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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Further investigation into calibration techniques for a magnetic suspension and balance system

Calibrations performed on three different magnetic cores for wind tunnel models suspended in the Southampton University Magnetic Suspension and Balance System (SUMSBS) are detailed. The first core investigated was the Southampton University pilot Superconducting Solenoid model, first flown in July 1983. Static calibrations of lift force, drag force and pitching moment, together with lift force and pitching moment calibrations determined by the dynamic method are detailed in this report. Other types of core investigated in a similar manner were conventional permanent magnets, Alnico and samarium-cobalt. All static calibrations gave a linear dependence of force on electromagnet current as expected. Dynamic calibrations are faster to perform but are proving to be not as easily analyzed as static calibrations. There are still some effects to be explained but dynamic lift calibration results were obtained agreeing to within 2 percent of the static calibration value.

Eskins, J.↗
NASA NTRS1989

Evaluating Statistical Process Control (SPC) techniques and computing the uncertainty of force calibrations

In recent years there has been a push within NASA to use statistical techniques to improve the quality of production. Two areas where statistics are used are in establishing product and process quality control of flight hardware and in evaluating the uncertainty of calibration of instruments. The Flight Systems Quality Engineering branch is responsible for developing and assuring the quality of all flight hardware; the statistical process control methods employed are reviewed and evaluated. The Measurement Standards and Calibration Laboratory performs the calibration of all instruments used on-site at JSC as well as those used by all off-site contractors. These calibrations must be performed in such a way as to be traceable to national standards maintained by the National Institute of Standards and Technology, and they must meet a four-to-one ratio of the instrument specifications to calibrating standard uncertainty. In some instances this ratio is not met, and in these cases it is desirable to compute the exact uncertainty of the calibration and determine ways of reducing it. A particular example where this problem is encountered is with a machine which does automatic calibrations of force. The process of force calibration using the United Force Machine is described in detail. The sources of error are identified and quantified when possible. Suggestions for improvement are made.

Navard, Sharon E.↗
NASA NTRS1992

Ground and flight calibration assessment of HiRAP accelerometer data from missions STS-35 and STS-40

A method of removing non-aerodynamic signals and calibrating the High Resolution Accelerometer Package (HiRAP) flight data was developed and is discussed for Shuttle Orbiter missions STS-35 and STS-40. These two mission data sets were analyzed using ground (dynamic) calibration data and flight calibrations using a flight calibration technique that was developed and refined over the HiRAP operational lifetime. This technique evolved early in the flight program, since it was recognized that ground calibration factors are insufficient to determine absolute low acceleration levels. The application of flight calibration factors to the data sets from these missions produced calibrated acceleration levels within an accuracy of less than plus or minus 1.5 micro-g of zero during a time in the flight when the acceleration level was known to be less than 1 micro-g. This analysis further confirms the theory that flight calibrations are required in order to obtain the absolute measurement of low-frequency, low-acceleration flight signals.

Blanchard, Robert C.↗
NASA NTRS1992

COBE differential microwave radiometers - Calibration techniques

The COBE spacecraft was launched November 18, 1989 UT carrying three scientific instruments into earth orbit for studies of cosmology. One of these instruments, the Differential Microwave Radiometer (DMR), is designed to measure the large-angular-scale temperature anisotropy of the cosmic microwave background radiation at three frequencies (31.5, 53, and 90 GHz). This paper presents three methods used to calibrate the DMR. First, the signal difference between beam-filling hot and cold targets observed on the ground provides a primary calibration that is transferred to space by noise sources internal to the instrument. Second, the moon is used in flight as an external calibration source. Third, the signal arising from the Doppler effect due to the earth's motion around the barycenter of the solar system is used as an external calibration source. Preliminary analysis of the external source calibration techniques confirms the accuracy of the currently more precise ground-based calibration. Assuming the noise source behavior did not change from the ground-based calibration to flight, a 0.1-0.4 percent relative and 0.7-2.5 percent absolute calibration uncertainty is derived, depending on radiometer channel.

