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The Pacific Ocean is the main region occurring the interannual and interdecadal variabilities of sea surface temperature. Comparing to the sea surface temperature, the variabilities of ocean heat content in the Pacific Ocean were less studied. Therefore, this paper studied the variabilities of ocean heat content (at depth of 0300 m) in the Pacific Ocean during the period from 1980 to 2020. The Ensemble Empirical Mode Decomposition method (EEMD) was applied to the Institute of Atmospheric Physics (IAP) heat content data to extract the signals at different time scales, and then the Empirical Orthogonal Function (EOF) was applied to analyze the temporal and spatial characteristics of the ocean heat content at different time scales. The results showed that besides the interannual variation, there were also evident interdecadal variations and longterm warming trends of heat content at depth of 0~300 m in the tropical northwest Pacific. In the eastern Pacific and the highlatitude western Pacific, the interdecadal variability of heat content was not prominent. In the tropical northwest Pacific, the heat content was higher during 19801988 and 19992013 than those during 19891998 and 20142020. Our analysis showed that the interdecadal variability was mostly occurred at 5°N—20°N, 120°E—180°E, and at depth of 50200 m in the tropical northwestern Pacific. The interdecadal variation of ocean heat content in the tropical northwestern Pacific played an important role in the interdecadal variation of global sea surface temperature.

There is strong tide in the Changjiang (Yangtze River) Estuary and its adjacent area. Except for the coast area, there is a lack of longterm tide level and tidal current data in the offshore area. Long time series of water level observation data was used in this study, and the results reveal that the tidal type in the Changjiang Estuary is a regular semidiurnal tide, with a significant shallow water division in the nearshore area; the M2 division is the most significant semidiurnal tide, and the amplitude tends to increase from the open sea in the east to the shallow water or island group at the mouth of Hangzhou Bay in the west. The M2 tidal current is the most significant semidiurnal tidal current, and the rotating tide is the most significant semidiurnal tide. The two stations to the south of the Changjiang mouth are rotating counterclockwise, while the stations to the east of the mouth are rotating clockwise. The vertical structure of the tide has significant spatial differences, the ellipticity of the M2 tidal current is mostly negative, the ellipticity of the M2 tidal current, the direction and the arrival time of maximum velocity all vary significantly with depth.

As a key parameter in hydrodynamic and sediment transport models, bottom shear stress is very important to study the initiation and erosion rates of bottom sediment. At present, there are six theoretical methods for calculating bottom shear stress based on field measured flow velocity data: LPmean method, LPmax method, TKE method, TKEW method, RS method and ID method, all of which have their specific applicable conditions. It is very important to select an appropriate method to calculate the bottom shear stress in the shallow water area of estuarine and coastal areas where the actions of current and wave are complex. In this study, one observation site at Dafeng Doulong Port, Jiangsu Province (median particle size: 68.56 μm) and two observation sites at Eastern Chongming Shoal, Shanghai (median particle size: 12.89 μm and 45.02 μm) were taken as examples. Field data were collected using Acoustic Doppler Velocimetry and wave measurement instrument (RBRwave), and the bottom shear stress was calculated by six theoretical methods. The results show that: (1) The LPmean method is affected by the average velocity, the distance from the probe to bed and the strength of waves, which underestimates the bottom shear stress and is not suitable for shallow water environment in intertidal flat; (2) LPmax method and TKE method can overestimate shear stress in shallow water environment of intertidal flat where flow velocity varies greatly and wave action is obvious; (3) TKEW method was modified on the basis of TKE method, which is more suitable for solving the bottom shear stress under strong wave action; (4) The results of RS method are affected by waves, and the results of ID method are more reliable than those of RS method when large waves exist, but ID method will overestimate the bottom shear stress when water depth is insufficient.

