Emerging technologies and the future of geotechnical instrumentation 

J.M. Girard and E.L. McHugh 

NIOSH Spokane Research Laboratory, Spokane, Washington, USA 

ABSTRACT: This paper discusses the results of two recent case studies in which high-tech prototype 

instruments were used. The first case study describes the results of a ground-based hyperspectral imaging 

tool used to map the geology of an open-pit mine highwall. The second case study outlines the use of 

interferometric synthetic aperture radar and how this type of radar can be used in a variety of geotechnical 

situations. These case studies are part of an on-going research project at the National Institute for 

Occupational Safety and Health’s (NIOSH) Spokane Research Laboratory. The project objective is to 

implement engineering controls and design methods in order to reduce the number of injuries and fatalities 

associated with slope failures at mining operations. Project personnel are hopeful that these new 

developments in technology will lead to better geotechnical monitoring and design in slope stability and other 

important areas of rock mechanics. 

1 INTRODUCTION 

The National Institute for Occupational Safety and 

Health (NIOSH), Spokane Research Laboratory is 

involved in research to improve methods for 

detecting conditions in open pit mines that could 

lead to catastrophic slope failures. Since 1995, 33 

miners have died in slope failure accidents at U.S. 

mines. Better methods for monitoring and design 

are needed to ensure the safety of mine workers. 

This paper highlights two emerging technologies 

that could potentially be adapted to improve mine 

safety. Applications to rock mechanics issues 

related to surface and underground mining, 

petroleum, geological, civil engineering and 

geohazards monitoring are also included. 

2 HYPERSPECTRAL IMAGING 

A contributing factor in many slope failures is the 

presence of mechanically incompetent, hydrothermally-altered rock (Watters & Delahaut, 

1995). Major structures are generally well 

mapped, but weak rock units may be much more 

difficult to identify and the degree of clay 

alteration is oftentimes difficult to determine by 

visual examination alone. Geologic maps can 

vary greatly in quality and detail due to the 

subjectivity of various geologists and the extreme 

complexity of many deposits. In addition, there 

are financial and practical limits to the number of 

samples that can be taken for geochemical or 

engineering analyses. Inevitably, a large 

percentage of data shown on geologic maps is 

subject to scrutiny. High turnover rates of 

engineers and geologists at many companies, 

financial and time limitations, and unfamiliarity 
with complex formations can contribute to crucial 

errors or omissions on geologic maps. 

 

2.1 Prototype Spectral Imager 

NIOSH recently completed field tests of a 

prototype imaging spectrometer that was built by 

Carnegie Mellon Research Institute (CMRI). The 

purpose of the tests was to evaluate a new method 

for objectively mapping the geology of an open-pit 

mine from a distance. 

 Every material on the earth’s surface reflects 

light in a characteristic pattern. The manner in 

which light of different wavelengths is reflected or 

absorbed by each material is known as its 

reflectance spectrum. By filtering light of specific 

wavelengths, images can be created that 

differentiate specific materials. Figure 1 illustrates 

examples of the spectral signatures of Neodymium 

Oxide and Kaolinite (Clark et al., 1998).

Figure 1. Examples of reflectance spectrum for 

Neodymium Oxide (top) and Kaolinite (bottom) 

(adapted from Clark et al., 1993) 

 A 

spectrometer is a device that collects these 

diagnostic spectral absorption features; 

identification of the minerals is then achieved by 

comparing the data to spectral libraries. 

 Field portable spectrometers are commercially 

available that can analyze light reflected from a 

single point, but the CMRI instrument is 

distinctive because it collects spectral reflectance 

data in a two-dimensional array. The instrument 

operates in the visible and near infrared ranges and 

employs an acousto-optical tunable filter to control 

wavelength, a phase retarder to measure 

polarization signatures, and a digital camera linked 

to a laptop computer to capture data (Figure 2). 

~10 cm

Figure 2. Spectro-polarimetric imager
 

developed by Carnegie Mellon Research 

Institute. 

The instrument is very robust since it has no 

moving parts, and is also field portable (Denes et 

al., 1998; Gupta et al., 1999; Sabine et al., 1999; 

McHugh et al., 2000). 

