Showing papers by "Jet Propulsion Laboratory published in 1990"
TL;DR: In this article, a radiative transfer model for simulating microwave brightness temperatures over land surfaces is described, which takes into account sensor viewing conditions (spacecraft altitude, viewing angle, frequency, polarization) and atmospheric parameters over a soil surface.
Abstract: A radiative transfer model for simulating microwave brightness temperatures over land surfaces is described. The model takes into account sensor viewing conditions (spacecraft altitude, viewing angle, frequency, polarization) and atmospheric parameters over a soil surface characterized by its moisture, roughness, and temperature and covered with a layer of vegetation characterized by its temperature, water content, single scattering albedo, structure and percent coverage. In order to reduce the influence of atmospheric and surface temperature effects, the brightness temperatures are expressed as polarization ratios that depend primarily on the soil moisture and roughness, canopy water content, and percentage of cover. The approach used is described, and the sensitivity of the polarization ratio to these parameters is investigated. Simulation of the temporal evolution of the microwave signal over semiarid areas in the African Sahel is presented and compared to actual satellite data from the SMMR instrument on Nimbus-7. >
268 citations
TL;DR: In this paper, the existence of a sharp break in the power spectrum of AE at about 5 hours is demonstrated and several possible explanations of the nonlinear response of AE to the IMF Bs driver are briefly discussed, including variable ionospheric conductivity (increasing with Bs) and several AE saturation mechanisms for the low frequency regime.
Abstract: The existence of a sharp break in the power spectrum of AE at about 5 hours is demonstrated Several possible explanations of the nonlinear response of AE to the IMF Bs driver are briefly discussed, including: variable ionospheric conductivity (increasing with Bs) for the high frequency regime, and several AE saturation mechanisms for the low frequency regime
170 citations
155 citations
[...]
TL;DR: A topic as complex as dextrous manipulation would best be addressed by collaborative, interdisciplinary research, combining high level and low level views, drawing parallels between human studies and analytic approaches, and integrating sensory data with motor commands.
Abstract: Manipulation using dextrous robot hands has been an exciting yet frustrating research topic for the last several years. While significant progress has occurred in the design, construction, and low level control of robotic hands, researchers are up against fundamental problems in developing algorithms for real-time computations in multi-sensory processing and motor control. The aim of this book is to explore parallels in sensorimotor integration in dextrous robot and human hands, addressing the basic question of how the next generation of dextrous hands should evolve. By bringing together experimental psychologists, kinesiologists, computer scientists, electrical engineers, and mechanical engineers, the book covers topics that range from human hand usage in prehension and exploration, to the design and use of robotic sensors and multi-fingered hands, and to control and computational architectures for dextrous hand usage. While the ultimate goal of capturing human hand versatility remains elusive, this book makes an important contribution to the design and control of future dextrous robot hands through a simple underlying message: a topic as complex as dextrous manipulation would best be addressed by collaborative, interdisciplinary research, combining high level and low level views, drawing parallels between human studies and analytic approaches, and integrating sensory data with motor commands. As seen in this text, success has been made through the establishment of such collaborative efforts. The future will hold up to expectations only as researchers become aware of advances in parallel fields and as a common vocabulary emerges from integrated perceptions about manipulation.
143 citations
TL;DR: In this article, an effort is made to determine relationships between reflectivity (Z) and rain rate (R) which are tuned to the local climatology, where the relation is tuned so that the probability distribution of reflectivity, P(Z), replicates that of R over some predetermined space-time climatic domain.
Abstract: An effort is made to determine relationships between reflectivity (Z) and rain rate (R) which are tuned to the local climatology. The development of such relations was motivated by the need to understand the role of precipitation in controlling general circulation and in affecting such phenomena as ENSO. Attention is given to methods of deriving such relations and how they are linked to area integral rainfall measurements. In essence, the relation is tuned so that the probability distribution of reflectivity, P(Z), replicates that of R over some predetermined space-time climatic domain. Thus, the accurate measurement of the average R over any smaller domain depends on how closely the sampled P(Z) approximates the climatic P(Z). The probability matching method used is a modification of the approach of Calheiros and Zawadzki (1987) and Rosenfeld (1980). The technique is applied to data from Germany and the eastern tropical Atlantic (GATE).
