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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A Technical basis for in-house calibration of 252 Cf neutron source emission rates

10CFR835 stipulates that radiation protection instruments must be calibrated at least annually. Accordingly, calibration of dose rate instruments are reliant on well-known reference fields. The neutron-free-in-air facility (NFIA) located at TA36-0214 provides such a capability for neutron remmeters. One of the reference NFIA sources, 252 Cf, must be replaced every 8-10 years due to its relatively short half-life (2.645 ± 0.008 y). In the past, each newly purchased 252 Cf source has been calibrated at NIST using the Mn-bath technique prior to shipping to LANL. However, because of COVID-19 complications, the most recently acquired 252 Cf source (FTC-CF-7167) has been stored at LANL pending approval to ship to NIST for calibration. Due to the considerable expense in transporting the source to and from NIST, this TBD was written to demonstrate that new sources can be accurately calibrated via intercomparison measurements with older NIST-calibrated 252 Cf sources. It had been previously noted that such measurements yielded emission rates that agreed very well with the official rates established by NIST

252cf↗
NASA NTRS1981

Multispectral scanner, thematic mapper, and beyond

The capabilities and functions of the Landsat D multispectral scanner (MSS) and thematic mapper (TM) are explored as a basis for improvements to satisfy increasing user demands. The MSS is an object-space line scanner for gathering data in four spectral bands ranging from 0.5-1.1 micron. In a 705 km near-polar sunsynchronous orbit, the MSS will generate 185 x 185 km imagery with 80 x 80 m ground resolution, mapping the entire earth every 16 days. Photomultiplier tubes are used for four of the bands and the other employs Si photodiodes. A calibration light source provides in orbit calibration during every reverse scan period of a pivotal on-board mirror. The TM collects data in seven bands from 0.45-12.5 microns, yielding a ground resolution of 30 x 30 m in six bands for reflected sunlight and 120 x 120 m for the 10.4-12.5 thermal bands. The addition of 16 Si detectors for 0.9-1.1 micron viewing for agricultural purposes, as well as higher resolution, is discussed.

Jones, C. R.↗
NASA NTRS1994

MODIS airborne simulator visible and near-infrared calibration, 1991 FIRE-Cirrus field experiment. Calibration version: FIRE King 1.1

Calibration of the visible and near-infrared channels of the MODIS Airborne Simulator (MAS) is derived from observations of a calibrated light source. For the 1991 FIRE-Cirrus field experiment, the calibrated light source was the NASA Goddard 48-inch integrating hemisphere. Laboratory tests during the FIRE Cirrus field experiment were conducted to calibrate the hemisphere and from the hemisphere to the MAS. The purpose of this report is to summarize the FIRE-Cirrus hemisphere calibration, and then describe how the MAS was calibrated from observations of the hemisphere data. All MAS calibration measurements are presented, and determination of the MAS calibration coefficients (raw counts to radiance conversion) is discussed. Thermal sensitivity of the MAS visible and near-infrared calibration is also discussed. Typically, the MAS in-flight is 30 to 60 degrees C colder than the room temperature laboratory calibration. Results from in-flight temperature measurements and tests of the MAS in a cold chamber are given, and from these, equations are derived to adjust the MAS in-flight data to what the value would be at laboratory conditions. For FIRE-Cirrus data, only channels 3 through 6 were found to be temperature sensitive. The final section of this report describes comparisons to an independent MAS (room temperature) calibration by Ames personnel using their 30-inch integrating sphere.

