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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The effect of lossy image compression on image classification

We have classified four different images, under various levels of JPEG compression, using the following classification algorithms: minimum-distance, maximum-likelihood, and neural network. The training site accuracy and percent difference from the original classification were tabulated for each image compression level, with maximum-likelihood showing the poorest results. In general, as compression ratio increased, the classification retained its overall appearance, but much of the pixel-to-pixel detail was eliminated. We also examined the effect of compression on spatial pattern detection using a neural network.

Paola, Justin D.↗
NASA NTRS1996

Extrinsic germanium photoconductors for far-IR astronomy: Research results and works in progress

Some Ge:Ga and Ge:Sb photoconductor materials and detectors that are currently under development are reported. The best Ge:Ga devices exhibit dark currents of lower than 200 electrons/s, with a concurrent responsivity of 2 A/W and a detective quantum efficiency (DQE) of 5 percent. For higher backgrounds, an operating temperature of 3 K can be used. This increases the DQE to 7 percent and the responsivity to 4.5 A/W. Investigations were initiated into n-type Ge:Sb as an alternative photoconductive material. Two crystals of Ge:Sb were grown and a number of test detectors were fabricated and evaluated. At 2 K, the best device produced dark currents of less than 100 electrons/s with concurrent responsivity of 1 A/W and DQE of 4 percent, and at 3 K, produced currents of 10(exp 5) electrons/s with a DQE of 7 percent and a responsivity of 4 A/W. Using p-type Ge:Ga crystals, two dimensional monolithic photoconductor arrays are being constructed. Future work will focus on measuring pixel-to-pixel homogeneity, cross talk issues, overall sensitivity and suitability for photometric instruments.

Beeman, J. W.↗
NASA NTRS1997

Laboratory test data on the stability of the STIS MAMAs

STIS has two MAMA detectors systems with distinctly different tube configurations. The first (designated BAND 1) has an opaque CsI photocathode deposited on the microchannel plate (MCP) providing wavelength coverage from 1150A to 1700A. The other MAMA (designated BAND 2) has a semitransparent CS2Te photocathode deposited on the faceplate in close proximity to the input of the MCP. It covers the 1650A to 3100A bandpass and serves as a backup for the short wavelength detector. Laboratory test data indicate that both of these detectors have good sensitivity, have good uniformity and provide stable response, making each capable of collecting data with a signal-to-noise ratio in excess of 100 per Space Telescope Imaging Spectrograph (STIS) optical resolution element. Over a multiyear development effort, a substantial body of laboratory test data (more than 6 GBytes spanning more than 6 years of collection) has accumulated on more than a dozen fabricated tubes. These tests even included a few destructive evaluations to examine the limitations and operating life. In addition, analyses where conducted regarding impact caused by the specified electronic tolerances and expected changes in the Hubble Space Telescope (HST) thermal environment. Perhaps the simplest test of stability is to collect a sequence of images, each with a uniform illumination, and use these individual "flat fields" to remove the pixel-to-pixel sensitivity in the other flat fields. These sequences typically spanned 3-5 weeks of time. The detectors are very stable, allowing the pixel-to-pixel sensitivity to be removed with good precision. The STIS specification for stability is 1% (sufficient for data with a S/N = 100) over a 1 week period and 2% over 30 days. All Engineering Model Units as well as Flight Detectors tested exceeded this specification.

Joseph, Charles L.↗
NASA NTRS2004

Least-Squares Self-Calibration of Imaging Array Data

When arrays are used to collect multiple appropriately-dithered images of the same region of sky, the resulting data set can be calibrated using a least-squares minimization procedure that determines the optimal fit between the data and a model of that data. The model parameters include the desired sky intensities as well as instrument parameters such as pixel-to-pixel gains and offsets. The least-squares solution simultaneously provides the formal error estimates for the model parameters. With a suitable observing strategy, the need for separate calibration observations is reduced or eliminated. We show examples of this calibration technique applied to HST NICMOS observations of the Hubble Deep Fields and simulated SIRTF IRAC observations.

