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NASA NTRS1995

The multidimensional Self-Adaptive Grid code, SAGE, version 2

This new report on Version 2 of the SAGE code includes all the information in the original publication plus all upgrades and changes to the SAGE code since that time. The two most significant upgrades are the inclusion of a finite-volume option and the ability to adapt and manipulate zonal-matching multiple-grid files. In addition, the original SAGE code has been upgraded to Version 1.1 and includes all options mentioned in this report, with the exception of the multiple grid option and its associated features. Since Version 2 is a larger and more complex code, it is suggested (but not required) that Version 1.1 be used for single-grid applications. This document contains all the information required to run both versions of SAGE. The formulation of the adaption method is described in the first section of this document. The second section is presented in the form of a user guide that explains the input and execution of the code. The third section provides many examples. Successful application of the SAGE code in both two and three dimensions for the solution of various flow problems has proven the code to be robust, portable, and simple to use. Although the basic formulation follows the method of Nakahashi and Deiwert, many modifications have been made to facilitate the use of the self-adaptive grid method for complex grid structures. Modifications to the method and the simple but extensive input options make this a flexible and user-friendly code. The SAGE code can accommodate two-dimensional and three-dimensional, finite-difference and finite-volume, single grid, and zonal-matching multiple grid flow problems.

Davies, Carol B.↗
NASA NTRS1995

Advanced Small Rocket Chambers. Option 3: 110 1Bf Ir-Re Rocket, Volume 1

This report describes the AJ10-221, a high performance Iridium-coated Rhenium (Ir-Re) 110 lbf (490N) welded rocket chamber with 286:1 area ratio nozzle. This engine was designed, built, and hot fired for over 6 hours on this program. It demonstrated an I(s) of 321.8 sec, which is 10 sec higher than conventional 110 lbf silicide coated Cb chambers now in use. The approach used in this portion of the program was to demonstrate the performance improvement that can be made by the elimination of fuel film cooling and the use of a high temperature (4000F) (2200C) iridium-coated rhenium (Ir-Re) rocket chamber. Detailed thermal, performance, mechanical, and dynamic design analyses of the full engine were conducted by Aerojet. Two Ir-Re chambers were built to the Aerojet design by Ultramet, using the chemical vapor deposition (CVD) process. Incorporation of a secondary mixing device or Boundary Layer Trip (BLT) within the combustion chamber (Aerojet Patents 4882904 and 4936091) results in improvement in flow uniformity, and a significant life and performance increase. The 110 lbf engine design was verified in bolt-up hardware tests at sea level and altitude. The effects of injector design on performance were studied. Two duplicate injectors were fabricated matching the preferred design and were demonstrated to be interchangeable in operation. One of these units was fabricated matching the preferred design and was demonstrated to be interchangeable in operation. One of these units was welded into a flight type thruster which was tested for an accumulated duration of 22,590 sec in 93 firings, one of which was a continuous burn of two hours. A design deficiency in the C-103 nozzle near the Re-Cb transition joint was discovered, studied and corrected design has been prepared. Workhardening studies have been conducted to investigate methods for increasing the low yield strength of the Re in the annealed conditions. An advanced 490N high performance engine has been demonstrated which, when proven to be capable of withstanding launch vibration, is ready for flight qualification.

Jassowski, Donald M.↗
NASA NTRS1991

Evaluation of discretization procedures for transition elements in adaptive mesh refinement

Three transition interpolation schemes for use in h-or r-refinement have been analyzed in terms of accuracy, implementation ease and extendability. They include blending-function interpolation, displacement averaging, and strain matching at discrete points along the transition edge lines. The results suggest that the choice of matching depends strongly on the element formulations, (viz. displacement or assumed strain, etc.) and mesh refinement criteria employed, and to a lesser extent the choice of computer architecture (serial vs. parallel) and the equation solution procedures. A recommended pairing of some of the elements with the choice factors is suggested.

