Spectral Unmixing for Mapping a Hydrothermal Field in a Volcanic Environment Applied on ASTER, Landsat-8/OLI, and Sentinel-2 MSI Satellite Multispectral Data: The Nisyros (Greece) Case Study

Abstract

The aim of this study was to propose a methodology that provides a detailed description of the argillic zone of a hydrothermal field, based on satellite multispectral data. More specifically, we developed a method based on spectral unmixing where hydroxyl-bearing alteration is represented by a single endmember (representing clays) and the three (nearly) non-altered primary volcanic lithologies, namely, two types of lava flows (basic and acidic compositions) and the loose materials (alluvial/beach deposits, scree, pyroclastic deposits, etc.), are represented by three endmembers. We also used one endmember representing elemental sulfur that is present in fumarolic vents hosted by active hydrothermal craters. The methodology was applied in the south part of Lakki plain inside the Nisyros volcano caldera (Greece), using Sentinel-2, Landsat-8/OLI, and ASTER satellite multispectral datasets. Specifically, it was applied separately to each one of the three datasets. The spectral unmixing results, combined with the relative geological map, provide quantitative estimations of the primary volcanic and loose material areas affected by alteration. In addition, pixels with high abundance values of hydroxyl-bearing alteration corresponded to mapped areas with strong hydrothermal alteration. The developed methodology is superior to conventional approaches (e.g., alteration spectral index) in terms of its ability to describe the overall pattern of the hydrothermal field. The most accurate results were taken when applied to ASTER or Sentinel-2 MSI data.

Investigating the capability of Sentinel-2 and Worldview-3 VNIR satellite data to detect mineralized zones at an igneous intrusion in the Koutala islet (Lavreotiki, Greece) using laboratory mineralogical analysis, reflectance spectroscopy and spectral indices

“…This is consistent with the alteration SI map (Fig.10d) which shows that the highest values are observed at the eastern part of the islet. We note that the SI alteration values are most probably indicative of the degree of alteration according to the results of a similar study presented byTompolidi et al (2020) on the hydrothermal field of Nisyros volcano (Greece).…”

“…A special case of SIs is represented by band ratios, where the ratio of two spectral bands is computed. Several SIs have been proposed using a range of wavelength combinations for mapping various mineral assemblages (Cloutis, 1996;Sabins, 1999;Cudahy and Hewson, 2002;Yamaguchi and Naito, 2003;Henrich et al, 2009;Shim et al, 2021), especially after the arrival of ASTER data with their SWIR spectral bands (Abrams et al, 1983;Abrams & Hook, 1995;Yamaguchi et al, 1998;Yamagushi & Naito, 2003;Kalinowski and Oliver, 2004;Gad and Kusky, 2007;Rajendran et al, 2011;Abrams et al, 2015;Ferrier et al 2016;Askari et al, 2018;Shuai et al, 2022) and/or Landsat 8 data (Anifadi et al, 2016;Ferrier et al 2016;Tompolidi et al, 2020;Anifadi et al, 2022;Sykioti et al 2022), spectral unmixing on (i) S-2, ASTER and Landsat 8 OLI data (Tompolidi et al, 2020) and (ii) EO-1 Hyperion hyperspectral data (Nikolakopoulos et al, 2007), Spectral Angle Mapping and Mixture-Tuned Matched…”

“…During the last three decades, the use of satellite imagery in geological mapping and mineral exploration has grown rapidly in order to detect mineralization-related alterations and associated ore deposits (Van der Meer et al, 2012;Van der Meer and Van der Werff, 2014;Van der Meer, 2015, 2016;Ge et al, 2018(a), 2018(b); Hu et al, 2018;Van der Meer et al, 2018;Pour et al, 2019;Vasuki et al, 2019;Ferrier et al 2019;Tompolidi et al, 2020;Anifadi et al, 2022). Recent multispectral satellites such as the Landsat Operational Land Imager (OLI), and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) have been the most widely used multispectral satellite sensors for the detection and mapping of minerals related to alteration, such as iron oxides, hydroxyl-bearing minerals, and Volume 59 carbonates (Rowan and Mars, 2003;Rowan et al, 2006;Ferrier et al, 2010Ferrier et al, , 2016Mars and Rowan, 2010;Hosseinjani et al, 2011;Pour et al, 2011;Rajendran et al, 2017;Yang et al, 2018;El Kati et al 2018;Abubakar et al, 2019;Pour et al 2019;Ferrier et al 2019;Tompolidi et al 2020;Vural et al, 2021), especially, when the satellites provide spectral information in the shortwave infrared (SWIR) part of the electromagnetic spectrum.…”

“…Since 2015, additional studies have been conducted in order to reveal the potential of Sentinel-2 (S-2) Multispectral Imager (MSI) in geological remote sensing, mineral exploration and discrimination (Mielke et al, 2014;Van der Meer and Van der Werff, 2014;Yokova et al, 2016;Hu et al, 2018;Adiri et al, 2020;Ge et al, 2020;Purwadi et al, 2020;Tompolidi et al, 2020;Lanfranchi et al, 2021;Soydan et al, 2021;Anifadi et al, 2022). Sentinel-2 provides spectral information in twelve spectral bands, namely ten (10) in the visible-near infrared (VNIR) and two (2) in the SWIR (Table 1).…”

A Novel Method for Hyperspectral Mineral Mapping Based on Clustering-Matching and Nonnegative Matrix Factorization

“…Over the past decades, different hyperspectral mineral mapping methods have been developed, including supervised classification [11], spectral unmixing [12], and spectral matching (SM) [13]. Supervised methods can provide promising classification performance when training samples are sufficient [14].…”