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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

A Broad Bank Lidar for Precise Atmospheric CO2 Column Absorption Measurement from Space

Accurate global measurement of carbon dioxide column with the aim of discovering and quantifying unknown sources and sinks has been a high priority for the last decade. In order to uncover the "missing sink" that is responsible for the large discrepancies in the budget the critical precision for a measurement from space needs to be on the order of 1 ppm. To better understand the CO2 budget and to evaluate its impact on global warming the National Research Council (NRC) in its recent decadal survey report (NACP) to NASA recommended a laser based total CO2 mapping mission in the near future. That's the goal of Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission - to significantly enhance the understanding of the role of CO2 in the global carbon cycle. Our current goal is to develop an ultra precise, inexpensive new lidar system for column measurements of CO2 changes in the lower atmosphere that uses a Fabry-Perot interferometer based system as the detector portion of the instrument and replaces the narrow band laser commonly used in lidars with a high power broadband source. This approach reduces the number of individual lasers used in the system and considerably reduces the risk of failure. It also tremendously reduces the requirement for wavelength stability in the source putting this responsibility instead on the Fabry- Perot subsystem.

Georgieva, E. M.↗
NASA NTRS2014

Verification of Dosimetry Measurements with Timepix Pixel Detectors for Space Applications

The current capabilities of modern pixel-detector technology has provided the possibility to design a new generation of radiation monitors. Timepix detectors are semiconductor pixel detectors based on a hybrid configuration. As such, the read-out chip can be used with different types and thicknesses of sensors. For space radiation dosimetry applications, Timepix devices with 300 and 500 microns thick silicon sensors have been used by a collaboration between NASA and University of Houston to explore their performance. For that purpose, an extensive evaluation of the response of Timepix for such applications has been performed. Timepix-based devices were tested in many different environments both at ground-based accelerator facilities such as HIMAC (Heavy Ion Medical Accelerator in Chiba, Japan), and at NSRL (NASA Space Radiation Laboratory at Brookhaven National Laboratory in Upton, NY), as well as in space on board of the International Space Station (ISS). These tests have included a wide range of the particle types and energies, from protons through iron nuclei. The results have been compared both with other devices and theoretical values. This effort has demonstrated that Timepix-based detectors are exceptionally capable at providing accurate dosimetry measurements in this application as verified by the confirming correspondence with the other accepted techniques.

Kroupa, M.↗
NASA NTRS2018

MCT Avalanche Photodiode Detector for Two-Micron Active Remote Sensing Applications

Mercury Cadmium Telluride electron initiated avalanche photodiodes demonstrated a breakthrough in lidar active remote sensing technology. A lidar detection system, based on an array of these devices, was integrated and characterized for 2-μm applications. Characterization experiments were focused on evaluating the dark current, gain and responsivity variations with bias voltage. Quantum efficiency and input dynamic range including noise-equivalent-power and maximum detectable power, were calculated from these results. Operating the detection system using four pixels at 77.6 K, 12 V bias resulted in a current responsivity of 615.8 A/W and a voltage responsivity of 1.45 GV/W. Minimum detectable power of 14 pW was obtained, which is equivalent to 5.7 fW/Hz(exp 1/2) noise-equivalent-power, indicating an average noise-equivalent-power of 1.4 fW/Hz(exp 1/2) per pixel. Work is in progress to integrate and validate this detection system using a newly developed triple-pulse integrated path differential absorption lidar for simultaneous and independent atmospheric measurements of water vapor and carbon dioxide.

Refaat, Tamer F.↗
NASA NTRS2000

Observed On-Orbit Background of the ACIS Detector on the Chandra X-Ray Observatory