Park, K. C.↗
NASA NTRS1995

The composite classification problem in optical information processing

Optical pattern recognition allows objects to be recognized from their images and permits their positional parameters to be estimated accurately in real time. The guiding principle behind optical pattern recognition is that a lens focusing a beam of coherent light modulated with an image produces the two-dimensinal Fourier transform of that image. When the resulting output is further transformed by the matched filter corresponding to the original image, one obtains the autocorrelation function of the original image, which has a peak at the origin. Such a device is called an optical correlator and may be used to recognize the locate the image for which it is designed. (From a practical perspective, an approximation to the matched filter must be used since the spatial light modulator (SLM) on which the filter is implemented usually does not allow one to independently control both the magnitude and phase of the filter.) Generally, one is not just concerned with recognizing a single image but is interested in recognizing a variety of rotated and scaled views of a particular image. In order to recognize these different views using an optical correlator, one may select a subset of these views (whose elements are called training images) and then use a composite filter that is designed to produce a correlation peak for each training image. Presumably, these peaks should be sharp and easily distinguishable from the surrounding correlation plane values. In this report we consider two areas of research regarding composite optical correlators. First, we consider the question of how best to choose the training images that are used to design the composite filter. With regard to quantity, the number of training images should be large enough to adequately represent all possible views of the targeted object yet small enough to ensure that the resolution of the filter is not exhausted. As for the images themselves, they should be distinct enough to avoid numerical difficulties yet similar enough to avoid gaps in which certain views of the target will be unrecognized. One method that we introduce to study this problem is called probing and involves the creation of the artificial imagery. The second problem we consider involves the clasification of the composite filter's correlation plane data. In particular, we would like to determine not only whether or not we are viewing a training image, but, in the former case, we would like to determine which training image is being viewed. This second problem is investigated using traditional M-ary hypothesis testing techniques.

Hall, Eric B.↗
NASA NTRS1995

High Accuracy In-Flight Wavelength Calibration of Imaging Spectrometry Data

Accurate wavelength calibration of imaging spectrometer data is essential if proper atmospheric transmission corrections are to be made to obtain apparent surface reflectance. Accuracies of 0.1 nm are necessary for a 10 nm-sampling instrument in order to match the slopes of the deep atmospheric water vapor features that dominate the 0.7-2.3 micrometer regions. The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) is calibrated in the laboratory to determine the wavelength position and full-width-half-maximum (FWHM) response for each of the 224 channels. The accuracies are limited by the quality of the monochromator used as a source. The accuracies vary from plus or minus to plus or minus 1.5 nm depending on the wavelength region, in general decreasing with increasing wavelength. Green et al. make corrections to the wavelength calibrations by using the known positions of 14 atmospheric absorption features throughout the 0.4-2.5 micrometer wavelength region. These features, having varying width and intensity, were matched to the MODTRAN model with a non-linear least squares fitting algorithm. A complete calibration was developed for all 224 channels by interpolation. Instrument calibration cannot be assumed to be stable to 0.1 nm over a flight season given the rigors of thermal cycling and launch and landing loads. The upcoming sensor HYDICE will require a means for in-flight spectral calibration of each scene because the calibration is both temperature and pressure sensitive. In addition, any sensor using a two-dimensional array has the potential for systematic wavelength shifts as a function of cross-track position, commonly called 'smile'. Therefore, a rapid means for calibrating complete images will be required. The following describes a method for determining instrument wavelength calibration using atmospheric absorption features that is efficient enough to be used for entire images on workstations. This study shows the effect of the surface reflectance on the calibration accuracy and the calibration history for the AVIRIS B spectrometer over the 1992 flight season.

Goetz, Alexander F. H.↗
NASA NTRS1994

The luminosity function for stars with minus 0.6 less than or equal to M (sub nu) less than or equal to 6.5 in the globular cluster M30: Is there a problem with stellar evolution models?

