Monitoring ocean acidification from space

Enhanced pseudo-true colour composite of the United Kingdom showing coccolithophore blooms in light blue. Image acquired by MODIS-Aqua on 24th May 2016. Data courtesy of NASA.

Enhanced pseudo-true colour composite of the United Kingdom showing coccolithophore blooms in light blue. Image acquired by MODIS-Aqua on 24th May 2016. Data courtesy of NASA.

What is ocean acidification?
Since the industrial revolution the oceans have absorbed approximately 50% of the CO2 produced by human activities (The Royal Society, 2005). Scientists previously saw this oceanic absorption as advantageous, however ocean observations in recent decades have shown it has caused a profound change in the ocean chemistry – resulting in ocean acidification (OA); as CO2 dissolves into the oceans it forms carbonic acid, lowering the pH and moving the oceans into a more acidic state. According to the National Oceanic Atmospheric Administration (NOAA) ocean pH has already decreased by about 30% and some studies suggest that if no changes are made, by 2100, ocean pH will decrease by 150%.

Impacts of OA
It’s anticipated OA will impact many marine species. For example, it’s expected it will have a harmful effect on some calcifying species such as corals, oysters, crustaceans, and calcareous plankton e.g. coccolithophores.

OA can significantly reduce the ability of reef-building corals to produce their skeletons and can cause the dissolution of oyster’s and crustacean’s protective shells, making them more susceptible to predation and death. This in turn would affect the entire food web, the wider environment and would have many socio-economic impacts.

Calcifying phytoplankton, such as coccolithophores, are thought to be especially vulnerable to OA. They are the most abundant type of calcifying phytoplankton in the ocean, and are important for the global biogeochemical cycling of carbon and are the base of many marine food webs. It’s projected that OA may disrupt the formation and/or dissolution of coccolithophores, calcium carbonate (CaCO3) shells, impacting future populations. Thus, changes in their abundance due to OA could have far-reaching effects.

Unlike other phytoplankton, coccolithophores are highly effective light scatterers relative to their surroundings due to their production of highly reflective calcium carbonate plates. This allows them to be easily seen on satellite imagery. The figure at the top of this page shows multiple coccolithophore blooms, in light blue, off the coast of the United Kingdom on 24th March 2016.

Current OA monitoring methods
Presently, the monitoring of OA and its effects are predominantly carried out by in situ observations from ships and moorings using buoys and wave gliders for example. Although vital, in situ data is notoriously spatially sparse as it is difficult to take measurements in certain areas of the world, especially in hostile regions (e.g. Polar Oceans). On their own they do not provide a comprehensive and cost-effective way to monitor OA globally. Consequently, this has driven the development of satellite-based sensors.

How can OA be monitored from space?
Although it is difficult to directly monitor changes in ocean pH using remote sensing, satellites can measure sea surface temperature and salinity (SST & SSS) and surface chlorophyll-a, from which ocean pH can be estimated using empirical relationships derived from in situ data. Although surface measurements may not be representative of deeper biological processes, surface observations are important for OA because the change in pH occurs at the surface first.

In 2015 researchers at the University of Exeter, UK became the first scientists to use remote sensing to develop a worldwide map of the ocean’s acidity using satellite imagery from the European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) satellite that was launched in 2009 and NASA’s Aquarius satellite that was launched in 2011; both are still currently in operation. Thermal mounted sensors on the satellites measure the SST while the microwave sensors measure SSS; there are also microwave SST sensors, but they have a coarse spatial resolution.

Future Opportunities – The Copernicus Program
The European Union’s Copernicus Programme is in the process of launching a series of satellites, known as Sentinel satellites, which will improve understanding of large scale global dynamics and climate change. Of all the Sentinel satellite types, Sentinels 2 and 3 are most appropriate for assessment of the marine carbonate system. The Sentinel-3 satellite was launched in February this year andwill be mainly focussing on ocean measurements, including SST, ocean colour and chlorophyll-a.

Overall, OA is a relatively new field of research, with most of the studies being conducted over the last decade. It’s certain that remote sensing will have an exciting and important role to play in the future monitoring of this issue and its effects on the marine environment.

