A new perspective on marine life
Interview: Dr David McKee…
A new perspective on marine life
Interview: Dr David McKee
Why is a physicist involved in Scotland's most ambitious project to advance marine science? Why does he “sail the seven seas,” analysing samples of water? And why does he want to send new spectral cameras hundreds of miles into Space to find out what is happening under the surface of the oceans below?
Dr David McKee describes his job as “measuring the colour of the sea.” But this simple description disguises the fact that McKee is grappling with some highly complex scientific problems, using optical sensors to reveal what is happening in the marine environment – focusing on very tiny particles (including organic material and minerals) floating in the water, and ultimately building up a picture of the oceans which shows the carbon cycle in action and helps to monitor possible climate change.
McKee explains that he is trying to understand the ocean on a wide range of scales, from the microscopic to full ocean basins, using remote sensing data. The methods employed are very similar to those used in astronomy to analyse the properties of planets and stars by studying the light they emit. Sensors on satellites orbiting Earth are turned in the other direction to analyse the photons which reflect from the surface. By creating images at different colours (wavelengths), and removing the effects of the Earth’s atmosphere, it is possible to build up maps of the materials that cause the colour of the ocean to change, including living organisms such as phytoplankton, as well as minerals and other dissolved materials. McKee also uses underwater optical sensors to observe how different particles respond to the light – e.g. absorption, fluorescence, reflectance and scattering, and can use this information to provide “ground truth” (or sea truth) for the remote sensing data. This is what McKee means when he says he “measures colour” to identify the particles in water.
To explain the different scales involved, McKee displays a time-lapse image of the “Blue Planet” built up from satellite data, showing photosynthesis on a planetary scale, then a picture of the microscopic phytoplankton so small we can't even see individual cells without using microscopes. Soon, says McKee, his research will go down even further to the sub-micron level, examining particles less than a millionth of a metre across. McKee's work also concentrates on “optically complex shelf seas” such as the Bristol Channel, Irish Sea and Mediterranean, where there is a lot of interaction between “natural” processes and anthropogenic activity – e.g., fish farms and fisheries, plus agricultural and industrial pollution from rivers.
McKee, a Senior Lecturer in the Department of Physics at the University of Strathclyde in Glasgow, explains that a lot of his work is concerned with “error correction” – helping to understand what's going on in the ocean by pointing out that often, things are not quite what they seem. For example, NASA satellites take pictures of the Earth which appear to show large areas of algal bloom around the Irish Sea, by detecting or “measuring” the colour of the chlorophyll. According to images produced using standard algorithms, these blooms seem to occur even in winter, when there's virtually no growth at all. Worse, they also suggest that there are permanent blooms in major estuaries that, if true, would suggest that the rivers were being heavily polluted with excess nutrients. But when McKee and other scientists go out in boats and take samples to measure the presence of algae in the real world, they discover that the real concentrations are much less than the remote sensing data suggests. The standard algorithms were designed for deep, clear oceans.
But not all the oceans are like that – in the sea around Scotland, sediments are kicked up by winds and tides, and there are natural inputs from rivers, as well as from agricultural, industrial and urban sources. The traditional algorithms are badly affected by the presence of suspended sediments in shallow coastal seas, so McKee and his research group have come up with new solutions which help to correct this misleading impression. To see the true picture, the algorithms have to be adjusted to accommodate these additional effects. Ideally, says McKee, for every remote sensing image he'd like to produce an accompanying map of error distributions that would act as a “health warning.”
“It’s all a question of perspective,” says McKee. “There is a tendency to view satellite images as if they are maps, but what you see is not a map, it is a distribution of data points. And like all data, there are errors and we need to understand those errors and try to present them to users, so that they can get a better idea of what's really there.”
The only way to solve this problem is by boarding a vessel and sampling the water in situ, then using the results to recalibrate or fine-tune the satellite data, making allowances for seasonal variations. McKee explains: “We understand the physics of how the signal is generated, and the optical significance of what we observe (scattering, absorption and reflectance), so we can change the algorithm accordingly.” The raw data from the satellite sensors is exactly the same, but the way it is processed is different. But no matter how sophisticated the technology may become, there is no escape from field work in the real world below, determining “what’s in the water.”
The technology evolves...
Whilst optical sensors have evolved through the years, so have the platforms they are deployed from, going from ship-based sampling water at depth and mounting the sensors on fixed moorings, to piggybacking on remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), to using underwater “gliders” and remote-controlled aircraft and drones, as well as putting sensors in orbit – including the new generation of micro-satellites called CubeSats.
