Sentinel-2A dips its toe into the water

Detailed image of algal bloom in the Baltic Sea acquired by Sentinel-2A on 7 August 2015. Data courtesy of Copernicus Sentinel data (2015)/ESA.

Detailed image of algal bloom in the Baltic Sea acquired by Sentinel-2A on 7 August 2015. Data courtesy of Copernicus Sentinel data (2015)/ESA.

With spectacular images of an algal bloom in the Baltic Sea, ESA’s Sentinel-2A has announced its arrival to the ocean colour community. As we highlighted an earlier blog, Sentinel-2A was launched in June predominately as a land monitoring mission. However, given it offers higher resolution data than other current marine focussed missions; it was always expected to dip it’s toe into ocean colour. And what a toe it has dipped!

The images show a huge bloom of cyanobacteria in the Baltic Sea, with the blue-green swirls of eddies and currents. The image at the top of the blog shows the detail of the surface floating bloom caught in the currents, and there is a ship making its way through the bloom with its wake producing a straight black line as deeper waters are brought to the surface.

Algal bloom in the Baltic Sea acquired by Sentinel-2A on 7 August 2015. Data courtesy of Copernicus Sentinel data (2015)/ESA.

Algal bloom in the Baltic Sea acquired by Sentinel-2A on 7 August 2015. Data courtesy of Copernicus Sentinel data (2015)/ESA.

To the right is a wider view of the bloom within the Baltic Sea. The images were acquired on the 7th August using the Multispectral Imager, which has 13 spectral bands and the visible, which were used here, have a spatial resolution of 10 m.

The Baltic Sea has long suffered from poor water quality and in 1974 it became the first entire sea to be subject to measures to prevent pollution, with the signing of the Helsinki Convention on the Protection of the Marine Environment of the Baltic Sea Area. Originally signed by the Baltic coastal countries, a revised version was signed by the majority of European countries in 1992. This convention came into force into force on the 17th January 2000 and is overseen by the Helsinki Commission – Baltic Marine Environment Protection Commission – also known as HELCOM. The convention aims to protect the Baltic Sea area from harmful substances from land based sources, ships, incineration, dumping and from the exploitation of the seabed.

Despite the international agreements, the ecosystems of the Baltic Sea are still threatened by overfishing, marine and chemical pollution. However, the twin threats that cause the area to suffer from algal blooms are warm temperatures and excessive levels of nutrients, such as phosphorus and nitrogen. This not only contributes towards the algal blooms, but the Baltic Sea is also home to seven of the world’s ten largest marine dead zones due to the low levels of oxygen in the water, which prevent marine life from thriving.

These images certainly whet the appetite of marine remote sensors, who also have Sentinel-3 to look forward to later this year. That mission will focus on sea-surface topography, sea surface temperature and ocean colour, and is due to the launched in the last few months of 2015. It’s an exciting time to be monitoring and researching the world’s oceans!

Ocean Colour Partnership Blooms

Landsat 8 Natural Colour image of Algal Blooms in Lake Erie acquired on 01 August 2014. Image Courtesy of NASA/USGS.

Landsat 8 Natural Colour image of Algal Blooms in Lake Erie acquired on 01 August 2014. Image Courtesy of NASA/USGS.

Last week NASA, NOAA, USGS and the US Environmental Protection Agency announced a $3.6 million partnership to use satellite data as an early warning system for harmful freshwater algae blooms.

An algae bloom refers to a high concentration of micro algae, known as phytoplankton, in a body of water. Blooms can grow quickly in nutrient rich waters and potentially have toxic effects. Shellfish filter large quantities of water and can concentrate the algae in their tissues, allowing it to enter the marine food chain and potentially causing a risk to human consumption. Blooms can also contaminate drinking water. For example, last August over 40,000 people were banned from drinking water in Toledo, Ohio, after an algal bloom in Lake Erie.

The partnership will use the satellite remote sensing technique of ocean colour as the basis for the early warning system.  Ocean colour isn’t a new technique, it has been recorded as early as the 1600s when Henry Hudson noted in his ship’s log that a sea pestered with ice had a black-blue colour.