The V band luminosity function (LF) for stars ranging from the tip of the giant branch to approximately 2.5 mag fainter than the main-sequence turnoff (MSTO) in M30 (=NGC 7099, GC 2137-234) is derived from CCD observations. Comparison with the theoretical LFs of Bergbusch & VandenBerg (1992) for (M/H) = -2, 16 Gyr models shows discrepancies which can be described either of two ways: (1) If the observations are normalized to the models over a few magnitudes fainter than the MSTO, then there is an excess (N (sub obs) greater than N(sub predicted)) of subgiant stars within 0.5 mag of the MSTO at the level of 4.8 sigma and an excess of stars (approximately 20%) compared to the models all along the giant branch. (2) If the normalization is made to match predicted and observed numbers of stars on the giant branch, then there is a discrepancy between models and observations in the sense that there is a broad depression in the observed LF fainter than the MSTO that is not present in the models. Consideration of LFs generated from 12 Gyr models or models adjusted to a shorter (m - M)(sub nu) = 14.5) distance modulus diminishes the magnitude of some of these discrepancies but introduces other mismatches between the observations and models. LFs constructed from stellar models that have 10% of the stellar mass in an isothermal core qualitatively match the observations better than the 'standard' models.

Bolte, Michael↗
NASA NTRS1994

Far-ultraviolet photometry of the globular cluster omega Cen

We present far-ultraviolet images of the globular cluster omega Centauri obtained with the Ultraviolet Imaging Telescope (UIT) during the 1990 December Astro-1 mission. A total of 1957 sources are detected at 1620 A to a limiting ultraviolet (UV) magnitude of 16.4 in the central 24 min diameter region of the field and a limit of 15.6 over the remainder of the 40 min diameter field. Over 1400 of these sources are matched with stars on a Stroemgren u band charge coupled devices (CCD) frame obtained with the Cerro Tololo Inter-American Observatory (CTIO) 0.9 m telescope to produce a (far-UV, u) color-magnitude diagram (CMD). Completeness of the sample and error estimates are determined by photometry of artificial stars added to the images. The horizontal branch (HB) of the CMD is heavily populated hotter than 9000 K. A large number of 'extreme HB' stars are found hotter than a conspicuous break in the HB at T(sub e) approximately 16000 K. There is also a significant population of stars above the HB, the brightest of which is 4 mag brighter than the HB. Most of the hotter of these appear to be 'AGB-manque' or 'Post-Early Asymptotic Giant Branch' stars. We compare the observations to recent theoretical evolutionary tracks for the zero-age HB and subsequent phases. The tracks match the data well, with the exception of the hotter HB stars, many of which fall below the zero-age horizontal branch. It is unclear as yet whether these are a special population or an artifact of errors in the models or photometry. We identify 33 stars with T(sub e) greater than or approximately = 50000 K, which are hotter than zero-age HB stars with envelope masses of 0.003 solar mass.

Whitney, Jonathan H.↗
NASA NTRS1994

Voids and constraints on nonlinear clustering of galaxies

Void statistics of the galaxy distribution in the Center for Astrophysics Redshift Survey provide strong constraints on galaxy clustering in the nonlinear regime, i.e., on scales R equal to or less than 10/h Mpc. Computation of high-order moments of the galaxy distribution requires a sample that (1) densely traces the large-scale structure and (2) covers sufficient volume to obtain good statistics. The CfA redshift survey densely samples structure on scales equal to or less than 10/h Mpc and has sufficient depth and angular coverage to approach a fair sample on these scales. In the nonlinear regime, the void probability function (VPF) for CfA samples exhibits apparent agreement with hierarchical scaling (such scaling implies that the N-point correlation functions for N greater than 2 depend only on pairwise products of the two-point function xi(r)) However, simulations of cosmological models show that this scaling in redshift space does not necessarily imply such scaling in real space, even in the nonlinear regime; peculiar velocities cause distortions which can yield erroneous agreement with hierarchical scaling. The underdensity probability measures the frequency of 'voids' with density rho less than 0.2 -/rho. This statistic reveals a paucity of very bright galaxies (L greater than L asterisk) in the 'voids.' Underdensities are equal to or greater than 2 sigma more frequent in bright galaxy samples than in samples that include fainter galaxies. Comparison of void statistics of CfA samples with simulations of a range of cosmological models favors models with Gaussian primordial fluctuations and Cold Dark Matter (CDM)-like initial power spectra. Biased models tend to produce voids that are too empty. We also compare these data with three specific models of the Cold Dark Matter cosmogony: an unbiased, open universe CDM model (omega = 0.4, h = 0.5) provides a good match to the VPF of the CfA samples. Biasing of the galaxy distribution in the 'standard' CDM model (omega = 1, b = 1.5; see below for definitions) and nonzero cosmological constant CDM model (omega = 0.4, h = 0.6 lambda(sub 0) = 0.6, b = 1.3) produce voids that are too empty. All three simulations match the observed VPF and underdensity probability for samples of very bright (M less than M asterisk = -19.2) galaxies, but produce voids that are too empty when compared with samples that include fainter galaxies.