Arendt, R. G.↗
NASA NTRS2004

Background Count Rates and the Anti-Coincidence Detector on the Instrument on Astro-E2

Minimum ionizing particles incident on the XRS microcalorimeter array will deposit energy in the pixels on the same scale as an x-ray photon and would be confused with x-rays without an anti-coincidence detector. The XRS anti-coincidence detector is a silicon ionization detector placed directly behind the calorimeter array. Given an isotropic particle flux, 98% of those particles that pass through a calorimeter pixel will also deposit energy in the anti-coincidence detector. Particle events that are not rejected by coincidence are those that pass through at small angles relative to the plane of the array, and thus deposit more energy. Modeling with GEANT4 showed that only 0.1% of all protons incident on the array miss the anti-coincidence detector yet deposit less than 10 keV in a pixel. The unrejected background will thus be dominated by secondary events; we will provide an estimate of this rate. Protons incident on the thick silicon frame around the active area of the array deposit enough energy t o heat the whole chip slightly. This results in small simultaneous pulses on multiple pixels. These can be easily rejected by pixel-to-pixel coincidence. We will discuss the impact of these events on the instrument dead time and will present the expected rate. We will present laboratory background data demonstrating the performance of the anti-coincidence detector and the effectiveness of coincidence analysis in the laboratory environment.

Kilbourne, C. A.↗
NASA NTRS1999

A Spectralon BRF Data Base for MISR Calibration Application

The Multi-angle Imaging SpectroRadiometer (MISR) is an Earth observing sensor which will provide global retrievals of aerosols, clouds, and land surface parameters. Instrument specifications require high accuracy absolute calibration, as well as accurate camera-to-camera, band-to-band and pixel-to-pixel relative response determinations.

spectralon MISR spectroradiometer remote sensing↗
NASA NTRS2006

Comparison of Measured Leakage Current Distributions with Calculated Damage Energy Distributions in HgCdTe

This paper presents a combined Monte Carlo and analytic approach to the calculation of the pixel-to-pixel distribution of proton-induced damage in a HgCdTe sensor array and compares the results to measured dark current distributions after damage by 63 MeV protons. The moments of the Coulombic, nuclear elastic and nuclear inelastic damage distribution were extracted from Monte Carlo simulations and combined to form a damage distribution using the analytic techniques first described in [I]. The calculations show that the high energy recoils from the nuclear inelastic reactions (calculated using the Monte Car10 code MCNPX [2]) produce a pronounced skewing of the damage energy distribution. The nuclear elastic component (also calculated using the MCNPX) has a negligible effect on the shape of the damage distribution. The Coulombic contribution was calculated using MRED [3,4], a Geant4 [4,5] application. The comparison with the dark current distribution strongly suggests that mechanisms which are not linearly correlated with nonionizing damage produced according to collision kinematics are responsible for the observed dark current increases. This has important implications for the process of predicting the on-orbit dark current response of the HgCdTe sensor array.

Marshall, C. J.↗
NASA NTRS2007

Comparison of Measured Dark Current Distributions with Calculated Damage Energy Distributions in HgCdTe

This paper presents a combined Monte Carlo and analytic approach to the calculation of the pixel-to-pixel distribution of proton-induced damage in a HgCdTe sensor array and compares the results to measured dark current distributions after damage by 63 MeV protons. The moments of the Coulombic, nuclear elastic and nuclear inelastic damage distributions were extracted from Monte Carlo simulations and combined to form a damage distribution using the analytic techniques first described in [1]. The calculations show that the high energy recoils from the nuclear inelastic reactions (calculated using the Monte Carlo code MCNPX [2]) produce a pronounced skewing of the damage energy distribution. While the nuclear elastic component (also calculated using the MCNPX) contributes only a small fraction of the total nonionizing damage energy, its inclusion in the shape of the damage across the array is significant. The Coulombic contribution was calculated using MRED [3-5], a Geant4 [4,6] application. The comparison with the dark current distribution strongly suggests that mechanisms which are not linearly correlated with nonionizing damage produced according to collision kinematics are responsible for the observed dark current increases. This has important implications for the process of predicting the on-orbit dark current response of the HgCdTe sensor array.