In this study, Particle Image Velocimetry (PIV) and Wave Gauge (WG) were used to measure the wave height, wave velocity and other hydrodynamic parameters within inner surf and swash zones under three slopes. Based on the second-order spectrum method, the probability density distribution of wave height and velocity between different sections, as well as high-order nonlinear statistical variables such as skewness, asymmetry and kurtosis were analyzed. The results show that the wave height and velocity deviate from the normal distribution, the skewness and kurtosis of wave height decrease first and then increase during the nearshore propagation, the asymmetry increase first and then decrease, and the nonlinear characteristics of wave height are not affected by the slope. The velocity in the three cases shows different nonlinear distribution characteristics. In the steep slope and composite slope, section distribution of velocity skewness characteristics are not obvious. Only the vertical distribution of velocity skewness at each section of gentle slope increases first and then decreases. The velocity asymmetry of the three cases increases first and then decreases with the increase of the distance from the bed.

As an ecological buffer zone, the salt marsh plants growing in the coastal zone play an important role in reducing the current velocity, weakening wave energy and preventing coastal erosion, it is of great significance to investigate the mechanism of wave attenuation by salt marsh plants in estuaries and coastal zones. Based on the open source CFD software package of OpenFOAM software, a 3D numerical model considering the effect of vegetation on flow and wave was established in this study. Firstly, the model was applied to investigate the propagation processes of dambreak wave over the triangle obstacle and the solitary wave climbing on the sloping beach, the results show that the OpenFOAM model can accurately capture the propagation of dambreak waves and free water movement of solitary waves. Then this model was also used to simulate the formation, development and attenuation of solitary waves in a vegetated wave flume, where the wave height of solitary waves decreases obviously through the vegetation zone, the vegetation can effectively attenuate wave energy on a coastal beach. Lastly, the propagation process of sine waves on the vegetated beach was numerically studied, the obtained numerical results show that the attenuation of wave height is directly proportional to the incident wave height, plant density, the drag force coefficient of plant and the steepness of the coast.

Orbital data are important parameters involved in the satellite data processing and HY1C satellite products with high quality are inseparable from the accurate calculation of the orbit. In this study, data were extracted from the TLE (TwoLine Orbital Element) and used to accurately simulate satellite orbit based on STK (Satellite Tool Kit) software. The ephemeris was outputted to compare the accuracy of two satellite orbit algorithms of HY1C and evaluate the influence of perturbation factors on orbit calculation. Method one uses an algorithm which does not consider perturbation factors and extrapolates the ephemeris parameters of the observation time based on the orbit elements of the reference time, and then calculates the satellite orbit data. Method two adopts the SGP4 model which considers perturbation to calculate the orbit data. The results show that perturbation has a significant impact on the orbit calculation. The algorithm error without considering the perturbation increases significantly with the passage of time, and the position errors are less than 10 km with the speed errors less than 10 m/s in half an hour. While SGP4 model algorithm runs fast with high calculation accuracy and good stability, the position and speed errors within 24 hours are less than 68 m and 0.051 m/s respectively. Therefore, SGP4 model algorithm can be used for the highprecision orbit calculation of the loworbit satellite HY1C.

 Suspended sediment concentration (SSC) is one of the important water quality parameters in estuarine water research. Remote sensing determination of SSC is an important method. In order to study the quantitative gradient relationship between remote sensing spectral data and surface suspended sediment concentration(SSSC), the surface sediments near the Nanhuizui of the Changjiang (Yangtze River) Estuary were collected, the gradient changes of SSSC were designed quantitatively, and the optical characteristics of sediment laden water with different concentrations were measured by ASD hyperspectral spectrometer. The results show that with the increase of SSSC, the spectral reflectance curve of water has similar morphology, but there are also some differences. When SSSC<36.59 mg/L, the spectral curve has only one reflection peak at 560-580 nm. When SSSC>52.69 mg/L, the first reflection peak of the spectral curve is at 570-710 nm, and the second reflection peak appears at 780-820 nm in the near infrared band. There is an obvious “red shift” phenomenon in the first peak interval of the spectral curve, and the linear fitting R2 between the “red shift” change of wavelength and SSSC reaches 0.91, indicating a strong linear correlation between them. In the spectral range of 400~900 nm, 600-860 nm band is sensitive and stable to the change of SSSC in the range of 0~200 mg/L, and 740900 nm band has stronger response to the change of SSSC>200 mg/L.

