Abstract
Abstract. This paper addresses the problems of overlapping sea level time series measured using different technologies and sometimes from different locations inside a harbour. The renovation of the Spanish REDMAR (RED de MAReógrafos) sea level network is taken here as an example of the difficulties encountered: up to seventeen old tide gauge stations have been replaced by radar tide gauges all around the Spanish coast, in order to fulfil the new international requirements on tsunami detection. Overlapping periods between old and new stations have allowed the comparison of records in different frequency ranges and the determination of the impact of this change of instrumentation on the long-term sea level products such as tides, surges and mean sea levels. The differences encountered are generally within the values expected, taking into account the characteristics of the different sensors, the different sampling strategies and sometimes the different locations inside the harbours. However, our analysis has also revealed in some cases the presence of significant scale errors that, overlapping with datum differences and uncertainties, as well as with hardware problems in many new radar gauges, may hinder the generation of coherent and continuous sea level time series. Comparisons with nearby stations have been combined with comparisons with altimetry time series close to each station in order to better determine the sources of error and to guarantee the precise relationships between the sea level time series from the old and the new tide gauges.
Highlights
The REDMAR (RED de MAReógrafos) sea level network was established by the Spanish Harbour Authorities in 1992
It was originally based on 13 acoustic tide gauges (SRD) and enlarged later with 4 additional stations based on AANDERAA (AAND) pressure sensors (Pérez and Rodríguez, 1994; Pérez and López Maldonado, 2003)
As the adequacy of the MIROS radar sensor was assessed in previous experiments, such as the one in Vilagarcía (Martín Míguez et al, 2005), the objective of this study is focused on the scientific impact of the technological renovation of the network, assessed by identifying the differences in the sea level signals and their influence on the different products such as the long-term time series provided to the Permanent Service for Mean Sea Level (PSMSL)
Summary
The REDMAR (RED de MAReógrafos) sea level network was established by the Spanish Harbour Authorities in 1992. Mean sea levels of the REDMAR network are provided annually to the Permanent Service for Mean Sea Level (PSMSL, www.psmsl.org) and the data are used by scientists all around the world For this reason one of the main concerns during this process of renovation was to guarantee the continuity of the longer time series of sea level. As the adequacy of the MIROS radar sensor was assessed in previous experiments, such as the one in Vilagarcía (Martín Míguez et al, 2005), the objective of this study is focused on the scientific impact of the technological renovation of the network, assessed by identifying the differences in the sea level signals and their influence on the different products such as the long-term time series provided to the PSMSL. The paper is structured as follows: the second section presents a review of the main sources of error, general or specific to REDMAR, that can result in differences between two simultaneous tide gauge data sets from the same harbour; the third section will describe the data employed and the methodology for data comparison during REDMAR renovation; and the fourth section will present the results and discussion of this comparison exercise as well as the impact of the network renovation on the main sea level products
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