Phytoplankton within algae blooms are microscopic, some only 1,000th of a millimetre in size, and so it’s not possible to see individual organisms from space. Phytoplankton contain a photosynthetic pigment visible with the human eye, and in sufficient quantities this material can be measured from space. As the phytoplankton concentration increases the reflectance in the blue waveband decreases, whilst the reflectance in the green waveband increases slightly. Therefore, a ratio of blue to green reflectance can be used to derive quantitative estimates of the concentration of phytoplankton.

The US agency partnership is the first step in a five-year project to create a reliable and standard method for identifying blooms in US freshwater lakes and reservoirs for the specific phytoplankton species, cyanobacteria. To detect blooms it will be necessary to study local environments to understand the factors that influence the initiation and evolution of a bloom.

It won’t be easy to create this methodology as inland waters, unlike open oceans, have a variety of other organic and inorganic materials suspended in the water through land surface run-off, which will also have a reflectance signal. Hence, it will be necessary to ensure that other types of suspended particulate matter are excluded from the prediction methodology.

It’s an exciting development in our specialist area of ocean colour. We wish them luck and we’ll be looking forward to their research findings in the coming years.

A Few Days In Portland: Phytoplankton, Sea Ice and Cake!

Early morning photograph of Portland, Maine

Early morning photograph of Portland, Maine

As I talked about in my last blog, this week I’m attending the Ocean Optics XXII Conference in Portland, Maine in the USA. I arrived last Thursday and spent the weekend at a two day pre-conference meeting entitled ‘Phytoplankton Composition From Space’; where we discussed techniques for mapping phytoplankton – the microscopic plants in the ocean.

The smallest phytoplankton taxa (group) are the single celled cyanobacteria known as blue-green algae, they are an ancient life form with a fossil remains of over 3.5 billion years old. They can be mapped from space using ocean colour satellites which measure a signal based on the scattering and absorption of light within the ocean. This enables Earth observation to map the total biomass, via the concentration of the main pigment that’s normally Chlorophyll, and also get a glimpse into which taxa are present.

Understanding the concentration, and diversity, of phytoplankton is valuable as they play a key role in climate processes by absorbing the greenhouse gas carbon dioxide. In addition, they are the very essence of the bottom of the food chain, as they are eaten by zooplankton, who in turn are eaten by small fish and so on. Therefore, significant changes in the concentration or diversity of phytoplankton may have ripple effects through the aquatic food chain. The film Ocean Drifters provides an overview of the role of plankton in the ocean.

The conference itself began on Monday and we’ve had a number of interesting and varied presentations, but I’ve particularly enjoyed two plenary sessions. The first was by Don Perovich, of the Thayer School of Engineering looking at the impact of sunlight on sea ice in the artic. The brightness of sea ice determines the amount of light reflected back to space. If the ice is older, and hence snow covered, then it’s bright white whilst ice that’s melting is much darker due to the pools of water and so absorbs more sunlight. Therefore, there is a positive link between melting ice causing ice to melt quicker. In the Artic, sea ice reaches a minimum in September and causes an increase in melting. There is a scientific analysis on Arctic sea ice conditions here.

The second plenary was given by Johnathan Hair from NASA Langley Research Centre, presenting a paper co-authored with his colleague Yongziang Hu and Michael Behrenfeld from Oregon State University. It focussed on using lasers for mapping vertical profiles throughout the water column from space and applications for inland waters, and how this might be used in global ocean plankton research. Regular readers of the blog will know this is topic is something that particularly interests me, and I have previously written about the subject.

Tuesday morning was eventful, as the conference venue was evacuated just as the first session was starting, due to a strong smell of gas. I took the unexpected networking opportunity, and to catch up with one of my former colleagues over a coffee. Thankfully, we were let back into the venue a couple of hours later, and everything went ahead with a bit of rescheduling. My plenary session on Crowdfunding Ocean Optics went ahead in the afternoon, and seemed to generate a good level of interest. I had lot of questions within the session, and a number of people sought me out during the rest of the day to discuss the idea and the project.

I’ve really enjoyed my time in Portland, and have found a fantastic coffee shop and bakery – Bam Bam Bakery on Commercial Street – which I highly recommend! I’m looking forward to the rest of the week.