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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/11722

Title: 地形與內波對於雷達背向散射的影響---子計畫---海洋表面波譜對雷達背向散射的效應(II)
Effects on Radar Backscatter by Ocean Surface Spectrum (II)
Authors: 董東璟;莊士賢;高家俊
Contributors: NTOU:Department of Marine Environmental Informatics
國立臺灣海洋大學:海洋環境資訊系
Keywords: 內波;波譜量測
Internal wave;spectrum measurement
Date: 2008-08
Issue Date: 2011-06-28T08:44:01Z
Abstract: 摘要:衛載合成孔徑雷達(SAR)是目前常用來觀測海洋內波的工具之一。衛星 能夠偵測到水下的現象,尤其是內波波前的形狀、傳播、波長等,是因為 水下的現象造成流速分佈不均勻,在水體表面產生流速輻合與輻散的現象 所導致。水面流速輻合的地方是聚集表面波的地方,如內波發生時的前波 面是流速輻合區,造成小波聚集,表面粗糙度增加,雷達背向散射強烈, 在SAR 影像造成亮帶;反之,內波的後波面是流速輻散區,在影像上形成 暗帶。雷達電磁波和表面小波之間的作用關係?不同尺度小波(公分等級與 公尺等級)對雷達背向散射有何影響?是本群體計畫主要的研究目的。本子 計畫負責的部分是表面波譜的量測與分析。 內波發生時海水表面的微尺度波波長大約介於幾公分到數公尺長,這 種尺度的表面波難以利用現有的測波技術量測,尤其目前研究內波發生只 能藉由研究船進行觀測,因此如何在研究船上量測水面流速輻合/輻散區的 波譜特徵是本計畫重要的工作之一。本計畫的研究區域將設定在基隆海 域,基隆港外和基隆嶼之間海檻地形受潮流的作用下出現類似內波發生時 海表面輻合與輻散的現象,輻合帶出現明顯的激浪,此現場每日發生,且 位置幾乎不變(內波的輻合輻散區會快速傳遞),是本課題研究最良好的地 點。本計畫改良在實驗室造波水槽中量測波浪的電容式波高計,使其可以 在研究船上進行觀測,第一年的計畫已經將波譜儀改良至第三代,大致上 已經可以正常運作。計畫第二年度將持續現場量測試驗的進行,搭配其它 子計畫,設計現場試驗,量測表面流速輻合/輻散區在時間上(發生之初、 最強烈時與衰落時)與空間上(平浪區、激浪區與交界面)的波譜。波譜的計 算本文採用傅立葉轉換計算一維波譜,利用小波轉換計算時頻譜。藉由表 面波譜的量測與分析,配合其它子計畫針對本區SAR影像以及光學影像的 分析,期能對衛星SAR影像反應海表面輻合現象的現場有所瞭解。 本計畫完成後預期可以對於內波發生處,海水表面輻合/輻散區的波譜 特性有更多的掌握,根據波譜在時間與空間上的演變分析,以及同步海 流、光學影像以及雷達影像的分析,增加內波表面徵兆造成雷達背向散射 機制的瞭解。
abstract:Satellite images (such as SAR image) are often used for Internal Waves (IW) observation. Surface current distortion to induce convergence and divergence areas in the surface is the main mechanism for SAR to detect the location of IW. In the forward slope, the surface water converges as well as divergence happens in the backward slope when an IW passes. In the convergence surface, sea surface roughness is high therefore a white belt is visible in the SAR image. SAR emits EM wave in C band. The resonance ocean waves should be few centimeter. However, we see the wavelengths within the rough area when IW passes are not in the same scale of resonance waves. The mechanism of how SAR images IW surface is valid to be studied. It is the main purpose of this group project. In this sub‐project, the objective is to measurement and analysis of wave spectra in the rough surface (convergence area). The first target of this project is to design a device to measure the surface wave spectrum from a research vessel. In the first year of this project, a shipboard wave spectrum detection system (SWASD) using the capacitance transducer was developed. It was examined many times on research vessels to verify its capability for experiment. This project is the second phase. The SWASD is going to be further improved to be more automatic for field measurement. The field experiment will be carried out at the Keelung sill area because of the daily surface water convergence phenomenon happens due to interaction of strong tidal current and rapid change of bottom topography. It is designed to measure the temporal variations of wave spectra during the period when convergence phenomenon happens (from start, grow up, strongest and decay) over Keelung sill. In addition, spatial variations will also be measured at convergence and divergence areas respectively. Fourier and Wavelet transformations will be used to estimate the wave spectra. By combination of the measurement and analysis results of wave spectrum at water surface convergence/divergence areas in this sub‐project and simultaneously measurements within other sub‐projects, it is helpful to understand the mechanism of SAR images sea surface convergence phenomenon. This is helpful to know more on the IW images of SAR.
Relation: NSC97-2611-M019-008
URI: http://ntour.ntou.edu.tw/ir/handle/987654321/11722
Appears in Collections:[海洋環境資訊系] 研究計畫

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