We have analyzed calibration data acquired during the Orbital Activation and Checkout (OAC) phase of the Chandra X-ray Observatory (CXO) mission in order to characterize the background of the Advanced CCD Imaging Spectrometer (ACIS) produced by charged particles and non-cosmic X-rays. The ACIS instrument contains 8 Front-Illuminated (FI) CCDs and 2 Back-Illuminated (BI) CCDs. The FI and BI CCD)s exhibit dramatically different responses to enhancements in the particle flux. The F1 CCDs show relatively little increase in the overall count rate, typical increases are 1 - 3 counts/s; the BI CCDs show large excursions to as high as 100 counts/s. The duration of these intervals of enhanced background are highly variable ranging from 100 s to 5000 s. The spatial distribution of these background events is relatively flat across the power-law. The events produce morphologies which are similar to cosmic X-ray events, so that morphology alone cannot be used as a rejection criterion. We explore the correlation of these times of high background with the data from Chandra's on-board radiation monitor, the EPHIN (Electron, Proton, Helium Instrument particle detector) instrument and archival data from the Advanced Composition Explorer (ACE) satellite. We discuss strategies for observers to identify and exclude times of high background and to model and subtract the background events from their data.

Plucinsky, P. P.↗
NASA NTRS2011

PING Gamma Ray and Neutron Measurements of a Meter-Sized Carbonaceous Asteroid Analog

Determining the elemental composition of carbonaceous (spectral type C) asteroids is still one of the basic problems when studying these objects. The only main source of elemental composition information for asteroids is from their optical, NIR and IR properties, which include their spectral reflectance characteristics, albedo, polarization, and the comparison of optical spectroscopy with meteorite groups corresponding to asteroids of every spectral type. Unfortunately, these sources reflect observations from widely contrasting spatial scales that presently yield a void in the continuum of microscopic and macroscopic evidence, a lack of in situ measurement confirmation, and require deeper sensing techniques to discern the nature of these asteroids. The Probing In situ with Neutrons and Gamma rays (PING) instrument is ideally suited to address this problem because it can be used to determine the bulk elemental composition, H and C content, the average atomic weight and density of the surface and subsurface layers of C-type asteroids, and can provide measurements used to determine the difference between and distinguish between different types of asteroids. We are currently developing the PING instrument that combines gamma ray and neutron detectors with a 14 Me V pulsed neutron generator to determine the in-situ bulk elemental abundances and geochemistry of C-type asteroids with a spatial resolution of 1 m down to depths of tens of cm to 1 m. One aspect of the current work includes experimentally testing and optimizing PING on a known meter-sized Columbia River basalt C-type asteroid analog sample that has a similar composition and the same neutron response as that of a C-type asteroid. An important part of this effort focuses on utilizing timing measurements to isolate gamma rays produced by neutron inelastic scattering, neutron capture and delayed activation processes. Separating the gamma ray spectra by nuclear processes results in higher precision and sensitivity elemental composition measurements. Using gated data acquisition techniques allows for the unambiguous identification of gamma ray lines from different isotopes and nuclear processes, especially in situations when limited detector resolution results in overlapping gamma ray lines that cannot be individually resolved. In this paper, we will present the PING basalt layering experimental data, taken at the test facility at NASA Goddard Space Flight Center using the time tagged event-by-event data analysis technique, compared to our MCNPX computer simulation results for the C-type asteroid and basalt layering simulant models. Comparison of these data will show the advantages, validity, and measurement sensitivity of PING's nuclear interrogation methods to obtain more precise and sensitive in situ bulk elemental composition and density measurements of the subsurface of asteroids.

Bodnarik, J.↗
NASA NTRS1978

An instrument to measure the spectrum of cosmic ray iron and other nuclei to above 100 GeV-nucleon

A balloon-borne detector system for extending the study of cosmic ray composition to the energy region beyond 100 GeV/nucleon is described. The instrument incorporates an ionization calorimeter and a gas Cherenkov counter filled with freon for the determination of energies, and a charge module, consisting of scintillation and a lucite Cherenkov counter, for determining the charge of the incoming particle. The scintillators were utilized to determine the position of the incoming particle in addition to its charge. The characteristics of these detectors with respect to resolution, and the methods employed in laboratory calibration, cross-checks with flight data and actual performance in the flights are described in detail. Monte Carlo simulation of the ionization calorimeter and comparison of the response of the calorimeter and gas Cherenkov counter for complex nuclei was used to convert the observed calorimeter signal to absolute energy in a consistent manner.

