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NASA NTRS1980

Experimental verification of propeller noise prediction

Results of experimental measurements of the sound fields of 1/4-scale general aviation propellers are presented and experimental wake surveys and pressure signatures obtained are compared with theoretical predictions. Experiments were performed primarily on a 1C160 propeller model mounted in front of a symmetric body in an anechoic wind tunnel, and measured the thrust and torque produced by propeller at different rotation speeds and tunnel velocities, wakes at three axial distances, and sound pressure at various azimuths and tip speeds with advance ratio or tunnel velocity constant. Aerodynamic calculations of blade loading were performed using airfoil section characteristics and a modified strip analysis procedure. The propeller was then modeled as an array of point sound sources with each point characterized by the force and volume of the corresponding propeller section in order to obtain the acoustic characteristics. Measurements are found to agree with predictions over a wide range of operating conditions, tip speeds and propeller nacelle combinations, without the use of adjustable constants.

Succi, G. P.↗
NASA NTRS1981

Analytical study of twin-jet shielding

Development of jet noise source model, and comparison to experiments with a point noise source are summarized. The refinement of the noise source is expected to resolve discrepancies noted between previous analytical results with a point noise source model and experimental results for twin-jet shielding. Comparison of the analytical model with experimental program which include shielding of a point noise source by a jet and twin jet shielding are also made. The comparisons should serve to define more completely the mechanisms of shielding

Gerhold, C. H.↗
NASA NTRS2004

Chandra Deep X-ray Observation of a Typical Galactic Plane Region and Near-Infrared Identification

Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), we have carried out a deep hard X-ray observation of the Galactic plane region at (l,b) approx. (28.5 deg,0.0 deg), where no discrete X-ray source has been reported previously. We have detected 274 new point X-ray sources (4 sigma confidence) as well as strong Galactic diffuse emission within two partidly overlapping ACIS-I fields (approx. 250 sq arcmin in total). The point source sensitivity was approx. 3 x 10(exp -15)ergs/s/sq cm in the hard X-ray band (2-10 keV and approx. 2 x 10(exp -16) ergs/s/sq cm in the soft band (0.5-2 keV). Sum of all the detected point source fluxes account for only approx. 10 % of the total X-ray fluxes in the field of view. In order to explain the total X-ray fluxes by a superposition of fainter point sources, an extremely rapid increase of the source population is required below our sensitivity limit, which is hardly reconciled with any source distribution in the Galactic plane. Therefore, we conclude that X-ray emission from the Galactic plane has truly diffuse origin. Only 26 point sources were detected both in the soft and hard bands, indicating that there are two distinct classes of the X-ray sources distinguished by the spectral hardness ratio. Surface number density of the hard sources is only slightly higher than observed at the high Galactic latitude regions, strongly suggesting that majority of the hard X-ray sources are active galaxies seen through the Galactic plane. Following the Chandra observation, we have performed a near-infrared (NIR) survey with SOFI at ESO/NTT to identify these new X-ray sources. Since the Galactic plane is opaque in NIR, we did not see the background extragalactic sources in NIR. In fact, only 22 % of the hard sources had NIR counterparts which are most likely to be Galactic origin. Composite X-ray energy spectrum of those hard X-ray sources having NIR counterparts exhibits a narrow approx. 6.7 keV iron emission line, which is a signature of Galactic quiescent cataclysmic variables (CVs).

Ebisawa, K.↗
NASA NTRS2016

A Global Catalogue of Large SO2 Sources and Emissions Derived from the Ozone Monitoring Instrument

Sulfur dioxide (SO2) measurements from the Ozone Monitoring Instrument (OMI) satellite sensor processed with the new principal component analysis (PCA) algorithm were used to detect large point emission sources or clusters of sources. The total of 491 continuously emitting point sources releasing from about 30 kt yr(exp -1) to more than 4000 kt yr(exp -1) of SO2 per year have been identified and grouped by country and by primary source origin: volcanoes (76 sources); power plants (297); smelters (53); and sources related to the oil and gas industry (65). The sources were identified using different methods, including through OMI measurements themselves applied to a new emission detection algorithm, and their evolution during the 2005- 2014 period was traced by estimating annual emissions from each source. For volcanic sources, the study focused on continuous degassing, and emissions from explosive eruptions were excluded. Emissions from degassing volcanic sources were measured, many for the first time, and collectively they account for about 30% of total SO2 emissions estimated from OMI measurements, but that fraction has increased in recent years given that cumulative global emissions from power plants and smelters are declining while emissions from oil and gas industry remained nearly constant. Anthropogenic emissions from the USA declined by 80% over the 2005-2014 period as did emissions from western and central Europe, whereas emissions from India nearly doubled, and emissions from other large SO2-emitting regions (South Africa, Russia, Mexico, and the Middle East) remained fairly constant. In total, OMI-based estimates account for about a half of total reported anthropogenic SO2 emissions; the remaining half is likely related to sources emitting less than 30 kt yr(exp -1) and not detected by OMI.

