| Wave is an important part of ocean hydrology.It is of great significance to monitor wave in a real-time,stable,long-term and effective way in the fields of ocean forecasting,disaster prevention,marine engineering,and navigation safety.The realtime wave measurement technology using BeiDou(Navigation Satellite System)drifting buoy,has the advantages of traditional GNSS(Global Navigation Satellite System)wave measurement technology and provides short message communication services.The wave measuring buoy obtains wave elements and position by the same positioning module.Without the acceleration sensor and other precision components,the buoy can be more portable and less costly,and there is no accumulation of systematic errors,no need to calibrate regularly,so it is suitable for unattended longterm monitoring.To address the issues of expensive and non-real-time wave observations for the global ocean,firstly,this thesis evaluates the feasibility of the GNSS variometric algorithm based on broadcast ephemeris in real-time and highprecision wave elements retrieval.Secondly the influence of GNSS sampling frequency variation on wave elements retrieved by different GNSS methods is examined.The experimental results show that the retrieved wave elements of the variometric method are closer to the results of the PPP(Precise Point Positioning)and PPK(Post-Processing Kinematic)methods than the results of the Doppler method.Moreover,based on the broadcast ephemerides and without the need of base station and real-time precision correction service,the variometric method can operate in global waters at low cost,indicating that has high practical value.As the GNSS sampling frequency decreases from 5 Hz to 1 Hz,similar to the retrieved results of the PPP and PPK methods,the retrieved significant wave height of the variometric method decreases slightly by 0.9cm,and the retrieved average wave period gradually increases by 1.04 s.However,the Doppler retrieved results deviated from the results retrieved by the variometric,PPP and PPK methods,with the significant wave height and average wave period increased by 19.5 cm and 0.55 s respectively.In addition,the variation from 5 to 2.5 Hz is 1/5and 1/10 of the variation from 5 to 1 Hz,respectively,in the significant wave height and average wave period,which means wave elements retrieval is stable at 2.5 Hz and higher.The power spectral density shows that when the sampling frequency is lower than 1.25 Hz,there is a serious energy deficit in high frequency area above 0.6 Hz,which seriously affects wind waves detection.The dominant wave direction is insensitive to the sampling frequency variation,ranges of 1 ～ 2°.Thirdly,on the basis of above,the technology and implementation of the real-time wave measurement using BeiDou drifting buoy based on the GNSS variometric algorithm is also studied,which includes the hardware selection and integration,realtime on-line software design and implementation.And the feasibility of real-time wave measurement with BeiDou single system is verified.Finally,the reliability and accuracy of the technology and software for the real-time wave measurement using BeiDou drifting buoy are verified by comparing the real-time transmission retrieved results of offshore and open ocean experiments.In the offshore sea trials,the transmission retrieved results of the two test buoys were compared with the retrieved results postderived by the Datawell DWR-G4.The significant wave height difference RMS(Root Mean Square)were 6 cm and 4 cm,respectively,better than the technical criteria of dominant products(0.1 m+5% H,H is wave height),and the average wave period difference RMS were 0.48 s and 0.49 s,respectively,means that the real-time transmission results are well retrieved.In open ocean trials,the variation tendency of the significant wave height and the average wave period of four test buoys show a high consistency with the ECMWF(European Centre for Medium-Range Weather Forecasts)reanalysis products. |
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