Mineralogy by h y p e r s p e c t r a l imaging in V NIR AND SWIR region

1. Mineralogy byhyperspectralimagingin VNIRAND SWIRregion

2. Introduction • Hyper-spectral imaging • Hyper-spectral imaging is the remote sensing technique in which images are taken in large number of narrow spectral bands of same region. Number of bands may vary from few tens to hundreds. • By this technique one can get the nearly continuous spectral signature of an object, which can help in its identification and properties determination. • Broad applications of this technique are Mineralogy, Vegetation and Forest studies, Oceanography and Atmospheric studies etc.

3. Introduction • Mineralogy • Mineralogy is the study of minerals for their identification and properties determination. • Hyper-spectral imaging is the important tool for mineralogical studies, which is based on the spectral signature or properties obtained through Hyper-spectral imaging. • For example Pyroxene has different spectral signature than the Quartz and thus can be distinguished. • Hyper-spectral imaging for mineralogy can helps in mineral mapping, which in turn can tell about soil type or soil properties, which can give some information about present and potential agriculture or vegetation.

4. Description: Various minerals [4] • Major minerals on Earth for studies are Feldspar, Quartz, Pyroxene and Olivine etc. • Feldspar is generally aluminum silicate of Sodium, Potassium, Calcium and Barium etc. It is most abundant on Earth-Crust. General chemical formula of Feldspar is (Na, K, Ca, Ba) Al Si3 or 2O8. • Quartz is the second-most-abundant mineral in the Earth-crust, after feldspar. It is made up of a continuous framework of SiO4 tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. • Pyroxene has the general formula XY(Si, Al)2O6( where X represents Calcium, Sodium,Iron+2 and Magnesium and more rarely zinc, manganese and lithium and Y represents ions of smaller size, such as Chromium, Aluminum, Iron+3, Magnesium, Manganese, Scandium, Titanium, Vanadium and even Iron+2) • Olivineis amagnesium-ironsilicate mineral (typically green color) with the formula (Mg,Fe)2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface.

5. Description: Various minerals –Feldspar [4] • Feldspar is derived from the German Feld, "field", and Spath, “a rock that does not contain ore”. Nearly 60% of Earth-Crust is made up of Feldspar. • Sodium (Na) and Potassium (K) feldspar are called alkali feldspar. • Sodium (Na) and Calcium (Ca) feldspar are called  plagioclase feldspar. • The plagioclase series follows (with percent anorthite in parentheses): • albite (0 to 10) —(Sodium end-member) NaAlSi3O8 • oligoclase (10 to 30) • andesine (30 to 50) • labradorite (50 to 70) • bytownite (70 to 90) • anorthite (90 to 100) — (Calcium end-member) CaAl2Si2O8 • Albite (form at low temperature) color range White to gray, bluish, greenish, reddish • Anorthite (form at high temperature) color range White, grayish, reddish

6. Description-Feldspar-Albite Spectral Signature [3]

7. Description-Feldspar-Anorthite Spectral Signature [3]

8. Description-Quartz Spectral Signature [3]

9. Description-Olivine Spectral Signature [3]

10. Description-Pyroxene Spectral Signature [3]

11. Description-Biotite Spectral Signature [3]

12. Description-Hemetite Spectral Signature [3]

13. Description: Bowen’s Reaction Series :–Tells about how different minerals form at different temperature in sequential manner [4]

14. Imaging Requirements • Wavelength region • Bandwidth • Minimum SNR • Minerals of interest

15. Wavelength region [3], [4], [5] • Spectral studies in VNIR(0.4-1.0um) and SWIR(1.0-3.0um) region can give adequate information for mineral studies. • Most of the minerals have good spectral signature in wavelength range of 0.2-3um. They have enough distinct spectral feature or pattern in this range.

16. Bandwidth [3],[4] • Spectral bandwidth more than 25nm is not acceptable because of lack of feature extraction with this bandwidth • Spectral bandwidth less than 10nm can give some useful results. • Spectral bandwidth nearly 5nm or less can result into adequate feature extraction for mineral identification and properties determination.

17. Minimum SNR • Minimum SNR of 90 or 100 is desired for mineral studies by spectral analysis . [1], [2] • It is observed that SNR from 50 to 500 is used for Hyper-spectral imaging in SWIR region for mineralogy. Higher SNR is always preferred and can give additional information.[6]

18. Minerals of interest [3] • Major minerals on Earth for studies are Feldspar, Quartz, Pyroxene and Olivine, Kaolinite etc. • Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5(OH)4. • Other mineral category can be hydroxyl-bearing minerals, sulfates, and carbonates etc. [3],[6]

19. Conclusion *Hyper-spectral imaging for mineralogy demands: • Spectral bandwidth around 5nm or less. • Spectral range 0.4-3.0um (i.e. VNIR+SWIR). • SNR of 90 or more. • Focus on major minerals like Feldspar, Quartz, Olivine and Pyroxene etc.*Hyper-spectral imaging for mineralogy can helps in mineral mapping, which in turn can tell about soil type or soil properties, which can give some information about present and potential agriculture or vegetation.

20. References • [1] “The high resolution optical instruments for the PLEIADES-HR earth observation satellites” by Catherine Gaudin-Delrieu, Jean-Luc Lamard, Philippe Cheroutre, Bruno Bailly, Pierre Dhuicq, Olivier Puig. • [2] “Enhancing space-based signal-to-noise ratios without redesigning the satellite” by Shen-En Qian • [3] “http://speclab.cr.usgs.gov/spectral.lib06/ds231/datatable.html” website • [4] “http://en.wikipedia.org” website • [5] “google.com” website • [6] “Comparison of AVIRIS and Hyperion for Hyper-spectral Mineral Mapping” by Fred A. Kruse