Vogeley, Michael S.↗
NASA NTRS1994

Asymptotic Giant Branch stars as a source of short-lived radioactive nuclei in the solar nebula

We carried out a theoretical evaluation of the contribution of Asymptotic Giant Branch (AGB) stars to some short-lived (10(exp 6) less than or equal to Tau-bar less than or equal to 2 x 10(exp 7) yr) isotopes in the Interstellar Medium (ISM) and in the early solar system using stellar model calculations for thermally pulsing evolutionary phases of low-mass stars. The yields of s-process nuclei in the convective He-shell for different neutron exposures tau(sub 0) were obtained, and AGB stars were shown to produce several radioactive nuclei (especially Pd-107, Pb-205, Fe-60, Zr-93, Tc-99, Cs-135, and Hf-182) in diferent amounts. Assuming either contamination of the solar nebula from a single AGB star or models for continuous injection and mixing from many stars into the ISM, we calculate the ratios of radioactive to stable nuclei at the epoch of the Sun's formation. The dilution factor between the AGB ejecta and the early solar system matter is obtained by matching the observed Pd-107/Pd-108 and depends on the value of tau(sub 0). It is found that small masses M(sub He) of He-shell material (10(exp -4)-10(exp -7) solar mass) enriched in s-process nuclei are sufficient to contaminate 1 solar mass of the ISM to produce the Pd-107 found in the early solar system. Predictions are made for all of the other radioactive isotopes. The optimal model to explain several observed radioactive species at different states of the proto-solar nebula involves a single AGB star with a low neutron exposure (tau(sub 0) = 0.03 mbarn(sup -1)) which contaminated the cloud with a dilution factor of M(sub He)/solar mass approximately 1.5 x 10(exp -4). This will also contribute newly synthesized stable s-process nuclei in the amount of approximately 10(exp -4) of their abundances already present in the proto-solar cloud. Variations in the degree of homogenization (approximately 30%) of the injected material may account for some of the small general isotopic anomalies found in meteorites. It is also found that Fe-60 is produced in small but significant quantities that may be sufficient to explain the observations if the time elapsed delta from the contamination of the ISM to the formation of protoplanetary bodies is not higher than delta = 5 x 10(exp 6) yr. If delta is longer, up to 10 x 10(exp 6) yr, this would require the single AGB star to experience enhanced neutron densities (n(sub n) approximately 3 x 10(exp 9)n/cu cm) in the s-processing zone in order to compensate for the branching at Fe-59. The alternative model of long-term continuous ejection of matter from many AGB stars does not appear to match the observations. We also estimate the Al-26 production from the H-shell and find that the Al-26 abundance in the early solar system may be readily explained in a self-consistent manner. Moreover, Al-26 from AGB stars may contribute substantially to the galactic Al-26 gamma-source, while no significant gamma-flux from Co-60 (deriving from Fe-60 decay) is to be expected.

