【摘要】：海洋是大自然的天然屏障，它擁有豐富的水資源、生物及礦產(chǎn)資源，對其進(jìn)行探索和開發(fā)利用，是拓展我們?nèi)祟惿婵臻g的重要途徑。我國海岸線綿長，臨海廣闊，海洋資源十分豐富，這使得研究海洋遙感技術(shù)有著非常重要的意義。X波段雷達(dá)（XBR）可以對海面成像，是目前監(jiān)測海洋環(huán)境的重要手段。其工作頻率為8GHz~12GHz，它以價(jià)格低廉、方便可靠、實(shí)時全天候以及高時空分辨率等優(yōu)點(diǎn)在各國引起了不小反響。 本文簡要敘述了XBR在海洋遙感獲取海態(tài)參數(shù)技術(shù)應(yīng)用上的發(fā)展歷程以及目前國內(nèi)外的研究狀況。國內(nèi)外的研究都是基于X波段非相參雷達(dá)的，本文提出X波段寬帶相參雷達(dá)的海浪反演方法。相比于非相參雷達(dá)，一方面它可以通過相參積累直接得到海浪的徑向速度信息，并且形成的海面圖像為復(fù)序列，，另一方面采用大帶寬可以獲得更高的距離分辨率，從而可以更小尺度觀測波浪。模擬仿真中采用200MHz大帶寬，距離分辨率可以精確到0.75m。 本文的主要工作是對岸基X波段寬帶相參雷達(dá)反演海浪特征參數(shù)算法進(jìn)行分析討論，提出對雷達(dá)回波進(jìn)行相參積累（二維FFT處理），對同一距離門的海浪速度加權(quán)平均得到海浪的徑向速度，并對得到的徑向速度進(jìn)行單站矢量合成，即可得到海表層流場。進(jìn)而對雷達(dá)圖像進(jìn)行基于傅氏變換頻譜分析的反演算法提取海浪參數(shù)。首先，對XBR成像機(jī)理進(jìn)行了理論分析。雷達(dá)發(fā)射的電磁波以幾乎與海平面平行的方式到達(dá)到粗糙的海表面，海浪的波動起伏，與相近波長的毛細(xì)波發(fā)生Bragg共振散射，而同時毛細(xì)波又受到較長波長的海面重力波的調(diào)制。后向散射回波到達(dá)雷達(dá)天線，生成海雜波圖像。對一系列連續(xù)的隨時間演變的海雜波圖像序列做三維離散傅里葉變換得到雷達(dá)圖像譜。利用頻散關(guān)系設(shè)計(jì)帶通濾波器對圖像譜濾波，從背景噪聲中分離出海浪能量。對圖像譜積分，并用MTF對其進(jìn)行校正得到海浪方向譜，從而可以提取出海浪的一維頻譜以及特征參數(shù)等信息。仿照SAR圖像中提到的有效波高與雷達(dá)接收到的回波SNR有線性關(guān)系，估計(jì)出海浪有效波高。 最后，對提出的X波段寬帶相參雷達(dá)的海態(tài)參數(shù)反演算法進(jìn)行了仿真驗(yàn)證。選取P-M譜的派生形式ITTC雙參數(shù)譜作為海浪靶譜以及選擇余弦平方函數(shù)作為海浪方向函數(shù)，建立三維隨機(jī)海浪模型。對考慮陰影調(diào)制影響以及加入了系統(tǒng)噪聲的雷達(dá)圖像進(jìn)行相關(guān)算法處理仿真。將反演得到的參數(shù)與輸入?yún)?shù)進(jìn)行對比分析，結(jié)果顯示在誤差允許范圍內(nèi)，反演算法是合理可行的。
[Abstract]:The ocean is the natural barrier of nature. It has abundant water resources, biological resources and mineral resources. Exploring and exploiting it is an important way to expand the living space of human beings. China has a long coastline, vast coastal area and abundant marine resources, which makes the study of marine remote sensing technology of great significance. X-band radar (XBR) can image the sea surface, and it is an important means to monitor the marine environment at present. Its operating frequency is 8 GHz and 12 GHz. It has the advantages of low price, convenient and reliable, real-time all-weather and high spatial and temporal resolution. This paper briefly describes the development of the application of XBR in marine remote sensing technology for obtaining marine parameters and the current research situation at home and abroad. The research at home and abroad is based on X-band non-coherent radar. In this paper, a wave inversion method for X-band wideband coherent radar is proposed. Compared with non-coherent radar, on the one hand, it can obtain radial velocity information of ocean waves directly by coherent accumulation, and the resulting sea surface image is a complex sequence, on the other hand, it can obtain higher range resolution by using large bandwidth. Thus, waves can be observed on a smaller scale. In the simulation, 200MHz is used for large bandwidth, and the range resolution can reach 0.75m. The main work of this paper is to analyze and discuss the algorithm of wave characteristic parameter inversion of shore-based X-band wideband coherent radar, and propose the coherent integration of radar echo (2-D FFT processing). The radial velocity of the ocean wave is obtained by weighted mean of the wave velocity of the same distance gate, and the ocean surface current field can be obtained by the single station vector synthesis of the obtained radial velocity. Furthermore, the inversion algorithm based on Fourier transform spectrum analysis is used to extract ocean wave parameters from radar images. Firstly, the imaging mechanism of XBR is analyzed theoretically. The electromagnetic waves emitted by radar reach the rough sea surface almost parallel to the sea level. The waves fluctuate and Bragg resonance scattering occurs with the capillary waves of similar wavelengths. At the same time, the capillary waves are modulated by the gravity waves at longer wavelengths. The backscattering echo reaches the radar antenna to generate sea clutter images. Three dimensional discrete Fourier transform (DFT) is used to obtain radar image spectrum for a series of successive sea clutter image sequences. A band pass filter is designed to filter the spectrum of the image by using the dispersion relation, and the wave energy is separated from the background noise. The spectral integral of the image is corrected by MTF to obtain the directional spectrum of the ocean wave, so that the information of the one-dimensional spectrum and the characteristic parameters of the wave can be extracted. The effective wave heights mentioned in the SAR images are linearly related to the echo SNR received by the radar, and the wave effective wave heights are estimated. Finally, the proposed algorithm of sea parameter inversion for X band wideband coherent radar is simulated. A three-dimensional random wave model was established by selecting the P-M spectrum as a derived form of the ITTC two-parameter spectrum as the wave target spectrum and the cosine square function as the wave direction function. Simulation of radar image processing with shadow modulation and system noise is carried out. The inversion parameters are compared with the input parameters. The results show that the inversion algorithm is reasonable and feasible within the range of error.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN957.52

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