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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Absolute radiometric calibration of advanced remote sensing systems

The distinction between the uses of relative and absolute spectroradiometric calibration of remote sensing systems is discussed. The advantages of detector-based absolute calibration are described, and the categories of relative and absolute system calibrations are listed. The limitations and problems associated with three common methods used for the absolute calibration of remote sensing systems are addressed. Two methods are proposed for the in-flight absolute calibration of advanced multispectral linear array systems. One makes use of a sun-illuminated panel in front of the sensor, the radiance of which is monitored by a spectrally flat pyroelectric radiometer. The other uses a large, uniform, high-radiance reference ground surface. The ground and atmospheric measurements required as input to a radiative transfer program to predict the radiance level at the entrance pupil of the orbital sensor are discussed, and the ground instrumentation is described. Previously announced in STAR as N83-28544

Slater, P. N.↗
NASA NTRS1983

SAR calibration: A technology review

Various potential applications of amplitude-calibrated SAR systems are briefly described, along with an estimate of calibration performance requirements. A review of the basic SAR calibration problem is given. For background purposes and to establish consistent definition of terms, various conventional SAR performance parameters are reviewed along with three additional parameters which are directly related to calibrated SAR systems. Techniques for calibrating a SAR are described. Included in the results presented are: calibration philosophy and procedures; review of the calibration signal generator technology development with results describing both the development of instrumentation and internal calibration measurements for two SAR systems; summary of analysis and measurements required to determine optimum retroreflector design and configuration for use as a reference for the absolute calibration of a SAR system; and summary of techniques for in-flight measurements of SAR antenna response.

Larson, R. W.↗
NASA NTRS2004

Method of Calibration for a Large Cathetometer System

A method of calibration has been devised for a pair of mutually orthogonal two-axis cathetometers that, when used together, yield measurements of three-dimensional positions of objects mounted on an optical bench. Each cathetometer has a horizontal travel of 1.8 m and a vertical travel of 1.2 m. The cathetometers are required to measure X, Y, and Z coordinates (see figure) to within plus or minus 0.005 in. (plus or minus 0.127 mm). Each cathetometer consists of an alignment telescope on a platform mounted on a two-dimensional translation stage. The knowledge required for calibration of each cathetometer is (1) the two-dimensional position of the cathetometer platform as a function of the electronic readouts of position encoders on the translation stage and (2) the amount of any angular misalignment (roll, pitch, and/or yaw) of the cathetometer platform as a function of the two-dimensional coordinates or the position-encoder readouts. By use of three equations derived from the applicable trigonometric relationships, the calibrated X, Y, and Z coordinates can be computed from the raw encoder readouts.

Toland, Ronald↗
NASA NTRS1978

S-band radar calibration test of the Lightning Detection and Ranging system (LDAR)

A calibration and an accuracy assessment of the Lightning Detection and Ranging System (LDAR) were attempted through a simultaneous track of an S Band radar transponder and a lightning simulator carried by the NASA 6 airplane on a test flight. Included in the report are the results of the calibration test, error analyses of the radar, and the LDAR systems, and recommendations for future calibration tests.

Poehler, H. A.↗
NASA NTRS1981

Optimization of thrust algorithm calibration for Computing System (TCS) for Thrust the NASA Highly Maneuverable Aircraft Technology (HiMAT) vehicle's propulsion system

A simplified gross thrust computing technique for the HiMAT J85-GE-21 engine using altitude facility data was evaluated. The results over the full engine envelope for both the standard engine mode and the open nozzle engine mode are presented. Results using afterburner casing static pressure taps are compared to those using liner static pressure taps. It is found that the technique is very accurate for both the standard and open nozzle engine modes. The difference in the algorithm accuracy for a calibration based on data from one test condition was small compared to a calibration based on data from all of the test conditions.

Hamer, M. J.↗
NASA NTRS1988

DSS 14 64-meter antenna S- and X-band efficiency and system noise temperature calibrations, September 1987

The efficiency and noise temperature characteristics of the DSN 64 m antenna network prior to its upgrading to 70 m configuration are documented. The DSS 14 (Goldstone, California) is the last of the three large antennas to be upgraded, and the test results presented document its performance just prior to its downtime during the end of 1987. Antenna area efficiency was found to be somewhat higher at DSS 14 than at DSS 43 (Australia) and DSS 63 (Spain). The peak X-band efficiency was determined to be 49.8 percent (without atmosphere), compared with 45.4 and 45.1 percent for DSS 43 and DSS 63, respectively. The X-band zenith system noise temperature was found to be 1 to 3 Kelvins higher than at the other two stations, depending on which maser was chosen for the measurements. Ascribing efficiency differences to small-scale antenna surface roughness, DSS 14 may be regarded as having a 1.5 to 1.6 mm rms surface as compared to the other two antennas with 1.7 to 1.8 mm rms surfaces.

Slobin, S. D.↗
NASA NTRS1978

A small gas inlet system for orbital mass-spectrometer calibrations

A gas inlet system is described for generating precise gas pressures that are to be used as calibration references for the mass spectrometers aboard the dual air density Explorer satellites. This gas inlet system was developed as an inflight calibration technique in which a known amount of onboard gas is released in the satellite cavity and is detected by the mass spectrometer. Although several flight mass spectrometer experiments have been proposed, none make use of the inflight calibration technique described in this report. Laboratory measurements and calibration of the metering leak technique for the gas inlet systems are discussed. The systems tested have metering leak rates between 2 and 4 microliters/sec at 298 K for argon-40, and they produce molecular flow up to 100 torr, which is the highest test pressure in this experiment. Test data show that metering leak rates are reproducible within 1 percent of established means for helium-3, helium-4, and argon-40.