Emissions↗
NASA NTRS1983

The probable association of SN 1957d in NGC 5236 (M83) with an unresolved radio source

Astrometric measurements of the position of SN 1957d in the spiral galaxy NGC 5236 using archival plates indicate that it is within 2 arcsec of the position of a point radio source of approximately Cas A strength on a VLA map made by Cowan and Branch (1982). This coincidence strongly suggests that the radio source originated from the supernova. If further investigation shows this point source to indeed be a supernova remnant, then this would be the first reported detection of an intermediate-age supernova remnant.

Pennington, R. L.↗
NASA NTRS2008

Algorithm for Wavefront Sensing Using an Extended Scene

A recently conceived algorithm for processing image data acquired by a Shack-Hartmann (SH) wavefront sensor is not subject to the restriction, previously applicable in SH wavefront sensing, that the image be formed from a distant star or other equivalent of a point light source. That is to say, the image could be of an extended scene. (One still has the option of using a point source.) The algorithm can be implemented in commercially available software on ordinary computers. The steps of the algorithm are the following: 1. Suppose that the image comprises M sub-images. Determine the x,y Cartesian coordinates of the centers of these sub-images and store them in a 2xM matrix. 2. Within each sub-image, choose an NxN-pixel cell centered at the coordinates determined in step 1. For the ith sub-image, let this cell be denoted as si(x,y). Let the cell of another subimage (preferably near the center of the whole extended-scene image) be designated a reference cell, denoted r(x,y). 3. Calculate the fast Fourier transforms of the sub-sub-images in the central NxN portions (where N < N and both are preferably powers of 2) of r(x,y) and si(x,y). 4. Multiply the two transforms to obtain a cross-correlation function Ci(u,v), in the Fourier domain. Then let the phase of Ci(u, v) constitute a phase function, phi(u,v). 5. Fit u and v slopes to phi (u,v) over a small u,v subdomain. 6. Compute the fast Fourier transform, Si(u,v) of the full NxN cell si(x,y). Multiply this transform by the u and phase slopes obtained in step 4. Then compute the inverse fast Fourier transform of the product. 7. Repeat steps 4 through 6 in an iteration loop, cumulating the u and slopes, until a maximum iteration number is reached or the change in image shift becomes smaller than a predetermined tolerance. 8. Repeat steps 4 through 7 for the cells of all other sub-images.

Sidick, Erkin↗
DOE OSTI2022

TDCOSMO. VII. Boxyness/discyness in lensing galaxies: Detectability and impact on H 0

In the context of gravitational lensing, the density profile of lensing galaxies is often considered to be perfectly elliptical. Potential angular structures are generally ignored, except to explain flux ratios of point-like sources (i.e. flux ratio anomalies). Surprisingly, the impact of azimuthal structures on extended images of the source has not been characterised, nor has its impact on the H 0 inference. We address this task by creating mock images of a point source embedded in an extended source and lensed by an elliptical galaxy on which multipolar components are added to emulate boxy or discy isodensity contours. Modelling such images with a density profile free of angular structure allows us to explore the detectability of image deformation induced by the multipoles in the residual frame. Multipole deformations are almost always detectable for our highest signal-to-noise ratio (S/N) mock data. However, the detectability depends on the lens ellipticity and Einstein radius, on the S/N of the data, and on the specific lens modelling strategy. Multipoles also introduce small changes to the time-delays. We therefore quantify how undetected multipoles would impact H 0 inference. When no multipoles are detected in the residuals, the impact on H 0 for a given lens is in general less than a few k ms -1 Mpc -1 , but in the worst-case scenario, combining low S/N in the ring and large intrinsic boxyness or discyness, the bias on H0 can reach 10-12 km s -1 Mpc -1 . If we now look at the inference on H 0 from a population of lensing galaxies with a distribution of multipoles representative of what is found in the light profile of elliptical galaxies, we find a systematic bias on H 0 of less than 1%. A comparison of our mock systems to the state-of-the-art time-delay lens sample studied by the H0LiCOW and TDCOSMO collaborations indicates that multipoles are currently unlikely to be a source of substantial systematic bias on the inferred value of H 0 from time-delay lenses.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2017