99 citations
[...]
TL;DR: Although the outermost planet, Pluto, is 6xl09km from the Sun, the Sun's gravitational sphere of influence extends much further, out to ∼2x1013 km as mentioned in this paper.
Abstract: Although the outermost planet, Pluto, is 6xl09km from the Sun, the Sun's gravitational sphere of influence extends much further, out to ∼2x1013 km. This space is occupied by the Oort cloud, comprising 1012–1013 cometary nuclei, formed in the primordial solar nebula. Observations and computer modelling have contributed to a detailed understanding of the structure and dynamics of the cloud, which is thought to be the source of the long-period comets and possibly comet showers.
96 citations
01 Jul 1990
TL;DR: In this article, a non-destructive output circuit operating near its 1/f noise regime is clocked in a special manner to read a single pixel multiple times, reducing the random noise by the square root of the number of samples taken.
Abstract: This paper reports on two new advancements in CCD technology. The first area of development has produced a special purpose CCD designed for ultra low-signal level imaging and spectroscopy applications that require sub-electron read noise floors. A nondestructive output circuit operating near its 1/f noise regime is clocked in a special manner to read a single pixel multiple times. Off-chip electronics average the multiple values, reducing the random noise by the square-root of the number of samples taken. Noise floors below 0.5 electrons rms are reported. The second development involves the design and performance of a high resolution imager of 4096 x 4096 pixels, the largest CCD manufactured in terms of pixel count. The device utilizes a 7.5-micron pixel fabricated with three-level poly-silicon to achieve high yield.
93 citations
01 May 1990
TL;DR: The algebraic decoding algorithm developed recently by Elia is compared with the shift-search method and both algorithms decode efficiently the 1/2-rate (24,12) Golay code for correcting three errors and detecting four errors.
Abstract: A simplified procedure, called the shift-search method, is developed to decode the three possible errors in a (23,12,7) Golay codeword. The algebraic decoding algorithm developed recently by Elia is compared with this algorithm. A computer simulation shows that both algorithms are modular, regular and naturally suitable for either VLSI or software implementation. Both of these algorithms decode efficiently the 1/2-rate (24,12) Golay code for correcting three errors and detecting four errors. The algebraic technique is a slightly faster algorithm in software than the shift-search procedure.
82 citations
TL;DR: Examples of ozone profiles measured, and intercomparisons with measurements made by other instruments are presented which show that the lidar, in its present configuration, is capable of producing high quality ozone measurements from 20 km up to at least 45 km.
Abstract: A ground-based differential absorption lidar system has been implemented to make long-term, precise measurements of stratospheric ozone concentration profiles from about 20 to 50 km altitude. This lidar is located at an elevation of 2300 m in the San Gabriel Mountains, Southern California, and has been in operation since January 1988. A high power (100-W) excimer laser system and a 90-cm diam telescope are used to achieve the desired performance levels. This paper describes the implementation of the system and its operation including the procedures for data analysis. Examples of ozone profiles measured, and intercomparisons with measurements made by other instruments, are presented which show that the lidar, in its present configuration, is capable of producing high quality ozone measurements from 20 km up to at least 45 km.
78 citations
01 Sep 1990
TL;DR: In this article, the spectral and radiometric calibration of the AVIRIS data acquired by the US Air Force is described, along with the laboratory procedures, algorithms, measurements, and uncertainties associated with generation of the spectrometers.
Abstract: The laboratory procedures, algorithms, measurements, and uncertainties associated with generation of the spectral and radiometric calibration of data acquired by AVIRIS are described. AVIRIS is an airborne sensor that obtains high-spatial-resolution image data of the earth in 224 spectral channels in four spectrometers covering the range from 400 to 2450 nm. The spectral calibration of AVIRIS agrees with the in-flight data to within two nanometers, and the absolute radiometric calibration is consistent with the in-flight verification to 10 percent over the spectral range. In-flight radiometric stability as measured by five consecutive passes over the surface calibration site is reported to be between three and five percent.
