About the Near Surface Observatory (NSO)
The NSO is an aggregation of several research groups and individuals who conduct studies focused on the surface and near-surface environment. Augmenting the efforts of the researchers, interns, and students is a suite of airborne, surface, and borehole instruments that provide information on the physical properties of the near surface and allow NSO researchers to conduct geologic mapping in diverse environments and studies on coastal hazards and geomorphic change, wetlands status and trends, coastal rookeries vulnerability, landscape characterization and evolution, periglacial landforms, soils, and water bodies, and soil-moisture monitoring.
Bureau researchers apply modern geophysical, geologic, and remote-sensing methods to address problems in the surface and near-surface environment. Surface, airborne, and borehole tools scale from regional to local studies involving issues such as coastal geology, surface water and groundwater salinization, neotectonics and surface faulting, subsidence, transportation infrastructure, Quaternary geology, sinkhole characterization and assessment, and many other related topics.
• Near-surface geophysics applied to geologic, hydrologic, and engineering issues
• Airborne Lidar and Hyperspectral Imaging
• Coastal geology
• Geologic mapping (regional and detailed)
• Geohazards assessment and monitoring (sinkholes, surface faulting, and subsidence)
• Soil and water salinization
• Groundwater resource assessments
Rather than apply a single favorite approach or all available approaches to a near-surface geological, hydrologic, or engineering issue, we seek to fully understand the issue before selecting a tool or method, identify relevant physical properties that can serve as a reliable proxy for the problem or issue, select the appropriate instruments and platforms (airborne, surface, or borehole), and then design a measurement campaign to address the lateral and vertical scale of the problem. The final step is to analyze and interpret the proxy measurements in a manner that gives insight into the geologic, hydrologic, or engineering issue.
Research Assets and Expertise
- Frequency-domain electromagnetic induction system: Geonics EM34-3. A surface instrument that measures apparent ground conductivity at selectable depths as great as 50m. Produces conductivity profiles along the ground surface and depth sections depicting lateral and vertical variation in ground conductivity that are useful for characterizing surficial deposits and bedrock lithology, water-saturation trends, and pore-fluid salinity.
- Time-domain electromagnetic induction system: terraTEM three-channel acquisition, three-component receiver, continuous recording). Produces generalized models of ground conductivity from depths of a few to a few hundred meters. Can explore deeper than the EM34 and serves as a nonintrusive borehole proxy.
- Geoprobe: mobile, track-mounted push probe for shallow logging and sampling.
- Slim-hole borehole geophysical logging system: 1024-channel spectral natural gamma and electrical conductivity probes, 400-m cable, motorized winch, WellCAD analysis software. Produces high-resolution gamma and conductivity logs in slim-hole borings and water wells. Useful for determining site-specific lithology, water saturation, and groundwater salinity.
- Shallow seismic reflection and refraction: 24- and 48-channel seismographs, 40-Hz geophones, Seismic Processing Workshop software. Shallow (a few to a few hundred meters) exploration of geologic features.
- Ground-penetrating radar: GSSI SIR-2000 and 3000 systems with multiple antennas. Ultra-shallow (surface to a few meters) investigations of geologic and engineering features.
- Airborne geophysics: high-resolution electromagnetic induction and magnetometer surveys from helicopters and fixed-wing aircraft. Produces high-resolution maps, cross sections, and volumes that allow sophisticated interpretation of near-surface lithology, structure, and water content and salinity.
- Airborne lidar, digital photogrammetry, and radar interferometry: airborne- and satellite-based surveys to determine elevation and elevation change over time. Useful for subsidence studies.