Quantifying and characterizing suspended sediment is essential to successful monitoring and management of estuaries and coastal environments. To quantify suspended sediment, optical and acoustic backscatter instruments are often used. Optical backscatter systems are more sensitive to mud particles (<63 μm) and flocs, whereas acoustic backscatter systems are more responsive to larger sand grains (>63 μm). It is thus challenging to estimate the relative proportion of sand or mud in environments where both types of sediment are present. The suspended sediment concentration measured by these devices depends on the composition of that sediment, thus it is also difficult to confidently measure concentration with a single instrument when the composition varies and extensive calibration is not possible. The objective of this paper is to develop a methodology for characterizing the relative proportions of sand and mud in mixed sediment suspensions by comparing the response of simultaneous optical and acoustic measurements. We derive a sediment composition index (SCI) that is used to directly predict the relative fraction of sand in suspension. Here, we verify the theoretical response of these optical and acoustic instruments in laboratory experiments and successfully apply this approach to field measurements from Ameland ebb-tidal delta (the Netherlands). Increasing sand content decreases SCI, which was verified in laboratory experiments. A reduction in SCI appears during more energetic conditions when sand resuspension is expected. Conversely, the SCI increases in calmer conditions when sand settles out, leaving behind mud. This approach provides crucial knowledge of suspended sediment composition in mixed sediment environments.

中文翻译：

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使用组合光学和声学测量表征沿海和河口环境中沙子和泥浆悬浮液的成分

悬浮沉积物的量化和表征对于河口和沿海环境的成功监测和管理至关重要。为了量化悬浮沉积物，经常使用光学和声学反向散射仪器。光学背向散射系统对泥粒 (<63 μm) 和絮凝物更敏感，而声学背向散射系统对较大的沙粒 (>63 μm) 更敏感。因此，在存在两种类型的沉积物的环境中估计沙子或泥土的相对比例具有挑战性。这些设备测量的悬浮泥沙浓度取决于该泥沙的成分，因此当成分变化且无法进行广泛校准时，也很难用单一仪器可靠地测量浓度。本文的目的是通过比较同步光学和声学测量的响应，开发一种表征混合沉积物悬浮液中沙子和泥土的相对比例的方法。我们推导出一个沉积物成分指数 (SCI)，用于直接预测悬浮沙子的相对比例。在这里，我们在实验室实验中验证了这些光学和声学仪器的理论响应，并成功地将这种方法应用于 Ameland 潮汐三角洲（荷兰）的现场测量。增加砂含量会降低 SCI，这在实验室实验中得到了验证。当预计沙子重新悬浮时，在能量更高的条件下会出现 SCI 的减少。相反，当沙子沉降并留下泥浆时，SCI 在较平静的条件下增加。