77 citations
TL;DR: An algebraic decoding algorithm for the 1/2-rate (32, 16, 8) quadratic residue (QR) code is found and is expected that the algebraic approach developed here and by M. Elia (1987) applies also to longer QR codes and other BCH-type codes that are not fully decoded by the standard BCH decoding algorithm.
Abstract: An algebraic decoding algorithm for the 1/2-rate (32, 16, 8) quadratic residue (QR) code is found. The key idea of this algorithm is to find the error locator polynomial by a systematic use of the Newton identities associated with the code syndromes. The techniques developed extend the algebraic decoding algorithm found recently for the (32, 16, 8) QR code. It is expected that the algebraic approach developed here and by M. Elia (1987) applies also to longer QR codes and other BCH-type codes that are not fully decoded by the standard BCH decoding algorithm. >
TL;DR: A Doppler lidar system, employing a near ultraviolet laser with a pulse energy of 5 J, could achieve the performance objectives required by the major potential users of a global space-borne wind observing system.
Abstract: Reliable Nd:YAG laser technology and currently available optical sensors are presently used to reevaluate the performance of an incoherent Doppler lidar system operating at 354.7 nm. This system makes a more efficient use of output laser power than heretofore possible through a matching of the usable and detectable field of view of the Fabry-Perot interferometer receiver with that of the transmitter. Major advantages accrue to this system from the lower output power requirement, which is a primary cost driver for the prospective Spaceborne Doppler Wind Lidar.
TL;DR: A novel Fourier technique for digital signal processing is developed based on the number-theoretic method of the Mobius inversion of series that competes with the classical FFT (fast Fourier transform) approach in terms of accuracy, complexity, and speed.
Abstract: A novel Fourier technique for digital signal processing is developed. This approach to Fourier analysis is based on the number-theoretic method of the Mobius inversion of series. The Fourier transform method developed is shown also to yield the convolution of two signals. A computer simulation shows that this method for finding Fourier coefficients is quite suitable for digital signal processing. It competes with the classical FFT (fast Fourier transform) approach in terms of accuracy, complexity, and speed. >
TL;DR: The microwave detection of SO2 at 222 GHz in Io's atmosphere is reported in this paper, which implies an SO2 surface pressure of 4-35 nanobars, covering 3-15 percent of the surface on both leading and trailing sides of Io when illuminated by the sun.
Abstract: The microwave detection of SO2 at 222 GHz in Io's atmosphere is reported. The observations imply an SO2 surface pressure of 4-35 nanobars, covering 3-15 percent of the surface on both leading and trailing sides of Io when illuminated by the sun. This supports atmospheric models in which the partial pressure of SO2 at the surface is determined by the Io surface temperature, favoring, in particular, the 'albedo cold-trap' models. The failure to detect H2S at 169 GHz suggests that the pressure of this gas is probably below 10 to the -10th bar. These results, taken together with Pioneer ionospheric data, suggest that an atmospheric gas other than SO2 is present. It is proposed that the locally buffered SO2 atmosphere coexists with a background atmosphere of oxygen with a partial surface pressure of about 20 nanobars.
TL;DR: In this paper, an active structural element for use in precision control of large space structures is described, which is intended to replace a passive strut in a truss-like structure, and incorporates an eddy current displacement sensor and an actuator that is either piezoelectric (PZT) or electrostrictive (PMN).
Abstract: An active structural element for use in precision control of large space structures is described. The active member is intended to replace a passive strut in a truss-like structure. It incorporates an eddy current displacement sensor and an actuator that is either piezoelectric (PZT) or electrostrictive (PMN). The design of the device is summarized. Performance of separate PZT and PMN actuators is compared for several properties relevant to submicrometer control of precision structures.
TL;DR: An algorithm to generate a relatively long pseudorandom number sequence is presented and it is shown that the period of this sequence is significantly increased compared to that of the sequence generated by the most commonly used maximal length shift register scheme.
