DOI: 10.5281/zenodo.4035038
title: Digital surface model and orthomosaic of the Chã das Caldeiras lava fields (Fogo Island, Cape Verde, December 2016)

description: Fogo in the Cape Verde archipelago off Western Africa is one of the most prominent and active ocean island volcanoes on Earth, posing an important hazard to both local populations and at a regional level. The last eruption took place between 23 November 2014 and 8 February 2015 in the Chã das Caldeiras area at an elevation close to 1,800 m above sea level The eruptive episode gave origin to extensive lava flows that almost fully destroyed the settlements of Bangaeira, Portela and Ilhéu de Losna. In December 2016 a survey of the Chã das Caldeiras area was conducted using a fixed-wing unmanned aerial vehicle and RTK GNSS, with the objective of improving the mapping accuracy derived from satellite platforms. The main result is an ultra-high resolution 3D point cloud with a Root Mean Square Error of 0.08 m in X, 0.11 m in Y and 0.12 m in Z, which provides unprecedented accuracy. The survey covers an area of 23. 9 km<sup>2</sup> and used 2909 calibrated images with an average ground sampling distance of 7.2 cm. A digital surface model and an orthomosaic with 25 cm resolution are provided, together with elevation contours with an equidistance of 50 cm and a 3D texture mesh for visualization purposes. The delineation of the 2014-15 lava flows shows an area of 4.53 km<sup>2</sup> by lava, which is smaller but more accurate than the previous estimates from 4.8 to 4.97 km<sup>2</sup>. The difference in the calculated area, when compared to previously reported values, is due to a more detailed mapping of flow geometry and the exclusion of the areas corresponding to kīpukas. Our study provides an ultra high-resolution dataset of the areas affected by Fogo’s latest eruption – crucial for local planning – and provides a case study to determine the advantages of ultra high-resolution UAV surveys in disaster-prone areas. The details on surveying and processing are described in the manuscript "Very high-resolution terrain surveys of the Chã das Caldeiras lava fields (Fogo Island, Cape Verde) submitted to the journal Earth System Science Data and under peer review. Files:<br> - cha_caldeiras_contours_50cm.zip: Compressed shapefile (shp) and auxiliary files. Contour lines of the Chã das Caldeiras in December 2016 with 50 cm equidistance, interpolated from the digital surface model. CRS: ESPG 32626 - WGS 84 / UTM Zone 26N, elevation: ellipsoidal ITRF2014 (WGS84).<br> - cha_caldeiras_dsm_25cm.tif: Digital surface model of the Chã das Caldeiras in December 2016 with 25 cm resolution. CRS: ESPG 32626 - WGS 84 / UTM Zone 26N, elevation: ellipsoidal ITRF2014 (WGS84).<br> - cha_caldeiras_error_assessment_areas.zip: Compressed shapefile (shp) and auxiliary files. . Areas with errors in the point cloud obtained by visual analysis. 1. Low accuracy, 2. Moderate accuracy. CRS: ESPG 32626 - WGS 84 / UTM Zone 26N.<br> - cha_caldeiras_ortho_25cm.tif: Orthomosaic RGB of the Chã das Caldeiras in December 2016 with 25 cm resolution. CRS: ESPG 32626 - WGS 84 / UTM Zone 26N.<br> - cha_caldeiras_pix4d_report.pdf: Report of the processing of the aerial imagery in PIX4D.<br> - lava-2014-15.zip: Compressed shapefile (shp) and auxiliary files. Lava flows of the eruption of 2014-15 digitised from the original 10 cm resolution orthomosaic. CRS: ESPG 32626 - WGS 84 / UTM Zone 26N
description: This research was conducted in the framework of the project FIRE – Fogo Island Volcano: multidisciplinary research on the 2014 eruption (FCT - PTDC/GEO-GEO/1123/2014) funded by the Fundação para a Ciência e a Tecnologia. R. Ramalho acknowledges his IF/01641/2015 contract funded by FCT. The project 3DAntártida funded the acquisition of the UAV. The INGT – Instituto Nacional de Gestão do Território and INMG – Instituto Nacional de Meteorologia e Geofísica de Cabo Verde are thanked for their cooperation. Pedro Almeida, Carla Candeias, Stéphanie Dumont, Bento Martins and Carlos Oliveira are thanked for their support in the collection of ground control points. Carlos Oliveira, Bruno Faria, Euda Miranda, Fátima Fernandes and Jair Rodrigues are thanked for their support to the project and field activities. Co-funding by FCT I.P. UIDB/00295/2020 – CEG and UIDP/00295/2020, FCT - UIDB/50019/2020 – IDL and C4G – POCI-01-0145-FEDER-022151.