McLoughlin, Patrick J. and McCarthy, Gerard D. and Nolan, Glenn and Lawlor, Rosemarie and Hickey, Kieran (2024) The accurate digitization of historical sea level records. Geoscience Data Journal. pp. 1-16. ISSN 2049-6060

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Abstract

Understanding regional sea level variations is crucial for assessing coastal vulnerability, with accurate sea level data playing a pivotal role. Utilizing historical sea level marigrams can enhance datasets, but current digitization techniques face challenges such as bends and skews in paper charts, impacting sea level values. This study explores often-overlooked issues during marigram digitization,focusing on the case study of Dún Laoghaire in Ireland (1925–1931). The methodology involves digitizing the original marigram trace and underlying grid to assess offsets at the nearest ft (foot) interval on the paper chart, corresponding to changes in the water level trace for each hour interval. Subtracting the digitized value from the known value (the actual measurement) allows for the determination of differences, which are then subtracted from each hourly trace value. After adjusting for offsets ranging from −3.962 to 13.716 mm (millimetres), the study improves the final accuracy of sea level data to approximately the 10 mm level. Notably, data from 1926 and 1931 exhibit modest offsets (<7 mm), while other years show more substantial offsets (>9–14 mm), emphasizing the importance of adjustments for accuracy. Such 10 mm accuracy is compatible with requirements of the Global Sea Level Observing System. Comparing the adjusted digitized data with other survey data shows similar amplitudes and phases for Dún Laoghaire in both the historical and modern datasets, and there is an overall mean sea level rise of 1.5 mm/year when combined with the available data from the Dublin region

Item Type:	Article
Additional Information:	This Article is funded (Grant-Aid Agreement No.CS/21/006 with the support of the Marine Institute and funded under the Marine Research Programme by the Irish Government)
Keywords:	digitization; historical data; sea level;
Academic Unit:	Faculty of Social Sciences > Geography Faculty of Social Sciences > Research Institutes > Irish Climate Analysis and Research Units, ICARUS
Item ID:	18720
Identification Number:	https://doi.org/10.1002/gdj3.256
Depositing User:	IR Editor
Date Deposited:	10 Jul 2024 16:22
Journal or Publication Title:	Geoscience Data Journal
Publisher:	Wiley
Refereed:	Yes
Funders:	Marine Institute
URI:	https://rmets.onlinelibrary.wiley.com/do...
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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