The application of remote sensing to the measurement of marine particle sizes and their relation to turbulence

悬浮在海水中的微小颗粒很重要，因为它们会衰减阳光，并在其表面传输包括污染物在内的物质。这些颗粒还通过将碳从陆地和大气输送到深海海底，在碳循环和气候变化中发挥作用。这些过程中的每一个都受到颗粒大小的影响：小颗粒比大颗粒更善于散射光线，而大颗粒下沉得更快。因此，为了对这些粒子的行为和影响进行建模，我们需要更多地了解它们的大小以及这种变化在地理上和时间上的变化方式。在这项提议中，我们的目标是开发一种利用卫星数据测量海洋颗粒大小的新方法。这将具有一个优势，即可以在大范围内几乎瞬间绘制出颗粒大小的地图--例如整个爱尔兰海--并且可以观察到随着时间的变化。有局限性：只有海面附近的颗粒大小才能确定，而且只有在无云的天空下才能确定；即便如此，这也是向前迈出的一大步。这项技术的原理是，给定浓度的颗粒对光的散射随着颗粒变小而增加。因此，对浓度和散射的同时测量(两者都可以用目前可用的卫星图像实现)可以用来推算平均颗粒大小。为了实现这种方法，我们需要在海上进行测量，以建立单位浓度散射与颗粒大小之间的关系。将使用传统的光学仪器测量散射，并将使用新的全息相机来测量颗粒大小。该相机可以对尺寸从20微米到7毫米的颗粒形成清晰的聚焦图像。通过使用其中两个直角的摄像头，可以形成颗粒的三维图像，并可以记录颗粒的形状和大小。小于20微米的颗粒将使用商用仪器(LISST 100B)进行测量，该仪器可以测量到1微米(大约是光波长的两倍)的颗粒，但不具备相机的成像能力。这些测量将使我们能够建立从太空遥感平均颗粒尺寸所需的关系，并了解这种关系是否以及如何依赖于颗粒形状和密度。众所周知，悬浮在海面上的颗粒的大小取决于当时的湍流度。在一定程度上，湍流将粒子聚集在一起，它们粘在一起形成粒子群，称为絮状物。然而，更大的湍流水平往往会扰乱絮团。我们想通过在测量颗粒大小的同时测量湍流来检验这些想法。湍流将使用声学多普勒仪(ADCP和ADV)和湍流剪切探头(Fly)进行测量。它将有可能在与全息相机成像的水体积完全相同的水中测量湍流，从而产生独特的数据集。我们想要在两个固定的地点进行这些测量，在海床上的框架上，在不同的环境中-一个是中等湍流，另一个是高度湍流。此外，我们还想在一艘游轮上进行测量，该游轮访问了一系列颠簸程度不同的地点。巡航还将使我们能够测量混合和分层水中颗粒大小和湍流的垂直分布。最后，还有关于活的、游泳的粒子对海洋湍流的贡献的问题。有人认为，在低湍流度和高稳定度的区域，如海洋温跃层，浮游动物和小鱼的运动对局地湍流的产生有重要的贡献。这一贡献目前只是推测，但我们同时拍摄的粒子图像和湍流测量结果将使这一想法得到验证。

Microscopic particles suspended in seawater are important because they attenuate sunlight and transport materials, including pollutants, on their surfaces. The particles also play a role in the carbon cycle and climate change by transporting carbon from the land and the atmosphere to the floor of the deep ocean. Each of these processes is influenced by the size of the particles: small particles are better at scattering light than large ones, and large particles sink faster. To model the behaviour and impact of these particles we therefore need to know more about their size and the way this varies geographically and with time. In this proposal we aim to develop a new way of measuring the size of marine particles by using satellite data. This will have the advantage that particle size could be mapped virtually instantaneously over large areas - the whole of the Irish Sea, for example - and changes with time could be observed. There are limitations: only the size of particles near the sea surface could be determined, and only under cloud-free skies; even so this would be a big step forward. The principle of the technique is that the scattering of light by a given concentration of particles increases as the particles become smaller. Simultaneous measurements of concentration and scattering (both of which can be achieved with currently available satellite imagery) can therefore be used to derive an estimate of mean particle size. To implement this method, we need to make measurements at sea to develop a relationship between scattering per unit concentration and particle size. Scattering will be measured using conventional optical instruments, and a new holographic camera will be used to measure particle size. The camera can form sharp focused images of particles of size from 20 microns up to 7mm. By using two of these cameras at right angles, three-dimensional images of the particles can be formed and the shape of the particles as well as the size can be recorded. Particles smaller than 20 microns will be measured using commercially available instruments (LISST 100B) which can measure particles down to 1 micron (about twice the wavelength of light) but don't have the imaging capability of the camera. These measurements will allow us to establish the relationship needed for the remote sensing of mean particle size from space, and to see if and how the relationship depends on particle shape and density. It is known that the size of the particles suspended in the sea depends on the prevailing level of turbulence. To a certain extent, turbulence brings particles together and they stick to form particle groups called flocs. Greater levels of turbulence, however, tend to disrupt the flocs. We would like to test these ideas by measuring turbulence at the same time as particle size. Turbulence will be measured with acoustic Doppler instruments (ADCP and ADV) and with a turbulence shear probe (FLY). It will be possible to measure turbulence in exactly the same volume of water as the holographic camera is imaging, thus producing a unique data set. We would like to make these measurements at two fixed sites, on frames lying on the sea bed, in contrasting environments - one of medium, the other of high turbulence. In addition we would like to make the measurements on a cruise visiting a range of sites of contrasting levels of turbulence. The cruise will also enable us to measure vertical profiles of particle size and turbulence in mixed and stratified water. Finally, there are questions about the contribution of living, swimming particles to turbulence in the sea. It has been suggested that, in regions of low turbulence and high stability, such as the oceanic thermocline, the motion of zooplankton and small fish can make a significant contribution to local turbulent production. This contribution is presently speculative, but our simultaneous images of particles and measurements of turbulence will enable this idea to be tested.