In applying earth resistivity methods to the problem of locating and delineating subsurface structures, surface elevation variations along the surveyed terrain introduce distortions in the soundings. The analysis presented here is aimed at characterizing such terrain variations in the detection of relatively small subsurface targets such as caves, sinks, and tunnels in otherwise homogeneous earth materials. The analytical approach involves, first, the development of a suitable earth resistivity model for localized three‐dimensional subsurface anomalies in a homogeneous flat half‐space. Next, in order to apply the half‐space resistivity model to irregular terrain, a Schwarz‐Christoffel transformation is utilized to map the terrain surface variations into an equivalent flat half‐space. The technique is illustrated by calculating the resistivity response of three tunnels located below a hill with 40-m valleys on either side.

A dipping fractured layer zone has a characteristic seismic signature in interwell seismic data. A fracture zone is simulated as a dipping low-velocity layer in an unbounded medium using the elastodynamic Green’s function for layered earth to include absorption and dispersion effects. The vector wave displacement solution is developed for a point force at an arbitrary angle with respect to the axis of symmetry of a horizontal layer. The source and detector boreholes are rotated such that the new boreholes are perpendicular to the force to form a new plane which contains a dipping layer and horizontal force. To simulate interwell seismic responses, a modified Clenshaw–Curtis quadrature method for wave-number integrals of the Bessel function type is developed to evaluate the wave displacement vector in the frequency-space domain. The model results demonstrate that the presence of a dipping low-velocity layer produces seismic signatures associated with the attitude of the low-velocity layer and the angle of the layer with respect to the source. Also, the results suggest that the amplitudes of shear wave events associated with the presence of a dipping low-velocity layer diminish and their hyperbolic moveout patterns are modified as the dipping layer becomes horizontal.

No abstract

ABS TRACTAs robotic systems are applied to more and more complex tasks there is an increasing need for sensor based control of the manipulator motions and of the process being performed.Recently completed systems for polishing aircraft canopies and for depainting aircraft provide good illustrations of the types of control structures and strategies that are required for these adaptive systems. This paper describes experiences with actual systems using sensor based control of process parameters, manipulator motions, and manipulator paths. The paper presents requirements for sensor integrated control based on these experiences and discusses features and capabilities that should be included in manipulator controllers for future applications.

A mobile robot work center has been constructed for the Navy by Southwest Research Institute for the purpose of removing rivets from airplane wings during overhaul and repair. This system is referred to as a deriveter. Two features of the robotic deriveter system required the derivation of new mathematical relationships. The first feature is the computation of the transformation relating the robot and wing reference frames to each other based on measurements made by the robot, which is mounted on a movable vehicle. Four methods for finding this transformation are presented and the applicability of each to the deriveter is discussed. The second feature is that of positioning the end-effector, tool centerline so that it is perpendicular to the wing surface, with the tool center point at a given offset from the wing based on measurements made by the robot end effector.