A Separation Algorithm Of Wind Sea And Swell Inversion Of Navigation Radar Image

Wave is the most common phenomenon of a sea wave.In general,the ocean wave is made up of wind sea and swell,their internal mechanisms of action and external characteristics are significantly different.Wind sea and swell representing different meteorological conditions generally coexist in both open sea and coastal areas,which result in double-peaked or multiple-peaked features in wave spectrum.Because they make wave parameters such as mean wave period and significant wave height of the mixed sea state less meaningful,the processes of separation and identification of wind sea and swell are crucial.Therefore,relying on the research project of "the ocean wave inversion technology by shipborne X-band radar" test,this paper develops the inversion research of separation of wind sea and swell.It is found that wind sea and swell separation inversion research mostly under buoy,rare use of X-band navigational radar images to obtain wave spectrum data to realize separation of wind sea and swell.Therefore,basing on the algorithm of separation of wind sea and swell under the buoy platform,this paper develops the separation of wind sea and swell under X-band navigation radar platform.At present,the method of separation can be typically categorized into one-dimensional spectral and two-dimensional spectral techniques,respectively.It is regarded that two-dimensional spectral technique gives more reliable result,however,the two-dimensional spectral technique is very limited in practical application due to considering more information.In this paper,the composition of wind sea and swell is determined by using the wind sea-swell separation OP method,and the method is by comparing the peak value of the correspongding one-dimensional wave spectrum with the peak amplitude of the PM spectrum at the same peak frequency.This paper discusses how to handle the raw wave height data firstly.The one-dimensional wave spectrum is obtained by Fourier transforming the pre-processed buoy data.Then get the a partition frequency of the ocean wave spectrum from buoy by the fixed frequency method,the PM method and the OP method respectively and tested the separation effect of the three separation methods with reference to the variation of the wave direction with frequency in the case of pure wind wave and mixed wave.The measured data shows the OP method can get a better separation,comparing with the fixed frequency and PM method.The algorithm of separation of wind sea and swell under the buoy platform is further popularized,this paper proposes the algorithm of the separation of wind sea and swell from X-band navigation radar images.Firstly,selecting the radar images region sequence which is same with the time and region of the buoy measurement,and pre-process the selected image sequence,aiming to remove the interference signal such as the target and the same frequence in the image.Then the processed radar image sequence is Fourier transformed to achieve radar image spectrum.The band-pass filter is designed basing on the maximum estimation metod to extract the real ocean waves.The obtained wave spectrum is calibrated by adjusting the modulation transfer function so that the one-dimensional spectrum obtained by radar and buoy is consistent.Lastly,the one-dimensional ocean wave spectrum is separated by the fixed frequency method,the PM method and the OP method,The results show that the OP method can get a better separation.The wave parameters have a good correlation by using the OP method to separate the waves from the two platform of radar and buoy.Lastly,according to the relationship between wind information and wave height and by analyzing a large number of test data,which proves that separation of wind sea and swell is feasible under X-band navigation radar platform.