Smith, A.↗
NASA NTRS2012

System and method for calibrating a rotary absolute position sensor

A system includes a rotary device, a rotary absolute position (RAP) sensor generating encoded pairs of voltage signals describing positional data of the rotary device, a host machine, and an algorithm. The algorithm calculates calibration parameters usable to determine an absolute position of the rotary device using the encoded pairs, and is adapted for linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters. A method of calibrating the RAP sensor includes measuring the rotary position as encoded pairs of voltage signals, linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters, and calculating an absolute position of the rotary device using the calibration parameters. The calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse. The voltage signals may include an encoded sine and cosine of a rotary angle of the rotary device.

Davis, Donald R.↗
NASA NTRS2000

Self-calibration of Laser Tracking Systems

In this paper, a methodology for self-calibrating a multi-beam laser tracking measurement system with planar constraints is proposed.

Self-calibration planar constraints Laser Tracking↗
NASA NTRS1976

Meteorological radar facility. Part 1: System design

A compilation of information regarding systems design of space shuttles used in meteorological radar probes is presented. Necessary radar equipment is delineated, while space system elements, calibration techniques, antenna systems and other subsystems are reviewed.

Brassaw, L. L., Jr.↗
NASA NTRS1980

Outer planet investigations using a CCD camera system

Problems related to analog noise, data transfer from the camera buffer to the storage computer, and loss of sensitivity of a two dimensional charge coupled device imaging system are reported. To calibrate the CCD system, calibrated UBV pinhole scans of the Saturn disk were obtained with a photoelectric area scanning photometer. Atmospheric point spread functions were also obtained. The UBV observations and models of the Saturn atmosphere are analyzed.

Price, M. J.↗
NASA NTRS2004

System and method for calibrating inter-star-tracker misalignments in a stellar inertial attitude determination system

A method and apparatus for determining star tracker misalignments is disclosed. The method comprises the steps of defining a defining a reference frame for the star tracker assembly according to a boresight of the primary star tracker and a boresight of a second star tracker wherein the boresight of the primary star tracker and a plane spanned by the boresight of the primary star tracker and the boresight of the second star tracker at least partially define a datum for the reference frame for the star tracker assembly; and determining the misalignment of the at least one star tracker as a rotation of the defined reference frame.

Li, Rongsheng↗
NASA NTRS1990

A convenient technique for polarimetric calibration of single-antenna radar systems

A practical technique for calibrating single-antenna polarimetric radar systems is introduced. This technique requires only a single calibration target such as a conducting sphere or a trihedral corner reflector to calibrate the radar system, both in amplitude and phase, for all linear polarization configurations. By using a metal sphere, which is orientation independent, error in calibration measurement is minimized while simultaneously calibrating the crosspolarization channels. The antenna system and two orthogonal channels (in free space) are modeled as a four-port passive network. Upon using the reciprocity relations for the passive network and assuming the crosscoupling terms of the antenna to be equal, the crosstalk factors of the antenna system and the transmit and receive channel imbalances can be obtained from measurement of the backscatter from a metal sphere. For an X-band radar system with crosspolarization isolation of 25 dB, comparison of values measured for a sphere and a cylinder with theoretical values shows agreement within 0.4 dB in magnitude and 5 deg in phase. An effective polarization isolation of 50 dB is achieved using this calibration technique.

Sarabandi, Kamal↗
NASA NTRS2010

Method of calibrating a fluid-level measurement system

A method of calibrating a fluid-level measurement system is provided. A first response of the system is recorded when the system's sensor(s) is (are) not in contact with a fluid of interest. A second response of the system is recorded when the system's sensor(s) is (are) fully immersed in the fluid of interest. Using the first and second responses, a plurality of expected responses of the system's sensor(s) is (are) generated for a corresponding plurality of levels of immersion of the sensor(s) in the fluid of interest.

Woodard, Stanley E.↗
NASA NTRS1990

Calibration of polarimetric radar systems with good polarization isolation

A practical technique is proposed for calibrating single-antenna polarimetric radar systems using a metal sphere plus any second target with a strong cross-polarized radar cross section. This technique assumes perfect isolation between antenna ports. It is shown that all magnitudes and phases (relative to one of the like-polarized linear polarization configurations) of the radar transfer function can be calibrated without knowledge of the scattering matrix of the second target. Comparison of the values measured (using this calibration technique) for a tilted cylinder at X-band with theoretical values shows agreement within + or - 0.3 dB in magnitude and + or - 5 degrees in phase. The radar overall cross-polarization isolation was 25 dB. The technique is particularly useful for calibrating a radar under field conditions, because it does not require the careful alignment of calibration targets.

Sarabandi, Kamal↗
NASA NTRS1987

AVIRIS foreoptics, fiber optics and on-board calibrator

The foreoptics, fiber optic system and calibration source of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) are described. The foreoptics, based on a modified Kennedy scanner, is coupled by optical fibers to the four spectrometers. The optical fibers allow convenient positioning of the spectrometers in the limited space and enable simple compensation of the scanner's thermal defocus (at the -23 C operating temp) by active control of the fiber focal plane position. A challenging requirement for the fiber optic system was the transmission to the spectral range 1.85 to 2.45 microns at .45 numerical aperture. This was solved with custom fluoride glass fibers from Verre Fluore. The onboard calibration source is also coupled to the spectrometers by the fibers and provides two radiometric levels and a reference spectrum to check the spectrometers' alignment. Results of the performance of the assembled subsystems are presented.

Chrisp, Michael P.↗