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Assessment of Range and Geophysical Corrections and Mean Sea Surface Models - Impacts on Sea Level Variability around the Indonesian Seas
Eko Yuli Handoko1,2, Maria Joana Fernandes1,3, Clara Lázaro1,3
1Faculdade de Ciências, Universidade do Porto, Porto, Portugal; 2Department of Geomatics Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia; 3Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR/CIMAR), Universidade do Porto, Porto, Portugal
Due to their unique characteristics and large complexity the Indonesian seas are a very interesting area for coastal altimetry studies. The determination of sea level variation for this region requires precise knowledge of all range and geophysical corrections needed to correct the altimeter range for the effects of the atmosphere, the sea state and the geophysical phenomena that need to be removed from the signal of interest. In addition, due to the large gradients of the mean sea surface (MSS) in this part of the ocean, the choice of a suitable MSS is also of relevance. For this purpose, the selection of the best range and geophysical corrections and mean sea surface models is important to estimate precise sea level anomalies around Indonesia.
The focus of this study is twofold (i) to assess the accuracy of range and geophysical corrections and mean sea surface models in the Indonesian seas, (ii) to determine sea level variation in this region by selecting the best choice of corrections and models for each mission.
For this purpose, three-reference missions were used, TOPEX/Poseidon, Jason-1 and Jason-2, over the 23 years (1993-2015) period. All altimeter data, including the corrections and MSS models, were used as they are made available in RADS, except for the wet tropospheric corrections from the GNSS-derived Path Delay Plus (GPD+) algorithm, provided by the University of Porto. The assessment of the various corrections and MSS models is performed using analyses of sea level anomaly (SLA) variance differences, function of distance from coast and at altimeter crossovers with time difference less than 10 days.
The selected set of corrections and MSS have been used to estimate the SLA time series. The rate of sea level rise for the Indonesian seas was found to be 4.2 ± 0.2 mm/year over the 23-year period (1993-2015) with very strong inter-annual variability.
8:50 - 9:10
Assessment of the FES2014 Tidal Currents on the Shelves Around Australia
Mathilde Cancet1, Florent Lyard2, David Griffin3, Loren Carrère4, Nicolas Picot5
1NOVELTIS, France; 2LEGOS/CNRS, France; 3CSIRO, Australia; 4CLS, France; 5CNES, France
The accuracy of the ocean tide correction is crucial for altimetry data, especially in the coastal regions, where the ocean tide signal shows the largest amplitudes.
The FES2014 global tidal model benefits from a high resolution mesh, improved hydrodynamic modelling and data assimilation techniques, as well as a 20-year-long altimeter time series and a large dataset of tide gauge observations for data assimilation. The validation of the FES2014 tidal elevations has shown the very good performance of this atlas, and particularly on the shelves.
In addition to the tidal elevations, the FES2014 global tidal atlas provides the tidal current velocity, which is of particular interest for many scientific (ocean circulation analysis, ocean dynamics modelling…) and industrial (offshore activities, tidal energy site assessment…) applications. Validation of the tidal currents is challenging as it requires long and accurate time series of current-meter observations. Luckily, for more than 10 years Australia has been maintaining a network of about 50 ADCP instruments all around the country, principally through its government-supported Integrated Marine Observing System (IMOS). The Australian continental shelf has a wide range of tidal regimes ranging from macro-tidal to micro-tidal, thus providing ideal conditions to thoroughly test a model.
This paper presents an assessment of the FES2014 tidal current atlas against the tidal constituents computed from the IMOS current meter data around Australia. The results show the very good agreement between the FES2014 tidal currents and the measured tidal currents, in most of the regions around Australia. Some differences have also been noticed and analysed and some potential improvements to the model have been identified.
This study provides new insights on the FES2014 tidal model quality and possibilities of improvements that would benefit to both the tidal currents and the tidal elevations, and subsequently to the coastal altimetry observations.