Wasserburg, G. J.↗
NASA NTRS1994

'Spherical' disks: Moving toward a unified source model for L1551

To predict the effects of a disk on the spectral energy distribution of a deeply embedded protostar, we construct disk models with power-law temperature distributions T is proportional to r(exp -q). We then use the spherically averaged disk emission as the central source for a spherical envelope, hence the term, 'spherical' disk. We then calculate the predicted spectral energy distribution of the disk and envelope, using a spherically symmetric radiative transport code. Applying this procedure to L1551 IRS 5, we find that the predicted far-infrared flux is not very sensitive to the nature of the central source. The best source model is consistent with the far-infrared emission arising from the infalling region in an 'inside-out' collapse model, independent of the nature of the central source. Disk models are superior to the star-only model when we try to match millimeter interferometer data. While disks with various q can reproduce the observed 2.7 mm interferometer flux, only an active disk (q = 0.5) can produce enough emission in a region small enough to match the observed 2.7 mm visibilities. However, if the disk is backwarmed by the envelope, even purely reprocessing disks can meet this constraint. All types of backwarmed disks are virtually in distinguishable in their millimeter properties. We find that all reasonable envelope models are sufficiently opaque in the mid-infrared to attenuate any disk model to a level well below the observations, unless the ratio of the mid-infrared to far-infrared dust opacities is similar to that of the dust opacities advocated by Mathis, Mezger, & Panagia (1983).

Butner, Harold M.↗
NASA NTRS1994

What we have learned about Mars from SNC meteorites

The SNC meteorites are thought to be igneous martian rocks, based on their young crystallization ages and a close match between the composition of gases implanted in them during shock and the atmosphere of Mars. A related meteorite, ALH84001, may be older and thus may represent ancient martian crust. These petrologically diverse basalts and ultramafic rocks are mostly cumulates, but their parent magmas share geochemical and radiogenic isotopic characteristics that suggest they may have formed by remelting the same mantle source region at different times. Information and inferences about martian geology drawn from these samples include the following: Planetary differentiation occured early at approximately 4.5 GA, probably concurrently with accretion. The martian mantle contains different abundances of moderately volatile and siderophile elements and is more Fe-rich than that of the Earth, which has implications for its mineralogy, density, and origin. The estimated core composition has a S abundance near the threshold value for inner core solidification. The former presence of a core dynamo may be suggested by remanent magnetization in Shergottite-Nakhlite-Chassignite (SNC) meteorites, although these rocks may have been magnetized during shock. The mineralogy of martian surface units, inferred from reflectance spectra, matches that of basaltic shergottites, but SNC lithologies thought to have crystallized in the subsurface are not presently recognized. The rheological properties of martian magmas are more accurately derived form these metorites than from observations of martian flow morphology, although the sampled range of magma compositions islimited. Estimates of planetary water abundance and the amount of outgassed water based on these meteorites are contridictory but overlap estimates based on geological observations and atmospheric measurements. Stable isotope measurements indicate that the martian hydrosphere experienced only limited exchange with the lithosphere, but it is in isotopic equilibrium with the atmosphere and has been since 1.3 Ga. The isotopically heavy atmosphere/hydrosphere composition deduced from these rocks reflects a loss process more severe than current atmospheric evolution models, and the occurence of carbonates in SNC meteorites suggest that they, rather than scapolite or hydrous carbonates, are the major crustal sink for CO2. Weathering products in SNC meteorites support the idea of limited alteration of the lithosphere by small volumes of saline, CO2-bearing water. Atmospheric composition and evolution are further constrained by noble gases in these meteorites, although Xe and Kr isotopes suggest different origins for the atmosphere. Planetary ejection of these rocks has promoted an advance in the understanding of impact physics, which has been accomplished by a model involving spallation during large cratering events. Ejection of all the SNC meteorites (except ALH84001) in one or two events may provide a plausible solution to most constraints imposed by chronology, geochemistry, and cosmic ray exposure, although problems remain with this scenario; ALH84001 may represent older martian crust sampled during a separate impact.

