變頻聲納對海床表面底質分類的應用研究

Chirp變頻聲納回聲探測儀是以變頻的方式傳送電子脈衝，其信號傳送時頻率由低逐漸增高。接收到的信號則需與原發射出的信號做互對比(correlation)，以獲得高解析度的海底聲納回聲剖面，由於水中各項條件對於聲波探測影響相當大，具體來說可由反射強度來表現，反射強度會受水文環境、底質特性、海底地形、表面粗糙度等各種因素影響，因此選用Chirp，因為其訊號發射穩定又一致，越能掌握水下聲波傳遞的實際情形，進而全面了解底質的實際情況。理論上Chirp訊號頻寬很寬，具有較高的訊雜比和穿透力，因此不同的底質對於寬頻的各頻率有不同的反應，可求得更精確的沉積物的反射係數R值，相較之下，岩心採樣雖無法提供大範圍的資料，卻代表真實的底質特性，使用chirp資料辨識底質可以獲得較全面性的地質資料，大量資料整理比對後可得該區底質的分佈情況。　　根據研究區域內的岩心資料和連續變頻聲納(chirp sonar)的資料比對，可以了解不同沉積物的聲學特性，粗顆粒的沉積物因具有較高的衰減系數故能量容易衰減，剖面上的訊號穿透度較差，反之，細顆粒沉積物的剖面則常呈現清楚且連續的次層反射訊號，訊號穿透度良好，探索表層沉積物反射係數值，粗糙面的散射影響很大。預期結果不同的底質會產生不同的能量變化。利用聲納的音傳耗損過程，來預測或對比出海床淺層沉積物性質。

關鍵字

變頻聲納；反射係數

並列摘要

The chirp sonar frequency-modulated (FM) systems offer deterministic, repeatable source-signatures for high-resolution normal incidence marine seismic reflection data that it provides quantitative, high resolution and low-noise sub-bottom data by correlated the output pulse and received signal. Many factors affect the transmission of sound waves in the water. Specifically, reflectivity is important for acoustic classification of seafloor sediment, the reflectivity will be affected by hydrological environment, sediment characteristics, topography, surface roughness. The chirp sonar was developed with the objective of remote acoustic classification of seafloor sediments with the stable and consistent signal transmitter. Theoretically, chirp sonar record has a high signal to noise ratio and good penetration for seabed. Quantitative acoustic returns from the chirp sonar are used to estimate surficial acoustic impedance and to predict sediment properties by reflection coefficient (R). This study used core sample to account for the depositional environment. It represents the real sediment characteristics. The comparisons show a high correlation between the core-determined sediment properties and the estimates obtained from acoustic measurements. 　　According to the comparison between core and data of chirp sonar , we can understand the different acoustic characteristic of the sediment. For example the coarse sediments, it's higher attenuation coefficients for the energy decay easily and show the worse penetration on the sub-bottom profile than fine sediment. This purpose of this research is to predict marine sediment classification by different sediment will produce different reflectivity using the reflection coefficient of chirp sonar.

並列關鍵字

chirp sonar ； reflection coefficient

參考文獻

34. 陳彥勳，2004，淺海環境水文及底質對音傳特性之影響，國立臺灣大學工程科學及海洋工程學系研究所碩士論文。

36. 林智偉，2011，利用聲納反射係數探討海床沉積物特性。國立中央大學地球物理研究所碩士論文。

37. 蔡明格，2011，台灣東北海域反算底質音響參數分析研究，國立台灣大學工科海洋工程研究所碩士論文。

2. Bachman, R.T., 1985. Acoustic and physical property relationships in marine sediments. Journal of the Acoustical Society of America. 78 (2), 616-621

3. Brekhovskikh, L.M., and Lysanov, Y.P., 2003. Reflection of Sound from the Surface and Bottom of the Ocean: Plane Waves, Fundamentals of Ocean Acoustics: Modern Acoustics and Signal Processing, Springer New York, 61-79

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變頻聲納對海床表面底質分類的應用研究

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