Ocean Tides near Hawaii from Satellite Altimeter Data. Part I

Abstract

Sufficient and accurate tide data are essential for analyzing physical processes in the ocean. A method is developed to spatially fit the tidal amplitude and phase lag data along satellite altimeter tracks near Hawaii and construct reliable cotidal charts by using the Chebyshev polynomials. The method is completely dependent on satellite altimeter data. By using the cross-validation method, the optimal orders of Chebyshev polynomials are determined and the polynomial coefficients are calculated by the least squares method. The tidal amplitudes and phase lags obtained by the method are compared with those from the Finite Element Solutions 2014 (FES2014), National Astronomical Observatory 99b (NAO.99b) and TPXO9 models. Results indicate that the method yields accurate results as its fitting results are consistent with the harmonic constants of the three models. The feasibility of this method is also validated by the harmonic constants from tidal gauges near Hawaii.

Fitting Cotidal Charts of Eight Major Tidal Components in the Bohai Sea, Yellow Sea Based on Chebyshev Polynomial Method

“…The harmonic constants calculated by the adjoint assimilation model and the harmonic constants of the X-TRACK satellite are together fitted by the CPF method, in order to obtain the high-resolution harmonic constants in the full field. More details on data, methodology and error assessment can be found in Part I (Xu et al, 2021).…”

“…From the previous experience of other researchers, too high an order can cause overfitting [28]. To avoid over-fitting, the optimal order is determined using the cross-validation method.…”

“…In this study, the harmonic constants calculated by the CPF are compared with the Finite Element Solutions 2014 (FES2014) model at a horizontal resolution of 1/16 [34,35]. Refer to the study of Xu, Wang, Wang, Lv and Chen [28] for more details on the NAO.99b, TPXO9 and FES2014 models, and refer to the study of Wang, Zhang, Xu, Wang and Lv [27] for more details on the EOT20 model. The harmonic constants of eight tidal gauges (Figure 1) were also compared with the harmonic constants of the CPF, TPXO9, FES2014, NAO.99b and EOT20 solutions.…”

“…In the present study, a new method based on CPF is proposed to calculate the full-field tidal harmonic constants in the shallow-water region of BYS, which provides a new direction for obtaining reliable harmonic constants in this region. The CPF was successfully applied in the area near Hawaii (the open ocean) and obtained precise cotidal charts of eight major constituents and minor tidal constituents [27,28]. This paper presents the application and results of the CPF method in the shallow-water region of BYS.…”

Research on outlier detection in CTD conductivity data based on cubic spline fitting

“…Based on this physical constraint, a fitting function can help construct the marine elements, and the difference between the observed value and the fitted data larger than the given threshold will be discriminated as outliers (Tan et al, 2021). The cubic spline fitting function has become an extremely important numerical fitting method due to its good stability and smoothness, and it has achieved good application results in data analysis (Jiang et al, 2018;Jin et al, 2018;Zong et al, 2018;Wang et al, 2019;Xu et al, 2021). Based on the above situation, this paper aims to propose an outlier detection method based on Cubic Spline Fitting.…”