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Locations of tide gauges (green stars) and distribution of satellite altimeter ground tracks between 1993 and 2013 used for this study.
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The north of Australia is known for its complex tidal system, where the highest astronomical tides (HATs) reach 12 m. This paper investigates the tidal behaviour in this region by developing spectral climatology for tide gauge and altimetry data. Power spectral density analysis is applied to detect the magnitude of ocean tides in 20 years of sea-le...
Citations
... Unlike the grid interpolation, which refers to far and sparse observations on different satellite tracks that may be located outside of bays or straits, the along-track smoothing can reduce the noises of each observation by referring to dense distributions (7 km separation) along the same track, and thus suitable for coastal studies [6,7,9]. Note that the temporal smoothing also reduces residual errors in the corrections of aliased tides, except for the K 1 constituent whose aliased period is 173 days (e.g., [19]). The ALES SSH data refer to the mean sea surface data from the DTU15 model [20], but in this study, we only use the SSHA data Z(r, t) from the 17-year temporal mean. ...
Seasonal variations are significant in currents in the Makassar Strait, 80% of the Indonesian Throughflow (ITF) from the Pacific to the Indian Ocean, and they are in phase with both the monsoon and the sea surface height anomaly (SSHA) difference between two oceans. However, dynamics are not well discussed since gridded SSHA products within the strait are less reliable because of both over-smoothing and contamination in coastal areas. In this study, therefore, 17 years of along-track Jason altimetry data with the ALES retracker are used without grid interpolation to investigate seasonal SSHA variations in and around the Makassar Strait. All SSHA variations are in phase from the southern Celebes Sea to the northern Java Sea through the Makassar Strait, but their amplitude decreases by the distance from the southern shallow area. These amplitude modulations produce the pressure gradient force, which is maximum to the north of 4°S reaching 1.5 × 10−6 ms−2, and that would be balanced with the bottom friction of the upper-layer ITF velocity, rather than the wind stress whose magnitude 5 × 10−8 ms−2 is too small. The SSHA difference between the two oceans is in phase but is isolated from the Makassar Strait by adjacent uncorrelated SSHA variations.
... Firstly, we used the harmonic analysis method for sea level trend observation. The procedure involved fitting the observations with a function using a least-square computation [36][37][38]: m(t) = a 0 + a t t + a cos 1 cos ω 1 t + a sin 1 sin ω 1 t + a cos 2 cos ω 2 t + a sin 2 sin ω 2 t ...
... a 0 , a 1 , a 2 , a t , a cos 1 , a sin 1 , a cos 2 and a sin 2 are unknown coefficients that can be estimated through least squares. The sea level residual was assumed to have a zero mean and it follows Gaussian distribution [37][38][39]. The quality of the tide gauge data was screened by the Pope Blunder Test [40] to remove any spurious changes in the data. ...
Sea level rise is an important and topical issue in the South Pacific region and needs an
urgent assessment of trends for informed decision making. This paper presents mean sea level trend assessment using harmonic analysis and a hybrid deep learning (DL) model based on the Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) technique, Convolutional Neural Network (CNN), Gated Recurrent Unit (GRU) and Neighbourhood Component Analysis (NCA) to build a highly accurate sea level forecasting model for three small islands (Fiji, Marshall Island and Papua New Guinea (PNG)) in the South Pacific. For a 20-year period, the estimated mean sea level rise per year from the harmonic computation is obtained: 112 mm for PNG, 98 mm for Marshall Island and 52 mm for Fiji. The DL procedure uses climate and environment-based
remote sensing satellite (MODIS, GLDAS-2.0, MODIS TERRA, MERRA-2) predictor variables with tide gauge base mean sea level (MSL) data for model training and development for forecasting. The developed CEEMDAN-CNN-GRU as the objective model is benchmarked by comparison to the hybrid model without data decomposition, CNN-GRU and standalone models, Decision Trees (DT) and Support Vector Regression (SVR). All model performances are evaluated using reliable statistical metrics. The CEEMDAN-CNN-GRU shows superior accuracy when compared with other standalone and hybrid models. It shows an accuracy of >96% for correlation coefficient and an error of <1% for all study sites.
... The mean sea surface (MSS) was then removed from individual tide gauge time series. The inverse barometric was also corrected using the two-dimensional gravity waves model (MOG2D-IB) to decrease the noise in estimating the part of sea level variations that are not associated with atmospheric pressure [16]. ...
