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ASTER Mineral Mapping

Clays, carbonates, gypsum, iron oxides and quartz seen from space in ASTER’s short-wave and thermal infrared bands, with the anomalies outlined for field checking.

ASTER is the satellite sensor made for geology: six short-wave infrared bands catch the absorption features of clays, micas, carbonates, sulphates and chlorite, and five thermal bands those of quartz, carbonates and gypsum. Choose an area, find an image and a mineral index: ferric and ferrous iron, AlOH group (clays, micas, alunite), kaolin, FeOH, MgOH and carbonate, gypsum, silica, quartz and carbonate in the thermal range, or an RGB of AlOH, MgOH and ferric content. Vegetation and water are masked, the index is stretched and mapped, the strongest part of the rock surface is outlined on the image as anomalies with their area, and the result is exported as maps, polygons and numbers.

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ASTER Mineral Mapping
AlOH (B5+B7)/B62.21Anomaly top 5 %3.8 km²

Overview

In the Western Desert of Iraq the phosphates of Akashat, the kaolin and bauxitic clays of Hussainiyat and Ga’ara, the iron-rich beds and the gypsum of the Fat’ha Formation lie bare under a dry sky, the ideal setting for spectral mapping. The same indices find alteration zones around ore bodies, ophiolites in the Zagros and gypsum karst under roads and dams.

The images in this archive date from 2000 to 2006, before the short-wave detectors failed in 2008. Rocks do not change in that time, so they still map today’s geology.

What you enter · What you get

What you enter

  • An area from the list, found by name or drawn (up to 60 × 60 km)
  • ASTER image (date, cloud and coverage listed)
  • Mineral index, anomaly share, background
  • Vegetation and water mask

What you get

  • Mineral index map with colour scale
  • RGB of AlOH, MgOH and ferric content
  • Anomalies outlined on the image, with their area
  • Distribution of the index
  • Anomaly polygons (GeoJSON) and statistics (CSV)

How it works in the field

Choose the area
Find and pick an image
Choose the index and map it
Export the anomalies for the field

Method and equations

Images

Terra ASTER Level-1T: VNIR bands 1–3 at 15 m, SWIR bands 4–9 at 30 m and TIR bands 10–14 at 90 m, precision terrain-corrected. Neighbouring scenes fill the gaps of the chosen one.

AlOH = (B5 + B7) / B6

Indices

Band ratios of the Geoscience Australia ASTER geoscience products (ferric oxide B2/B1, ferrous iron B5/B4, AlOH content (B5+B7)/B6, kaolin B6/B5, FeOH (B6+B8)/B7, MgOH and carbonate (B6+B9)/(B7+B8), gypsum (B10+B12)/B11, silica B13/B10) and the thermal indices of Ninomiya for quartz B11/(B10+B12) and carbonate B13/B14. Each places the absorption band in the denominator against its shoulders.

QI = B11 / (B10 + B12)

Masks and anomalies

Vegetation (NDVI from bands 3 and 2 above 0.25) and water are masked. The index is stretched between its 2nd and 98th percentiles over the rock surface, and the highest 2, 5 or 10 % is outlined as anomaly with its true ground area.

anomaly: I ≥ P(100 − x)

Accuracy and error limits

  • Band ratios locate mineral groups well where rock is bare: published comparisons with field and laboratory spectra find the main alteration and lithological units in most dry-region tests. They give relative abundance, not percentages, and they identify groups (for example AlOH clays) rather than single minerals. Pixels are 30 m (short-wave) and 90 m (thermal), so small veins and thin beds are averaged with their surroundings.
  • What is not covered: images after 2006 (the short-wave detectors failed in 2008), areas under vegetation, water, cloud or recent construction, and absolute mineral content. Raw image values are used, so shadows, dark soils, wet ground, scene seams and different gain settings can shift the index.
  • To reduce the error: choose a cloud-free image from the dry season that covers the whole area, compare two or three indices, read the anomalies with the geological map, avoid scene seams, and confirm in the field with samples, acid tests and laboratory XRD or reflectance spectra.

Who uses it

Exploration geologistsRemote sensing researchers and studentsGeological survey and mining companiesEngineering geologists (gypsum and clays under structures)

Standards and references

  1. Cudahy, T. (2012). Satellite ASTER Geoscience Product Notes for Australia, version 1. CSIRO ePublish EP-30-07-12-44.
  2. Ninomiya, Y., Fu, B. & Cudahy, T. J. (2005). Detecting lithology with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) multispectral thermal infrared radiance-at-sensor data. Remote Sensing of Environment, 99, 127–139.
  3. Rowan, L. C. & Mars, J. C. (2003). Lithologic mapping in the Mountain Pass, California area using ASTER data. Remote Sensing of Environment, 84, 350–366.
  4. Abrams, M. (2000). The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER): data products for the high spatial resolution imager on NASA’s Terra platform. International Journal of Remote Sensing, 21, 847–859.
  5. van der Meer, F. D. et al. (2012). Multi- and hyperspectral geologic remote sensing: a review. International Journal of Applied Earth Observation and Geoinformation, 14, 112–128.
  6. Jassim, S.Z. & Goff, J.C. (eds.) (2006). Geology of Iraq. Dolin, Prague and Moravian Museum, Brno.
Results support professional judgement. They do not replace a licensed engineer’s or geologist’s sign-off.

At a glance

Category
Remote sensing
Runs on
Phone, tablet and desktop browser
Export
Index map and anomaly map as PNG, JPG and PDF; anomaly polygons as GeoJSON; statistics as CSV; histogram as PNG, JPG and PDF; full PDF report
Access
Free

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