Bennett, C. L.↗
NASA NTRS1992

Calibration of the ARID robot

The author has formulated a new, general model for specifying the kinematic properties of serial manipulators. The new model kinematic parameters do not suffer discontinuities when nominally parallel adjacent axes deviate from exact parallelism. From this new theory the author develops a first-order, lumped-parameter, calibration-model for the ARID manipulator. Next, the author develops a calibration methodology for the ARID based on visual and acoustic sensing. A sensor platform, consisting of a camera and four sonars attached to the ARID end frame, performs calibration measurements. A calibration measurement consists of processing one visual frame of an accurately placed calibration image and recording four acoustic range measurements. A minimum of two measurement protocols determine the kinematics calibration-model of the ARID for a particular region: assuming the joint displacements are accurately measured, the calibration surface is planar, and the kinematic parameters do not vary rapidly in the region. No theoretical or practical limitations appear to contra-indicate the feasibility of the calibration method developed here.

Doty, Keith L↗
NASA NTRS1993

Goddard Space Flight Center (GSFC) Flight Dynamics Facility (FDF) calibration of the Upper Atmosphere Research Satellite (UARS) sensors

Flight Dynamics Facility (FDF) responsibilities for calibration of Upper Atmosphere Research Satellite (UARS) sensors included alignment calibration of the fixed-head star trackers (FHST's) and the fine Sun sensor (FSS), determination of misalignments and scale factors for the inertial reference units (IRU's), determination of biases for the three-axis magnetometers (TAM's) and Earth sensor assemblies (ESA's), determination of gimbal misalignments of the Solar/Stellar Pointing Platform (SSPP), and field-of-view calibration for the FSS's mounted both on the Modular Attitude Control System (MACS) and on the SSPP. The calibrations, which used a combination of new and established algorithms, gave excellent results. Alignment calibration results markedly improved the accuracy of both ground and onboard Computer (OBC) attitude determination. SSPP calibration results allowed UARS to identify stars in the period immediately after yaw maneuvers, removing the delay required for the OBC to reacquire its fine pointing attitude mode. SSPP calibration considerably improved the pointing accuracy of the attached science instrument package. This paper presents a summary of the methods used and the results of all FDF UARS sensor calibration.

Hashmall, J.↗
NASA NTRS1993

Cross-calibration between airborne SAR sensors

As Synthetic Aperture Radar (SAR) system performance and experience in SAR signature evaluation increase, quantitative analysis becomes more and more important. Such analyses require an absolute radiometric calibration of the complete SAR system. To keep the expenditure on calibration of future multichannel and multisensor remote sensing systems (e.g., X-SAR/SIR-C) within a tolerable level, data from different tracks and different sensors (channels) must be cross calibrated. The 1989 joint E-SAR/DC-8 SAR calibration campaign gave a first opportunity for such an experiment, including cross sensor and cross track calibration. A basic requirement for successful cross calibration is the stability of the SAR systems. The calibration parameters derived from different tracks and the polarimetric properties of the uncalibrated data are used to describe this stability. Quality criteria for a successful cross calibration are the agreement of alpha degree values and the consistency of radar cross sections of equally sized corner reflectors. Channel imbalance and cross talk provide additional quality in case of the polarimetric DC-8 SAR.

Zink, Manfred↗
NASA NTRS1994

Software For Calibration Of Polarimetric SAR Data

POLCAL (Polarimetric Radar Calibration) software tool intended to assist in calibration of synthetic-aperture radar (SAR) systems. In particular, calibrates Stokes-matrix-format data produced as standard product by NASA/Jet Propulsion Laboratory (JPL) airborne imaging synthetic aperture radar (AIRSAR). Version 4.0 of POLCAL is upgrade of version 2.0. New options include automatic absolute calibration of 89/90 data, distributed-target analysis, calibration of nearby scenes with corner reflectors, altitude or roll-angle corrections, and calibration of errors introduced by known topography. Reduces crosstalk and corrects phase calibration without use of ground calibration equipment. Written in FORTRAN 77.

