Remote sensing technology is widely used in detection of earth resources, prediction of earthquake and volcanic eruption, monitoring of environmental pollution as well as departments such as metallurgy, geology, oil, agriculture, forestry, water conservancy, surveying and mapping, weather, ocean and so on. Remote sensing technology is superior with characteristics of wide range, fast speed and low cost in monitoring and is convenient for long-term dynamic monitoring, etc.
In mine monitoring, remote sensing data such as MSS, Landsat, ETM, SPOT, IKINOS, QUICKBIRD and so on are commonly used (Cheng Ting, 2006) Electromagnetic energy, when incident on a certain feature of earth surface, the energy can be reflected, absorbed, or transmitted, which will vary in proportion depending upon the material type and conditions of different earth features.
The distinctions allow recognizing diverse elements on a satellite image. At different wavelengths, extent of three basic energy interactions would differ even within a given feature type. In one spectral range two features may be distinguishable but altogether different on other band of wave- length.
The resultant optical effect due to spectral differences within the visible portion of the spectrum is called “colour.” To discriminate among various objects, spectral differences in the extent of reflected energy are utilized by human eyes Remote sensing has been utilized as a device for finding potential exploration targets from the initial stage of photogeology.
The quality of remotely detected information has expanded as the level of technology has improved. Aerial photographs were used in the early days for wide area topographic survey. The technique steadily progressed to be substantially more refined, and it was only posting World War II, obtaining of ground geological information was initiated. Using stereoscopes, it was possible to interpret geological structures from the aerial photographs. The essential utilization of remotely sensed information was relative.
The Basic Concept of remote sensing
Remote sensing is a process to acquire, prepare, and decipher information of spectral and spatiotemporal nature on objects, phenomenon or areas under investigation without being in direct physical contact. Transfer of information is carried out using “electromagnetic radiation” (EMR) in remote sensing. (Sabins, F.F., 2007) stated “EMR is a form of energy that reveals its presence by the observable effects that are produced when it strikes the matter.”
It can also simply be defined as an electromagnetic emission with specific wavelengths of an object i.e. in this case the earth from ultraviolet ray to microwave. It is the use of modern carrier, electronic and visual instrument in an active or passive manner as illustrated in figure 1 to receive as well as process electromagnetic wave of certain crossed wavelengths from UV ray to microwave transmitted or reflected by navigated object at deep or on the earth’s surface to finally.
Major Remote Sensing Satellite Systems
Most of the satellites orbit at an altitude between 700 and 920 km. The earth rotates and the satellites scan 185 km length of its swath. The remote sensing systems and their capabilities in the world is presented below as from (Taranik, 2009)
LANDSAT (Introduced by US Government) First generation (Landsats 1, 2, and 3 of 1972), Landsats 4 and 5 of 1984, Landsat MSS (repeat coverage: 16 days), Landsat Thematic mapper (TM) (repeat coverage: 16 days), and Landsat 6, Landsat enhanced TM, launched in 1999 (repeat coverage: 16 days).
SPOT (Introduced by French Government) Multispectral scanner (XS) multispectral mode acquires three bands of data green, red, reflected IR wavelength with spatial resolution of 20 m. Panchromatic (Pan) acquires a single band of data, primarily green and red wavelengths with spatial resolution of 10 m; both image modes cover 60 3 60 km of terrain (repeat coverage: 26 days).
AVIRIS (Advanced Visible/Infrared Imaging Spectrometer): Conventional multispectral scanning systems, such as Landsat TM, SPOT XS, record up to 10 spectral bands and bandwidths of 0.10 µm. Hyperspectral scanners are a special type of multispectral scanner that record many tens of bands with bandwidths on the order of 0.01 µm. At visible wavelengths and at reflected IR wavelengths, many minerals have distinctive spectral reflectance patterns. Many minerals may be identified on suitably processed hyperspectral data. AVIRIS image strips are 10.5 km wide and several tens of kilometers long.
