Showing papers by "Jet Propulsion Laboratory published in 1987"
TL;DR: A description and summary of the latest edition of the AFGL HITRAN molecular absorption parameters database are presented and a FORTRAN program is now furnished to allow rapid access to the molecular transitions and for the creation of customized output.
Abstract: A description and summary of the latest edition of the AFGL high-resolution transmission molecular absorption database (HITRAN) parameters are presented. This new database combines the information for the seven principal atmospheric absorbers and twenty-one additional molecular species previously contained on the AFGL atmospheric absorption line parameter compilation and on the trace gas compilation. In addition to updating the parameters on earlier editions of the compilation, new parameters have been added to this edition such as the self-broadened half-width, the temperature dependence of the air-broadened half-width, and the transition probability. The database contains 348,043 entries between 0 and 17,900/cm. A FORTRAN program is now furnished to allow rapid access to the molecular transitions and for the creation of customized output. A separate file of molecular cross sections of 11 heavy molecular species, applicable for qualitative simulation of transmission and emission in the atmosphere, has also been provided.
919 citations
TL;DR: This work presents methods for evaluation of these trees in approximate number of intersection calculations required and for automatic generation of good trees in O(nlogn) expected time where n is the number of objects in the scene.
Abstract: Intersection calculations dominate the run time of canonical ray tracers. A common algorithm to reduce the number of intersection tests required is the intersection of rays with a tree of extents, rather than the whole database of objects. A shortcoming of this method is that these trees are difficult to generate. Additionally, manually generated trees can be poor, greatly reducing the run-time improvement available. We present methods for evaluation of these trees in approximate number of intersection calculations required and for automatic generation of good trees. These methods run in O(nlogn) expected time where n is the number of objects in the scene. We report some examples of speedups.
475 citations
TL;DR: The combination of trellis coding and MPSK signaling with the addition of asymmetry to the signal set is discussed with regard to its suitabllity as a modulation/coding scheme for the fading mobile satellite channel.
Abstract: The combination of trellis coding and MPSK signaling with the addition of asymmetry to the signal set is discussed with regard to its suitabllity as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in this paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, our results will only reflect the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.
267 citations
TL;DR: In this paper, the authors present three independent pieces of evidence supporting a connection between comet showers and clustering in terrestrial cratering and mass extinctions, and the temporal profile of a comet shower triggered by a star passing through the Oort cloud is calculated.
Abstract: Three independent pieces of evidence supporting a connection between comet showers and clustering in terrestrial cratering and mass extinctions are presented The temporal profile of a comet shower triggered by a star passing through the Oort cloud is calculated Four weak peaks are found in the age of distribution of impact craters over the past 100 Myr, as well as two compact clusters of ages of impact glass broadly coincident with crater-age peaks Recent paleontological observations are reviewed that indicate a stepwise character for some well-documented mass extinctions in the past 100 Myr which roughly coincide with three of the four peaks in crater ages and which have a duration compatible with comet shower predictions
231 citations
TL;DR: In this article, it was shown that it takes Ω(n + cn$ switches to mix up two urns, the left containing n red balls, the right containing n black balls, at each time a ball is chosen at random in each urn and the two balls are switched.
Abstract: Consider two urns, the left containing n red balls, the right containing n black balls. At each time a ball is chosen at random in each urn and the two balls are switched. We show it takes $\tfrac{1} {4}n\log n + cn$ switches to mix up the urns. The argument involves lifting the urn model to a random walk on the symmetric group and using the Fourier transform (which in turn involves the dual Hahn polynomials). The methods apply to other “nearest neighbor” walks on two-point homogeneous spaces.
191 citations
Proceedings Article•
01 Jan 1987TL;DR: The back propagation algorithm for supervised learning can be generalized, put on a satisfactory conceptual footing, and very likely made more efficient by defining the values of the output and input neurons as probabilities and varying the synaptic weights in the gradient direction of the log likelihood, rather than the 'error'.
Abstract: We propose that the back propagation algorithm for supervised learning can be generalized, put on a satisfactory conceptual footing, and very likely made more efficient by defining the values of the output and input neurons as probabilities and varying the synaptic weights in the gradient direction of the log likelihood, rather than the 'error'.
186 citations
TL;DR: This paper describes the spectroscopic line parameter database compiled for the ATMOS experiment and referenced in other papers describing ATMOS results, and catalogs parameters of 46 minor and trace species in the 1–10,000-cm−1 region.
Abstract: During its first mission in 1985 onboard Spacelab 3, the ATMOS (atmospheric trace molecule spectroscopy) instrument, a high speed Fourier transform spectrometer, produced a large number of high resolution infrared solar absorption spectra recorded in the occultation mode. The analysis and interpretation of these data in terms of composition, chemistry, and dynamics of the earth's upper atmosphere required good knowledge of the molecular line parameters for those species giving rise to the absorptions in the atmospheric spectra. This paper describes the spectroscopic line parameter database compiled for the ATMOS experiment and referenced in other papers describing ATMOS results. With over 400,000 entries, the linelist catalogs parameters of 46 minor and trace species in the 1-10,000/cm region.
