Remote Sensing for Geological Mapping and Mineral Exploration – Spectral Imaging – (Part 3 of 4)

Spectral imaging utilizes a variety of sophisticated technology to process the interaction between matter and electromagnetic energy. Hyperspectral and multispectral data using satellite images or aerial photos are used for agriculture, forestry, oil exploration, mineral exploration and geological applications to map geology and geophysical structures that localize ore deposits by their spectral signatures.

Multispectral and hyperspectral resolution refers to the number of bands and the wavelength width of each band. A band is a narrow portion of the electromagnetic spectrum. Shorter wavelength widths can be distinguished in higher spectral resolution images.

Spectral analysis procedures are used to analyze:

Land cover classification and mapping

Extraction of culture data

Lithological classification and mapping

Change detection

Environmental monitoring

Environmental management

Geophysical features

Spectral signatures from hyperspectral vs. multispectral sensors

Multispectral for Mining

Multispectral satellite sensors such as the SPOT, IKONOS, WorldView-2 and ASTER acquire anywhere from three to ten simultaneous bands of information across a scene.  Each of these bands covers a relatively broad spectral range of electromagnetic radiation observation.

ASTER satellite images (15m) of the Saline Valley area, California. Each image displays data from a different spectral region, and illustrates the complementary nature of surface compositional information available as a function of wavelength. The LEFT image displays visible and near infrared bands 3, 2, and 1 in red, green, and blue (RGB). Vegetation appears red, snow and dry salt lakes are white, and exposed rocks are brown, gray, yellow and blue. Rock colors mainly reflect the presence of iron minerals, and variations in albedo. The MIDDLE image displays short wavelength infrared bands 4, 6, and 8 as RGB. In this wavelength region, clay, carbonate, and sulfate minerals have diagnostic absorption features, resulting in distinct colors on the image. For example, limestones are yellow-green, and purple areas are kaolinite-rich. The RIGHT image displays thermal infrared bands 13, 12 and 10 as RGB. In this wavelength region, variations in quartz content appear as more or less red; carbonate rocks are green, and mafic volcanic rocks are purple. (Image credit: NASA/Japanese Space Team).

Hyperspectral for Mining

The narrow bands of hyperspectral are more sensitive to variations in energy wavelengths and therefore have a greater potential to detect minerals than multispectral imagery. Multi- and hyper-spectral data are used together to provide a more complete picture of minerals.

The lithology of the area is very important because it gives us a description of the gross physical characteristics that define a particular rock, including color, texture, mineral composition, and grain size. The magnetic field layer is very important also because it gives us the region of physical space surrounding a permanent magnet, electromagnetic wave or current-carrying conductor, within which magnetic forces may be detected.

The successful application of this technique depends on determining the surface spectral signature of materials of interest. With this knowledge, image data collected from satellites can be processed to map the distribution of the materials of interest.

Hyperspectral imaging main objectives are:

  1. target detection
  2. material mapping
  3. material identification
  4. mapping details of surface properties

Radarsat Earth Observation Satellite

RADARSAT is a sophisticated Earth observation (EO) satellite developed by Canada to monitor environmental change and the planet’s natural resources and to support resource sustainability. Launched in November1995, RADARSAT provides Canada and the world with an operational radar satellite system capable of timely delivery of large amounts of data. RADARSAT also provides useful information to both commercial and scientific users in the fields of mining, agriculture, cartography, hydrology, forestry, oceanography, ice studies and coastal monitoring.

Radarsat-2 which was launched on December 14, 2007 is capable of large scale production and timely delivery of data. The data from the satellite meets the needs of commercial, government and scientific programs and provides a new and reliable source of high quality radar data.

Canadian Radar Earth Observation satellite RADARSAT-2 (Image: CSA)

At the heart of RADARSAT is an advanced radar sensor called Synthetic Aperture Radar (SAR). SAR is a microwave instrument that sends pulsed signals to Earth and processes the received reflected pulses. RADARSAT ‘s SAR-based technology provides its own microwave illumination and thus operates day or night, regardless of weather conditions.

RADARSAT is not hindered by weather, darkness or cloud cover to extract data. Archived data of our clients’ Regions of Interest (ROI) can be obtained quickly from our image providers, thus cutting down on delays and lead time on time-sensitive projects.

RADARSAT data is adjoined to our complement of high-resolution satellite data in order to enhance analysis of geophysical structures within the ROI, thus improving the spectral analysis of possible mineral deposits areas in our clients’ Regions of Interest.

RADARSAT Orbit

Type Sun-Synchronous
Altitude 798 km
Inclination 98.6 deg
Period 100.7 min
Repeat Cycle 24 days

Sensor

SAR (Synthetic Aperture Radar): The SAR is able to operate in several beam modes:

  • Standard: Seven beam modes with incidence angle ranging from 20 to 49 deg nominal, 100 km swath width and 25 m resolution.
  • Wide: Three beam modes with varying incidence angles, 150 km swath width.
  • Fine: Five beam modes with 50 km swath width and resolution better than 10 m.
  • Scansar: Wide swath width (300 – 500 km) with a coarser resolution of 50 to 100 m.
  • Extended mode.

RADARSAT Operating Modes

MODE RESOLUTION
(m)
Range x azimuth (m)
LOOKS WIDTH
(km)
INCIDENCE ANGLE
(degrees)
Standard 25 x 28 4 100 20-49
Wide – 1 48-30 x 28 4 165 20 – 31
Wide – 2 32-25 x 28 4 150 31 – 39
Fine resolution 11-9 x 9 1 45 37 – 48
ScanSAR narrow 50 x 50 2 – 4 305 20 – 40
ScanSAR wide 100 x 100 4 – 8 510 20 – 49
Extended (H) 22-19 x 28 4 75 50 – 60
Extended (L) 63-28 x 28 4 170 10 – 23

1. Nominal; ground range resolution varies with range

2. Nominal; range and processor dependent

3. Incidence angle depends on sub-mode

RADARSAT SAR Instrument Characteristics

Frequency/wavelength 5.3 GHz (C band)/ 5.6 cm
Polarisation Linear HH
Bandwidth 11.6, 17.3 or 30.0 MHz
Peak power 5 kW
Antennae size 15 m x 1.5 m
Incidence angle Mode dependent
Resolution Mode dependent

About Auracle Geospatial Science, Inc. (AGS)

Mineral maps generated using data from high and medium resolution satellite sensors has put Auracle Geospatial Science, Inc. (AGS) a leader in the remote sensing and geospatial technology. AGS specializes in the acquisition, analysis, and production of spatial data products tailored for mineral exploration and mining.

AGS has developed specialized algorithms and processing techniques to enable the extraction of complex features from projects requiring the manual interpretation and extraction of GIS features from satellite images as well as aerial photographs.

We have used land classification projects to create complex GIS layers with associate database tables consisting of detailed descriptions of classified types, making it possible to query databases for specific features.

Auracle Geospatial Science, Inc.

Coming up next Part 4 – Data Fusion

About Auracle Geospatial Science, Inc.

Auracle Geospatial Science Inc (AGS), a geospatial company that offers comprehensive range of geospatial information services that include Geographic Information Systems GIS, satellite image processing, spatial analysis and spatial modeling. Our global clients from mineral exploration, oil exploration, forestry management, and the agricultural industry have come to rely on our expertise to acquire, analyze, and visualize their geographic information. AGS also offers support services in Remote Sensing Consulting, project development, land-use management and litigation support.
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