Abstract
Mapping of lava flows in unvegetated areas of active volcanoes using optical satellite data is challenging due to spectral similarities of volcanic deposits and the surrounding background. Using very high-resolution PlanetScope data, this study introduces a novel object-oriented classification approach for mapping lava flows in both vegetated and unvegetated areas during several eruptive phases of three Indonesian volcanoes (Karangetang 2018/2019, Agung 2017, Krakatau 2018/2019). For this, change detection analysis based on PlanetScope imagery for mapping loss of vegetation due to volcanic activity (e.g., lava flows) is combined with the analysis of changes in texture and brightness, with hydrological runoff modelling and with analysis of thermal anomalies derived from Sentinel-2 or Landsat-8. Qualitative comparison of the mapped lava flows showed good agreement with multispectral false color time series (Sentinel-2 and Landsat-8). Reports of the Global Volcanism Program support the findings, indicating the developed lava mapping approach produces valuable results for monitoring volcanic hazards. Despite the lack of bands in infrared wavelengths, PlanetScope proves beneficial for the assessment of risk and near-real-time monitoring of active volcanoes due to its high spatial (3 m) and temporal resolution (mapping of all subaerial volcanoes on a daily basis).
Highlights
Hazards triggered by volcanic activity have massive environmental, economic, and humanitarian impacts [1,2]
The area derived without the incorporation of Normalized Hotspot Indices (NHI) pixels is significantly smaller and conlava area derived without the incorporation of NHI pixels is significantly smaller and centrated on the northern part of the W flank of the Karangetang
This is because in step 1 of the concentrated on the northern part of the W flank of the Karangetang. This is because in step 1 of the object-based image analysis (OBIA) methodology, the areas of change based on the dNDVI were intersected with the drainage network
Summary
Hazards triggered by volcanic activity have massive environmental, economic, and humanitarian impacts [1,2]. Satellite-based data are increasingly being integrated into the monitoring process of volcanoes, as they allow large-scale views of areas that are difficult to reach and hazardous due to active eruptions. Very high-resolution (VHR) optical systems have been used to map ash and tephra deposits [18], lava flows [19], pyroclastic flows, and lahars [20,21] at volcanoes. Using a dNDVI analysis, the detection of ash and tephra deposition on Anak K tau and surrounding islands (Krakatau II) was possible. For this purpose, a PlanetS scene before (14 March 2018) and after (1 July 2019) the eruption on 22 December 2018 selected.
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