【摘要】： 月球是地球的唯一一顆天然衛(wèi)星,它的內(nèi)部結(jié)構(gòu)是一直人類不斷探索的謎題之一。在漫長的月球歷史中,由于受到隕石小天體的撞擊以及太陽-宇宙射線的照射,月球表層儲存了月球地質(zhì)和太陽輻射活動的線索。研究月球的結(jié)構(gòu)有助于提高對月球資源的科學(xué)認(rèn)識,對于未來的探月、將月球作為人類探測更遙遠(yuǎn)天體的理想平臺等有著十分重要的意義。 在月球探測中,星載高頻雷達(dá)探測儀(Radar Sounder)是一種用于探測月球次表層結(jié)構(gòu)的有效工具。與其它微波頻段相比較,高頻波段(3-30MHz)的電磁波可以穿透到月表以下幾百米至幾千米的月表深層,從而可以揭示出月球次表層結(jié)構(gòu)特征。雷達(dá)探測儀接收到月球表層的回波主要有：表面天底點(diǎn)回波,表面非天底點(diǎn)回波和次表面天底點(diǎn)回波。高頻雷達(dá)探測儀主要通過表面天底點(diǎn)和次表面天底點(diǎn)回波的時延差和強(qiáng)度來判斷月球次表層的深度以及物質(zhì)成分。 本文首先討論了高頻雷達(dá)探測儀頻率與帶寬的選取準(zhǔn)則,介紹了基于粗糙面電磁散射的Kirchhoff近似與幾何光學(xué)射線追蹤方法對月表雷達(dá)回波的快速模擬方法。在雷達(dá)探測儀對月球次表層結(jié)構(gòu)探測的回波模擬中,由于選取的月球表面及次表面都是有限的,會使得月球表面及次表面場景邊緣所對應(yīng)的射程距離處產(chǎn)生虛假的峰值回波。因此在模擬中,需要在邊緣對應(yīng)的射程距離處對接收到的回波進(jìn)行截?cái)�。作為本研究的第一個問題,本文討論了回波截?cái)嗵幩鶎?yīng)的射程距離與月表層參數(shù)之間的定量關(guān)系。 電磁波在月球次表層內(nèi)部傳播過程中受衰減、透射、散射等影響,次表面天底點(diǎn)回波往往會很微弱。受月球表面粗糙度、環(huán)形山等月表地形的影響,來自表面非天底點(diǎn)的強(qiáng)雜波往往會淹沒微弱的次表面回波,成為對月球次表層結(jié)構(gòu)探測的最大障礙。對于如何從具有強(qiáng)烈背景雜波的雷達(dá)探測儀回波中提取微弱次表面回波的研究,到目前為止還比較少。為有效探測月球次表層結(jié)構(gòu),本文基于月球次表面天底點(diǎn)回波和表面非天底點(diǎn)回波(雜波)的相干與非相干特性,提出在月球次表面地形變化不大的情況下,由累積取平均的方法來抑制表面非天底點(diǎn)回波從而識別次表面回波。以數(shù)值模擬的月海與月陸表面雷達(dá)探測儀回波為例,驗(yàn)證了該方法的正確性與可行性,并討論了累積平均數(shù)目對次表面回波提取結(jié)果的影響。 本文所述方法也可以應(yīng)用到火星等其他外星球次表層結(jié)構(gòu)、以及液態(tài)水的探測中。
[Abstract]:The moon is the only natural satellite on Earth, and its inner structure is one of the mysteries that mankind has been exploring. In the long history of the moon, the lunar surface has stored clues to lunar geology and solar radiation activity because of the impact of meteorite small objects and the irradiation of solar-cosmic rays. The study of the structure of the moon is helpful to improve the scientific understanding of the lunar resources. It is of great significance for the future exploration of the moon as an ideal platform for human exploration of distant objects. In lunar exploration, the spaceborne high frequency radar detector (Radar Sounder) is an effective tool for detecting the subsurface structure of the moon. Compared with other microwave frequencies, the electromagnetic waves in the high frequency band (3-30MHz) can penetrate the deep layers of the lunar surface hundreds to thousands of meters below the lunar surface, thus revealing the structural characteristics of the subsurface layer of the moon. The echoes of the surface of the moon are mainly received by the radar detector, including the surface celestial point echo, the surface non-celestial point echo and the sub-surface celestial point echo. The depth and material composition of the subsurface layer of the moon are judged mainly by the delay difference and intensity of the echoes of the surface sky-bottom point and the sub-surface sky-bottom point by the high-frequency radar detector. In this paper, we first discuss the selection criteria of frequency and bandwidth for high frequency radar detectors, and introduce a fast simulation method for lunar radar echoes based on Kirchhoff approximation and geometric optical ray tracing method based on rough surface electromagnetic scattering. In the echo simulation of the lunar subsurface structure detected by the radar detector, the false peak echo will be generated at the range distance corresponding to the lunar surface and the sub-surface scene edge because the selected lunar surface and sub-surface are limited. Therefore, it is necessary to truncate the received echo at the range distance corresponding to the edge in the simulation. As the first problem in this study, the quantitative relationship between the range distance corresponding to the echo truncation and the parameters of the lunar surface is discussed in this paper. The electromagnetic wave propagation in the subsurface of the moon is affected by attenuation, transmission, scattering and so on. The echo of the sub-surface sky point is often very weak. Under the influence of lunar surface roughness, craters and other lunar topography, the strong clutter from the non-celestial surface often inundates the weak subsurface echoes, which becomes the biggest obstacle to the exploration of the subsurface structure of the moon. So far there is little research on how to extract weak subsurface echoes from radar detector echoes with strong background clutter. In order to detect the subsurface structure of the moon effectively, based on the coherent and non-coherent characteristics of the lunar subsurface celestial point echo and the surface non-celestial point echo (clutter), it is proposed that under the condition that the subsurface topography of the moon does not change much, The method of cumulatively averaging is used to suppress the surface non-celestial echo so as to identify the sub-surface echo. The validity and feasibility of the method are verified by numerical simulation of lunar sea and lunar land surface radar echo, and the effect of cumulative average number on the result of subsurface echo extraction is discussed. The method described in this paper can also be applied to the subsurface structure of other alien spheres, such as Mars, as well as to the exploration of liquid water.
【學(xué)位授予單位】：復(fù)旦大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2010
【分類號】：P184.5

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相關(guān)期刊論文 前2條

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2 ;SAR imaging simulation for an inhomogeneous undulated lunar surface based on triangulated irregular network[J];Science in China(Series F:Information Sciences);2009年04期

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本文編號：2442316