Development of a laser-based sea-ice chlorophyll sensor

我们想建造一种科学仪器，可以测量海冰下面生长的藻类的数量。海冰藻类是许多极地海洋食物网的基础，但由于采样困难，缺乏关于藻类丰度中尺度(数十至数百公里)变异性的数据。这阻碍了理解海冰生态系统功能的努力，以及对正在进行的海冰融化(由于气候变暖)可能产生的后果的预测。目前，测量海冰藻类丰度的最可靠方法是从上方在冰层上钻洞并收集藻类。这是劳动密集型的、耗时的，也不是没有风险的。在过去10年左右的时间里，自主水下机器人(AUV；本质上是一种无人驾驶的遥控潜水器)技术已经成熟，以至于这些潜水器可以在海冰下完成(数十至数百公里)长期任务，同时收集正在进行的数据：我们使用AUV对海冰下的磷虾进行超声测深仪调查。我们现在想使用AUV来调查海冰藻类，并在这里提议建造一台基于激光的仪器来进行藻类测量。该装置基本上是通过测量从海冰底部反射回来的光量来工作的。我们希望在藻类的数量(实际上是光合作用色素‘叶绿素’的数量)和反射的光量之间存在数量关系。在初步测量中，我们已经看到裸露的冰反射激光的方式与藻类栖息的冰不同，因此已经有一些实际证据表明这种方法应该是可行的。此外，还有大量关于藻类对不同波长的光的反射率的公开信息。我们将用这一理论来指导仪器的发展。该仪器将由一支才华横溢的工程师和技术人员组成的团队组装，他们拥有在恶劣环境中开发应用激光的丰富经验。一旦原型仪器建成，我们将在德国的一个实验设施(基本上是一个海冰水族馆)中，在海冰上生长的海冰藻类上对其进行测试。我们将测量不同波长(不同颜色；蓝色、绿色等)的激光的反射率，并构建叶绿素浓度与反射率之间的关系曲线。如果原型仪器成功，我们将再次提出拨款申请，在北极和南极的海冰下的AUV上部署一个坚固的版本，以进行生态调查。

We want to build a scientific instrument that can measure the amount of algae growing on the underside of sea ice. Sea-ice algae form the base of many polar marine foodwebs, but data on the mesoscale (tens to hundreds of km) variability in the abundance of algae are lacking because of sampling difficulties. This is hampering efforts to understand sea-ice ecosystem function, and predictions of consequences that ongoing sea-ice melt (due to climatic warming) might have. At present the most reliable way to measure sea-ice algal abundance is to drill holes through the ice from above and collect the algae. This is labour intensive, time consuming and not without risk. In the past 10 years or so autonomous underwater vehicle (AUV; essentially an unmanned, remotely operated submarine) technology has matured to the extent that these vehicles can complete extended (tens to hundreds of km) missions under sea ice, collecting data underway as they do so: we have used AUVs to conduct echosounder surveys of krill under sea ice. We now want to use AUVs to survey sea ice algae, and propose here to build a laser-based instrument to make the algal measurements. The device will basically work by measuring the amount of light reflected back from the underside of sea ice. We expect a quantitative relationship to exist between the amount of algae present (actually the amount of the photosynthesis pigment 'chlorophyll') and the amount of light reflected. In preliminary measurements we have already seen that bare ice reflects laser light differently than ice colonized by algae, so have some practical evidence already that the approach should work. In addition, there is a wealth of published information on the reflectance of light at various wavelengths by algae. We will use this theory to guide instrument development. The instrument will be assembled by a team of talented engineers and technicians who have much experience developing lasers for applied use in hostile environments. Once a prototype instrument is built, we will test it on sea-ice algae grown on sea ice in an experimental facility in Germany (essentially a sea-ice aquarium). We will make measurements of reflectance of laser light of various wavelengths (different colours; blue, green etc) and construct curves showing relationships between chlorophyll concentration and % reflectance. If the prototype instrument works, we will write another grant application for funds to deploy a robustly-housed version on AUVs under sea ice in the Arctic and Antarctic to pursue ecological investigations.