Dr. Bernard Hubbard, Research Geologist, Eastern Mineral and Environmental Resources Science Center, U.S. Geological Survey
Research interests: If you own a cell phone you also own a set of rare Earth elements (REEs). REEs are key ingredients in the circuitry and components of your phone. Actually, these elements are not that rare, but finding these elements in quantities large enough to justify the cost of mining them is, which makes them economically valuable. Identifying potential sources for these REEs in remote locations around the world is one facet of the work of Dr. Bernard Hubbard.
To identify specific minerals, Hubbard uses multispectral and hyperspectral instruments mounted on aircraft and satellite platforms (such as the Hyperion imaging spectrometer on the Earth Observing-1 (EO-1), satellite). These instruments detect energy emitted in various wavelengths from ground objects. While humans can detect light in the visible band of the electromagnetic spectrum (0.45 µm [blue] to 0.67 µm [red]), multispectral and hyperspectral instruments detect a much broader range of radiated energy—from longwave infrared and microwave radiation to shortwave ultraviolet and X-ray radiation. The difference between multispectral and hyperspectral is the number of wavelengths, or bands, the instrument can detect. A multispectral sensor, such as Landsat 8, might have 3-10 wide bands; a hyperspectral sensor, such as Hyperion, has hundreds of narrow bands and is much more sensitive.
Individual minerals can be identified by the specific wavelengths in which they emit or reflect radiant energy. For example, REEs have unique spectral signatures, especially in the near-infrared portion of the electromagnetic spectrum. Hyperspectral instruments can reveal these unique spectral signatures and allow geologists to identify specific REEs present in rocks. If these rocks are well exposed, these spectral signatures may even be detected by sensors on orbiting satellites. Hubbard uses these sensor returns to map the spatial distribution of minerals and combines these maps with digital geographic information system (GIS) information to help locate mineral resources.
Along with his work in economic geology identifying REEs, Hubbard uses satellite and airborne remote sensors to assess hazards from landslides, volcano edifice failures, and related debris flows. Since joining the USGS in 2001, Hubbard’s primary work has focused on using remote sensing to help assess mineral resources in areas that may be too remote (such as the Alaskan tundra) for extended field campaigns.
Current research: Hubbard is working on several projects across the continent. In the Southern Appalachian Mountains, he is conducting spectral studies of potential REE deposits. In Alaska and the Canadian Yukon, he is using remote sensing to help distinguish areas of permafrost from wildfire burns and exposed bedrock. In southern California, Hubbard is studying landslide, debris flow, and flood hazards along the mountainous border areas surrounding the Salton Sea basin. Finally, he is working on global mapping of clay-rich altered rocks on volcanoes to help determine the possible source volumes and extents of large flows of water and rock fragments triggered by volcanic eruptions. These flows are called lahars. Large lahars can crush, bury, or carry away almost anything in their paths, including homes, roads, bridges, and slope-stabilizing vegetation.
Data products used:
- Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 Total Precipitable Water Vapor product from NASA’s Terra (MOD05_L2) and Aqua (MYD05_L2) Earth observing satellites available through the Level 1 and Atmosphere Archive and Distribution System (Distributed Active Archive Center (LAADS DAAC).
- Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Level 1B radiance data (AST_L1B) and Level 2 emissivity data (AST_05) available through the Land Processes DAAC (LP DAAC).
- Global Digital Elevation Models (GDEMs) from ASTER and the Shuttle Radar Topography Mission (SRTM), which can be accessed through LP DAAC using the Global Data Explorer (GDEx)
- Advanced Land Imager (ALI) and Hyperion instrument data from the EO-1 satellite; these data are available through the USGS Earth Explorer data discovery and access tool, as well as the Global Visualization Viewer (GloVis) online search and order tool
- Landsat Thematic Mapper, Enhanced Thematic Mapper, and Operational Land Imager data available through the USGS Earth Explorer data discovery and access tool, as well as the GloVis online search and order tool
- Landsat landcover data
Research findings: Hubbard’s research shows that REE deposits associated with lateritic soils and bauxite deposits can successfully be explored and mapped using hyperspectral instruments. Lateritic soils have high concentrations of aluminum and iron, and are predominately found between the Tropic of Cancer and the Tropic of Capricorn. Bauxite is an aluminum ore and the world’s main source of aluminum. Bauxite deposits associated with lateritic soils are found primarily in the tropics. Hubbard also found that some of the same minerals that can be used to locate precious- and base-metal related ore deposits also can be used to assess slope stability and landslide hazards.
In his work in Alaska and the Canadian Yukon, Hubbard and his colleagues found that airborne electromagnetic (AEM) surveys and Landsat images can be used together to distinguish between exposed bedrock and dry and burnt vegetation as well as green vegetation. Exposed outcrops are crucial for evaluating mineral resources and collecting samples for analysis, and can be difficult to spot from helicopters since brown-colored moss or burned vegetation can be mistaken for rock outcrops. AEM data were processed to estimate electrical resistivity and this resistivity was found to correlate to specific areas of rock, vegetation, and permafrost, making identification of exposed bedrock in these remote locations much easier.
Read about the research:
Mars, J.C., Hubbard, B.E., Pieri, D. & Linick, J.L. (2015). Alteration, slope-classified alteration, and potential lahar inundation maps of volcanoes for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Volcanoes Archive. U.S. Geological Survey Scientific Investigations Report 2015–5035. doi:10.3133/sir20155035
Hubbard, B.E., Smith, B.D., Day, W., Gough, L., Kass, M.A., Emond, A. & Caine, J.S. (2014). Correlation of Alaska Landsat image analysis with airborne geophysical survey data: A promising tool of locating outcrops, monitoring burn recovery and assessing potential permafrost thaw. Presentation at the 2014 Geological Society of America Annual Meeting, Paper No. 324-1. Available online (link).
Hubbard, B.E., Sheridan, M.F., Carrasco-Núñez, G., Díaz-Castellón, R. & Rodríguez, S.R. (2007). Comparative lahar hazard mapping at Volcan Citlaltépetl, Mexico using SRTM, ASTER and DTED-1 digital topographic data. Journal of Volcanology and Geothermal Research, 160(1-2). doi:10.1016/j.jvolgeores.2006.09.005
For more information
- Moderate Resolution Imaging Spectroradiometer (MODIS)
- Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
- Landsat Thematic Mapper (TM)
- Enhanced Thematic Mapper (ETM+)
- Operational Land Imager (OLI)