Van Zyl, Jakob↗
NASA NTRS1995

Summary of OARE flight calibration measurements

To date, the Orbital Acceleration Research Experiment (OARE) has flown on the shuttle orbiter for five missions; namely, STS-40, STS-50, STS-58, STS-62, and STS-65. The OARE instrument system contains a three-axis accelerometer which can resolve accelerations to the nano-g (10(exp -9) g) level and a full calibration station to permit in situ bias and scale factor calibration measurements. This calibration capability eliminates the large uncertainty encountered with accelerometers flown in the past on the orbiter which use ground-based calibrations to provide absolute acceleration measurements. A detailed flight data report presentation is given for the OARE calibration measurements from all missions, along with an estimate of the calibration errors. The main aim is to collect, process, and present the calibration data in one archival report. These calibration data are the necessary key ingredient to produce the absolute acceleration levels from the OARE acceleration flight data.

Blanchard, Robert C.↗
NASA NTRS1996

Multifrequency, Multipolarization External Calibration of the SIR-C/X-SAR Radars

Progress and the future plans for the following objectives are discussed: (1) Assess the accuracy at which the SIR-C/X-SAR standard data products can be calibrated through the use of ground calibrators to estimate the end-to-end system polarization calibration constants (or distortion parameters) and incorporate the constants into the data processing; (2) Study the cross-calibration between three multipolarization systems: SIR-C, the National Aeronautics and Space Administration/Jet Propulsion Laboratory (NASA/JPL) DC-8 SAR, and the University of Michigan ground-based polarimetric scatterometer; (3) Evaluate the calibration "stability" of SIR-C/X-SAR (measured by variations in the calibration constants) over the range swath width and over a specified distance in azimuth. Variations over a 12-hour period (between ascending and descending passes) will also be studied; and (4) Develop a cost-effective calibration plan including development of inexpensive polarimetric active calibrators.

Freeman, Anthony↗
NASA NTRS1998

Self-Calibrating and Remote Programmable Signal Conditioning Amplifier System and Method

A self-calibrating, remote programmable signal conditioning amplifier system employs information read from a memory attached to a measurement transducer for automatic calibration. The signal conditioning amplifier is self-calibrated on a continuous basis through use of a dual input path arrangement, with each path containing a multiplexer and a programmable amplifier. A digital signal processor controls operation of the system such that a transducer signal is applied to one of the input paths, while one or more calibration signals are applied to the second input path. Once the second path is calibrated, the digital signal processor switches the transducer signal to the second path. and then calibrates the first path. This process is continually repeated so that each path is calibrated on an essentially continuous basis. Dual output paths are also employed which are calibrated in the same manner. The digital signal processor also allows the implementation of a variety of digital filters which are either programmed into the system or downloaded by an operator, and performs up to eighth order linearization.

Medelius, Pedro J.↗
NASA NTRS1998

The Algorithm for MODIS Wavelength On-Orbit Calibration Using the SRCA

The Spectro-Radiometric Calibration Assembly (SRCA) provides on-orbit spectral calibration of the MODerate resolution Imaging Spectroradiometer (MODIS) reflected solar bands and this paper describes how it is accomplished. The SRCA has two adjacent exit slits: 1) Main slit and 2) Calibration slit. The output from the main slit is measured by a reference silicon photo-diode (SIPD) and then passes through the MODIS. The output from the calibration slit passes through a piece of didymium transmission glass and then it is measured by a calibration SIPD. The centroids of the sharp spectral peaks of a didymium glass are utilized as wavelength standards. After normalization using the reference SIPD signal to eliminate the effects of the illuminating source spectra, the calibration SIPD establishes the relationship between the peaks of the didymium spectra and the grating angle; this is accomplished through the grating equation. In the grating equation the monochromator parameters, Beta (half angle between the incident and diffractive beams) and Theta(sub off) (offset angle of the grating motor) are determined by matching, in a least square sense, the known centroid wavelengths of the didymium peaks and the calculated centroid grating angles from the calibration SIPD signals for the peaks. A displacement between the calibration SIPD and the reference SIPD complicates the signal processing.