ASTER (Advanced Space borne Thermal Emission and Reflectance Radiometer); ATLAS (Airborne Terrestrial Applications Sensor) JV US & Japanese Govts, launched in 1999 VNR: 3 bands, 15 m resolution; SWIR: 6 bands, 30 m resolution; TIR: 5 bands, 90 m resolution. ASTER is a multispectral sensor with 14 “geoscience-tuned” spectral bands which provide geological information far superior to that available from Landsat TM but at lower accuracy and mineralogical detail compared with hyperspectral systems, such as the 126-channel airborne HyMap sensor Thailand Launch Theos: 4 bands R, G, B, IR; 2 m; Panchromatic, 15 m, color.
Application of Remote sensing in Mines
The use remote sensing in rock characterization, spatial analysis and monitoring deformation process uses different technologies, such as Light Detection and ranging (LiDAR) and Structure from motion, for data integration. LiDAR is a modern scanner measure distance by utilizing an Electronic Distance Measurement (EDM) unit and electronically capture angular measurements to compute a position.
Application in Slope Instability
A structure from motion is a photogrammetric process that leads to realization of a three dimensional model developed from a two dimensional model to permit the acquisition of three dimensional coordinates of points located in the overlapping zone of two photos of the same area taken from two different viewpoints. After remote sensing have been integrated analyses such as compliance rock trap geometry, monitoring slope regression and material deposition, spatial analyses can be used for identification of critical areas of potential slope instabilities. As instance monitoring rock trap geometry and spatial analyses of an open pit mine is presented below.
Monitoring Rock Trap Geometry
The different scans in the figure below were locally aligned from a mine using ICP algorithm on separated constraints with a specific mean absolute error. The local registration was then referenced and surveyed using Differential Global Navigation Satellite (DGNSS).
Spatial Analyses in an open pit mine
Spatial data about geometry of slope by AL and hand0held data can also be combined with geological data. The next example combines slope geometry attributes with spatial distribution of alteration grade within an open pit. For design purposes an initial analysis was required to highlight slope benches with high alteration and with slope angles greater than 45 degrees. The slope angle analysis was undertaken in a Geographic Information System (GIS) environment. Figure 3 shows the result of such an analysis using a high-resolution Digital Terrain Model (DTM) and integrated with ML information in order to have sufficient resolution at a single bench.
Remote Sensing in mine management
Studies show that changes in the natural vegetation as a function of production rate were determined using the NDVI. Tucker23 reported that the NDVI changes between -1.0 and +1.0 in general, and more specifically between +0.1 and +0.7. NDVI values were calculated using the (4–3) / (4+3) band ratio for Landsat images and the (3–2) / (3+2) band ratio for the ASTER images. The effect of marble quarries activities on vegetation from 8 years are determined using NDVI images and vector data from quarry boundaries for each years. The subset method was used to calculate the yearly changes by converting the vector data into an area of interest layer (AOI). To determine the extent of vegetation loss, NDVI images from one year to the next were subtracted from the AOI images.
Monitoring of harmful gases
Under man-made or natural conditions, the harmful gas produced for biology, such as SO2, fluoride and so on, is usually signed by indirect interpretation. The capability of the infrared reflection can decline after the vegetation is contaminated; even its colour, texture and dynamic signs are used to be different from the normal vegetation, such as dark colour in infrared images, decreases in tree canopy density and normal individual vegetation etc. These traits can be directly used to analyze contaminated instance. For the ground pollution, such as in farmland pollution, the polluted crops growth would have special changes and groundwater pollution would lead to changes of vegetation on the ground, which has different spectrum performance from crops in the normal growth areas. Multi-spectral imaging instrument can monitor these changes, thereby could delineate the distribution scope of the ground pollution, and make further prevention plans on ground pollution (Tan, 2008)
Reference
Mekonnen, Tamrat & Hussien, Bedru. (2021). Application of Remote Sensing in Mining. Global Science Education Journal. 9. 2385-2394. 10.11216/gsj.2021.08.53574.