2.2 Field Site Selection 

Since the current configuration of CMRI’s 

instrument is limited to the visible and near 

infrared ranges (0.45 – 1.0 μm), mineralization 

with diagnostic features within this particular 

spectral range was required for the field tests. For 
this reason, the Mountain Pass Mine, which is 

approximately 60 miles southwest of Las Vegas, 

Nevada, was selected as the test site for the CMRI 

prototype instrument. The Mountain Pass Mine 

geology is comprised of rare-earth elements of the 

lanthanide series (cerium, lanthanum, neodymium, 

europium, and others), which have at least eight 

distinctive absorption features between 0.45 – 1.0 

μm. Spectral data for the deposit were published 

by Rowan & others (1986; 1996) and Kingston 

(1993). 

2.3 Field Tests 

 Twelve multispectral images -- including pit 

highwalls (Figure 3), outcrops, drill core from the 

ore zone, and hand samples -- were collected at 

the site. 

Figure 3. West highwall of the Mountain 

Pass Main Pit. Study area is outlined. 

Supplemental images of hand specimens 

under artificial light sources were collected at 

CMRI to aid in calibration and evaluation of the 

instrument. Thin sections were made from both 

the ore and the host rock to assist with 

interpretation of the images. 

2.4 Analyses and Results 

After the spectro-polarimetric images of the area 

were collected, substantial processing, filtering, 

and computer analyses were performed using 

ENVI software Spectral profiles were compared 

to data in the U.S. Geological Survey’s Digital 

Spectral Library (Clark et al. 1993) to correlate the 

images with specific minerals. Detailed 

information regarding the spectral processing can 

be found in McHugh, et al., 2000. The results of 

the image analyses are illustrated in Figure 4. 

Figure 4. Results from the CMRI spectropolarimetric imager. Light areas correspond to ore; 

darker areas to waste or unclassified spectra. 

The 

white areas correspond to bastnaesite ore and the 

darker areas are waste rock or unclassified spectra. 

 The results from this field study successfully 

illustrate the capability of a field-portable imaging 

spectrometer to discriminate minerals within 

images of highwalls, outcrops, rock samples, and 

drill core. However, to effectively apply the 

AOTF-based technology to the characterization of 

alteration in rock masses caused by clays and 

other minerals, the instrument would need to be 

redesigned to extend into the shortwave and midinfrared region of the spectrum. At this time, 

funding for this advancement in technology is not 

available at NIOSH or at CMRI. 

 There are many advantages to using spectral 

analyses for geologic mapping. First, spectral 

identification of minerals would remove the 

human error and subjectivity of trying to visually 

determine the degree of alteration in a rock mass. 

Secondly, workers would be able to map mine 
highwalls, or other inaccessible or precarious 

areas, from a safe distance. Finally, spectral 

analyses could be used to define faults, shear 

zones, and fracture systems in rock masses. 

 

3 SYNTHETIC APERTURE RADAR 

3.1 Overview of Technology 

The second type of remote sensing technology that 

is being studied by NIOSH researchers is synthetic 

aperture radar (SAR). SAR is a type of groundmapping radar that was originally designed to be 

used from aircraft and satellites. SAR can be used 

to generate high quality digital elevation maps and 

to detect disturbances of the earth’s surface. A 

variation of SAR – Interferometric Synthetic 

Aperture Radar (also known as IFSAR or INSAR) 

– uses differences in successive SAR images to 

generate maps of displacements. One of the first 

applications that tracked ground motion without 

the aid of ground control points used Earth 

Resource Satellite (ERS-1) INSAR data to 

estimate ice-stream velocity in Anarctica 

(Goldstein et al., 1993). Although radar 

technology has been in widespread use since the 

1940’s, interferometric techniques have mostly 

been developed during the past decade. INSAR 

has also been successfully applied to produce the 

first displacement maps of ground movement 

caused by natural hazards such as earthquakes 

(Massonnet et al., 1993 & 1994; Zebker et al., 

1994), volcanic activity (Massonnet, 1995), and 

landslides (Fruneau & Achache, 1996). This 

technique can also be used to monitor 

displacement of unstable slopes or landslides 

(Reeves et al., 1997; Sabine et al., 1999), and 

subsidence caused by the extraction of ground 

water, oil & gas, or minerals (Fielding, et al., 

1998; Carnec, 1996; Stow 1996; Dixon, 1994). 

