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Research about Mirror Lake

Source-linked reports with geographic coverage including Mirror Lake.

26 records · Page 2Linked to original sources
USGS1998

Mapping hydraulically permeable fractures using directional borehole radar and hole-to-hole tomography with a saline tracer

Reflection-mode borehole radar and transmission-mode radar tomograms image heterogeneity in the electromagnetic properties of rock. Heterogeneity may be produced by interfaces between different rock types, foliation, and fracturing. In crystalline rock, hydraulic flow is primarily through fracture networks rather than through the rock matrix. Borehole radar methods have been applied to help map flow paths in crystalline rock. Correlation of features identified in borehole radar reflection records and tomograms with hydraulic flow paths is generally uncertain because the records show responses to heterogeneity of all- kinds, not just to hydraulically permeable fractures. Even in lithologically uniform rock, it is often not possible to distinguish fractures of high hydraulic permeabilities from those with low permeabilities. It is possible to “erase” signatures from lithologic interfaces and rock fabric to identify the signatures of hydraulically permeable fractures by using a saline tracer in fractured crystalline rock because the electrical properties of the rock, except for the fractures that are open to infiltration by the brine solution, remain the same after the injection of the brine and may be removed by examining differences. Saline tracer experiments were carried out in 1995, 1996, and 1997 in the FSE well field at the Mirror Lake fractured-rock hydrology research site in Grafton County, New Hampshire. Comparisons of results from directional radar reflection surveys to well-to-well difference attenuation tomography in the same pairs of wells show generally good correspondence between the location of radar reflections and attenuation anomalies. Our results demonstrate the advantage of using a saline tracer for before-and-after difference mapping of hydraulically permeable fractures in lithologically heterogeneous rock and the utility of the coordinated use of directional borehole radar and hole-to-hole radar tomography.

New Hampshire↗
USGS1997

Cross‐hole radar attenuation tomography using a frequency centroid down‐shift method: Consideration of non‐linear frequency dependence of EM wave attenuation

This paper presents a cross-hole radar attenuation tomography method based on analysis of the down-shift in the spectrum centroid frequency, and spectral broadening of the received radar signals. The method uses a parameter that combines centroid frequency down shift and variance increase for the projection function to construct the tomography algorithm. In comparison with other methods for estimating attenuation, the frequency down shift method is relatively insensitive to the effects of geometric spreading, antenna coupling, antenna radiation pattern,and instrument response, but the method requires the data to be broad-band so the frequency shift is easily measured. This method is well suited for difference tomography when electrically conductive tracers are used. The method was tested using cross-hole radar data acquired before and during a saline tracer injection experiment at the U.S.Geological Survey’s Fractured Rock Research Site at Mirror Lake, in Grafton County, New Hampshire. The attenuation-difference tomogram clearly outlines the location of the saline tracer within the tomography plane.

New Hampshire↗
USGS1988

Climatic data for Mirror Lake, West Thornton, New Hampshire: 1985

Research on the hydrology of Mirror Lake, West Thornton, New Hampshire, includes a study of evaporation. Those climatic data needed for energy-budget and mass-transfer evaporation studies are presented, including: water surface temperature, dry-bulb and wet-bulb air temperatures, vapor pressure at and above the water surface, wind speed, and short- and long-wave radiation. Data are collected at raft and land stations. (USGS)

New Hampshire↗
USGS1985

Geophysical well log data for study of water flow in fractures near Mirror Lake, West Thornton, New Hampshire

Four closely spaced boreholes were drilled through approximately 20 meters of till into schist bedrock near Mirror Lake, West Thornton, New Hampshire. The site was selected for borehole geophysical research because it is included in a detailed groundwater study where the effects of flow in fractures on flow in overlying drift deposits is being studied. Three of the boreholes are approximately 100 meters in depth, and the fourth is approximately 230 meters in depth. All four boreholes were logged with caliper, acoustic, gamma, single-point-resistivity, and acoustic televiewer logs. Fracture sets dipping approximately 45 degrees to the east were detected in all four boreholes. Two sets of deeper fractures were detected near the bottom of the deepest borehole. Acoustic waveform logs were obtained in all boreholes using three different source frequencies, 34, 15, and 5 kilohertz, for future comparison with surface to borehole seismic data.

New Hampshire↗