Mcsween, Harry Y., Jr.↗
NASA NTRS1993

Accessory phases in aubrites: Spectral properties and implications for asteriod 44 NYSA

The reflectance spectra of meteoritic metal, meteoritic troilite and the CR carbonaceous chondrite EET87770 have been measured in order to investigate the causes of the spectral differences between the surface of the E-class asteroid 44 Nysa and the opaque free fraction of the Happy Canyon aubrite meteorite. The data indicate that the spectral differences require the presence of Nysa's surface of a small amount of a spectrally red sloped material, of which metal and troilite are the most reasonable candidates, and a material possessing absorption bands near 0.9 micrometers and 1.8 micrometers. A material similar to the carbonaceous chondrite inclusions found in some aubrites can provide a match to the 0.9 micrometer feature and perhaps the 1.8 micrometer feature. The required abundances of these components depends on whether they are areally distributed or intimately mixed with an enstatite rich material. Based on the petrologic associations seen in aubrites and a series of simulated mineral mixtures, an intimate mixture of 69-92% enstatite and 1-11% metal + troilite and an areal component of 7-20% carbonaceous chondrite type material can provide a reasonable match to the 0.3-2.6 micrometer spectrum of Nysa.

Cloutis, Edward A.↗
NASA NTRS1994

Obscuration, orientation, and the infrared properties of radio-loud active galaxies

We report on a study of the mid- and far-infrared (MFIR) properties of several different classes of radio-loud active galactic nuclei (AGNs) using the IRAS database. Our goal is to try to improve the understanding of the possible relationships between the diverse classes of AGNs. The MFIR and radio properties of radio-loud AGNs are especially useful in this regard, since (excluding the blazar class, which we do not study here) the radio emission is thought to be emitted isotropically, and the radio and MFIR radiation should be much less affected by dust obscuration than radiation at shorter wavelengths. We have first compared samples of 3CR broad-line radio galaxies (BLRGs) and narrow-line radio galaxies (NLRGs) matched in radio flux and mean redshift. We find that the BLRGs are stronger than the NLRGs by a factor of 4-5 in their mid-IR emission but are similar to the NLRGs in the far-IR. This is qualitatively consistent with recent 'unification' models for NLRGs and BLRGs which invoke thermal MFIR emission from dusty 'obscuring tori,' but there may be an additional source of far-IR emission present in the more luminous broad-line objects (the radio-loud quasars) studied previously by Heckman, Chambers & Postman (1992). We have also compared samples of Fanaroff-Riley class I (FRI) and Fanaroff-Riley class II (FRII) radio galaxies matched in radio flux and redshift. The FRII galaxies are stronger MFIR emitters than the FRI galaxies by a factor of about 4. This is consistent with suggestions that the central engine in FRI galaxies produces relatively little radiant energy per unit jet power (expecially since we find that the weak MFIR emission from the FRI galaxies may not be powered by the AGN). Comparing samples of gigahertz-peaked spectrum (GPS) and compact steep spectrum (CSS) sources versus non-GPS-CSS sources, we find that the GPS-CSS and non-GPS-CSS sources have similar MFIR strengths. This suggests that the efficiency of the conversion of jet kinetic energy into radio emission is not much higher in the GPS-CSS sources, contrary to some theoretical predictions. Overall, we find that the MFIR and radio powers of all the classes of radio-loud AGNs we have studied correlate well with one another over a range of about 10(exp 3) in power. This is most naturally understood if the MFIR is primarily powered by the AGN in most highly luminous radio-loud AGNs. However, other processes (starbursts or the intracluster medium) may contribute significantly in the less radio-luminous radio galaxies.

Heckman, Timothy M.↗
NASA NTRS1995

Stellar models with microscopic diffusion and rotational mixing. 2: Application to open clusters

Stellar models with masses ranging from 05.5 to 1.3 solar mass were constructed for comparison with young cluster observations of Li and of rotation velocities. The amount of Li depletion in cool stars is sensitive to the amount of overshoot at the base of the surface convection zone, and the exact metallicity of the models. Even when this is taken into account, the Li observations are a severe constraint for the models and rule out standard models and pure diffusion models. Stellar models which include diffusion and rotational mixing in the radiative regions of stars are able to simultaneously match the Li abundances observed in the Pleiades, the UMa Group, The Hyades, Praesepe, NGC 752, and M67. They also match the observed rotation periods in the Hyades. However, these models are unable to simultaneously explain the presence of the rapidly rotating late G and K stars in the Pleiades and the absence of rapidly rotating late F and early G stars.