Blog written by Charlie Leaman, BSc, University of Bath during work placement at Pixalytics.

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!

Month on the World’s Oceans

San Francisco USA, Pseudo-true colour image. Landsat 8 data courtesy USGS/NASA/ESA

San Francisco USA, Pseudo-true colour image. Landsat 8 data courtesy USGS/NASA/ESA

June’s been a really busy month for me on the world’s oceans. I’ve not actually been out on the water, but flying over it having attended both the World Ocean Summit and the International Ocean Colour Science (IOCS) meeting. Both of these events focussed on the oceans, although they had very different participants and perspectives. In addition, the 8th June was also World Oceans Day and had the theme ‘Healthy Oceans, Healthy Planet’.

The World Ocean Summit, organised by The Economist, took place at the start of June in Cascais, Portugal. It focused on the development of the blue economy, with most of the participants from governments or non-profit non-governmental organizations. There were a number of talks highlighting the potential innovation opportunities the world’s ocean might offer, and the policy and worldwide governance framework needed. Throughout the summit, there was a repeatedly voiced concern over the state of the world’s oceans, and the serious peril and decline it’s in. Whilst many large organisations are now looking to exploit the oceans, many local communities have been doing this for years and they are seeing changes and challenges. The oceans are an integral part of Earth’s ecosystem, and without them we could not survive on this planet. The resources are potentially huge, but tapping into these requires a co-ordinated bottom up approach. Otherwise we risk damaging the ocean and our own existence.

My second major event was IOCS last week in San Francisco, and as the name suggests the meeting focused on mapping and understanding the ocean through the use of ocean colour remote sensing i.e., detecting and quantifying what causes changes in the colour. The participants were mostly scientists, students and space agencies, who were discussing current work and future plans. There was obvious excitement over the launch of Sentinel-2 (which incidentally occurred successfully very early yesterday morning) and Sentinel-3, which will carry the OLCI ocean colour sensor, due to be launched towards the end of this year. Cloud cover remains a limiting factor in many locations, as clouds get in the way when optically sensing of the ocean and so the more data collected the better insight we’ll gain into the complexities of the biological processes.

There were lots of new areas of focus discussed at the meeting. I was particularly interested in exporting of carbon to the deep ocean and the calculation of uncertainties i.e., how well have we estimated the values that have been derived.

I was also fascinated by the development in our understanding of rapidly changing ecosystems, such as the Arabian Sea and high latitude polar oceans, which are strongly affected by the effects of climate changing; for example, the reduction of the snow cover over the Himalayan-Tibetan Plateau region changes the strength of the Asian monsoon season, which in turn impacts the phytoplankton that bloom in the Arabian Sea. This has caused a particular species of plankton to bloom (Noctiluca, also known as sea sparkle because it can glow when disturbed at night), which are eaten by jellyfish but can negatively affect fisheries as they’re too big for zooplankton to eat.

I’d love to say after a busy month it’s good be home, but I’ve not quite got there yet! I went straight from San Francisco to Switzerland, where this week I’m attending the 2015 Dragon Symposium that’s focused on an Earth observation scientific exchange programme between the European Space Agency and China.

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.

Goodbye HICO, Hello PACE – Ocean Colour’s Satellite Symmetry

HICO™ Data, image of Hong Kong from the Oregon State University HICO Sample Image Gallery, provided by the Naval Research Laboratory

HICO™ Data, image of Hong Kong from the Oregon State University HICO Sample Image Gallery, provided by the Naval Research Laboratory

Ocean colour is the acorn from which Pixalytics eventually grew, and so we were delighted to see last week’s NASA announcement that one of their next generation ocean colour satellites is now more secure with a scheduled launched for 2022.

Unsurprisingly the term ocean colour refers to the study of the colour of the ocean, although in reality it’s a name that includes a suite of different products, with the central one for the open oceans being the concentration of phytoplankton. Ocean colour is determined by the how much of the sun’s energy the ocean scatters and absorbs, which in turn is dependent on the water itself alongside substances within the water that include phytoplankton and suspended sediments together with dissolves substances and chemicals. Phytoplankton can be used a barometer of the health of the oceans; in that phytoplankton are found where nutrient levels are high and oceans with low nutrients have little phytoplankton. Sam’s PhD involved the measurement of suspended sediment coming out of the Humber estuary back in 1995, and it’s remained an active field of her research for the last 20 years.