Marshall, C. J.↗
NASA NTRS2009

Mid-Infrared Reflectance Imaging of Thermal-Barrier Coatings

An apparatus for mid-infrared reflectance imaging has been developed as means of inspecting for subsurface damage in thermal-barrier coatings (TBCs). The apparatus is designed, more specifically, for imaging the progression of buried delamination cracks in plasma-sprayed yttria-stabilized zirconia coatings on turbine-engine components. Progression of TBC delamination occurs by the formation of buried cracks that grow and then link together to produce eventual TBC spallation. The mid-infrared reflectance imaging system described here makes it possible to see delamination progression that is invisible to the unaided eye, and therefore give sufficiently advanced warning before delamination progression adversely affects engine performance and safety. The apparatus (see figure) includes a commercial mid-infrared camera that contains a liquid-nitrogen-cooled focal plane indium antimonide photodetector array, and imaging is restricted by a narrow bandpass centered at wavelength of 4 microns. This narrow wavelength range centered at 4 microns was chosen because (1) it enables avoidance of interfering absorptions by atmospheric OH and CO2 at 3 and 4.25 microns, respectively; and (2) the coating material exhibits maximum transparency in this wavelength range. Delamination contrast is produced in the midinfrared reflectance images because the introduction of cracks into the TBC creates an internal TBC/air-gap interface with a high diffuse reflectivity of 0.81, resulting in substantially higher reflectance of mid-infrared radiation in regions that contain buried delamination cracks. The camera is positioned a short distance (.12 cm) from the specimen. The mid-infrared illumination is generated by a 50-watt silicon carbide source positioned to the side of the mid-infrared camera, and the illumination is collimated and reflected onto the specimen by a 6.35-cm-diameter off-axis paraboloidal mirror. Because the collected images are of a steady-state reflected intensity (in contrast to the transient thermal response observed in infrared thermography), collection times can be lengthened to whatever extent needed to achieve desired signal-to-noise ratios. Each image is digitized, and the resulting data are processed in several steps to obtain a true mid-infrared reflectance image. The raw image includes thermal radiation emitted by the specimen in addition to the desired reflected radiation. The thermal-radiation contribution is eliminated by subtracting the image obtained with the illumination off from the image obtained with the illumination on. A flat-field correction is then made to remove the effects of non-uniformities in the illumination level and pixel-to-pixel variations in sensitivity. This correction is performed by normalizing to an image of a standard object that has a known reflectance at a wavelength of 4 microns. After correction, each pixel value is proportional to the reflectance (at a wavelength of 4-microns) at the corresponding location on the specimen. Mid-infrared reflectance imaging of specimens that were thermally cyc led for different numbers of cycles was performed and demonstrated t hat mid-infrared reflectance imaging was able to monitor the gradual delamination progression that occurs with continued thermal cycling . Reproducible values were obtained for the reflectance associated w ith an attached and fully delaminated TBC, so that intermediate refle ctance values could be interpreted to successfully predict the numbe r of thermal cycles to failure.

Edlridge, Jeffrey I.↗
NASA NTRS2009

Comparison of GOES Cloud Classification Algorithms Employing Explicit and Implicit Physics

Cloud-type classification based on multispectral satellite imagery data has been widely researched and demonstrated to be useful for distinguishing a variety of classes using a wide range of methods. The research described here is a comparison of the classifier output from two very different algorithms applied to Geostationary Operational Environmental Satellite (GOES) data over the course of one year. The first algorithm employs spectral channel thresholding and additional physically based tests. The second algorithm was developed through a supervised learning method with characteristic features of expertly labeled image samples used as training data for a 1-nearest-neighbor classification. The latter's ability to identify classes is also based in physics, but those relationships are embedded implicitly within the algorithm. A pixel-to-pixel comparison analysis was done for hourly daytime scenes within a region in the northeastern Pacific Ocean. Considerable agreement was found in this analysis, with many of the mismatches or disagreements providing insight to the strengths and limitations of each classifier. Depending upon user needs, a rule-based or other postprocessing system that combines the output from the two algorithms could provide the most reliable cloud-type classification.

EXPLICIT PHYSICS ALGORITHMS↗
NASA NTRS2011

Small, Fast TES Microcalorimeters with Unprecedented X-ray Spectral Performance

Driven initially by the desire for X-ray microcalorimeter arrays suitable for imaging the dynamic solar corona, we have developed a transition-edge-sensor (TES) microcalorimeter optimization that exhibits a unique combination of high spectral resolving power and a wide X-ray bandpass. These devices have achieved spectral performance of dE approximately 1.3 eV FWHM at 1.5 keV, 1.6 eV at 6 keV, and 2.0 eV at 8 keV, using small TESs (e.g., approximately 35 micron x 35 micron) that operate in a regime in which the superconducting transition is highly current dependent. In order to accommodate high X-ray count rates, the devices sit directly on a solid substrate instead of on membranes, and we use an embedded heatsinking layer to reduce pixel-to-pixel crosstalk. We will present results from devices with a range of TES and absorber sizes, and from device wafers with varied embedded heatsink materials. This contribution will focus on count-rate capabilities, including a discussion of the trade-off between count rate and energy resolution, and the heatsinking design. We will also present preliminary tests of array readout using a code-division multiplexed SQUID readout scheme, which may be necessary to enable large arrays of these fast devices.