Arens, J. F.↗
NASA NTRS1990

Infrared fiber-optic fire sensors - Concepts and designs for Space Station applications

Various design configurations used for testing IR fiber-optic (IFO) fire-sensor concepts are presented. Responsibility measurements conducted to select the best concept are reviewed. The results indicate that IFO fire-sensor systems based on distributed fiber sensors are feasible for future aerospace applications. For Space Station Freedom, these systems offer alternative fire detectors for monitoring areas within equipment or stage compartments where the ventilation may be inadequate for proper operation of smoke detectors. They also allow a large number of areas to be monitored by a single central detector unit, which reduces the associated cost and weight.

Tapphorn, Ralph M.↗
NASA NTRS2018

Sensor Performance Assessment for Terra and Aqua MODIS Using Unscheduled Lunar Observations

The Moderate Resolution Imaging Spectroradiometer (MODIS) has been in operation for over 18 and 16 years on the Terra and Aqua spacecrafts, respectively. In order to maintain long-term calibration stability over the life of each mission, MODIS uses a set of on-board calibrators as well as observations of the Moon and selected Earth-view targets. The lunar observations nominally occur in a narrow phase angle range, 55 degrees - 56 degrees, and use scheduled spacecraft maneuvers in order to bring the Moon into alignment with the MODIS space-view port. These observations are used to help characterize the MODIS scan-mirror response versus scan-angle. In addition to these scheduled lunar observations, MODIS also views the Moon through the space-view port without a spacecraft maneuver when the geometry is appropriately aligned. This occurs over a wider phase angle range, between 51 degrees - 82 degrees, than those of the scheduled moon observations. While the phase angle restriction of our scheduled observations provides consistency between the calibration events, the unscheduled Moon data can provide a valuable assessment of many calibration related investigations that use the Moon. In this paper, we compare the results of unscheduled versus scheduled lunar observations for several sensor calibration and performance assessments. These include the lunar calibration trending used to characterize the scan-mirror response versus scan angle and the electronic crosstalk correction of bands 27-30, which are currently used in the MODIS Level-1B data products, as well as sensor performance assessments such as band-to-band and detector-to-detector spatial registration.

Aqua↗
NASA NTRS1987

Study of solid state photomultiplier

Available solid state photomultiplier (SSPM) detectors were tested under low-background, low temperature conditions to determine the conditions producing optimal sensitivity in a space-based astronomy system such as a liquid cooled helium telescope in orbit. Detector temperatures varied between 6 and 9 K, with background flux ranging from 10 to the 13th power to less than 10 to the 6th power photons/square cm-s. Measured parameters included quantum efficiency, noise, dark current, and spectral response. Experimental data were reduced, analyzed, and combined with existing data to build the SSPM data base included herein. The results were compared to analytical models of SSPM performance where appropriate models existed. Analytical models presented here were developed to be as consistent with the data base as practicable. Significant differences between the theory and data are described. Some models were developed or updated as a result of this study.

Hays, K. M.↗
NASA NTRS1990

Low dark current photovoltaic multiquantum well long wavelength infrared detectors

The authors have, for the first time, demonstrated photovoltaic detection for an multiple quantum well (MQW) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5 times 10(exp -14) A for an 100x100 square micron 10 micron detector at 40 K, 8 to 9 orders of magnitude lower than that of a similar 10 micron MQW detector without blocking layer. The ideality factor is about 1.01 to 1.05 at T = 40 to 80 K. The measured barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also, for the first time, report the measured effective Richardson constant (A asterisk asterisk) for the GaAs/AlGaAs heterojunction using this blocking layer structure. The A asterisk asterisk is low approx. 2.3 A/sq cm/K(exp 2).

Wu, C. S.↗
NASA NTRS2006

2.4 Micron Cutoff AlGaAsSb/InGaAsSb Phototransistors for Shortwave IR Applications

Shortwave infrared detectors are critical for several applications including remote sensing and optical communications. Several detectors are commercially available for this wavelength range, but they lack sufficient gain, which limits their detectivity. The characterization results of an AlGaAsSb/InGaAsSb phototransistor for shortwave IR application are reported. The phototransistor is grown using molecular beam epitaxy technique. Spectral response measurements showed a uniform responsivity between 1.2 and 2.4 micron region with a mean value of 1000 A/W. A maximum detectivity of 3.4 X 10(exp 11) cmHz1/2/W was obtained at 2 micron at -20 C and 1.3 V.

