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有什么错误在水深观测植被的存在?

我们如何能确定与水深测量相关的错误,当我们在淹没植被调查?假设我们使用单梁回声测深仪伊的补丁,预期的错误是什么,我们怎么能确定呢?

回答

在评论中指出,这实际上是一个比看起来更复杂的问题。回答完全需要一个非常复杂和技术讨论单光束测量固有的错误及其原因(水速度,反映边坡高度递送的富烃世淤泥,和其他类似的并发症)。我将跳过那些topics-thankfully,思考,仅仅关注OP的问题错误伊海草可能会引入一个假想的singlebeam调查。因此这可能是部分答案。假设您正在使用一个singlebeam仪器相当窄脉冲角,像3º。(你的船应该不是卷太多这种狭窄的光束,但它会给高分辨率)。你测量的殖民地伊在平坦的海底。伊叶子密度相当类似的水柱。取决于你是声音的频率测量,你可以得到一个ping稍微不同的形状从测量的“裸露的地面”。至少在理论上,这是由于轻微的变化水之间的密度列和伊叶片造成少量的声波的反射和折射之前点击根垫和沉积物。 Just for imagination's sake, I've included the conceptual "bare ground" model below. > ![Behavior of P-waves and S-waves at a impedance change boundary][1] > > Behavior of P-waves and S-waves at a impedance change boundary. Image reproduced from [Dragoset, B., *A historical reflection on reflections*, The Leading Edge, 2005, v. 24, p. S46-S71][2], Box 1. A good singlebeam acquisition program will allow you to choose the method of bottom tracking. Often these methods are not associated with the first return but rather the "strongest" part of the first return within some specified distance from the last known bottom position. This allows the minimization of error created by, for example, fish swimming in the path of the beam (see image below), and also the weaker first returns of soft vegetation. > ![Fish in the water column as seen during a singlebeam survey][3] > > Fish in the water column as seen on a singlebeam survey. A red band indicates the strongest return amplitude. An acquisition program would likely classify the bottom at or near the top of the red band. Image reproduced from the [University of New Hampshire Ongoing Education website][4]. So, if we assume that the acquisition program's bottom tracking capability is acceptable, the errors that Posidonia's leaves introduce will be minuscule, because the leaves do not present a large change in impedance and thus will not reflect much of the beam. You're left with deciding whether or not you want to classify the "bottom" of the water column as Posidonia's root mat, which may be several inches thick in a large colony, or the top of the sediment below. This is where your uncertainty will likely lie. What I don't know, and what may be difficult to figure out without some rather clinical testing, is whether or not the root mat provides a strong-enough first return to trigger the bottom tracking. I suspect it would, but I can't say that with any confidence without looking at a controlled test survey. I imagine companies like [Odom][5] and [Kongsberg][6] do this regularly and might be able to give you a more specific answer. Tobbe also correctly notes that lower frequencies won't be affected as much by vegetation as higher frequencies. If you were going to try to run a bathymetric survey over Posidonia—or any area with high concentrations of seafloor plant life—you would want to consider using a device capable of lower frequency surveys...at the cost of diminishing your resolution. [1]: http://i.stack.imgur.com/gxJSr.gif [2]: http://tle.geoscienceworld.org/content/24/Supplement/S46.full [3]: http://i.stack.imgur.com/MvEfG.jpg [4]: http://ccom.unh.edu/gebco2013/data_processing.html [5]: http://odomhydrographic.com/ [6]: http://www.km.kongsberg.com/

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