Continuation of Long-Term Global SO2 Pollution Monitoring from OMI to OMPS

Over the past 20 years, advances in satellite remote sensing of pollution-relevant species have made space-borne observations an increasingly important part of atmospheric chemistry research and air quality management. This progress has been facilitated by advanced UV-vis spectrometers, such as the Ozone Monitoring Instrument (OMI) on board the NASA Earth Observing System (EOS) Aura satellite, and continues with new instruments, such as the Ozone Mapping and Profiler Suite (OMPS) on board the NASA-NOAA Suomi National Polar-orbiting Partnership (SNPP) satellite. In this study, we demonstrate that it is possible, using our state-of-the-art principal component analysis (PCA) retrieval technique, to continue the long-term global SO2 pollution monitoring started by OMI with the current and future OMPS instruments that will fly on the NOAA Joint Polar Satellite System (JPSS) 1, 2, 3, and 4 satellites in addition to SNPP, with a very good consistency of retrievals from these instruments. Since OMI SO2 data have been primarily used for (1) providing regional context on air pollution and long-range transport on a daily basis and (2) providing information on point emission sources on an annual basis after data averaging, we focused on these two aspects in our OMI-OMPS comparisons. Four years of retrievals (2012-2015) have been compared for three regions: eastern China, Mexico, and South Africa. In general, the comparisons show relatively high correlations (r = 0. 79-0.96) of daily regional averaged SO2 mass between the two instruments and near-unity regression slopes (0.76-0.97). The annual averaged SO2 loading differences between OMI and OMPS are small (< 0.03 Dobson unit (DU) over South Africa and up to 0.1 DU over eastern China). We also found a very good correlation (r = 0. 92-0.97) in the spatial distribution of annual averaged SO2 between OMI and OMPS over the three regions during 2012-2015. The emissions from ∼ 400 SO2 sources calculated with the two instruments also show a very good correlation (r = ∼ 0.9) in each year during 2012-2015. OMPS-detected SO2 point source emissions are slightly lower than those from OMI, but OMI-OMPS differences decrease with increasing strength of source. The OMI-OMPS SO2 mass differences on a pixel by pixel (daily) basis in each region can show substantial differences. The two instruments have a spatial correlation coefficient of 0.7 or better on < ∼ 50 % of the days. It is worth noting that consistent SO2 retrievals were achieved without any explicit adjustments to OMI or OMPS radiance data and that the retrieval agreement may be further improved by introducing a more comprehensive Jacobian lookup table than is currently used.

satellite remote sensing of pollution↗
NASA NTRS2003

Possible Very Distant or Optically Dark Cluster of Galaxies

The goal of this proposal was an XMM followup observation of the extended X-ray source detected in our ROSAT PSPC cluster survey. Approximately 95% of extended X-ray sources found in the ROSAT data were optically identified as clusters of galaxies. However, we failed to find any optical counterparts for C10952-0148. Two possibilities remained prior to the XMM observation: (1) This is was a very distant or optically dark cluster of galaxies, too faint in the optical, in which case XMM would easily detect extended X-ray emission and (2) this was a group of point-like sources, blurred to a single extended source in the ROSAT data, but easily resolvable by XMM due to a better energy resolution. The XMM data have settled the case --- C10952-0148 is a group of 7 relatively bright point sources located within 1 square arcmin. All but one source have no optical counterparts down to I=22. Potentially, this can be an interesting group of quasars at a high redshift. We are planning further optical and infrared followup of this system.

Vikhlinin, Alexey↗
NASA NTRS1973

The use of a digital computer for calculation of acoustic fields of complex vibrating structures by the reciprocity principle

A program was compiled for calculating acoustical pressure levels, which might be created by vibrations of complex structures (an assembly of shells and rods), under the influence of a given force, for cases when these fields cannot be measured directly. The acoustical field is determined according to transition frequency and pulse characteristics of the structure in the projection mode. Projection characteristics are equal to the reception characteristics, for vibrating systems in which the reciprocity principle holds true. Characteristics in the receiving mode are calculated on the basis of experimental data on a point pulse space velocity source (input signal) and vibration response of the structure (output signal). The space velocity of a pulse source, set at a point in space r, where it is necessary to calculate the sound field of the structure p(r,t), is determined by measurements of acoustic pressure, created by a point source at a distance R. The vibration response is measured at the point where the forces F and f exciting the system should act.