Arnold, G. Thomas↗
DOE OSTI2023

Calibration strategy of the PROSPECT-II detector with external and intrinsic sources

This paper presents an energy calibration scheme for an upgraded reactor antineutrino detector for the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT). The PROSPECT collaboration is preparing an upgraded detector, PROSPECT-II (P-II), to advance capabilities for the investigation of fundamental neutrino physics, fission processes and associated reactor neutrino flux, and nuclear security applications. P-II will expand the statistical power of the original PROSPECT (P-I) dataset by at least an order of magnitude. The new design builds upon previous P-I design and focuses on improving the detector robustness and long-term stability to enable multi-year operation at one or more sites. The new design optimizes the fiducial volume by elimination of dead space previously occupied by internal calibration channels, which in turn necessitates the external deployment. In this paper, we describe a calibration strategy for P-II. Here, the expected performance of externally deployed calibration sources is evaluated using P-I data and a well-benchmarked simulation package by varying detector segmentation configurations in the analysis. The proposed external calibration scheme delivers a compatible energy scale model and achieves comparable performance with the inclusion of an additional AmBe neutron source, in comparison to the previous internal arrangement. Most importantly, the estimated uncertainty contribution from the external energy scale calibration model meets the precision requirements of the P-II experiment.

47 OTHER INSTRUMENTATION↗
NASA NTRS1994

MODIS airborne simulator visible and near-infrared calibration, 1992 ASTEX field experiment. Calibration version: ASTEX King 1.0

Calibration of the visible and near-infrared (near-IR) channels of the MODIS Airborne Simulator (MAS) is derived from observations of a calibrated light source. For the 1992 Atlantic Stratocumulus Transition Experiment (ASTEX) field deployment, the calibrated light source was the NASA Goddard 48-inch integrating hemisphere. Tests during the ASTEX deployment were conducted to calibrate the hemisphere and then the MAS. This report summarizes the ASTEX hemisphere calibration, and then describes how the MAS was calibrated from the hemisphere data. All MAS calibration measurements are presented and determination of the MAS calibration coefficients (raw counts to radiance conversion) is discussed. In addition, comparisons to an independent MAS calibration by Ames personnel using their 30-inch integrating sphere is discussed.

Arnold, G. Thomas↗
NASA NTRS1980

ORION S-band data acquisition for S-Y calibration

Error sources in the Operational Radio Interferometry Observing Network (ORION) are addressed. Specifically, the performance of the S-band receiver and the optimum allocation of data volume between S- and X-band observations is studied. It is found that the requirements on the S-band receiver are not very stringent. The system temperature of the ORION S-band receiver has a very small effect on baseline determination accuracy. It is unwise to pay a high cost for an S-band receiver with a low system temperature; a system temperature as high as 240 K is tolerable. Only 20 to 40 percent of data volume is to be allocated to S-band observations for minimum baseline error. The error remains low over a rather wide range of data volume ratio. Hence precise allocation of the 14 pairs of the Mark 3 very long base interferometer data channels between S- and X-band observations is not critical.

Wu, S. C.↗
NASA NTRS1994

Improvements to the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) Calibration System

As a continuing effort to increase the calibration accuracy of the AVIRIS data a number of recent improvements have been implemented and are in the process of being tested during the 1994 flight season. These include the following innovations: A direct observation of a laboratory radiance standard is now used to double check the wide field-of-view calibration via an integrating sphere source. Launch site field calibration of the AVIRIS sensor is now being planned to augment the laboratory and inflight calibration. Modification to a dry air conditioning unit has been made to enable ground calibration at flight operating temperatures. One hundred lines of dark imagery has been added to the end of each flight line to assist in the analysis and removal of residual coherent noise. The intensity of the onboard calibration lamp has been modified to improve response in the blue end of the spectrum. Novel spectral filters have been installed in the onboard calibration source.

Airborne Visible/Infrared Imaging Spectrometer Cal↗
NASA NTRS1986

A Penning discharge source for extreme ultraviolet calibration

A Penning discharge lamp for use in the calibration of instruments and components for the extreme ultraviolet has been developed. This source is sufficiently light and compact to make it suitable for mounting on the movable slit assembly of a grazing incidence Rowland circle monochromator. Because this is a continuous discharge source, it is suitable for use with photon counting detectors. Line radiation is provided both by the gas and by atoms sputtered off the interchangeable metal cathodes. Usable lines are produced by species as highly ionized as Ne IV and Al V. The wavelength coverage provided is such that a good density of emission lines is available down to wavelengths as short as 100A. This source fills the gap between 100 and 300A, which is inadequately covered by the other available compact continuous radiation sources.

