Source: NASA / JPL - Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
How much gold can still be mined on Earth? What about the lesser-known element indium, essential for smartphone and computer displays? With known sources of some crucial metals facing depletion within the next couple of decades, there is a lot of pressure on developing alternatives to current mining exploration technologies. How can one more easily find necessary deposits at scale? On Earth? And in space?
ultispectral imaging is already employed in drone, satellite, and aircraft-based systems in the hunt for new precious mineral deposits on Earth, and it’s also beginning to be used in space!
The following step is probably hyperspectral imaging. Regular use of current hyperspectral systems by the minerals sector has been hindered by the unattainability of systems for industrial use, the need for extra research into the processing of hyperspectral data, and the high cost of hyperspectral data (when available) compared to typical multispectral data.
After a few difficult years in terms of growth and investment from 2010-2015, with dipping prices and low investment, 2017 is beginning to look better, and companies may be wanting to invest in new technologies to better find and extract the resources the global economy is demanding.
A History of Innovation and Integration
Remote imaging has been applied in exploration for years. At its most rudimentary level, prospectors and geologists would just point their cameras out of aircrafts (first balloons, then airplanes, now drones) to take pictures of the ground below, gathering information on soil and topography that might reveal clues about the location of minerals. With the help of certain complicated math, comprehensive maps could be derived from these photographs. At present, remote sensing has become one of the most crucial techniques to rapidly and directly obtain information about the Earth’s surface
However, visible spectrum photography alone had restrictions – daylight, weather, and the simple fact that a lot of what they were searching for was hidden underground. A lot had to be inferred. It wasn’t until the post-World War II, that new sensing techniques came into play as technologies progressed during the war were then applied to commercial applications that would become hallmarks of advanced aerial-based mineral exploration. Infrared cameras could penetrate severe weather conditions better than conventional photography and more easily locate the mineral content of soil.
Magnetometers could detect the disturbances in the Earth’s magnetic field to find metallic ore deposits deep underground. Gravimeters function by measuring the pull of Earth’s gravity which differs marginally based on the position of numerous underground mineral deposits. Airborne gamma ray spectrometry was designed during the 1960s, where the deepening Cold War guaranteed there was a lot of demand for radioactive minerals like uranium. Radar has many of the same benefits that infrared film does, but can see through limited vegetation, showing the geological features underneath, night or day, including moisture content and surface texture.
Transferring imaging systems from aircraft to satellites also produced completely new possibilities. Government support was important in introducing this technology. Present-day technologies include the Landsat thematic mapper and the enhanced thematic mapper multispectral imager by the United States and high-resolution panchromatic imaging technology (SPOT) developed by the French Space Agency.
A 2014 high-tech mineral-mapping effort in Afghanistan by the U.S. Geological Survey is the first of its kind. It initially generates $146 million in yearly revenue, and Afghanistan’s minister of mines and petroleum hopes to report $1 billion in revenue by 2020. Source: Department of Defense
Enter Hyperspectral Imaging
Although the data from these various approaches was very beneficial, it still didn’t provide the detail of imaging. Imaging in the visual range simply didn’t offer the detail and information that the mining sector required. Introducing hyperspectral imaging, courtesy of NASA, the technology was first built in the late 1970s by Jet Propulsion Laboratory, enabling NASA to put hyperspectral imaging equipment in satellites sent to Jupiter and Saturn. While a few private companies constructed their own hyperspectral cameras, it really took off when NASA made the technology available to entrepreneurs and researchers, even offering grants to test the real-world efficiency of the technology, including one to Yellowstone Ecosystem Studies.
It is tough to hide things from this type of camera.
Like most remote sensing techniques, hyperspectral imaging makes use of the fact that all objects have a unique spectral fingerprint based on the wavelengths of invisible and visible light that they absorb and reflect. This reveals plenty of details that are otherwise not available in the visible spectrum, such as the difference between greens that signify natural plants, and those that are not natural, such as metals and plastics. Green plastic has varied reflectant properties than natural vegetation out beyond the visible spectrum – even cut or fallen branches have a different fingerprint than growing vegetation.