Chaboyer, B.↗
NASA NTRS1995

A new model for Mars atmospheric dust based upon analysis of ultraviolet through infrared observations from Mariner 9, Viking, and Phobos

We propose key modifications to the Toon et al. (1977) model of the particle size distribution and composition of Mars atmospheric dust, based on a variety of spacecraft and wavelength observations of the dust. A much broader (r(sub eff) variance approximately 0.8 micrometers), smaller particle size (r(sub mode) approximately 0.02 micrometers) distribution coupled with a 'palagonite-like' composition is argued to fit the complete ultraviolet-to-30-micrometer absorption properties of the dust better than the montmorillonite-basalt, r(sub eff) variance = 0.4 micrometers, r(sub mode) = 0.40 dust model of Toon et al. Mariner 9 (infrared interferometer spectrometer) IRIS spectra of high atmospheric dust opacities during the 1971-1972 Mars global dust storm are analyzed in terms of the Toon et al. dust model, and a Hawaiian palagonite sample (Rousch et al., 1991) with two different size distribution models incorporating smaller dust particle sizes. Viking Infrared Thermal Mapper (IRTM) emmission-phase-function (EPF) observations at 9 micrometers are analyzed to retrieve 9-micrometer dust opacities coincident with solar band dust opacities obtained from the same EPF sequences (Clancy and Lee, 1991). These EPF dust opacities provide an independent measurement of the visible/9-micrometer extinction opacity ratio (greater than or = 2) for Mars atmospheric dust, which is consistent with a previous measurement by Martin (1986). Model values for the visible/9-micrometer opacity ratio and the ultraviolet and visible single-scattering albedos are calculated for the palagonite model with the smaller particle size distributions compared to the same properties for the Toon et al. model of dust. The montmorillonite model of the dust is found to fit the detailed shape of the dust 9-micrometer absorption well. However, it predicts structured, deep aborptions at 20 micrometers which are not observed and requires a separate ultraviolet-visible absorbing component to match the observed behavior of the dust in this wavelength region. The modeled palagonite does not match the 8-to 9-micrometer absorption presented by the dust in the IRIS spectra, probably due to its low SiO2 content (31%). However, it does provide consistent levels of ultraviolet/visible absorption, 9-to 12-micrometer absorption, and a lack of structured absorption at 20 micrometers. The ratios of dust extinction opacities at visible, 9 micrometers, and 30 micrometers are strongly affected by the dust particle size distribution. The Toon et al. dust size distribution (r(sub mode) = 0.40,r(sub eff) variance = 0.4 micrometers, r(sub cwmu) = 2.7 micrometers) predicts the correct ratio of the 9- to 30-micrometer opacity, but underpredicts the visible/9-micrometer opacity ratio considerably (1 versus greater than or = 2). A similar particle distribution width with smaller particle sizes (r(sub mode) = 0.17, r(sub eff) variance = 0.4 micrometers, r(sub cwmu) = 1.2 micrometers) will fit the observed visible/9-micrometer opacity ratio, but overpredicts the observed 9-micrometer/30-micrometer opacity ratio. A smaller and much broader particle size distribution (r(sub mode) = 0.002, r(sub eff) variance = 0.8 micrometers, r(sub cwmu) = 1.8 micrometers) can fit both dust opacity ratios. Overall, the nanocrystalline structure of palagonite coupled with a smaller, broader distribution of dust particle sizes provides a more consistent fit than the Toon et al. model of the dust to the IRIS spectra, the observed visible/9-micrometer dust opacity ratio, the Phobos occulation measurements of the dust particle sizes (Chassefiere et al., 1992), and the weakness of surface near IR absorptions expected for clay minerals (Clark, 1992; Bell and Crisp, 1993).

