitude rate transducer. Sections of this report include the sensor description and experimental configuration, frequency response tests, analytical model development, and flight test results for several airplane maneuvers. The results section includes time history comparisons between data generated by the total energy rate sensor and calculated data derived from independent sources.

Ostroff, A. J.↗

NASA NTRS1984

Spaceborne sensors (1983-2000 AD): A forecast of technology

A technical review and forecast of space technology as it applies to spaceborne sensors for future NASA missions is presented. A format for categorization of sensor systems covering the entire electromagnetic spectrum, including particles and fields is developed. Major generic sensor systems are related to their subsystems, components, and to basic research and development. General supporting technologies such as cryogenics, optical design, and data processing electronics are addressed where appropriate. The dependence of many classes of instruments on common components, basic R&D and support technologies is also illustrated. A forecast of important system designs and instrument and component performance parameters is provided for the 1983-2000 AD time frame. Some insight into the scientific and applications capabilities and goals of the sensor systems is also given.

Kostiuk, T.↗