Neal Lord

A hybrid laser-tracking/GPS location method allowing GPR acquisition in rugged terrain

Ground-penetrating radar images of geologic structures provide information about the crucial third dimension, which is inaccessible to geologic mapping. In order to correlate images with geologic mapping, photomosaics, and behind-outcrop borehole logs, radar profiles must be accurately mapped. Moreover, accurate profile elevations are required during processing to avoid introducing into the radar image false structures associated with topographic relief. In recent years, radar station locations and elevations have been obtained very efficiently from a self-tracking laser theodolite operated at the same time the radar data are being acquired. The required physical link between radar and laser systems, however, may make such a system unusable in areas of rugged terrain.

UV-light microscope: improvements in optical imaging for a secondary ion mass spectrometer

A large radius secondary ion mass spectrometer (SIMS) has been used for in situ stable isotope analyses of geological samples at the scale of 1–10 μm. However, the original reflected light microscope of the CAMECA IMS 1280 SIMS had an optical resolution of ∼3.5 μm, which made it difficult to accurately position the analytical beam on the sample at the μm scale. We modified the optical microscope to use ultraviolet (UV) light illumination and UV compatible optical components, keeping the same mechanical design inside the vacuum chamber. The optical resolution was improved to 1.3 μm with the UV-light microscope system. In addition, we wrote Badgerscope©, a LabVIEW based software for sample imaging, which greatly enhanced the accuracy of positioning and efficiency of instrument operation. These improvements can be adapted to other micro-beam instruments where complex optical paths may be imposed by instrument design.

An Experimental Investigation of Distributed Acoustic Sensing (DAS) on Lake Ice

ABSTRACT A vibration-sensitive, Distributed Acoustic Sensor (DAS) array, using fiber-optic cables, was deployed in a triangularly shaped geometry on the frozen surface of Lake Mendota in Madison, Wisconsin, USA. The purpose of the array and testing program was to analyze the DAS response and to utilize the high spatial density of the distributed array for system response characterization in a well-constrained, small, surface array. A geophone array was also deployed to provide a reference system. The design of the array allowed us to assess the response of DAS with respect to distance from the seismic sources, the degradation of the response with length of the cable, the directivity of the fiber response with respect of the direction of the particle motion, and the quality of the signal with respect to cable type. The DAS array was examined for different cable constructions and orientations relative to the source propagation direction. Tight-buffered and loose-tube fiber-optic cable constructions were use...