Refaat, Tamer F.↗
NASA NTRS2011

Mobility Spectrometer Studies on Hydrazine and Ammonia Detection

An airborne vapor analyzer for detecting sub- to low- parts-per-million (ppm) hydrazine in the presence of higher concentration levels of ammonia has been under development for the Orion program. The detector is based on ambient pressure ionization and ion mobility characterization. The detector encompasses: 1) a membrane inlet to exclude particulate and aerosols from the analyzer inlet; 2) a method to separate hydrazine from ammonia which would otherwise lead to loss of calibration and quantitative accuracy for the hydrazine determination; and 3) response and quantitative determinations for both hydrazine and ammonia. Laboratory studies were made to explore some of these features including mobility measurements mindful of power, size, and weight issues. The study recommended the use of a mobility spectrometer of traditional design with a reagent gas and equipped with an inlet transfer line of bonded phase fused silica tube. The inlet transfer line provided gas phase separation of neutrals of ammonia from hydrazine at 50 C simplifying significantly the ionization chemistry that underlies response in a mobility spectrometer. Performance of the analyzer was acceptable between ranges of 30 to 80 C for both the pre-fractionation column and the drift tube. An inlet comprised of a combined membrane with valve-less injector allowed high speed quantitative determination of ammonia and hydrazine without cross reactivity from common metabolites such as alcohols, esters, and aldehydes. Preliminary test results and some of the design features are discussed.

Niu, William↗
NASA NTRS2018

Ground-Based X-Ray Calibration of the Astro-H/Hitomi Soft X-Ray Telescopes

We present the summary of the on-ground calibration of two soft x-ray telescopes (SXT-I and SXT-S), developed by NASA's Goddard Space Flight Center (GSFC), onboard Astro-H/Hitomi. After the initial x-ray measurements with a diverging beam at the GSFC 100-meter beamline, we performed the full calibration of the x-ray performance, using the 30-meter x-ray beamline facility at the Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency in Japan. We adopted a raster scan method with a narrow x-ray pencil beam with a divergence of approximately 15 arc secs. The on-axis effective area (EA), half-power diameter, and vignetting function were measured at several energies between 1.5 and 17.5 kiloelectronvolts. The detailed results appear in tables and figures in this paper. We measured and evaluated the performance of the SXT-S and the SXT-I with regard to the detector-limited field-of-view and the pixel size of the paired flight detector, i.e., SXS and the SXI, respectively. The primary items measured are the EA, image quality, and stray light for on-axis and off-axis sources. The accurate measurement of these parameters is vital to make the precise response function of the ASTRO-H SXTs. This paper presents the definitive results of the ground-based calibration of the ASTRO-H SXTs.

Iizuka, Ryo↗
NASA NTRS2013

Planar Superconducting Millimeter-Wave/Terahertz Channelizing Filter

This innovation is a compact, superconducting, channelizing bandpass filter on a single-crystal (0.45 m thick) silicon substrate, which operates from 300 to 600 GHz. This device consists of four channels with center frequencies of 310, 380, 460, and 550 GHz, with approximately 50-GHz bandwidth per channel. The filter concept is inspired by the mammalian cochlea, which is a channelizing filter that covers three decades of bandwidth and 3,000 channels in a very small physical space. By using a simplified physical cochlear model, and its electrical analog of a channelizing filter covering multiple octaves bandwidth, a large number of output channels with high inter-channel isolation and high-order upper stopband response can be designed. A channelizing filter is a critical component used in spectrometer instruments that measure the intensity of light at various frequencies. This embodiment was designed for MicroSpec in order to increase the resolution of the instrument (with four channels, the resolution will be increased by a factor of four). MicroSpec is a revolutionary wafer-scale spectrometer that is intended for the SPICA (Space Infrared Telescope for Cosmology and Astrophysics) Mission. In addition to being a vital component of MicroSpec, the channelizing filter itself is a low-resolution spectrometer when integrated with only an antenna at its input, and a detector at each channel s output. During the design process for this filter, the available characteristic impedances, possible lumped element ranges, and fabrication tolerances were identified for design on a very thin silicon substrate. Iterations between full-wave and lumped-element circuit simulations were performed. Each channel s circuit was designed based on the availability of characteristic impedances and lumped element ranges. This design was based on a tabular type bandpass filter with no spurious harmonic response. Extensive electromagnetic modeling for each channel was performed. Four channels, with 50-GHz bandwidth, were designed, each using multiple transmission line media such as microstrip, coplanar waveguide, and quasi-lumped components on 0.45- m thick silicon. In the design process, modeling issues had to be overcome. Due to the extremely high frequencies, very thin Si substrate, and the superconducting metal layers, most commercially available software fails in various ways. These issues were mitigated by using alternative software that was capable of handling them at the expense of greater simulation time. The design of on-chip components for the filter characterization, such as a broadband antenna, Wilkinson power dividers, attenuators, detectors, and transitions has been completed.

