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Measuring Wave Fields Using a Marine Radar
Marine radar;wave fields;radar images: transfer functions;empirical constants;significant wave heights
|Issue Date: ||2017-06-16T06:42:03Z
|Abstract: ||摘要:利用雷達波探測海面波場的特性有許多優點。譬如說，和（傳統的）量測法－如波高計、浮標、流速儀等－比起來，它可以一次獲得（較廣大）『面』的資訊，而不是局限在一個（或數個）點；另外，雖然同樣是屬於所謂的『遙測』，雷達波也比應用光學原理的遙測法較不受天候的影響。不過，由於衛星運轉軌道所需要的時間較長，這使得藉由雷達影像來量測即時海象變得有點不切實際。相對地來說，利用船用雷達就有它的優勢了。它除了能有比直接量測法量測到較廣大的面外，更有同樣較不受天候影響，却比衛星雷達購置費用低廉許多的特點。不過，由於它是屬於『間接量測』，所得到的結果並不是真實的物理量，而必需藉著一些所謂的『轉換函數』(Transfer function)纔能利用這些量測結果估算所要量測的物理現象。海洋大學從數年前開始分析台北港區雷達影像，並藉與在附近觀測樁的實測資料比對，判斷分析結果的好壞。本文簡單地介紹一下目前的研究成果。從本文可以發現，雖然有部份估算結果與實測資料有一些明顯的差異，兩者的整體趨勢則頗近似。
Abstract:There are many advantages in using radio-electromagnetic waves to explore the characteristics of ocean surface. Like all remote sensing techniques, a rather large area can be covered simultaneously than using those more traditional ”point” instruments, such as wave gauges, buoys, as well as current meters. Remote sensing using radio waves are relatively weather independent, and this makes them more appealing than using passive optical measuring devices. On the other hand, satellites have a rather long period of orbiting, and the devices on board expansive. In searching for devices to monitor the sea surface, say on an hourly basis, researchers have used marine radar. Being inexpensive and weather-independent, it can also cover a relatively large area of the sea surface. It is no wonder that there has being researches conducted all over the world for using marine radar to monitor the sea surface. Unlike direct measurements, remote sensing, being indirect, does not measure the real changes of those being measured. The results of the measurements must be connected to physical realities using some ”transfer functions”. These are established through comparisons with the so-called ”ground truth”, which being usually measured results on site.The Department of Harbour & River Engineering of the National Taiwan Ocean University has started analyzing radar images some years ago. Radar images of areas around Taipei Harbour were used for the analyses, and results compared with on site measurements. In this paper we show some of our present results. It is shown that, although discrepancies between measured and estimated wave heights exists, the overall trend of the two results are very much similar. Possible reasons for the inconsistencies of the two results are also given.
|Relation: ||11(1), pp.31-55|
|Appears in Collections:||[河海工程學系] 期刊論文|
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