Abstract: A VLSI design for computing exponentiation in finite fields is developed. An algorithm to generate a relatively long pseudorandom number sequence is presented. It is shown that the period of this sequence is significantly increased compared to that of the sequence generated by the most commonly used maximal length shift register scheme. >
TL;DR: The split symbol moments estimator (SSME) is an algorithm that is designed to estimate symbol signal-to-noise ratio (SNR) in the presence of additive white Gaussian noise (AWGN).
Abstract: The split symbol moments estimator (SSME) is an algorithm that is designed to estimate symbol signal-to-noise ratio (SNR) in the presence of additive white Gaussian noise (AWGN). The performance of the SSME algorithm in bandlimited channels is examined, and the effects of the resulting intersymbol interference (ISI) are quantified. All results obtained are in closed form and can be easily evaluated numerically for performance-prediction purposes. The results are also validated through digital simulations. >
TL;DR: In this article, an IR array camera was used to obtain direct IR images of Io with resolution better than 0.5 arcsec, so that more than one hotspot is seen on Io in Jupiter eclipse.
Abstract: First results are presented using two new techniques for ground-based observation of Io's hotspots. An IR array camera was used to obtain direct IR images of Io with resolution better than 0.5 arcsec, so that more than one hotspot is seen on Io in Jupiter eclipse. The camera was also used to make the first observations of the Jupiter occultation of the hotspots. These new techniques have revealed and located at least three hotspots and will now permit routine ground-based monitoring of the locations, temperatures, and sizes of multiple hotspots on Io.
TL;DR: In this article, a comparison is made between seven different numerical methods for calculating two-dimensional thermal convection in an infinite Prandtl number fluid, including finite difference and finite element techniques.
Abstract: A comparison is made between seven different numerical methods for calculating two-dimensional thermal convection in an infinite Prandtl number fluid. Among the seven methods are finite difference and finite element techniques that have been used to model thermal convection in the Earth's mantle. We evaluate the performance of each method using a suite of four benchmark problems, ranging from steady-state convection to intrinsically time-dependent convection with recurring thermal boundary layer instabilities. These results can be used to determine the accuracy of other computational methods, and to assist in the development of new ones.
TL;DR: In this paper, the potential vorticity and potential temperature of each measurement as coordinates were used to reconstruct the chemical composition of the polar vortex during the Airborne Arctic Stratospheric Expedition.
Abstract: Measurements of N2O and O3 during the Airborne Arctic Stratospheric Expedition have been composited using the potential vorticity and potential temperature of each measurement as coordinates. For ozone, data sources included the ER-2 and balloon ozonesonde in situ measurements, DC-8 DIAL lidar, and Stratospheric Aerosol and Gas Experiment satellite profiles. For N2O, only ER-2 data were used. These chemical composites have been reconstructed onto average meteorological fields for the mission in a latitude-altitude cross section, yielding a picture of the chemical composition of the polar vortex during this period. Tracers inside the vortex show an apparent descent of about 2 km relative to those outside, resulting in an apparent chemical edge on isentropic and isobaric surfaces.
TL;DR: The variation of the measured strengths allows the energy of the lower state of the transition to be determined empirically using the temperature dependence of the methane partition function and the Boltzmann factor for the energy level populations.
Abstract: The strengths of more than 1600 lines of CH(4) have been measured in the spectral interval between 5500 and 6150 cm(-1) at room temperature and reduced temperatures. The variation of the measured strengths allows the energy of the lower state of the transition to be determined empirically using the temperature dependence of the methane partition function and the Boltzmann factor for the energy level populations. An error analysis, based on assumed errors in the strength and temperature measurements, is included. The average measured uncertainty in J is 0.2.
01 Jan 1990
TL;DR: For the Earth-crossing Halley-type comets, the mean impact probability for long-period comets is 2.4× 10−9 per comet per perihelion passage, with a most probable encounter velocity of 53.5 km sec−1 as discussed by the authors.