Clancy, R. T.↗
NASA NTRS1995

Prediction of the interplanetary magnetic field strength

A new model of the coronal and interplanetary magnetic field can predict both the interplanetary magnetic field strength and its polarity from measurements of the photospheric magnetic field. The model includes the effects of the large-scale horizontal electric currents flowing in the inner corona, of the warped heliospheric current sheet in the upper corona, and of volume currents flowing in the region where the solar wind plasma totally controls the magnetic field. The model matches the MHD solution for a simple dipole test case better than earlier source surface and current sheet models. The strength and polarity of the radial interplanetary magnetic field component predicted for quiet time samples in each year from 1977 to 1986 agree with observations made near the Earth's orbit better than the hybrid MHD-source surface model (Wang and Sheeley, 1988). The results raise the question of whether coronal holes are the only solar source of the interplantary magnetic field in the solar wind. If some interplanetary flux originates outside coronal holes, the model can match the observed field using the accepted 1.8 saturation correction factor for lambda 5250 A magnetograph observations. Requiring open flux to come exclusively from coronal holes requires and additional factor of two.

Zhao, Xuepu↗
NASA NTRS1995

Saturn's central flash from the 3 July 1989 occultation of 28 Sgr

We present observations of Saturn's central flash obtained from Palomar and McDonald Observatories during the 3 July 1989 occultation of 28 Sgr. As the star passed close to the geometric center of Saturn's shadow, the focusing of the incident starlight by the planet's atmosphere formed multiple stellar images along the limb which were detected in infrared images obtained at wavelengths of 3.9 (Palomar) and 2.1 microns (McDonald). These are the first reported observations of a central flash due to Saturn, and the first of any planet in which the signal flash from each stellar image could be determined separately, permitting a comparison of both intensity and position for each image with model predictions. Four separate flashes were observed from each observatory, corresponding to points on the limb where the starlight passed through the Cassini Division and the relatively transparent C Ring, with maximum brightness reaching 1-2% of the unocculted stellar intensity. The timing of the flashes is quite sensitive to the shape of Saturn's limb, which depends in turn on the planet's zonal gravity harmonics and on the zonal wind profile in the lower stratosphere, near the 2.5-mbar pressure level. The locations of the images along the limb, as well as the timing, shapes, and amplitudes of the individual flash light curves, are well matched by a smoothed model based on a tropospheric zonal wind profile obtained from tracking cloud features in Voyager images and the Saturn ring optical depth profile obtained from the Voyager Photopolarimeter experiment. The smoothing required to give the best match to the data exceeds that attributable to the finite angular extent of the occulted star and may be due to refractive scattering by turbulence or wave structure in Saturn's atmosphere. There is no evidence of significant atmospheric absorption at the observed wavelengths, which correspond to spectral regions of weak methane absorption.

Nicholson, Philip D.↗
NASA NTRS1995

A comparison of model-based VQ compression with other VQ approaches

In our previous work on Model-Based Vector Quantization (MVQ), we presented some performance comparisons (both rate distortion and decompression time) with VQ and JPEG/DCT. In this paper, we compare the MVQ's rate distortion performance with Mean Removed Vector Quantization (MRVQ) and include our previous comparison with VQ. MVQ is similar to MRVQ in many ways. Both of these techniques extract means of the vectors (raster-scanned image blocks) and reduce them to mean removed residuals by subtracting block means from the elements of the vectors. In the case of MRVQ, a codebook of residual vectors is generated using a training set. For every vector from the input image, the block mean and address of the codevector from the codebook that matches the input vector closest are transmitted to the decoder. The codebook is generated using generalized Lloyd algorithm on training set of residual vectors. For MVQ the pairs consist of vector means and address of the closest matching vector from codebook generated by models based on statistical properties of the residuals and Human Visual System (HVS). In our experiments, we found that MVQ performance in rate distortion sense is almost always better than VQ and is comparable to MRVQ. Further, MVQ is much easier to use than either VQ or MRVQ, since the training and managing of explicit codebooks is not required.

Manohar, Mareboyana↗