Rimskiy-Korsakov, A. V.↗
NASA NTRS2020

High-Resolution Mapping of SO2 Using Airborne Observations from the GeoTASO Instrument During the KORUS-AQ Field Study: PCA-Based Vertical Column Retrievals

The Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) instrument is an airborne hyperspectral spectrometer measuring backscattered solar radiation in the ultraviolet (290–400 nm) and visible (415–695 nm) wavelength regions. This paper presents high-resolution sulfur dioxide (SO2) maps over the Korean Peninsula, produced by SO2 retrievals from GeoTASO measurements during the Korea–United States Air Quality Field Study (KORUS-AQ) from May to June 2016. The highly sensitive GeoTASO instrument with a spatial resolution of ~250 m × 250 m can detect point emission sources of SO2 within its fields of view, even without merging multiple overlapping observations. To retrieve SO2 vertical columns from the GeoTASO measurements, we apply an algorithm based on principal component analysis (PCA), which is effective in suppressing noise and biases in SO2 retrievals. The retrievals successfully capture SO2 plumes and various point sources such as power plants, a petrochemical complex, and a steel mill, located in South Chungcheong Province, some of which are not detected by a ground-based in situ measurement network. Spatial distributions of SO2 from GeoTASO observations in source areas are consistent with those from the Stack Tele-Monitoring System reports and airborne in situ SO2 measurements. Comparisons of SO2 retrievals from GeoTASO and existing satellite sensors demonstrate the significance of high-resolution SO2 observations, by indicating that GeoTASO detects small SO2 emission sources that are not precisely resolved by single overpasses of satellites. To assess future geostationary SO2 observations having a higher spatial resolution, we upscale the GeoTASO SO2 retrievals to a spatial resolution of the Geostationary Environment Monitoring Spectrometer (GEMS). Since the upscaled GeoTASO retrievals also detect SO2 plumes clearly, we expect from GEMS to identify even small SO2 emission sources over Asia.

Chong, Heesung↗
DOE OSTI2022

The miniJPAS survey quasar selection – I. Mock catalogues for classification

In this series of papers, we employ several machine learning (ML) methods to classify the point-like sources from the miniJPAS catalogue, and identify quasar candidates. Since no representative sample of spectroscopically confirmed sources exists at present to train these ML algorithms, we rely on mock catalogues. In this first paper, we develop a pipeline to compute synthetic photometry of quasars, galaxies, and stars using spectra of objects targeted as quasars in the Sloan Digital Sky Survey . To match the same depths and signal-to-noise ratio distributions in all bands expected for miniJPAS point sources in the range 17.5 ≤ r < 24, we augment our sample of available spectra by shifting the original r-band magnitude distributions towards the faint end, ensure that the relative incidence rates of the different objects are distributed according to their respective luminosity functions, and perform a thorough modelling of the noise distribution in each filter, by sampling the flux variance either from Gaussian realizations with given widths, or from combinations of Gaussian functions. Finally, we also add in the mocks the patterns of non-detections which are present in all real observations. Although the mock catalogues presented in this work are a first step towards simulated data sets that match the properties of the miniJPAS observations, these mocks can be adapted to serve the purposes of other photometric surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2002

The STIS CCD Spectroscopic Line Spread Functions

We characterize the spectroscopic line spread functions of the spectroscopic CCD modes for high contrast objects. Our long range goal is to develop tools that accurately extract spectroscopic information of faint, point or extended sources in the vicinity of bright, point sources at separations approaching the realizable angular limits of HST with STIS. Diffracted and scattered light due to the HST optics, and scattered light effects within the STIS are addressed. Filter fringing, CCD fringing, window reflections, and scattering within the detector and other effects are noted. We have obtained spectra of several reference stars, used for flux calibration or for coronagraphic standards, that have spectral distributions ranging from very red to very blue. Spectra of each star were recorded with the star in the aperture and with the star blocked by either the F1 or F2 fiducial. Plots of the detected starlight along the spatial axis of the aperture are provided for four stars. With the star in the aperture, the line spread function is quite noticeable. Placing the star behind one of the fiducials cuts the scattered light and the diffracted light, is detectable even out to 1OOOOA. When the star is placed behind either fiducial, the scattered and diffracted light components, at three arcseconds displacement from the star, are below lop6 the peak of the star at wavelengths below 6000A; at the same angular distance, scattered light does contaminate the background longward of 6000A up to a level of 10(exp -5).