Aiming at the problem of low inversion accuracy and time resolution in single-system GNSS-MR tide level monitoring, a multi-system fusion tide level inversion method based on LS-SVM was proposed. Using GPS, BDS, Galileo and GLONASS satellite data from Hong Kong's HKQT station for 30 consecutive days, experiments were conducted to compare three multi-system fusion methods based on sliding window least square, SVR, and LS-SVM. The results show that compared with the BDS system with the smallest RMSE for single-system GNSS-MR tide level inversion, the RMSE value of multi-system fusion tide level inversion based on LS-SVM reduced by 55.8% and the correlation coefficient increased by 4.1%. Compared with the GLONASS system with the highest time resolution, the time resolution increased by 59.3%; Compared with the multi-system fusion tide level inversion based on the SVR model, the RMSE value reduced by 52.3%, and the correlation coefficient increased by 2.2%; Compared with the multi-system fusion tide level inversion of the sliding window least square method, the RMSE value reduced by 41.1%, and the correlation coefficient is increased by 1.2%. Multi-system fusion tide level inversion based on LS-SVM has better tide level inversion performance than that of sliding window least square method and SVR algorithm.

Optical dissolved oxygen sensor based on fluorescence quenching principle can obtain spatiotemporal data of dissolved oxygen in seawater, which is widely used in long-term monitoring of marine environment. However, due to the “storage drift” and “measurement drift” occurring during storage and distribution, it is necessary to calibrate and correct the data drift of the instrument. Existing calibration methods have long cycle and complex operation. In this project, the response characteristics of optical dissolved oxygen sensor in air and water medium were studied, and a field calibration method of optical dissolved oxygen sensor using air medium was proposed, and a two-point calibration model of the instrument was established. Experimental results show that the calibration method can effectively correct the data drift of the dissolved oxygen sensor, and the deviation between the measured value of the sensor and the standard value of Winkler titration is within  ±6 μmol·L-1. This method can realize the convenient and rapid correction of optical dissolved oxygen sensor, avoid the tedious steps of laboratory maintenance, improve the quality of monitoring data, maintain the continuity of monitoring data, and has important application value.

A bibliometric method was employed to evaluate the global scientific production of tidal bore research and seek the characteristics of publication outputs including countries, institutions, authors, journals and keywords from papers related to tidal bore. The basic data were obtained from CNKI and Web of Science core collection database. The 652 papers published by 632 authors from 433 research institutions in 239 publications were retrieved from CNKI. “Qiantang River Estuary” and “North branch of the Yangtze River Mouth” were areas of high concern in China. “tidal bore pattern”, “river bed evolution”, “tidal bore pressure” and “tidal bore height” were hot keywords in the researchs. “numerical modelling” and “physical modelling” had become important means of tidal bore research. A total of 277 articles published in 143 journals by 447 authors from 224 institutions in 34 countries were retrieved by Web of Science. The literatures payed high attention to Qiantang River in China, Seine and Garonne River in France, Amazon River in Brazil and other estuaries. “turbulence”, “sediment transport”, “hydraulic jump”, “wave”, and “environmental impact” were hot issues on tidal bore, and “physical modelling”, “field measurements” and “numerical modelling” had become important means of research on tidal bore. Although the number of research papers published at home and abroad fluctuated in different years, it showed a rapid growth trend and rich research results. Due to the limitation of specific estuarine area, the research institutions were relatively concentrated and the total amounts of papers published were not much. This study objectively analyzed the current status of tidal bore research at home and abroad to provide data reference for researchers and decision makers.