The commercial impact will be huge, especially in the field of mineral exploration. While gold occurs in quantities too small to detect with any existing technology, more common minerals like arsenic and kaolinite, which are products of some of the same geological processes, are evidently visible in open landscapes, as is the case in much of the Australian desert or American West. For the diamond sector, kimberlite pipes, the volcanic formations that pushed diamonds to the surface, are easy to spot from the air with hyperspectral imaging.
Scientists have collected hyperspectral imagery between 1999 and 2014 of the Lamar Valley in Yellowstone National Park. By performing a series of classifications on these images and after carefully aligning each image, they can we can see how the landscape has changed. Source: Yellowstone Ecological Research Center
In contrast to radar, hyperspectral technology cannot penetrate below ground, or through buildings or vegetation, but it can be integrated with radar to make it even more powerful.
Additional integrations yield even more accurate views of the Earth’s surface and its secrets below. LIDAR is an even more accurate system for mapping topography, with all systems integrating GPS data to remove the need to conduct expensive image correlation or ground surveys.
The data demands are heavy, putting great pressure on each organization’s computing power. For instance, when NASA used hyperspectral imaging to examine the 16-square-mile Superfund site in Leadville, Colorado, it saved years of on-the-ground work, with 45 seconds of satellite imaging. Still, it took another 10 months to derive data from the numbers. Only with the development of more robust computers has this kind of imaging been able to move out of the lab. The fast growth in computing power and storage capacity in extensively-available computing platforms has allowed the very large data sets, terabytes and exabytes of information from airborne instruments to be handled in the time frame needed by mineral exploration operations.
Hyperspectral Remote Sensing Data and a Multi-proxy Investigation for Characterizing Mineral Resources in Alaska.
The project’s goal is to define the geologic footprint of a few deposits using imaging spectroscopy, and regionally extrapolate this knowledge to areas not properly characterized. It is anticipated that the synthesis of results from this multidisciplinary project will improve the understanding of the regional geology and be used to develop a predictive exploration model for the identification of base and valuable metal-bearing deposits in Alaska and related remote regions of the world.
Presently, hyperspectral imaging is well-developed with regards to mineral exploration. Many minerals can be identified from airborne images, and their relation to the presence of prized minerals such as diamonds and gold is well understood. Hyperspectral imaging can be used to map massive amounts of land and narrow down the search area for valuable deposits of minerals. In certain cases, hyperspectral imaging can be used to locate the specific minerals of interest, but can also find indicator minerals that hint of a neighboring location of a valuable ore deposit.
Looking Deeper and Looking Forward
This latest data demands new understanding of the movement of fluids across the Earth. What is the relationship between the locations of specific valuable minerals? Optimized hydrologic models will be crucial for future mineral exploration. This is also pertinent to the effective closing of mines that have concluded their life cycle. Models for ore deposits that, when mined, have marginal impacts on the environment (such as deposits with no acid-generating capacity) and for deposits that may be available to pioneering in-situ extraction will be vital for the future.
Technology has advanced to a point where it is currently possible to predict 3D images from 2D analyzes in certain mineral systems. Refinements in this technology could result in defining liberation in an ore, therefore eliminating overgrinding and decreasing both energy usage and extreme loss of fine-grained particles.
Currently, many research challenges are being looked at for hyperspectral technology, particularly for spaceborne systems. These include the development of focal planes with sufficient signal-to-noise spectral resolution to resolve mineral species of significance and the capability of obtaining data at a 10 meter spatial resolution while maintaining a minimum swath width of 10 km. The focal planes must also be lightweight, compact, have accurate pointing capabilities, and be powerful enough to maintain calibration for long-duration spaceflights.
Regular use of current hyperspectral systems by the minerals industry has been hindered by the unattainability of systems for industrial use, the high cost of hyperspectral data (when available) compared to common multispectral data, and the need for extra research into the processing of hyperspectral data. There is still plenty of work to be done. In numerous countries, national governments are funding, and companies are investing in, system development and deployment as well as regular research on the analysis of hyperspectral data that would confirm that these new technologies would be beneficial for the mineral exploration sector, as well as for a broad range of other users, including environmental scientists and land-use planners.
This information has been sourced, reviewed and adapted from materials provided by Teledyne DALSA.
For more information on this source, please visit Teledyne DALSA.