Montgomery, Harry↗
NASA NTRS1999

Uncertainty Analysis of Instrument Calibration and Application

Experimental aerodynamic researchers require estimated precision and bias uncertainties of measured physical quantities, typically at 95 percent confidence levels. Uncertainties of final computed aerodynamic parameters are obtained by propagation of individual measurement uncertainties through the defining functional expressions. In this paper, rigorous mathematical techniques are extended to determine precision and bias uncertainties of any instrument-sensor system. Through this analysis, instrument uncertainties determined through calibration are now expressed as functions of the corresponding measurement for linear and nonlinear univariate and multivariate processes. Treatment of correlated measurement precision error is developed. During laboratory calibration, calibration standard uncertainties are assumed to be an order of magnitude less than those of the instrument being calibrated. Often calibration standards do not satisfy this assumption. This paper applies rigorous statistical methods for inclusion of calibration standard uncertainty and covariance due to the order of their application. The effects of mathematical modeling error on calibration bias uncertainty are quantified. The effects of experimental design on uncertainty are analyzed. The importance of replication is emphasized, techniques for estimation of both bias and precision uncertainties using replication are developed. Statistical tests for stationarity of calibration parameters over time are obtained.

Tripp, John S.↗
NASA NTRS1997

The Algorithm for MODIS Wavelength On-Orbit Calibration using the SRCA

The Spectro-Radiometric Calibration Assembly (SRCA) provides on-orbit spectral calibration of the MODerate resolution Imaging Spectroradiometer (MODIS) reflected solar bands and this paper describes how it is accomplished. The SRCA has two adjacent exit slits: 1) Main slit and 2) Calibration slit. The output from the main slit is measured by a reference silicon photo-diode (SIPD) and then passes through the MODIS. The output from the calibration slit passes through a piece of didymium transmission glass and then it is measured by a calibration SIPD. The centroids of the sharp spectral peaks of a didyrnium glass are utilized as wavelength standards. After normalization using the reference SIPD signal to eliminate the effects of the illuminating source spectra, the calibration SIPD establishes the relationship between the peaks of the didymium spectra and the grating angle; this is accomplished through the grating equation. In the grating equation the monochromator parameters, beta (half angle between the incident and diffractive beams) and theta(sub ff) (offset angle of the grating motor) are determined by matching, in a least square sense, the known centroid wavelengths of the didymium peaks and the calculated centroid grating angles from the calibration SIPD signals for the peaks. A displacement between the calibration SIPD and the reference SIPD complicates the signal processing. The response of the MODIS bands to the SRCA output is also normalized by the reference SIPD signal to eliminate the effect of the source spectrum. That response differs from what is measured by MODIS using the Spectral Measurements Assembly (SpMA), a laboratory double-monochromator, due to the wider slit width of the SRCA. The SRCA slit function, calculated using measurements by the SPMA and the SRCA at the same MODIS temperature, will be used to recover the MODIS spectral response using the SRCA data measured on-orbit.

Montgomery, Harry↗
NASA NTRS1999

Comparison of Continuous Wave CO2 Doppler Lidar Calibration Using Earth Surface Targets in Laboratory and Airborne Measurements

Routine backscatter, beta, measurements by an airborne or space-based lidar from designated earth surfaces with known and fairly uniform beta properties can potentially offer lidar calibration opportunities. This can in turn be used to obtain accurate atmospheric aerosol and cloud beta measurements on large spatial scales. This is important because achieving a precise calibration factor for large pulsed lidars then need not rest solely on using a standard hard target procedure. Furthermore, calibration from designated earth surfaces would provide an inflight performance evaluation of the lidar. Hence, with active remote sensing using lasers with high resolution data, calibration of a space-based lidar using earth's surfaces will be extremely useful. The calibration methodology using the earth's surface initially requires measuring beta of various earth surfaces simulated in the laboratory using a focused continuous wave (CW) CO2 Doppler lidar and then use these beta measurements as standards for the earth surface signal from airborne or space-based lidars. Since beta from the earth's surface may be retrieved at different angles of incidence, beta would also need to be measured at various angles of incidences of the different surfaces. In general, Earth-surface reflectance measurements have been made in the infrared, but the use of lidars to characterize them and in turn use of the Earth's surface to calibrate lidars has not been made. The feasibility of this calibration methodology is demonstrated through a comparison of these laboratory measurements with actual earth surface beta retrieved from the same lidar during the NASA/Multi-center Airborne Coherent Atmospheric Wind Sensor (MACAWS) mission on NASA's DC8 aircraft from 13 - 26 September, 1995. For the selected earth surface from the airborne lidar data, an average beta for the surface was established and the statistics of lidar efficiency was determined. This was compared with the actual lidar efficiency determined with the standard calibrating hard target.

