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標題: | 多頻道震測訊號接收浮纜之定位及海流對浮纜漂移影響之探討 Multichannel Seismic Streamer Relocation and the Relationship of Stream Feathering and Ocean Current |
作者: | Kuo-Han Chao 趙國涵 |
指導教授: | 劉家瑄 |
關鍵字: | 多頻道反射陣測,定位,浮纜漂移,海流, streamer,feathering,relocation,current,reflection, |
出版年 : | 2016 |
學位: | 碩士 |
摘要: | 海上進行多頻道震測作業是由探測船拖著一至數支空氣槍組成的陣列作為聲源,及一至數條數十公尺至數公里的信號接收浮纜沿規劃的測線位置航行,震波經空氣槍擊發後於海水中傳遞,在接觸到海床及其底下之地層反射及折射後,被浮纜上密集分布的接收器接收,隨後再經由資料處理產生震測剖面。進行震測資料處理時,會將具有相同反射點位置的訊號組合整理成為同中點/同深度集合(common midpoint/common depth point gather, CMP/CDP gather),再透過疊加重合來提升資料的訊躁比(signal-to-noise ratio, S/N),及轉成由一系列垂直入射描線組成的反射震測剖面。為此,聲源與接收器皆需有精準的定位,以求得正確的反射點位置。理想狀態下,震測作業中被拖行的浮纜會在船的正後方,且能保持為一直線。然而實際上,浮纜在海中會受到海流、風或波浪的擾動,使得浮纜於海水中未必位於船的正後方,其形狀也未必為一直線,連帶使得反射點的位置產生偏移。這些由浮纜偏移所產生的反射點位置誤差在一般二維震測中較能接受,但在測線間距小至50或100公尺的三維震測作業時就會產生不容忽視的誤差。為了定出接收器在每次炸測時在海中的正確位置,在信號接收浮纜上裝上全球定位系統(GPS)是最有效的方法。本研究利用海研一號於仿三維震測作業中所記錄到船的GPS與裝在尾端浮標(tail-buoy)上的GPS定位資料,藉由簡單的幾何關係推得浮纜於海中的形狀與位置,進一步計算出每個炸點與其對應的各接收器位置,另藉由同樣的方法推得每一個炸點其聲源的位置。希望建立一套標準作業流程以提供震測資料處理流程中的幾何定位(geometry)提供更準確的定位資訊。另外,船上裝備的都普勒流速儀在航行中會即時蒐集海流資料,本研究亦由分析海流資料與浮纜漂移程度,試圖找到其中的關聯,在未來便能藉由海流資料去預測浮纜可能漂移的位置。 In marine multichannel seismic reflection survey, a vessel tows one to several air guns as seismic source, and one to several streamers from few tens meters to a few kilometers long. When air guns fire, the seismic waves generated will transmit through sea water to the sea bed and deeper sedimentary layers, and reflect back to streamer. The hydrophones in the streamer receive these signals and send them to recording system for converting to seismic data. When processing seismic data, we sort out those traces which have common midpoint to form a common midpoint/common depth gather (CMP/CDP). To do this, we need the accurate locations of shots and receivers. Normally, during marine multichannel seismic reflection survey, we assume that the streamer is behind the vessel and the shape of the streamer maintains a straight line. Unfortunately, the cross current and other factors may cause streamer to draft sidewise, called feathering. To know how much the streamer has drifted away from right behind the ship, we put a global positioning system (GPS) device on the tail buoy at the end of the streamer to record the exact positon of the streamer during seismic surveys. In this study, we use a recently collect pseudo 3D seismic data set in which the tail buoy positions have been recorded by a GPS system, to reconstruct the exact shape and locations of the streamer, and to derive the accurate source and receiver positions for each shot record. Finally, these information enable us to construct a true 3D geometry in the 3D seismic processing. In addition, this study also examines the current data from Acoustic Doppler Current Profiler (ADCP) records, then to compare feathering angles and current data, in the hope that we may find some relationships between the ocean current and the feathering angle, and to evaluate if the ocean current is the sole factor which causes streamer feathering. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/51424 |
全文授權: | 有償授權 |
顯示於系所單位: | 海洋研究所 |
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