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At least 217 records · Page 12

The final WaZP galaxy cluster catalog of the Dark Energy Survey and comparison with SZE data

In this work, we present and characterize the galaxy cluster catalog detected by the WaZP cluster finder, which is not based on red-sequence identification, on the full six years of observations of the Dark Energy Survey (DES-Y6). The full catalog contains over 400k detected clusters with richnesses, Ngals, above 5 and that reach redshifts up to 1.3. We also provide a version of the catalog where the observation depth and richness computation are homogenized to be used for cosmology, containing 33k rich (Ngals >25) clusters. We compare our results with the previous WaZP catalog obtained from the DES first-year data release (DES-Y1). We find that essentially all clusters within the common footprint and depth limit are recovered. The deeper observations on DES-Y6 and the more complete available spectroscopic redshift sample lead to improvements in the redshifts of the clusters, resulting in an average scatter of 1.4% and offset of 0.2%. The optical clusters are also cross-matched with Sunyaev Zel'dovich Effect (SZE) cluster samples detected by the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT). We find that essentially all SZE clusters with reasonable overlapping footprint have a corresponding WaZP cluster. Conversely, 90% of the optical detections with richness greater than 150 have a counterpart in the deeper regions of the SZE surveys. Based on cross-match with the SZE catalogs, we also find that 15-20% of the SZE matched systems have more than one possible WaZP counterpart at the same redshift and within the SZE R500c, indicating possible interacting or unrelaxed systems. Finally, given the optical and SZE beams, WaZP and SZE centerings are found to be consistent. A more detailed study of the SZE-WaZP mass-richness relation will be presented in a separate paper.

Benoist, C. [OCA, Nice, Lab. Lagrange; LIneA, Rio ↗

Simple scale interpolator facilitates reading of graphs

Set of cards with scale divisions and a scale finder permits accurate reading of the coordinates of points on linear or logarithmic graphs plotted on rectangular grids. The set contains 34 different scales for linear plotting and 28 single cycle scales for log plots.

Fazio, A.↗

Gradient estimates from stereo measurements for a Martian vehicle

The Martian roving vehicle requires an autonomous obstacle detection and path selection system. A laser range finder will be used to determine the locations of a number of discrete points at distances of 3 to 30 meters from the vehicle. The system might measure angles, ranges or a combination of both types of measurements.

Pfeifer, W. J.↗

Design of a laser rangefinder for Martian terrain measurements

Three methods for using a laser for rangefinding are discussed: optical focusing, the phase difference method, and timed pulse. For application on a Mars Rover, the timed pulse method proves to be the better choice in view of the requirements set down. This is made possible by pulse expansion techniques described in detail. Initial steps taken toward building the range finder are given, followed by a conclusion.

Palumbo, D. L.↗

Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration

The following tasks related to the design, construction, and evaluation of a mobile planetary vehicle for unmanned exploration of Mars are discussed: (1) design and construction of a 0.5 scale dynamic vehicle; (2) mathematical modeling of vehicle dynamics; (3) experimental 0.4 scale vehicle dynamics measurements and interpretation; (4) vehicle electro-mechanical control systems; (5) remote control systems; (6) collapsibility and deployment concepts and hardware; (7) design, construction and evaluation of a wheel with increased lateral stiffness, (8) system design optimization; (9) design of an on-board computer; (10) design and construction of a laser range finder; (11) measurement of reflectivity of terrain surfaces; (12) obstacle perception by edge detection; (13) terrain modeling based on gradients; (14) laser scan systems; (15) path selection system simulation and evaluation; (16) gas chromatograph system concepts; (17) experimental chromatograph separation measurements and chromatograph model improvement and evaluation.

Frederick, D. K.↗

Recognition of three dimensional obstacles by an edge detection scheme

The need for an obstacle detection system on the Mars roving vehicle was assumed, and a practical scheme was investigated and simulated. The principal sensing device on this vehicle was taken to be a laser range finder. Both existing and original algorithms, ending with thresholding operations, were used to obtain the outlines of obstacles from the raw data of this laser scan. A theoretical analysis was carried out to show how proper value of threshold may be chosen. Computer simulations considered various mid-range boulders, for which the scheme was quite successful. The extension to other types of obstacles, such as craters, was considered. The special problems of bottom edge detection and scanning procedure are discussed.