185 citations
TL;DR: A new high dynamic global positioning system (GPS) receiver is presented and its performance characterized by analysis, simulation, and demonstration.
Abstract: A new high dynamic global positioning system (GPS) receiver ispresented and its performance characterized by analysis,simulation, and demonstration. The demonstration receiver is abreadboard model capable of tracking a single simulated satellitesignal in pseudorange and range rate. Pseudorange and range rateestimates are made once every 20 ms, using a maximum likelihoodestimator, and are tracked by means of a third-order fadingmemory filter in a feedback configuration. The receiver trackspseudorange with rms errors of under 1 m when subjected tosimulated 50 g, 40 g/s circular trajectories. The tracking thresholdis approximately 28 dB·Hz, which provides 12 dB margin relativethe the minimum specified signal strength, assuming 3.5 dB systemnoise figure and 0 dB antenna gain.
120 citations
TL;DR: Methodological aspects of planning and evaluating this study, including the choice of the study population, procedures for recruitment, experimental design including sample size considerations, methods for evaluating outcome, and methods for evaluate compliance to treatment are reported on.
115 citations
TL;DR: In this article, the average strength and radial variation of the coronal magnetic field at solar minimum at solar distances from 3-10 solar radii were determined using the linearly polarized carrier signals of the Helios spacecraft.
Abstract: Coronal Faraday rotation of the linearly polarized carrier signals of the Helios spacecraft was recorded during the regularly occurring solar occultations over almost a complete solar cycle from 1975 to 1984 These measurements are used to determine the average strength and radial variation of the coronal magnetic field at solar minimum at solar distances from 3-10 solar radii, ie, the range over which the complex fields at the coronal base are transformed into the interplanetary spiral The mean coronal magnetic field in 1975-1976 was found to decrease with radial distance according to r exp-alpha, where alpha = 27 + or - 02 The mean field magnitude was 10 + or - 05 x 10 to the -5th tesla at a nominal solar distance of 5 solar radii Possibly higher magnetic field strengths were indicated at solar maximum, but a lack of data prevented a statistical determination of the mean coronal field during this epoch
111 citations
TL;DR: In this paper, the presence of magnetotactic bacteria and ultrafine-grained single domain magnetite in carbonate oozes and calcareous laminated sediments from Laguna Figueroa, Baja California, Mexico has been investigated.
TL;DR: In this paper, Salo et al. showed that friction and surface irregularity typically reduce the equilibrium velocity dispersion, and that the equilibrium ratio of rotational energy random kinetic energy is 2β/(14 − 5β), or ≲0.2, for spherical identical particle and 2(1 + α)/7 ≈ 0.44 for irregular but frictionless identical particles, α and β being the coefficients of resitution and friction.
TL;DR: In this article, the authors developed a mobile satellite channel simulator in hardware to enable system designers and technologists to optimize their design and pursue their research and development, the simulator has sufficient flexibility to facilitate many forms of tests and experiments.
Abstract: In designing a mobile satellite network, engineers and technologists are faced with wide-ranging issues for which there is no prior database. System engineers must address such issues as adequate margin to combat multipath fading, the level of adjacent channel protection required to allow transmission in narrow-band channels, the cochannel protection required to allow for frequency reuse in a multiplebeam system, and the level of intermodulation distortion tolerable for single-channel-per-carrier operation. Technologists, on the other hand, must determine the performance of various system components. For example, in the ground segment, modem and speech codec performance must be evaluated in the presence of thermal noise, fading, and other impairments. To enable system designers and technologists to optimize their design and pursue their research and development, the Jet Propulsion Laboratory has developed a mobile satellite channel simulator in hardware. This simulator has sufficient flexibility to facilitate many forms of tests and experiments.
TL;DR: In this article, the authors present dynamic spectrograms of the low-frequency interplanetary radio emissions as observed by Voyagers 1 and 2 from 1983 through mid-1986.
Abstract: Dynamic spectrograms of the low-frequency interplanetary radio emissions as observed by Voyagers 1 and 2 from 1983 through mid-1986 are reported. The radio emissions were observed to be most intense in the latter portion of 1983 at 3 kHz but have also been detected at 2 kHz. The emission has been present almost continuously at either 2 or 3 kHz since late 1983. The spectrograms presented herein show that the phenomenon appears almost identically as observed by the two spacecraft separated by more than 10 AU, at least at the higher frequency. One feature revealed by the dynamic spectrograms which had not been noticed previously is a gradual rise in frequency of the 3-kHz component following the onset of the late 1983 event. These new observations reinforce the conclusion that the low-frequency emissions are freely propagating radio waves, but the two-component spectral structure implies that the previous model of emission at twice the plasma frequency at the inner heliosphere shock is inadequate to fully account for the observations. Either an additional source region or an additional source mechanism is suggested.