Abstract: Comets account for a small but very significant fraction of impactors on the Earth. Although the total number of Earth-crossing comets is modest as compared with asteroids, the more eccentric and inclined orbits of the comets result in much higher encounter velocities with the planet. Additionally, some Earth-crossing comets are significantly larger than any current near-Earth asteroids (NEAs); comets 1P/Halley and C/1995 O1 Hale-Bopp are good examples of this. Thus, the most energetic impacts on the Earth likely result from comets and not NEAs. The mean impact probability for long-period comets is 2.4× 10−9 per comet per perihelion passage, assuming the perihelion distribution of Everhart (1967), with a most probable encounter velocity of 53.5 km sec−1. There are 21 known Earth-crossing Jupiter-family comets with a mean impact probability of 1.6× 10−9 per comet per year and a most probable encounter velocity of 17.0 km sec−1. For the 16 known Earth-crossing Halley-type comets the mean impact probability is 1.2× 10−10 per year with a most probable encounter velocity of 51.3 km sec−1. The poor knowledge of the size distribution of cometary nuclei makes it difficult to estimate actual impact energies at this time, though that situation is slowly improving, in particular for the Jupiter-family comets.
TL;DR: In this article, the authors used a matrix formalism to describe the polarization dependence of the diffraction patterns and optical transfer function, and analyzed both the degree of depolarization and image degradation from the polarization aberrations of the pseudodepolarizer.
Abstract: The objective of a number of optical instruments is to measure the intensity accurately without bias as to the incident polarization state. One method to overcome polarization bias in optical systems is the insertion of a spatial pseudodepolarizer. Both the degree of depolarization and image degradation (from the polarization aberrations of the pseudodepolarizer) are analyzed for two depolarizer designs: (1) the Cornu pseudodepolarizer, effective for linearly polarized light, and (2) the dual Babinet compensator pseudodepolarizer, effective for all incident polarization states. The image analysis uses a matrix formalism to describe the polarization dependence of the diffraction patterns and optical transfer function.
TL;DR: Because Triton's southern hemisphere is nearing a maximum summer solstice, insolation as a driver or a trigger for Tritons' geyser-like plumes is an attractive hypothesis and Trapping of solar radiation in a translucent, low-conductivity surface layer (in a solid-state greenhouse) could provide the required energy.
Abstract: Four geyser-like plumes were discovered near Triton's south pole in areas now in permanent sunlight. Because Triton's southern hemisphere is nearing a maximum summer solstice, insolation as a driver or a trigger for Triton's geyser-like plumes is an attractive hypothesis. Trapping of solar radiation in a translucent, low-conductivity surface layer (in a solid-state greenhouse), which is subsequently released in the form of latent heat of sublimation, could provide the required energy. Both the classical solid-state greenhouse consisting of exponentially absorbed insolation in a gray, translucent layer of solid nitrogen, and the 'super' greenhouse consisting of a relatively transparent solid-nitrogen layer over an opaque, absorbing layer are plausible candidates. Geothermal heat may also play a part if assisted by the added energy input of seasonal cycles of insolation.
TL;DR: The VLBI tracking experiment provided measurements of balloon positions and horizontal winds along their trajectories as mentioned in this paper, and the VEGA Balloons obtained in-situ measurements of pressure, temperature, vertical winds, cloud density, ambient illumination, and the frequency of lightning during their 48 hour flights in the Venus middle cloud layer.
TL;DR: Hapke's photometric model has been combined with a plane-parallel thin atmospheric haze model to describe Voyager whole-disk observations of Triton, in the violet, blue, and green wavelength bands, to obtain estimates ofTriton's geometricAlbedo, phase integral, and Bond albedo.
