Nautical Studies

about Marine Navigation & Technology

Can a buoy help in setting up a radar properly? (可以利用導航標調教雷達嗎?)

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Navigation buoys may be considered as an object to tell if a radar system is properly setup. It has been suggested that it can be considered properly setup and tuned if buoys can be seen on-screen. Is it a reliable mean?

The reflective quality of a radar object depends on numerous factors such as material, size and shape. Amongst the others, they affect the echoed strength and returned direction of radar pulses.

Navigational marks are normally made with steel. In the contrary, those sampan and fishing boats in the picture are constructed with fibre-glass and wood. The reflective quality of these sampan and fishing boats are far inferior to those of steel navigational buoys. The echoes strength of these sampan and fishing boats should be much weaker than those of buoys.

As illustrated, a navigational buoy on the left is not a small object in comparison to sampan and fishing boats. Buoys are taller than most of the small boats in the photo. Apparently, the navigational buoy should have greater chance in reflecting detectable signals.

It may be argued that a can or cone shaped buoy is a poor radar object due to its rounded structure. Except the base that provides buoyancy, a buoy is normally made out of steel frame. Very often, radar reflector is fitted on the top. It appears to be a conspicuous radar object.

In fact, navigational buoys are designed to be picked up with eyes as well as by radar at a reasonable distance. Navigational marks are rather good radar objects in comparison to small boats. Apparently, the detection of navigational buoys will not assure the signals echoed from small objects such as sampan can be detected.

導航標可能被視作一個用來判斷雷達系統是否正確調教的功具,認為如:浮標可以在屏幕上看到時,就代表該雷達已適當地調教,這是一個可靠的方法嗎?

雷達目標的反射質量取決於很多因素,例如目標的物料,尺寸和形狀等,它們都影響雷達回波的強度及方向。

導航標通常是利用鋼鐵製造的,而那些如圖片中的舢舨及漁船就多以纖維或木材製造,這些物料的反射質量都遠不如鋼鐵,這些舢舨及漁船的回波強度理應大大低於那些浮標所反射的回波。

如圖片上所示,相比起舢舨及漁船,位於左邊的導航標不是一個小的目標。導航標比大部分在照片中的小船都要高,顯然,導航標應該有更大機會成功反射雷達的探測信號。

有人可能認為,浮標是筒形或錐形的,其圓形的結構令它成為一個差勁的雷達目標。細觀一般導航標的結構,除基本提供浮力的部份外,其他部份多是以鋼鐵製造的框架構成,很多時候,頂部更會裝上雷達反射器,這些都會令導航標成為是一個比較突出的雷達目標。

在一個合理的距離內,導航標是需要設計成可似被眼睛及雷達都可以偵測到的目標,跟小型船隻相比,導航標應該是一個比較好的雷達目標。顯然,在雷達上檢測到導航標並不能保證其他小目標亦可以被檢測出來的。

Written by Bruce Chun

June 10, 2010 at 11:25

Posted in Radar Operation

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