f287da43-4913-77ff-e053-0937940a0d43 English dataset British Geological Survey +44 115 936 3100 Environmental Science Centre,Keyworth NOTTINGHAM NOTTINGHAMSHIRE NG12 5GG United Kingdom enquiries@bgs.ac.uk pointOfContact 2026-04-28 UK GEMINI 2.3 http://data.bgs.ac.uk/id/dataHolding/13608017 WGS 84 / UTM zone 1S (EPSG::32701) Waterlines delimiting the edge of the Hunga Tonga - Hunga Ha'apai island between April 2017 and April 2022 (NERC Grant NE/X002454/1) 2022-11-24 creation http://data.bgs.ac.uk/id/dataHolding/13608017 Waterlines have been extracted to delimit the edge of the Hunga Tonga - Hunga Ha'apai island between April 2017 and April 2022. Waterline is defined as the instantaneous land - water boundary at the time of the imaging process. Waterlines have been generated by BGS - Earth Observation team through a thresholding-based classification based on Sentinel-2 multispectral imagery and developed on Google Earth Engine. Specifically, the thresholding has been applied to the Normalized Difference Water Index (NDWI) has been derived as a basis to discriminate between the land and sea based on their spectral characteristics. Changes in waterlines over volcanic islands can provide key information to understand volcanic processes. For more info on the methodology, see Novellino et al. (2020) https://doi.org/10.3390/app10020536 Enquiries British Geological Survey 0115 936 3143 0115 936 3276 Environmental Science Centre, Nicker Hill, Keyworth NOTTINGHAM NOTTINGHAMSHIRE NG12 5GG United Kingdom enquiries@bgs.ac.uk distributor Enquiries British Geological Survey 0115 936 3143 0115 936 3276 Environmental Science Centre, Nicker Hill, Keyworth NOTTINGHAM NOTTINGHAMSHIRE NG12 5GG United Kingdom enquiries@bgs.ac.uk originator Enquiries British Geological Survey United Kingdom not available distributor Enquiries British Geological Survey United Kingdom not available pointOfContact notApplicable https://resources.bgs.ac.uk/images/geonetworkThumbs/f287da43-4913-77ff-e053-0937940a0d43.png Geology GEMET - INSPIRE themes, version 1.0 2008-06-01 publication Imagery Volcanic activity Satellite imagery BGS Thesaurus of Geosciences 2022 revision NGDC Deposited Data dataCentre NERC_DDC otherRestrictions licenceOGL Available under the Open Government Licence subject to the following acknowledgement accompanying the reproduced NERC materials "Contains NERC materials ©NERC [year]" otherRestrictions The copyright of materials derived from the British Geological Survey's work is vested in the Natural Environment Research Council [NERC]. No part of this work may be reproduced or transmitted in any form or by any means, or stored in a retrieval system of any nature, without the prior permission of the copyright holder, via the BGS Intellectual Property Rights Manager. Use by customers of information provided by the BGS, is at the customer's own risk. In view of the disparate sources of information at BGS's disposal, including such material donated to BGS, that BGS accepts in good faith as being accurate, the Natural Environment Research Council (NERC) gives no warranty, expressed or implied, as to the quality or accuracy of the information supplied, or to the information's suitability for any use. NERC/BGS accepts no liability whatever in respect of loss, damage, injury or other occurence however caused. Available under the Open Government Licence subject to the following acknowledgement accompanying the reproduced NERC materials "Contains NERC materials ©NERC [year]" vector English geoscientificInformation ISO 3166_1 alpha-2 2009 revision TO ISO 3166_1 alpha-3 2009 revision TON British Geological Survey Gazetteer: Geographical hierarchy from Geosaurus 1979 creation TONGA [id=936000] -175.4000 -175.3700 -20.5500 -20.5300 2017-04-01 2022-04-30 ESRI Shapefile 1994 Enquiries British Geological Survey 0115 936 3143 0115 936 3276 Environmental Science Centre, Nicker Hill, Keyworth NOTTINGHAM NOTTINGHAMSHIRE NG12 5GG United Kingdom enquiries@bgs.ac.uk distributor Enquiries British Geological Survey United Kingdom not available distributor https://webapps.bgs.ac.uk/services/ngdc/accessions/index.html#item176958 WWW:DOWNLOAD-1.0-http--download Data download dataset dataset INSPIRE Implementing rules laying down technical arrangements for the interoperability and harmonisation of Geology 2011 publication See the referenced specification false Commission Regulation (EU) No 1089/2010 of 23 November 2010 implementing Directive 2007/2/EC of the European Parliament and of the Council as regards interoperability of spatial data sets and services 2010-12-08 publication See http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:323:0011:0102:EN:PDF false The Sentinel-2 images used as input to the workflow comprised Level-1C image products. These are composed of 100 × 100 km2 tiles that are ortho-images in cartographic geometry according to the UTM/WGS84 projection, with radiometric corrections applied to convert each pixel value from the digital number (DN) to Top of Atmosphere (TOA) reflectance. We use median values within a month period, pending availability of the data due to cloud coverage. The remaining images have been thresholded based on the Normalized Difference Water Index (NDWI) is used to as a basis to discriminate between the land and sea based on their spectral characteristics. Methodology is described in detail in Novellino et al., (2021) at https://doi.org/10.3390/app10020536