Abstract: Hapke's photometric model has been combined with a plane-parallel thin atmospheric haze model to describe Voyager whole-disk observations of Triton, in the violet (0.41 microm), blue (0.48 microm), and green (0.56 microm) wavelength bands, in order to obtain estimates of Triton's geometric albedo, phase integral, and Bond albedo. Phase angle coverage in these filters ranging from approximately 12 degrees to 159 degrees was obtained by combining narrow- and wide-angle camera images. An upturn in the data at the highest phase angles observed can be explained by including scattering in a thin atmospheric haze layer with optical depths systematically decreasing with wavelength from approximately 0.06 in the violet to 0.03 for the green filter data. The geometric albedo, phase integral, and spherical albedo of Triton in each filter corresponding to our best fit Hapke parameters yield an estimated Bond albedo of 0.82 +/- 0.05. If the 14-microbar N(2) atmosphere detected by Voyager is in vapor equilibrium with the surface (therefore implying a surface temperature of 37.5 K), our Bond albedo implies a surface emissivity of 0.59 +/- 0.16.
01 Sep 1990
TL;DR: In this article, a comparison between two ground-based atmospheric water-vapor measurement techniques, each of which uses data from a solar-pointing radiometer, is made.
Abstract: A comparison is made between two ground-based atmospheric water-vapor measurement techniques, each of which uses data from a solar-pointing radiometer. One technique uses visible wavelength channels to retrieve aerosol loading, surface pressure readings for Rayleigh scattering analyses, and the 0.94 micron channel to extract water vapor from the residual of total versus scattering opacity. The other technique requires only the ratio of channels centered at 0.94 and 0.87 micron. Results are given for the April 13, 1989 AVIRIS in-flight calibration.
01 Jul 1990
TL;DR: In this paper, a charge coupled device designed for celestial spectroscopy has achieved readout noise as low as 0.6 electrons rms using a non-destructive output circuit.
Abstract: A charge coupled device designed for celestial spectroscopy has achieved readout noise as low as 0.6 electrons rms. A nondestructive output circuit was operated in a special manner to read a single pixel multiple times. Off-chip electronics averaged the multiple values, reducing the random noise by the square root of the number of readouts. Charge capacity was measured to be 500,000 electrons. The device format is 1600 pixels horizontal by 64 pixels vertical. Pixel size is 28 microns square. Two output circuits are located at opposite ends of the 1600 bit CCD register. The device was thinned and operated backside illuminated at -110 degrees C. Output circuit design, layout, and operation are described. Presented data includes the photon transfer curve, noise histograms, and bar-target images down to 3 electrons signal. The test electronics are described, and future improvements are discussed.
01 Jan 1990
TL;DR: The inheritance feature, more than any, makes OOP a viable approach.
Abstract: A software system is a model of a problem domain in an attempt to solve the problem. Traditionally the system is constructed of units consisting of related functions-related by virtue of being constituents of a higher level function. Recently, a new approach to system decomposition has become popular. The new approach looks at the objects that make up the problem domain. Hence the name object-oriented. The data and it’s operations are collected into a unit called a class. An object is an instance of a class with its own copy of the class’ private data. In structured programming one thinks in terms of inputs, function, and outputs. In objectoriented programming (OOP) the approach is different-a message is passed to an object requesting an operation on the object. A class can inherit data and/or operations from an existing parent (or base) class. In C + + the new class is called a detived class. The inheritance feature, more than any, makes OOP a viable approach. Stroustrup [27] says, “Object-oriented programming is programming with inheritance. ”
TL;DR: Aeolian features on Triton that were imaged during the Voyager Mission have been grouped and those indicators which give information on wind direction and speed have been measured.
Abstract: Aeolian features on Triton that were imaged during the Voyager Mission have been grouped. The term "aeolian feature" is broadly defined as features produced by or blown by the wind, including surface and airborne materials. Observations of the latitudinal distributions of the features probably associated with current activity (known plumes, crescent streaks, fixed terminator clouds, and limb haze with overshoot) all occur from latitude -37° to latitude -62°. Likely indicators of previous activity (dark surface streaks) occur from latitude -5° to -70°, but are most abundant from -15° to -45°, generally north of currently active features. Those indicators which give information on wind direction and speed have been measured. Wind direction is a function of altitude. The predominant direction of the surface wind streaks is found to be between 40° and 80° measured clockwise from north. The average orientation of streaks in the northeast quadrant is 59°. Winds at 1- to 3- kilometer altitude are eastward, while those at >8 kilometers blow west.