Ehsan, Negar↗
NASA NTRS1979

Gamma-ray burst observations by Pioneer Venus Orbiter

The Pioneer Venus Orbiter gamma burst detector is an astrophysics experiment for monitoring cosmic gamma-ray bursts. It is included in this planetary mission to provide a long baseline for accurately locating the sources of these bursts in order to identify them with specific astronomical objects. Responses to 14 gamma-ray burst events were examined; these events were verified from data acquired by other systems. Preliminary locations are proposed for three events, based on data from the Pioneer Venus Orbiter, ISEE C, and Vela spacecraft. These locations will be improved, and additional locations will be determined by including in the analyses data from Helios B and the Russian Venera 11, Venera 12, and Prognoz 7 spacecraft.

Evans, W. D.↗
NASA NTRS1992

X-ray spectroscopy with silicon pin and avalanche photo diodes

Results of an evaluation of silicon P-Intrinsic-N (PIN) photodiodes and Avalanche Photodiodes (APD) for the direct detection of soft x rays from 1 to 20 keV and for the detection of scintillation light output from CsI(TI) for higher x ray energies (30 to 1000 keV) are presented. About one keV resolution was achieved at room temperature for both the PIN and APD detectors for soft x rays (1 to 20 keV). Commercially available, low power (18 mV), low noise, hybrid preamplifiers, were used. These photodiodes were also coupled to CsI(TI) scintillator and obtained about 6 resolution at 662 keV. The photodiode frequency response matches well with the emission spectrum of the CsI(TI) scintillator providing good spectral resolution and a higher signal than NaI(TI) when viewed by conventional photomultipliers. A PIN-CsI(TI) combination provides a low energy threshold of around 60 keV while for the APD-CsI(TI) it is 15 keV.

Desai, U. D.↗
NASA NTRS1993

A Hybrid Gas Detector/Phoswich for Hard X-ray Astronomy

A hybrid detector, which combines an optical avalanche chamber with a phoswich, is currently under development. The optical avalanche chamber - a proportional counter designed to give large quantities of light photons during charge multiplication, mounts on the front of the scintillator and gives response at low energies, while the solid scintillator takes over at energies where the gas becomes transparent (greater than 90 keV). Both sections of the hybrid will be read out by a common set of photomultipliers under the phoswich. The addition of the gas section to the phoswich improves the energy resolution of the instrument by a factor of 2.5 at 25 keV and the spatial resolution by a factor of 10 at the same energy. The net result is an instrument with broad band coverage and high sensitivity which will be used for coded aperture imaging on long duration balloon flights.

Ramsey, B. D.↗
NASA NTRS2011

New Broadband LIDAR for Greenhouse Carbon Dioxide Gas Sensing in the Earth's Atmosphere

We present demonstration of a novel broadband lidar technique capable of dealing with the atmospherically induced variations in CO2 absorption using a Fabry-Perot based detector and a broadband laser. The Fabry-Perot solid etalon in the receiver part is tuned to match the wavelength of several CO2 absorption lines simultaneously. The broadband technique tremendously reduces the requirement for source wavelength stability, instead putting this responsibility on the Fabry- Perot based receiver. The instrument technology we are developing has a clear pathway to space and realistic potential to become a robust, low risk space measurement system.

Georgieva, Elena↗