TL;DR: In this article, a comparison between synthetic aperture radar (SAR) images of ice sheets and Landsat images in western Greenland is presented. But the comparison is limited to a part of eastern Greenland where a direct comparison can be made between two images.
Abstract: Numerous examples of synthetic aperture radar (SAR) imagery of ice sheets are shown and prominent features of glaciological importance which appear in the images are discussed. Features which can be identified include surface undulations, ice-flow lines, crevasses, icebergs, lakes, and streams (even lakes and streams which are inactive or covered by snow), and possibly, the extent of the ablation and wet snow zones. SAR images presented here include both L-band data from the Seasat satellite and X-band data from an airborne radar. These two data sets overlap at a part of eastern Greenland where a direct comparison can be made between two images. Comparison is also made between SAR and Landsat images in western Greenland. It is concluded that SAR and Landsat are highly complementary instruments; Landsat images contain minimal distortion while SAR’s all-weather, day/night capability plus its ability to penetrate snow provide glaciologists with an additional and very powerful tool for research.
TL;DR: In this article, a comparison of backside-illuminated scientifc CCD imagers to an electron flux varying from 1 to 100 pA and beam energy ranging from less than 1 keV up to 20 keV is presented.
Abstract: Recent developments of backside treatment for the backside-illuminated scientifc CCD imagers have shown near-theoretical efficiency even at the short wavelength region of the spectrum. By using SEM performance comparisons of backside-treated and untreated CCDs to an electron flux varying from 1 to 100 pA and beam energy ranging from less than 1 keV up to 20 keV are obtained. The theoretical analysis, the SEM testing procedure, and the quantum efficiency measurement results are presented. It is shown, for example, that the average quantum efficiency increases from less than 1 percent for an untreated CCD to nearly 40 percent for a backside-treated CCD at a beam energy of 1 kev.
TL;DR: This is the, first in a series of columns on whatever I want to say about Computer Graphics, to explore ideas of interest to me-primarily geometdic and algorithmic games pertaining to picture making-perhaps interspersed with my foaming at the mouth over philosophical issues about what-it-allmeans.
Abstract: This is the, first in a series of columns on whatever I want to say about Computer Graphics. I intend in this column to explore ideas of interest to me-primarily geometdic and algorithmic games pertaining to picture making-perhaps interspersed with my foaming at the mouth over philosophical issues about what-it-allmeans.1I have a bunch of ideas to start with, bbut as time goes on, 'I hope others will write in ideas and suggestions I can report on.
TL;DR: In this paper, a method for real-time estimation of tone restfrequency and minimal distance between source and receiver, using digital signal processing techniques, is presented for acoustic source generates an amplitude-modulated tone.
Abstract: An acoustic source generates an amplitude-modulated tone, with Doppler variations due to the relative motion between source andreceiver. A method is presented for real-time estimation of tone restfrequency and minimal distance between source and receiver, usingdigital signal processing techniques. The algorithm presented herewas implemented using a Texas Instruments TMS32010 processor.
TL;DR: The preliminary calculations of Delitsky (1983) have suggested that there should be a significant resultant chemistry in a possible N2 ocean with dissolved CH4, given charged-particle radiolysis of gaseous mixtures and gamma radiolyisation of N2-CH4 solutions.
TL;DR: In this paper, the authors made recommendations for processing and distributing passive microwave data for snow and ice research obtained with the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) are discussed.
Abstract: Recommendations which have been made for processing and distributing passive microwave data for snow and ice research obtained with the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) are discussed. The general objectives for SSM/I data are reviewed, and the sensor and data flow are described. The SSM/I sea ice products are discussed, and algorithm/product validation is addressed. Proposed services and implementation after SSM/I launch are summarized.
TL;DR: In this article, an autofocus technique is used to focus the image and produce a measure of the quadratic phase error that in turn can be used to estimate the geometric distortions that will be present in the final image.
Abstract: The synthetic aperture radar (SAR) is an imaging system that achieves high azimuthal resolution by tracking individual point scatterers using their phase histories, with the expected phase history of a particular point scatterer being derived from the assumed motion of the airborne SAR platform. Normally, it is assumed that the platform travels along a straight line path and that the radar pulses are emitted at equal spatial intervals. However, the aircraft carrying the SAR will be susceptible to extraneous across tracl motions and errors in the pulse spacing also may occur. These errors manifest themselves. as two forms of image degradation in the final image. Firstly, the image will be defocused due to an error in the expected quadratic phase history, and secondly, the image will contain geometric distortions due to an error in the linear phase history. An autofocus technique can be used to focus the image and produce a measure of the quadratic phase error that in turn can be used to estimate the geometric distortions that will be present in the final image. These distortions can be independently measured by direct comparison with a map of the imaged area. This paper describes the application of these methods to some real SAR data and discusses the results of the comparison of the measurements of autofocus and geometric distortions in terms of both the likely platform motions present and the viability of predicting geometric distortion using the autofocus measurements.