Reed, M. A.↗

A practical obstacle detection system for the Mars Rover

Discussion of an obstacle detection system which uses a laser range finder as the principal sensing device. The laser scans the scene ahead and stores the range data for the terrain in a matrix form. This matrix can be thought of as a 'range image'. This range varies from point to point, but sharp changes are caused by the presence of obstacles. Some existing algorithms and one developed by the authors were used to obtain the outlines of obstacles from the 'range image'. All these algorithms end with a thresholding operation. A theoretical analysis shows how a proper value of the threshold may be chosen, given the type of irregularity of the terrain to be detected. The analysis also shows how large the statistics of measurement noise can be allowed without leading to false alarms.

Reed, M.↗

Design of a laser rangefinder for Martian terrain measurements

Methods for using a laser for rangefinding are discussed. These are: (1) Optical Focusing, (2) the Phase Difference Method, and (3) Timed Pulse. For application on a Mars Rover, the Timed Pulse Method proves to be the better choice in view of the requirements set down. This is made possible by pulse expansion techniques described in detail. Initial steps taken toward building the range finder are given, followed by a conclusion which is actually a proposal for future steps.

Palumbo, D. L.↗

Interactive handling of TV and range data for remotely controlled systems

The sensory subsystem of the JPL robotics project is described. The first sensory instrument is a pair of TV cameras, which provides a stereo view of the area of interest. The second is a laser range finder, which can be aimed in a requested direction and measure distance to a surface point that reflects the beam back. Both instruments are controlled by and are interfaced to computer. The calibration process and basic applications to obtain measurements of the external environment are described.

Yakimovsky, Y.↗

Guidance system for a roving vehicle

Computer controlled guidance system for semiautonomous robot guides robot in incompletely defined environment. System operates in real time avoiding obstacles detected by "stereo television and laser range finder eyes."

Miller, J. A.↗

The relationship of storm severity to directionally resolved radio emissions

Directionally resolved atmospheric radio frequency emission data were acquired from thunderstorms occurring in the central and southwestern United States. In addition, RF sferic tracking data were obtained from hurricanes and tropical depressions occurring in the Gulf of Mexico. The data were acquired using a crossed baseline phase interferometer operating at a frequency of 2.001 MHz. The received atmospherics were tested for phase linearity across the array, and azimuth/elevation angles of arrival were computed in real time. A histogram analysis of sferic burst count versus azimuth provided lines of bearing to centers of intense electrical activity. Analysis indicates a consistent capability of the phase linear direction finder to detect severe meteorological activity to distances of 2000 km from the receiving site. The technique evidences the ability to discriminate severe storms from nonsevere storms coexistent in large regional scale thunderstorm activity.

Johnson, R. O.↗

Errors in magnetic direction finding due to nonvertical lightning channels

A theory showing that errors in lightning magnetic direction finding due to nonvertical source orientations are minimized by detecting the field from the lowest possible channel section is presented. For 99 cloud-to-ground lightning channels photographed in Arizona, 45 exhibited a bottom few hundred meters within about 8 deg of the vertical, the standard deviation of the distribution of lower-channel tilt angles being about 18 deg. These experimental results, coupled with theory, suggest that if a wideband gated direction finder is used, polarization errors due to nonvertical sources can be kept less than 1 deg for lightning beyond 10 km.

Uman, M. A.↗

Automatic technique for accurately locating planet centers in Voyager images

An algorithm has been developed for locating with sub-pixel accuracy planet centers in the Voyager images of the Jovian system based upon automatic recognition of the planet limb. The planet center finder, called FARENC (for far encounter imaging mode), is a single VICAR program operating on IBM 360/65 computer. FARENC is designed to handle images of the order of 800 to 1000 pixels, to operate unaided in a batch environment, and to complete the process reliably in 2 minutes or less. The procedure is outlined step by step and limitations of the algorithm are discussed.

Lorre, J. J.↗