Finley, David S.↗
DOE OSTI2022

Dark Energy Survey Year 3 results: Exploiting small-scale information with lensing shear ratios

Using the first three years of data from the Dark Energy Survey (DES), we use ratios of small-scale galaxy-galaxy lensing measurements around the same lens sample to constrain source redshift uncertainties, intrinsic alignments and other systematics or nuisance parameters of our model. Instead of using a simple geometric approach for the ratios as has been done in the past, we use the full modeling of the galaxy-galaxy lensing measurements, including the corresponding integration over the power spectrum and the contributions from intrinsic alignments and lens magnification. We perform extensive testing of the small-scale shear-ratio (SR) modeling by studying the impact of different effects such as the inclusion of baryonic physics, nonlinear biasing, halo occupation distribution descriptions and lens magnification, among others, and using realistic N -body simulations of the DES data. We validate the robustness of our constraints in the data by using two independent lens samples with different galaxy properties, and by deriving constraints using the corresponding large-scale ratios for which the modeling is simpler. The results applied to the DES Y3 data demonstrate how the ratios provide significant improvements in constraining power for several nuisance parameters in our model, especially on source redshift calibration and intrinsic alignments. For source redshifts, SR improves the constraints from the prior by up to 38% in some redshift bins. Such improvements, and especially the constraints it provides on intrinsic alignments, translate to tighter cosmological constraints when shear ratios are combined with cosmic shear and other 2pt functions. In particular, for the DES Y3 data, SR improves S 8 constraints from cosmic shear by up to 31%, and for the full combination of probes ( 3 × 2 pt ) by up to 10%. The shear ratios presented in this work are used as an additional likelihood for cosmic shear, 2 × 2 pt and the full 3 × 2 pt in the fiducial DES Y3 cosmological analysis.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

X-ray sources for in situ wavelength calibration of x-ray imaging crystal spectrometers

X-ray sources for a range of wavelengths are being considered for in situ calibration of X-ray Imaging Crystal Spectrometers (XICSs) and for monitoring line shifts due to changes in the crystal temperature, which can vary during experimental operation over a day [A. Ince-Cushman et al., Rev. Sci. Instrum. 79, 10E302 (2008), L. Delgado-Aparicio et al., Plasma Phys. Control. Fusion 55, 125011 (2013)]. Such crystal temperature dependent shifts, if not accounted for, could be erroneously interpreted as Doppler shifts leading to errors in plasma flow-velocity measurements. The x-ray sources encompass characteristic x-ray lines falling within the wavelength range of 0.9–4.0 Å, relevant for the XICSs on present and future fusion devices. Several technological challenges associated with the development of x-ray sources for in situ calibration are identified and are being addressed in the design of multiple x-ray tubes, which will be installed inside the spectrometer housing of the XICS for the JT-60SA tokamak. These x-ray sources will be especially useful for in situ calibration between plasma discharges. Here, in this paper, laboratory experiments are described that were conducted with a Cu x-ray source, a heated quartz (102) crystal, and a pixelated Pilatus detector to measure the temperature dependent shifts of the Cu Kα 1 and Kα 2 lines at 1.5405 and 1.5443 Å, respectively, and to evaluate the 2d-lattice constant for the Bragg reflecting crystal planes as a function of temperature, which, in the case of in situ wavelength calibration, would have to be used for numerical analysis of the x-ray spectra from the plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
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 NTRS1998

Issues in Absolute Spectral Radiometric Calibration: Intercomparison of Eight Sources