TL;DR: In this article, rate coefficients for collision-stabilized association of a protonated ion AH + and its parent molecule A to form the proton bound dimer A 2 H + were measured in an ion cyclotron resonance (ICR) cell at room temperature for the systems where A dimethyl ether and acetonitrile.
TL;DR: The present Voyagers I and II measurements of Saturn A ring azimuthal brightness variations in reflected light are noted to be in general agreement with earth-based measurements as discussed by the authors.
TL;DR: In this paper, an adaptive control algorithm along with the proposed inner-loop plant augmentation for controlling the space station under severe conditions of shuttle docking, mass and inertia change, and model truncation is described.
Abstract: This paper describes an adaptive control algorithm along with the proposed inner-loop plant augmentation for controlling the space station under severe conditions of shuttle docking, mass and inertia change, and model truncation. Simulation results with a simplified model show that the controller is robust and the plant dynamics closely follows that of the reference model. Reasonable results have been observed even with saturation constraints on the control hardware.
TL;DR: In this article, a period of rotation of 3.0655 + or - 0.0008 hr is established for the 1862 Apollo asteroid on the basis of photoelectric light curves obtained during December 1980 and April-May 1982.
TL;DR: In this article, the authors extended Hameen-Anttila's (1984) theory of self-gravitating collisional particle disks to include the effects of particle spin.
Abstract: Hameen-Anttila's (1984) theory of self-gravitating collisional particle disks is extended to include the effects of particle spin. Equations are derived for the coupled evolution of random velocities and spins, showing that friction and surface irregularity both reduce the local velocity dispersion and transfer significant amounts of random kinetic energy to rotational energy. Results for the equilibrium ratio of rotational energy to random kinetic energy are exact not only for identical nongravitating mass points, but also if finite size, self-gravitating forces, or size distribution are included. The model is applied to the dynamics of Saturn's rings, showing that the inclusion of rotation reduces the geometrical thickness of the layer of cm-sized particles to, at most, about one-half, with large particles being less affected.
TL;DR: Infrared absorption spectra of a low-albedo water-rich asteroid appear to show a weak 3.4-micrometer carbon-hydrogen stretching mode band, which suggests the presence of hydrocarbons on asteroid 130 Elektra.
Abstract: Infrared absorption spectra of a low-albedo water-rich asteroid appear to show a weak 3.4-micrometer carbon-hydrogen stretching mode band, which suggests the presence of hydrocarbons on asteroid 130 Elektra. The organic extract from the primitive carbonaceous chondritic Murchison meteorite shows similar spectral bands.
TL;DR: In this paper, a hybrid electrostatic-acoustic levitator that can levitate and manipulate a large liquid drop in one gravity is presented, which is the first time such large drops (up to 4 mm in diameter in the case of water) have been levitated against 1-gravity.
Abstract: A hybrid electrostatic-acoustic levitator that can levitate and manipulate a large liquid drop in one gravity is presented. To the authors' knowledge, this is the first time such large drops (up to 4 mm in diameter in the case of water) have been levitated against 1-gravity. This makes possible, for the first time, many new experiments both in space and in ground-based laboratories, such as 1) supercooling and superheating, 2) containerless crystal growth from various salt solutions or melts, 3) drop dynamics of oscillating or rotating liquid drops, 4) drop evaporation and Rayleigh bursting, and 5) containerless material processing in space. The digital control system, liquid drop launch process, principles of electrode design, and design of a multipurpose room temperature levitation chamber are described. Preliminary results that demonstrate drop oscillation and rotation, and crystal growth from supersaturated salt solutions are presented.
TL;DR: In this paper, the configuration and properties of the draped Giacobini-Zinner magnetotail and its field-reversing current sheet were studied using the combined magnetic field and plasma electron data sets obtained from the International Cometary Explorer spacecraft when it traversed (in October 1985) the comet 7800 km downstream of the nucleus.
Abstract: The configuration and properties of the draped Giacobini-Zinner magnetotail and its field-reversing current sheet are studied using the combined magnetic field and plasma electron data sets obtained from the International Cometary Explorer spacecraft when it traversed (in October 1985) the comet 7800 km downstream of the nucleus. The MHD equations are used to derive pressure balance and plasma acceleration conditions. The implications of the various properties derived are examined, particularly with regard to the upstream near-nucleus region where the tail formation process occurs.