Eckart, M. E.↗
NASA NTRS2011

Kilopixel X-Ray Microcalorimeter Arrays for Astrophysics: Device Performance and Uniformity

We are developing kilo-pixel arrays of TES microcalorimeters to enable high-resolution X-ray imaging spectrometers for future X-ray observatories and laboratory astrophysics experiments. Our current array design was targeted as a prototype for the X-ray Microcalorimeter Spectrometer proposed for the International X-ray Observatory, which calls for a 40x40-pixel core array of 300 micron devices with 2.5 e V energy resolution (at 6 keV). Here we present device characterization of our 32x32 arrays, including X-ray spectral performance of individual pixels within the array. We present our results in light of the understanding that our Mo/Au TESs act as weak superconducting links, causing the TES critical current (Ic) and transition shape to oscillate with applied magnetic field (B). We show Ic(B) measurements and discuss the uniformity of these measurements across the array, as well as implications regarding the uniformity of device noise and response. In addition, we are working to reduce pixel-to-pixel electrical and thermal crosstalk; we present recent test results from an array that has microstrip wiring and an angle-evaporated Cu backside heatsinking layer, which provides Cu coverage on the four sidewalls of the silicon wells beneath each pixel.

Eckart, M. E.↗
NASA NTRS2011

The Preflight Calibration of the Thermal Infrared Sensor (TIRS) on the Landsat Data Continuity Mission

The preflight calibration testing of TIRS evaluates the performance of the instrument at the component, subsystem and system level, The overall objective is to provide an instrument that is well calibrated and well characterized with specification compliant data that will ensure the data continuity of Landsat from the previous missions to the LDCM, The TIRS flight build unit and the flight instrument were assessed through a series of calibration tests at NASA Goddard Space Flight Center. Instrument-level requirements played a strong role in defining the test equipment and procedures used for the calibration in the thermal/vacuum chamber. The calibration ground support equipment (CGSE), manufactured by MEI and ATK Corporation, was used to measure the optical, radiometric and geometric characteristics of TIRS, The CGSE operates in three test configurations: GeoRad (geometric, radiometric and spatial), flood source and spectral, TIRS was evaluated though the following tests: bright target recovery, radiometry, spectral response, spatial shape, scatter, stray light, focus, and uniformity, Data were obtained for the instrument and various subsystems under conditions simulating those on orbit In the spectral configuration, a monochromator system with a blackbody source is used for in-band and out-of-band relative spectral response characterization, In the flood source configuration the entire focal plane array is illuminated simultaneously to investigate pixel-to-pixel uniformity and dead or inoperable pixels, The remaining tests were executed in the GeoRad configuration and use a NIST calibrated cavity blackbody source, The NIST calibration is transferred to the TIRS sensor and to the blackbody source on-board TIRS, The onboard calibrator will be the primary calibration source for the TIRS sensor on orbit.

Smith, Ramsey↗
NASA NTRS2012

The Transition-Edge-Sensor Array for the Micro-X Sounding Rocket

The Micro-X sounding rocket program will fly a 128-element array of transition-edge-sensor microcalorimeters to enable high-resolution X-ray imaging spectroscopy of the Puppis-A supernova remnant. To match the angular resolution of the optics while maximizing the field-of-view and retaining a high energy resolution (< 4 eV at 1 keV), we have designed the pixels using 600 x 600 sq. micron Au/Bi absorbers, which overhang 140 x 140 sq. micron Mo/Au sensors. The data-rate capabilities of the rocket telemetry system require the pulse decay to be approximately 2 ms to allow a significant portion of the data to be telemetered during flight. Here we report experimental results from the flight array, including measurements of energy resolution, uniformity, and absorber thermalization. In addition, we present studies of test devices that have a variety of absorber contact geometries, as well as a variety of membrane-perforation schemes designed to slow the pulse decay time to match the telemetry requirements. Finally, we describe the reduction in pixel-to-pixel crosstalk afforded by an angle-evaporated Cu backside heatsinking layer, which provides Cu coverage on the four sidewalls of the silicon wells beneath each pixel.