The application of atmospheric models to AVIRIS and other spectral imaging data to derive surface reflectance requires that the sensor output be calibrated to absolute radiance. Uncertainties in absolute calibration are to be expected, and claims of 92% accuracy have been published. Measurements of accurate surface albedos and cloud absorption to be used in radiative balance calculations depend critically on knowing the absolute spectral-radiometric response of the sensor. The Earth Observing System project is implementing a rigorous program of absolute radiometric calibration for all optical sensors. Since a number of imaging instruments that provide output in terms of absolute radiance are calibrated at different sites, it is important to determine the errors that can be expected among calibration sites. Another question exists about the errors in the absolute knowledge of the exoatmospheric spectral solar irradiance.

Goetz, Alexander F. H.↗
NASA NTRS1985

Lidar aerosol backscatter measurements - Systematic, modeling, and calibration error considerations

Sources of systematic, modeling, and calibration errors that affect the interpretation and calibration of lidar aerosol backscatter data are discussed. The treatment pertains primarily to ground-based pulsed CO2 lidars that probe the troposphere and are calibrated using hard calibration targets. However, a large part of the analysis is relevant to other types of lidar system such as lidars operating at other wavelengths; CW focused lidars; airborne or earth-orbiting lidars; lidars measuring other regions of the atmosphere; lidars measuring nonaerosol elastic or inelastic backscatter; and lidars employing other calibration techniques.

Kavaya, M. J.↗
NASA NTRS2011

Technique for Radiometer and Antenna Array Calibration with Two Antenna Noise Diodes

This paper presents a new technique to calibrate a microwave radiometer and phased array antenna system. This calibration technique uses a radiated noise source in addition to an injected noise sources for calibration. The plane of reference for this calibration technique is the face of the antenna and therefore can effectively calibration the gain fluctuations in the active phased array antennas. This paper gives the mathematical formulation for the technique and discusses the improvements brought by the method over the existing calibration techniques.

Srinivasan, Karthik↗
NASA NTRS1991

A technique for improving the calibration of large-area sphere sources

A new technique for improving the accuracy of radiance calibrations for large-area integrating-sphere sources has been investigated. Such sources are used to calibrate numerous aircraft and spacecraft remote sensing instruments. Recent measurements performed at NIST and NASA Goddard Space Flight Center have demonstrated that the uncertainty of sphere-source radiance measurements can be improved from the present 5 to 10 percent level to a 1 to 2 percent level. Silicon detectors with bandpass filters mounted in front of them and calibrated for absolute spectral responsivity can be used to confirm and to monitor the absolute radiance of a sphere source.

Walker, James H.↗
DOE OSTI2021

Dark Energy Survey Year 3 Results: clustering redshifts – calibration of the weak lensing source redshift distributions with redMaGiC and BOSS/eBOSS

ABSTRACT We present the calibration of the Dark Energy Survey Year 3 (DES Y3) weak lensing (WL) source galaxy redshift distributions n(z) from clustering measurements. In particular, we cross-correlate the WL source galaxies sample with redMaGiC galaxies (luminous red galaxies with secure photometric redshifts) and a spectroscopic sample from BOSS/eBOSS to estimate the redshift distribution of the DES sources sample. Two distinct methods for using the clustering statistics are described. The first uses the clustering information independently to estimate the mean redshift of the source galaxies within a redshift window, as done in the DES Y1 analysis. The second method establishes a likelihood of the clustering data as a function of n(z), which can be incorporated into schemes for generating samples of n(z) subject to combined clustering and photometric constraints. Both methods incorporate marginalization over various astrophysical systematics, including magnification and redshift-dependent galaxy-matter bias. We characterize the uncertainties of the methods in simulations; the first method recovers the mean z of tomographic bins to RMS (precision) of ∼0.014. Use of the second method is shown to vastly improve the accuracy of the shape of n(z) derived from photometric data. The two methods are then applied to the DES Y3 data.

79 ASTRONOMY AND ASTROPHYSICS↗