Jarzembski, Maurice A.↗
NASA NTRS1999

Landsat-7 EMT+ On-Orbit Radiometric Calibration

Landsat-7 was launched on April 15, 1999 and completed its on orbit initialization and verification period on June 28, 1999. The ETM+ payload is similar to the TM sensors on previous Landsat satellites and incorporates two new devices to improve its absolute radiometric calibration. The Full Aperture Solar Calibrator (FASC) is a deployable diffuser panel. This device has been deployed 9 times to date, with a normal deployment schedule of once per month. The initial analysis of the FASC data has given absolute calibration results within 5% of the prelaunch integrating sphere calibrations and a range of variation of 2% between dates. The Partial Aperture Solar Calibrator (PASC), is a set of auxiliary optics that allows the ETM+ to view the sun through a reduced aperture. Data have normally been acquired on a daily basis with the PASC. Initial results with the PASC were encouraging, despite some unexpected saturation in the shortest wavelength band. The response of the ETM+ short wavelength (silicon) bands to the PASC increased initially and has begun to decrease in some of these bands. The longer wavelength (InSb) bands have shown up to 30% oscillations that vary between detectors within the band. Studies are ongoing to better characterize the response to the PASC. The ETM+ also incorporates an internal calibrator (IC), a shutter that oscillates in front of the focal plane that directs light from the internal calibrator lamps to the focal plane. The responses to this device are also varying, though differently than the PASC results. Both the IC and PASC results are attributable to the calibration devices as opposed to the ETM+ itself.

Markham, Brian L.↗
NASA NTRS2001

Solar-Reflectance-Based Calibration of Spectral Radiometers

A method by which to calibrate a spectral radiometer using the sun as the illumination source is discussed. Solar-based calibrations eliminate several uncertainties associated with applying a lamp-based calibration to field measurements. The procedure requires only a calibrated reflectance panel, relatively low aerosol optical depth, and measurements of atmospheric transmittance. Further, a solar-reflectance-based calibration (SRBC), by eliminating the need for extraterrestrial irradiance spectra, reduces calibration uncertainty to approximately 2.2% across the solar-reflective spectrum, significantly reducing uncertainty in measurements used to deduce the optical properties of a system illuminated by the sun (e.g., sky radiance). The procedure is very suitable for on-site calibration of long-term field instruments, thereby reducing the logistics and costs associated with transporting a radiometer to a calibration facility.

Cattrall, Christopher↗
NASA NTRS2002

Prelaunch Instrument Calibration in the Real World: The GOES Example

The pre-launch ground infrared calibration of the Geostationary Operational Environmental Satellite (GOES) N-Q Imager and Sounder is presented. Ground calibration provides information necessary to the accurate on-orbit calibration of these radiometers. Infrared channels are calibrated in a thermal vacuum environment, under minimum and maximum mission operation temperatures, using a variable-temperature warm target to simulate the Earth scene and a cold target to simulate the space scene. Brightness temperatures derived from observation of the instrument internal calibration target, used for on-orbit calibration, are compared to brightness temperatures of the external calibration target as a check of relative accuracy using these two sources. Changes to the GOES N-Q specification from GOES I-M are highlighted, as well as results of noise, relative calibration accuracy, and spectral response performance to date. For completeness, results of spatial and pointing performance will be presented. Enhancements to test methodology and data processing techniques are highlighted throughout.

Murphy-Morris, J.↗