These pioneering studies have generated 

enormous interest in the Earth science community 

because they point to an entirely new way to study 

the surface of the Earth. 

 INSAR’s have many advantages over current 

types of monitoring systems. Able to work in 

nearly all weather, an INSAR can acquire imagery 

through fog, mist, rain, haze, or cloud cover, and 

can operate day or night. Also, an INSAR can 

sample large areas for ground displacement, which 

gives them a tremendous advantage over survey 

networks, extensometers, and other instruments 

which sample movement on a discrete set of 

points. Recent developments in instruments such 

as prismless laser range finders partially address 

the problem of under sampling large areas for 

movement. However, the range and accuracy of 

these units can vary greatly depending on the 

reflectivity of the rock, the angle of the rock face, 

weather, and other factors. 

Figure 5. Photograph of the prototype 

interferometric radar system. The transmit 

antenna is seen in the center and the receive 

antennas are on the top-right and bottomright. 

3.2 Field Tests 

The Microwave Earth Remote Sensing Laboratory 

at Brigham Young University (BYU) has recently 

designed and built a small synthetic aperture radar 

system capable of operating from light aircraft or 
from stationary ground-based locations

(Thompson, 1998.) The prototype system, as seen 

in Figure 5, consists of a transmitter, two 

receivers, three antennas, and an embedded 

computer. 

 The first field tests related to geohazard 

monitoring using this instrument were performed 

by BYU for the Canadian National Railways 

(CN). The railways were interested in finding for 

a method to accurately detect rockfalls and 

washouts on railroad tracks before trains

approached those dangerous areas. CN reports 

that approximately 20% of all their train 

derailments are caused by slope failures -- either 

rockslides or washouts (Figure 6. Arnold & 

Clegg, 1999).

Figure 6. Rail track demolished by a slope 

failure. 

 Corrective action requires a lot of 

time and can expose repair personnel to the risk of 

injury from additional falling debris. CN needed 

a system that could detect problems along the 

railroad track without having to send out 

personnel. 

 In the field tests for CN, the BYU 

interferometric radar system generated a terrain 

topography map accurate to within a few 

centimeters. Successive radar images were 

compared to watch for sudden changes in the 

topography caused by rockfalls or washouts along 

the track. 

 The initial results from the CN railways tests 

were positive, and BYU researchers are confident 

that their system can be adapted to monitor 

highwalls at mines. Research and development 

needs to be completed and the prototype system is 

currently undergoing engineering tests. As soon 

as BYU has completed modifications to the 

instrument, NIOSH is planning to perform 

ground-based field tests of an open-pit highwall at 

an active mine site. An established survey 

network of prisms and GPS data will be used to 

calibrate the radar results. 

 

 

4 CONCLUSIONS 

Remote sensing, at the present time, cannot 

replace conventional geotechnical methods of 

investigation. However, emerging technologies 

such as hyperspectral imaging and interferometric 

synthetic aperture radar should not be ignored. 

The satellite versions of this technology are 

already widely used to monitor ground 

subsidence, landslides, volcanoes, and active 

faults. As computer technology continues to 

advance and processing speeds increase, 

integration of remote sensing tools into mining, 

petroleum, and civil engineering applications will 

also increase. 

 The potential benefits of using multiple remote 

sensing methods to better understand slope 

failures is merely one aspect of the current 

research to reduce the number of deaths caused by 

ground instability at surface mines. The NIOSH 

Slope Stability Hazard Recognition Team is 

pursuing many other options to minimize the 

dangers associated with surface ground control 

problems. Results of this research will hopefully 

benefit others involved in the study of landslides, 

rock falls, avalanches, volcanic activity, and other 

geohazards. 
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