The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a multi-spectral sensor which sits in the Terra satellite launched by NASA in 1999. The ASTER sensor provides arguably the most useful imagery for mining and exploration projects. This can be attributed to its ability to capture imagery between the visible, near infra-red, short-wave infra-red and thermal electromagnetic bands. These bands, particularly the near and short-wave infra-red, are particularly useful for geological mapping in the form of:
- Clay and argillic alterations
- Ferric and ferrous oxides
- Silica content
- Gossan features
- Intrusion features
- Hydrothermal zones
- Palaeo-drainage
In addition, the ASTER sensor has the ability to capture Night-Time thermal imagery which makes it a candidate for further mineral exploration. The merit of using this technology for geology is relatively new and has lots of potential since certain minerals ‘hold heat’ and if mapped against a cooler environment (at night time) they can be better identified.
Image Specifications
- Scene Size: 60km x 60km
- Fourteen spectral bands
- Band 1 Visible Green (0.52 to 0.6 µm)
- Band 2 Visible Red (0.63 to 0.69 µm)
- Band 3 Near Infra-Red (0.78 to 0.86 µm)
- Ground Sampling Interval (pixel size): 15m x 15m
- Band 4 Short-Wave Infra-Red (1.6 to 1.7 µm)
- Band 5 Short-Wave Infra-Red (2.145-2.185 µm)
- Band 6 Short-Wave Infra-Red (2.185-2.225 µm)
- Band 7 Short-Wave Infra-Red (2.235-2.285 µm)
- Band 8 Short-Wave Infra-Red (2.295-2.365 µm)
- Band 9 Short-Wave Infra-Red (2.36-2.43 µm)
- Ground Sampling Interval (pixel size): 30m x 30m
- Band 10 Thermal Infra-Red (8.125-8.475 µm)
- Band 11 Thermal Infra-Red (8.475-8.825 µm)
- Band 12 Thermal Infra-Red (8.925-9.275 µm)
- Band 13 Thermal Infra-Red (10.25-10.95 µm)
- Band 14 Thermal Infra-Red(10.95-11.65 µm)
- Ground Sampling Interval (pixel size): 90m x 90m
Advantages and Disadvantages
Advantages
- Spectral bands exceptionally suited for geological purposes
- Supported by NASA database with the spectral properties of over 2400 natural and man made materials
- Supported by broad range of academic and industry papers focused on mineral exploration
- Extensive global archives starting from 2000
- Band 4 is stereo which means DEM can be created allowing for easy ortho-rectification of imagery
Disadvantages
- Requires more intensive image processing techniques in-order to achieve optimal results
- The sensor has experienced some intermediated problem periods concerning the short-wave infra-red bands
- Thermal infra-red bands can be sometimes too coarse for applications requiring better than 1:100,000 scales
Sample
Imagery from a gold and copper mine in the Atacama Desert, Chile, highlighting the capabilities of the ASTER sensor. The left image is a conventional 3-2-1 RGB composite. The right image displays short wave infra-red bands 4-6-8 in RGB, and highlights lithologic and alteration differences of surface units (Image Source JPL).