Gull, T.↗
DOE OSTI2022

eROSITA study of the globular cluster 47 Tucanae

Here, we present the results of the analysis of five observations of the globular clutser 47 Tucanae (47 Tuc) with the extended Roentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spektrum-Roentgen-Gamma (Spektr-RG, SRG). We study the X-ray population in the field of one of the most massive globular clusters in our Milky Way. We focused on the classification of point-like sources in the field of 47 Tuc. The unresolved dense core of 47 Tuc (1.7 radius) and also sources that show extended emission are excluded from this study. We applied different methods of X-ray spectral and timing analysis together with multi-wavelength studies to classify the X-rays sources in the field of 47 Tuc. We detected 888 point-like sources in the energy range of 0.2–5.0 keV. We identified 126 background active galactic nuclei and 25 foreground stars. One of the foreground stars is classified as a variable M dwarf. We also classified 14 X-ray sources as members of 47 Tuc, including one symbiotic star, two quiescent low-mass X-ray binaries, and four cataclysmic variables. There are also five X-ray sources that can either be a cataclysmic variable or a contact binary, and also one X-ray source can be an active binary (type RS CVn). We identified one X-ray binary that belongs to the Small Magellanic Cloud. Moreover, we calculated the X-ray luminosity function of 47 Tuc. No significant population that seems to belong to the globular cluster is observed in the energy range of 0.5–2.0 keV using eROSITA observations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2011

Loop Heat Pipe Operation Using Heat Source Temperature for Set Point Control

The LHP operating temperature is governed by the saturation temperature of its reservoir. Controlling the reservoir saturation temperature is commonly accomplished by cold biasing the reservoir and using electrical heaters to provide the required control power. Using this method, the loop operating temperature can be controlled within +/- 0.5K. However, because of the thermal resistance that exists between the heat source and the LHP evaporator, the heat source temperature will vary with its heat output even if LHP operating temperature is kept constant. Since maintaining a constant heat source temperature is of most interest, a question often raised is whether the heat source temperature can be used for LHP set point temperature control. A test program with a miniature LHP has been carried out to investigate the effects on the LHP operation when the control temperature sensor is placed on the heat source instead of the reservoir. In these tests, the LHP reservoir is cold-biased and is heated by a control heater. Tests results show that it is feasible to use the heat source temperature for feedback control of the LHP operation. Using this method, the heat source temperature can be maintained within a tight range for moderate and high powers. At low powers, however, temperature oscillations may occur due to interactions among the reservoir control heater power, the heat source mass, and the heat output from the heat source. In addition, the heat source temperature could temporarily deviate from its set point during fast thermal transients. The implication is that more sophisticated feedback control algorithms need to be implemented for LHP transient operation when the heat source temperature is used for feedback control.

Ku, Jentung↗
NASA NTRS2011

Loop Heat Pipe Operation Using Heat Source Temperature for Set Point Control

Loop heat pipes (LHPs) have been used for thermal control of several NASA and commercial orbiting spacecraft. The LHP operating temperature is governed by the saturation temperature of its compensation chamber (CC). Most LHPs use the CC temperature for feedback control of its operating temperature. There exists a thermal resistance between the heat source to be cooled by the LHP and the LHP's CC. Even if the CC set point temperature is controlled precisely, the heat source temperature will still vary with its heat output. For most applications, controlling the heat source temperature is of most interest. A logical question to ask is: "Can the heat source temperature be used for feedback control of the LHP operation?" A test program has been implemented to answer the above question. Objective is to investigate the LHP performance using the CC temperature and the heat source temperature for feedback control

Ku, Jentung↗
NASA NTRS1974

Acoustic theory of axisymmetric multisectioned ducts

Equations are developed for the acoustic field in a duct system which is made up of a number of connected circular and annular ducts. These equations are suitable for finding the acoustic field inside of and radiated from an aircraft turbofan engine. Acoustic modes are used as generalized coordinates in order to develop a set of matrix equations for the acoustic field. Equations for these modes are given for circular and annular ducts with uniform flow. Modal source equations are derived for point acoustic sources. General equations for mode transmission and reflection are developed and detailed equations are derived for ducts with multiple sections of acoustic treatment and for ducts with circumferential splitter rings. The general theory is applied to the special case of a uniform area circular duct with multisection liners and it is shown that the mode reflection effects are proportional to differences of the acoustic admittances of adjacent liners. A numerical example is given which shows that multisection liners may provide greater noise suppression than uniform liners.

Zorumski, W. E.↗