Geological Spectral Indices

A reliable, accurate tool is the key to good results. We use several tools based on various approaches and techniques in satellite data analysis. One of the most fundamental techniques is geological spectral indices.


What are geological spectral indices and their use cases?

Spectral indices allow the user to extract and highlight the targeted and most desirable information about the area of interest. It can be either information on mineralogy, alteration mineralogy, or lithology. For example, when you need to check whether the area has any clay minerals present, a spectral index can determine the answer. Another use case example is to analyze what the surface of the outcrop of a specific rock type is in a geologically complex location. In this case, spectral indices built for highlighting different lithotypes will be successful.

How is a spectral index built?

Every mineral has its own, individual spectral signature filled with spectral features, a reflectance spectrum, which reflects the chemical composition and crystal structure. Knowing the location of these features on the spectrum, it is possible to tailor the approach and design indices which will highlight the presence of those specific features in specific wavelengths. Thanks to these operations we can extract maps carrying information on the targeted mineralization or lithology type.

Geological spectral indices in the TerraEye platform

In TerraEye, the geological spectral indices are a part of the SaaS platform, which offers a suite of processing and analytical tools. The indices can be calculated using data from both multi and hyperspectral Sentinel-2, ASTER, EMIT, PRISMA, and EnMap satellites, depending on data availability. This allows for efficient monitoring of large areas, identifying mineralogical variations quickly and accurately. By analyzing spectral signatures, we can rapidly pinpoint areas of interest, speeding up the early stages of mineral exploration.


This approach is further enhanced by integrating other analyses available in the SaaS platform, such as mineralization maps based on SAM and MTMF analysis, AI clustering, composites and lineament maps. Mineralization maps highlight areas with surface mineralization, while lineament maps show geological structures like faults and fractures that can influence the style of mineral deposition. AI clustering identifies similar patterns in spectral data that may not be visible through other available methods.

By combining spectral indices with other tools provided in the platform, TerraEye delivers a comprehensive view of the exploration area, improving accuracy and reducing time and costs compared to traditional exploration methods. This analysis serves as an excellent foundation for planning field scouting and selecting locations for sample collection.

Table: List of currently available spectral indices.

No.

Index Name 

1 

ALUNITE HSI (ALI) 

2 

KAOLINITE 1 HSI (KAI1) 

3 

KAOLINITE 3 HSI (KAI3) 

4 

MONTMORILLONITE HSI (MONI) 

5 

EPI/CHLO/CALC HSI (ECAI) 

6 

FEAI HSI (FEAI) 

7 

FEI HSI (FEI) 

8 

SERPENTINES HSI 

9 

FE-SILICATES MSI (FE-SILICATES) 

10 

FE2O3 MSI (FE2O3) 

11 

FE3+ MSI (FE3+) 

12 

LATERITES MSI (LAI (LATERITE)) 

13 

GOETHITE MSI (GOETHITE) 

14 

LEPIDOLITE MSI  

15 

GOSSAN MSI (GOSSAN) 

16 

ALTERATIONS MSI (ALT) 

17 

ARGILLIC ZONE MSI (ARGZ) 

18 

CLAY MINERALS HSI 

19 

ILLITE HSI 

20 

MONTMORILLONITE (SMECTITE) HSI 

21 

KAOLINITE HSI 

22 

CALCITE HSI 

23 

IRON OXIDES HSI 

24 

GYPSUM HSI 

25 

PHOSPHATES HSI (PHOSPHORUS (APATITE)) 

26 

FELDSPAR HSI 

27 

MUSCOVITE/ ILLITE HSI 

28 

PEGMATITE HSI 

29 

LEPIDOLITE HSI (LEPIDOLITE (HSI) HSI)  

 

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