McKee is currently exploring how to work more closely with Glasgow-based CubeSat developer Clyde Space, and with other engineering and technology development groups in the central belt of Scotland. Whilst the big Space agencies still provide excellent data from conventional and massively expensive satellite systems, CubeSats offer the potential to expand the capabilities of sensors to entirely new levels, with “constellations of sensors” in Space sending back more data than ever before, using spectral cameras custom-built for dedicated tasks. “The images from NASA show one square kilometre per pixel,” says McKee, “but we need much finer detail in order to monitor sea-lochs, rivers and lakes.” Moreover, the CubeSat technology can be developed for a fraction of the cost of traditional spacecraft operations, opening the door to smaller organisations and nations taking on lead roles in Earth observation.
At the other end of the size scale, the group is starting to measure the optical properties of single cells and particles, using laser-based flow cytometry. This technology makes it possible to rapidly analyse thousands of particles per second, rather than laboriously counting them all one by one under a microscope. This will enable researchers to examine the whole population and analyse how different particles in the population interact with light and with each other. “This helps provide a context for the bulk optical measurements,” McKee says. “The physicists are interested in how the particles affect the optical signals, while the biologists are researching their impact on the ecosystem.”
The research group
McKee and his colleague, Professor Alex Cunningham, run the Marine Optics and Remote Sensing Laboratory, which is part of the Biomolecular and Chemical Physics Group at the University of Strathclyde, using light “to interrogate and understand fundamental processes in nature.” McKee and Cunningham focus on “radiance transfer in seawater, light utilisation by phytoplankton, optical monitoring of ecological processes, and remote sensing in the marine environment” – in other words, shining a light on what’s going on under the sea. The laboratory has received more than £1.1 million in funding from the Natural Environment Research Council (NERC), the Marine Alliance for Science and Technology for Scotland (MASTS), the Scottish Government and the European Space Agency.
Current research undertaken by the laboratory includes:
> Ocean colour remote sensing for optically complex natural water systems;
> Monitoring physical–biogeochemical interactions from space;
> Effect of multiple scattering on optical signals in the marine environment.
Before MASTS came onto the scene about five years ago, McKee’s research was funded by NERC and he was employed on a series of short-term contracts. MASTS funding helped to underwrite a Senior Lectureship at the University of Strathclyde that was awarded to McKee and provides significantly improved security of employment. “MASTS also provides an umbrella,” he says, “that encourages collaboration and helps us to go for joint funding, as well as share resources, expertise and training opportunities.” In McKee’s view, MASTS also encourages communication between researchers from different disciplines, and enables them to tackle much more complex problems, because the joint expertise of the alliance is greater than the sum of its parts. “Now that MASTS is better established”, says McKee, “it is starting to look at community projects that bring the broad range of expertise to bear on problems of national and international significance.”
A good example of a project where MASTS brings different scientists together is recent research into the Mingulay cold-water coral reef, which was discovered in 2003 near the outer Hebrides. The “MASTS Dynamics and Properties of Marine Systems” theme is attempting to assemble an interdisciplinary research team to develop our understanding of this important ecosystem. This includes experts on the biology of the corals, and mathematical modellers who can predict the current flows that determine the availability of nutrition for the corals. McKee hopes to contribute to this effort by using his optical techniques to assess the nature of the particulate material that the corals feed on.
Although much of their research is fundamental and curiosity-driven, McKee and his group are also interested in the practical impact that their technology can have. This could take the form of assessing the local impact of aquaculture, or using remote sensing to understand the distribution of basking sharks and where they are feeding. There are also potential industrial applications, including pipeline monitoring and assessing the impact of offshore marine renewables. In many cases, the demand for information in other areas stimulates and shapes the development of technology.
Remote sensing gives his work an international dimension, says McKee, but MASTS “helps to reinforce and anchor a local focus,” ensuring scientists make better use of the world-class expertise that is available closer to home. Sometimes, he adds, it’s possible for scientists to go to international conferences, only to discover that the partners they need actually work in the same building; but MASTS ensures that more researchers are better aware of resources in Scotland.
The collaborative ethos
McKee and his research group use optical sensors in orbit to show our planet breathing (there is as much photosynthesis going on in the sea as on land) and illuminate the impact of microscopic organisms that, added together, enable the planet to breathe, creating pictures which allow us to see at a glance what is happening across huge expanses of oceans – including what happens to carbon. But it is the collaboration with biologists, chemists and other disciplines, including areas such as economics and social sciences, that makes the research truly relevant to society.
“Physicists bring a very different perspective to marine science,” says McKee, “and different ways of analysing problems. Our focus on a rigorous physical approach, including the demand for uncertainty estimation, provides potential end-user communities with a better idea of the true capabilities and practical limitations of our data sets. Ultimately it’s the job of environmental scientists, such as ourselves, to provide better descriptions of the processes affecting the planet, to reduce the uncertainties in our models and to help decision makers understand the implications of future policies and actions.” It may be complex and challenging science, but along the way, McKee says he is lucky enough to get the chance to be not just a physicist but also part biologist, geologist, ecologist and chemist. “Doing all this and getting to sail the seven seas – it ain’t a bad life for a physicist,” says McKee.