Validation of recent altimeter missions at non-dedicated tide gauge stations in the Southeastern North Sea

Saskia Esselborn,Tilo Schöne,Robert Weiß,Xinge Huang,Julia Illigner,Thomas Artz

doi:10.5194/egusphere-egu21-16122

Abstract

&lt;p&gt;The absolute and relative accuracy of sea surface heights derived from six altimeter missions (Jason-1/2/3, Envisat, Saral, Sentinel-3A) is evaluated at five GNSS-controlled tide gauge stations in the German Bight (SE North Sea). The precision of the total water level envelope (TWLE) is assessed for the period 2000 to 2019 based on RMS errors and explained variances. The comparison is based on TWLE instead of dealiased sea level data since the tidal and barotropic dynamic is not known with sufficient accuracy in this area. The tide gauges are partly located at the open sea, partly at the coast close to mudflats. The tide gauge data is available every minute, the 20 Hz level 2 altimetry data is interpolated to virtual stations at distances between 2 and 15 km to the tide gauges. The altimeter data is based on standard retrackers, the correction models are adjusted to coastal applications and exclude the corrections for ocean tides and dynamic atmosphere to allow a direct comparison to the tide gauge data. To account for slight differences of the tidal dynamics between gauge and altimetry an optimal time shift and scale between each pair of locations is estimated and applied. This tidal correction improves the RMS errors by 15-75%. The explained variances are excellent at all stations (&gt; 96%). The resultant RMS errors are mainly between 2-5 cm depending on location and mission. The RMS errors rise up to 10 cm where coastal dynamics play a dominant role or the altimeter approaches the land very closely (&lt;7 km). The accuracy of the absolute biases is strongly dependent on the knowledge of the mean sea surface heights in the region.&lt;/p&gt;

Highlights

We aim to assess the accuracy of recent altimeter missions in the German Bight by comparing altimetry with tide gauges controlled by global navigation satellite systems (GNSS) measurements
The analysis is based on the collocated tide gauge and altimetry sea-level anomaly series for each station
We calculated the amount of variance of the tide gauge series explained by the altimetry series as well as the root mean square (RMS) of the difference series (RMS-D)

Summary

Introduction

Coastal zones are exposed to manifold natural and anthropogenic forces that are potentially threatening habitats and societies. Extreme sea levels and longterm sea-level rise are of special concern [1,2] and require substantial investments in coastal protection measures. For more than a century, the coastal sea level has been observed with tide gauges. They are well maintained and have a proven record of accuracy [3,4]. Tide gauges deliver localized high-resolution sea-level data which are valuable for operational purpose, and for monitoring surges, extremes, or tsunamis [2,5]. A number of studies employed this data to characterize global sea-level rise [6,7] or local effects such as coastal subsidence [5,8]

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Conclusion