Discriminating lava flows of different age within Nyamuragira’s volcanic field using spectral mixture analysis

Abstract

In this study, linear spectral mixture analysis (LSMA) is used to characterize the spectral heterogeneity of lava flows from Nyamuragira volcano, Democratic Republic of Congo, where vegetation and lava are the two main land covers. In order to estimate fractions of vegetation and lava through satellite remote sensing, we made use of 30 m resolution Landsat Enhanced Thematic Mapper Plus (ETM+) and Advanced Land Imager (ALI) imagery. 2 m Pleiades data was used for validation. From the results, we conclude that (1) LSMA is capable of characterizing volcanic fields and discriminating between different types of lava surfaces; (2) three lava endmembers can be identified as lava of old, intermediate and young age, corresponding to different stages in lichen growth and chemical weathering; (3) a strong relationship is observed between vegetation fraction and lava age, where vegetation at Nyamuragira starts to significantly colonize lava flows ~15 years after eruption and occupies over 50% of the lava surfaces ~40 years after eruption. Our study demonstrates the capability of spectral unmixing to characterize lava surfaces and vegetation colonization with time, which is particularly useful for poorly known volcanoes or those not accessible for physical or political reasons.

Impact of Environmental Factors on the Spectral Characteristics of Lava Surfaces: Field Spectrometry of Basaltic Lava Flows on Tenerife, Canary Islands, Spain

“…With the spectra of lava and vegetation endmembers, spectral unmixing has previously been used to map lava surfaces of different ages and vegetation colonization [20]. A thematic map of tephra distribution of Mt.…”

“…Whereas multispectral imagery can be acquired at very high spatial resolution (e.g., Pleiades, 0.5-2 m; [20]), spatial resolution of hyperspectral satellite data remains low (e.g., Hyperion, 30 m; [21,22]) and spectral mixing is thus a major issue. The spectral reflectance of lava of different compositions has also been documented using laboratory spectrometry with decimeter-size samples [15].…”

“…Studies of Nyamuragira volcano, for example, have shown that in humid, tropical climates, vegetation colonization has a significant impact on the spectra of aging lava flows by increasing the spectral response in the near infrared band [20,22]. The spectral reflectance of lava flows is also affected by lichen cover [25,26] and chemical weathering [26][27][28][29][30].…”

A Modified Multi-Source Parallel Model for Estimating Urban Surface Evapotranspiration Based on ASTER Thermal Infrared Data

“…In a linear spectral mixture analysis (LSMA) of an urban area, the spectrum of a pixel is considered as a linear combination of spectra of pure endmembers within the pixel weighted by their component abundance [30,39]. The fully constrained linear spectral mixture analysis where the sum of all components is one and no component is negative [39,40] was applied to inverse pixel component fraction using a least squares method.…”

“…The fully constrained linear spectral mixture analysis where the sum of all components is one and no component is negative [39,40] was applied to inverse pixel component fraction using a least squares method. The fully constrained LSMA is expressed by the following equations:…”