Relative Position Of Target Research Articles

Discrimination of fish layers using the three-dimensional information obtained by a split-beam echo-sounder

This study attempts to illustrate the three-dimensional pattern of a “pelagic” and a “benthic” layer of fish using single-target information obtained using a split-beam echo-sounder. Parameters such as the nearest-neighbour distance and separation angle between the two nearest neighbours around a reference fish were used to discriminate between the two layers. The parameters estimated were found to be significantly different between the two layers. The mean nearest-neighbour distance estimated was 6.3 m and 8.8 m for the “benthic” and the “pelagic” layers, respectively, and the mean separation angle between neighbours around a reference fish was 68° and 74°, respectively. The estimated mean target strength (TS) was found to be significantly different for the two layers and conforms to the theoretical TS calculated from the diurnal species and size composition of the layers. It was concluded that illustration and discrimination between the two layers was possible using parameters related to the relative position of targets.

Search deficits in neglect patients are dependent on size of the visual scene.

Patients with hemispatial neglect are impaired at moving their attention to a target on the conrralesional display side. In the present study, visual display area was varied independently of the number of items displayed within the area. Patients searched for the absence of a simple visual feature in displays that produce serial search performance in normals (R. Klein, 1988; A. Treisman & J. Souther, 1985; J. M. Wolfe & C. W. Pokorny, 1990). The contralesional delay was enhanced for stimulus arrays that were distributed over a larger display area, which suggests that neglect is more severe when attention has to be moved over a larger distance. The directional disengage deficit in neglect (M. I. Posner, J. A. Walker, F. A. Friedrich, & R. D. Rafal, 1984, 1987) therefore depends on the target's relative position within a display, the number of ipsilesional items competing for attention (M. Eglin, L. C. Robertson, & R. T. Knight, 1989), and the distance of the contralesional attention movements.

Does order of letter analysis contribute to the parafoveal identification asymmetry?

A parafoveally presented target character usually is identified more accurately when flanked by a nontarget character to its foveal side than when flanked by one to its peripheral side. An outside-in process of analysis produced by uncertainty about the target's position could contribute to this asymmetry. Current results revealed a greater asymmetry with relative target position blocked than with it mixed over trials, suggesting that target position uncertainty leads to inside-out, rather than outside-in, analysis.

Performance analysis of the spaceborne laser ranging system

The Spaceborne Laser Ranging System is a proposed short pulse laser on board an orbiting spacecraft.1,2,3,4 It measures the distance between the spacecraft and many laser retroreflectors (targets) deployed on the Earth’s surface. The precision of these range measurements is assumed to be about ±2 cm (M. W. Fitzmaurice, private communication). These measurements are then used together with the orbital dynamics of the spacecraft, to derive the relative position of the laser ground targets. Assuming a six day observing period with 50% cloud cover, uncertainties in the baseline for target separations of 50 km to 1200 km were estimated to be on the order of 1 to 3 cm and the corresponding values in the vertical direction, ranged from 1 cm to 12 cm. By redetermining the measurements of the relative target positions, the estimated precision in the baseline for a target separation of 50 km is less than 0.3 cm and for a separation of 1200 km is less than 1 cm. In the vertical direction, the estimated precision ranged from 0.4 cm to 4.0 cm respectively. As a result of the repeated estimation of the relative laser target positions, most of the non-temporal effects of error sources as exemplified by the errors in geopotential are reduced.The Spaceborne Laser Ranging System’s capability of determining baselines to a high degree of precision provides a measure of strain and strain rate as shown byCohen, 1979. These quantities are essential for crustal dynamic studies which include determination and monitoring of strain near seismic zones, land subsidence, and edifice building preceding volcanic eruptions. It is evident that such a system can also be used for geodetic surveys where such precisions are more than adquate.

A delayed induced-motion illusion.

We report a striking visual illusion which involves an induced motion that is delayed in time. An observer visually tracks a moving target in the neightborhood of a fixed target. The fixed target appears to be entrained by the moving target and appears to follow its movements after a lag of 0.33 second. A series of experiments showed that while the illusion depends on low background salience it obtains with both smooth and oscillatory motion in all directions including depth, under monocular and binocular viewing, in the absence of vestibular and kinesthetic motion cues or eye movements, and under a wide range of relative and absolute target luminance and position. The strength of the illusion and the magnitude of the induced movement's delay seem not to depend on any of the above factors. The illusion, by resisting a peripheral explanation, may provide some clues to central perceptual processing. In addition, we suggest the possibility that errors of judgment based on the nonveridical perception of motion displaced in time may play a role in nighttime automobile and aircraft accidents.

The Presentation of Information in Combat Aircraft

The prime purpose of the navigation system in a combat aircraft is to determine the relative positions of aircraft and target with sufficient accuracy to enable a weapon to be released. In practice the actual system installed in the aircraft is a compromise solution, which depends on three factors, namely, the mission to be flown, the type of aircraft and the navigation phases through which the aircraft flies while performing the mission. Broadly speaking there are two types of navigation phase; these will be termed macronavigation and micronavigation. Macronavigation is concerned with the navigation of an aircraft to some pre-determined point on the Earth's surface while micronavigation is the final, highly accurate navigation phase required for weapon release. Micronavigation can be further sub-divided into static and dynamic micronavigation; static when the target and the coordinate system within which it exists are fixed, and dynamic when the target moves within a coordinate system which is defined by the attacking aircraft.