Mean sea level rise is a significant emerging risk from climate change. This research paper is based on the use of artificial intelligence models to assess and predict the trend on mean sea level around northern Australian coastlines. The study uses sea-level times series from four sites (Broom, Darwin, Cape Ferguson, Rosslyn Bay) to make the prediction. Multivariate adaptive regression splines (MARS) and artificial neural network (ANN) algorithms have been implemented to build the prediction model. Both models show high accuracy (R2 > 0.98) and low error values (RMSE < 27%) overall. The ANN model showed slightly better performance compared to MARS over the selected sites. The ANN performance was further assessed for modelling storm surges associated with cyclones. The model reproduced the surge profile with the maximum correlation coefficients ~0.99 and minimum RMS errors ~4 cm at selected validating sites. In addition, the ANN model predicted the maximum surge at Rosslyn Bay for cyclone Marcia to within 2 cm of the measured peak and the maximum surge at Broome for cyclone Narelle to within 7 cm of the measured peak. The results are comparable with a MARS model previously used in this region; however, the ANN shows better agreement with the measured peak and arrival time, although it suffers from slightly higher predictions than the observed sea level by tide gauge station.
... Compared with the post-processing PPP method, the double difference (DD) method and tide gauge data, the root mean square (RMS) values of RT-PPP tide are 0.090, 0.194 and 0.167 m, respectively. tide behaviors [5,6,[9][10][11][12][13][14]. When comparing sea surface heights obtained by altimetry and tide gauges nearby, there is a RMS values in the range of 0.08-0.89 ...
... Tide gauge stations traditionally record tide measurements to obtain geophysical and oceanographic information [1]. Through long-term continuous observation of a certain sea areas, researchers can analyze the change of the sea level [1][2][3][4], study tide models [5,6] and investigate and forecast extreme sea level events such as hurricane storm surge and tsunami [2,[7][8][9]. Tide data measured by tide gauges can achieve high precision, however, it is limited to coastal areas near tide gauge stations, and it is difficult to build tide gauges in open sea areas far away from the shore. ...
Tide data plays a key role in many marine scientific research fields such as seafloor topography measurement and navigation safety. To obtain reliable tide data, various methods have been proposed, e.g., tide station measurement, satellite altimeter measurement, and differential global positioning system (GPS) buoy measurement. However, these methods suffer from the limitation that continuous observations at different areas might not be always available. In order to provide high-precision as well as continuous real-time tide data, we propose a method based on real-time precise point positioning (RT-PPP) by using International GNSS Service (IGS) real-time service (RTS) products. Firstly, compared with the IGS final products, the accuracy of the RTS satellite orbit and clock is evaluated. Secondly, the positioning performance of RT-PPP is compared with the IGS ultra-fast products. Finally, a robust Vondrak filter is proposed to eliminate the influence of high-frequency noise and errors and to obtain tide results. Experimental results show that three-dimensional (3D) accuracy of the RTS orbit is better than 0.05 m, and also has 0.22 ns less clock bias. An improvement of 60% is achieved for positioning accuracy using RTS products compared to IGS ultra-fast products. Compared with the post-processing PPP method, the double difference (DD) method and tide gauge data, the root mean square (RMS) values of RT-PPP tide are 0.090, 0.194 and 0.167 m, respectively.
Ce travail de thèse a concerné l’étude des mouvements du niveau de la mer aux niveaux des zones portuaires de la Baie d’Alger, et ce en périodes calmes et de fortes agitations. Ce travail a montré que la zone d’étude est concernée par plusieurs ondes marines non-tidales qui peuvent causer un danger même dans les endroits côtiers les plus abrités. Il a en outre montré que la détection des seiches et des météotsunamis, qui peuvent se produire au niveau de la zone d’étude, nécessite une instrumentation marégraphique spécifique ayant une fréquence de mesures (Fs) >= 0.016 Hz. Toutefois, cette Fs a clairement montré ses limites dans la détection et l’étude des ondes infragravitaires et des vagues/houles qui ont un rôle important dans la génération des seiches au niveau de la zone d’étude. Les résultats de ce travail ont également permis de souligner le rôle de la géomorphologie côtière, dans la génération des seiches au niveau de la baie d’Alger. En effet, les résultats ont distinctement montré que les fréquences des seiches observées au niveau de la zone d’étude correspondent aux fréquences de résonance de la baie d’Alger et de son plateau continental. Par ailleurs, ce travail a permis de qualifier les performances des différentes et méthodes d’analyses des données du niveau de la mer. A cet effet, l’analyse spectrale par la méthode de Welch et l’analyse par les ondelettes ont permis de comprendre, à des degrés différents, le comportement du niveau de la mer au niveau de la zone d’étude. Aussi, la toute récente méthode de Décomposition en Modes Empiriques, testée dans ce travail de thèse, a permis l’observation de certaines fréquences (hautes et basses), notamment celles qui sont proches de la Fs instrumentale. En résumé, ce travail a permis d’étudier l’ensemble ou presque des ondes de surface qui peuvent concerner la baie d’Alger qui sont importantes aussi bien pour les études d’ingénierie côtière que pour la réduction des risques côtiers.