Eckart, M. E.↗
NASA NTRS2011

Spectral Analysis of the Primary Flight Focal Plane Arrays for the Thermal Infrared Sensor

Thermal Infrared Sensor (TIRS) is a (1) New longwave infrared (10 - 12 micron) sensor for the Landsat Data Continuity Mission, (2) 185 km ground swath; 100 meter pixel size on ground, (3) Pushbroom sensor configuration. Issue of Calibration are: (1) Single detector -- only one calibration, (2) Multiple detectors - unique calibration for each detector -- leads to pixel-to-pixel artifacts. Objectives are: (1) Predict extent of residual striping when viewing a uniform blackbody target through various atmospheres, (2) Determine how different spectral shapes affect the derived surface temperature in a realistic synthetic scene.

Montanaro, Matthew↗
NASA NTRS2014

An Analysis of the Side Slither On-Orbit Calibration Technique Using the DIRSIG Model

Pushbroom-style imaging systems exhibit several advantages over line scanners when used on space-borne platforms as they typically achieve higher signal-to-noise and reduce the need for moving parts. Pushbroom sensors contain thousands of detectors, each having a unique radiometric response, which will inevitably lead to streaking and banding in the raw data. To take full advantage of the potential exhibited by push broom sensors, a relative radiometric correction must be performed to eliminate pixel-to-pixel non-uniformities in the raw data. Side slither is an on-orbit calibration technique where a 90-degree yaw maneuver is performed over an invariant site to flatten the data. While this technique has been utilized with moderate success for the QuickBird satellite and the RapidEye constellation, further analysis is required to enable its implementation for the Landsat 8 sensors, which have a 15-degree field-of-view and a 0.5% pixel-to-pixel uniformity requirement. This work uses the DIRSIG model to analyze the side slither maneuver as applicable to the Landsat sensor. A description of favorable sites, how to adjust the maneuver to compensate for the curvature of "linear" arrays, how to efficiently process the data, and an analysis to assess the quality of the side slither data, are presented.

Side slither↗
NASA NTRS2011

Micro-Pixel Image Position Sensing Testbed

The search for Earth-mass planets in the habitable zones of nearby Sun-like stars is an important goal of astrophysics. This search is not feasible with the current slate of astronomical instruments. We propose a new concept for microarcsecond astrometry which uses a simplified instrument and hence promises to be low cost. The concept employs a telescope with only a primary, laser metrology applied to the focal plane array, and new algorithms for measuring image position and displacement on the focal plane. The required level of accuracy in both the metrology and image position sensing is at a few micro-pixels. We have begun a detailed investigation of the feasibility of our approach using simulations and a micro-pixel image position sensing testbed called MCT. So far we have been able to demonstrate that the pixel-to-pixel distances in a focal plane can be measured with a precision of 20 micro-pixels and image-to-image distances with a precision of 30 micro-pixels. We have also shown using simulations that our image position algorithm can achieve accuracy of 4 micro-pixels in the presence of lambda/20 wavefront errors.

astrometry↗
NASA NTRS2012

Kilopixel X-Ray Microcalorimeter Arrays for Astrophysics: Device Performance and Uniformity

We are developing kilopixel arrays of TES microcalorimeters to enable high-resolution x-ray imaging spectrometers for future x-ray observatories and laboratory astrophysics experiments. Our current array design was targeted as a prototype for the X-ray Microcalorimeter Spectrometer proposed for the International X-ray Observatory, which calls for a 40×40-pixel core array of 300 micron devices with 2.5 eV energy resolution (at 6 keV). Here we present device characterization of our 32×32 arrays, including x-ray spectral performance of individual pixels within the array. We present our results in light of the understanding that our Mo/Au TESs act as weak superconducting links, causing the TES critical current (I(sub c)) and transition shape to oscillate with applied magnetic field (B). We show I(sub c)(B) measurements and discuss the uniformity of these measurements across the array, as well as implications regarding the uniformity of device noise and response. In addition, we are working to reduce pixel-to-pixel electrical and thermal crosstalk; we present recent test results from an array that has microstrip wiring and an angle-evaporated copper backside heatsinking layer, which provides copper coverage on the four sidewalls of the silicon wells beneath each pixel.

Transition-edge sensors A[center dot] Superconduct↗