Satellite ocean colour remote sensing began with the launch of NASA’s Coastal Zone Colour Scanner (CZCS) on the 24th October 1978. It had six spectral bands, four of which were devoted to ocean colour, and a spatial resolution of around 800m. Despite only having an anticipated lifespan of one year, it operated until the 22nd June 1986 and has been used as a key dataset ever since. Sadly, CZCS’s demise marked the start of a decade gap in NASA’s ocean colour data archive.

Although there were some intermediate ocean colour missions, it was the launch of the Sea-viewing Wide Field-of-view (SeaWiFS) satellite that brought the next significant archive of ocean colour data. SeaWiFS had 8 spectral bands optimized for ocean colour and operated at a 1 km spatial resolution. One of Sam’s first jobs was developing a SeaWiFS data processor, and the satellite collected data until the end of its mission in December 2010.

Currently, global ocean colour data primarily comes from either NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the twin Aqua and Terra satellites, or the Visible Infrared Imaging Radiometer Suite (VIIRS) which is on a joint NOAA / NASA satellite called Suomi NPP. MODIS has 36 spectral bands and spatial resolution ranging from 250 to 1000 m; whilst VIIRS has twenty two spectral bands and a resolution of 375 to 750 m.

Until recently, there was also the ONR / NRL / NASA Hyperspectral Imager for the Coastal Ocean (HICO) mission on-board the International Space Station. It collected selected coastal region data with a spectral resolution range of 380 to 960nm and 90m spatial resolution. It was designed to collect only one scene per orbit and has acquired over 10,000 such scenes since its launch. However, unfortunately it suffered during a solar storm in September 2014. Its retirement was officially announced a few days ago with the confirmation that it wasn’t possible to repair the damage.

In the same week we wave goodbye to HICO, NASA announced the 2022 launch of the Pre-Aerosol and ocean Ecosystem (PACE) mission in a form of ocean colour symmetry. PACE is part of the next generation of ocean colour satellites, and it’s intended to have an ocean ecosystem spectrometer/radiometer called built by NASA’s Goddard Space Flight Centre and will measure spectral wavebands from ultraviolet to near infrared. It will also have an aerosol/cloud polarimeter to help improve our understanding of the flow, and role, of aerosols in the environment.

PACE will be preceded by several other missions with an ocean colour focus including the European Sentinel-3 mission within the next year; it will have an Ocean and Land Colour Instrument with 21 spectral bands and 300 m spatial resolution, and will be building on Envisat’s Medium Resolution Imaging Spectrometer (MERIS) instrument. Sentinel-3 will also carry a Sea and Land Surface Temperature Radiometer and a polarimeter for mapping aerosols and clouds. It should help to significantly improve the quality of the ocean colour data by supporting the improvement of atmospheric correction.

Knowledge the global phytoplankton biomass is critical to understanding the health of the oceans, which in turn impacts on the planet’s carbon cycle and in turn affects the evolution of our planet’s climate. A continuous ocean colour time series data is critical to this, and so we are already looking forward to the data from Sentinel-3 and PACE.

British Science Won’t Be Eclipsed

Hawthorn leaves opening in Plymouth on 18th March 2015

Hawthorn leaves opening in Plymouth on 18th March 2015

We’re celebrating science in this blog, as it’s British Science Week in the UK! Despite its name British Science Week is actually a ten day programme celebrating science, technology, engineering, and maths (STEM). The week is co-ordinated by the British Science Association, a charity founded in 1831.

The British Science Association, like ourselves at Pixalytics, firmly believe that science should be at heart of society and culture and have the desire to inform, educate, and inspire people to get interested and involved in science. They promote their aims by supporting a variety of conferences, festivals, awards, training and encouraging young people to get involved in STEM subjects.

British Science week is one of their major annual festivals, and has hundreds of events running up and down the country. The website has a search facility, so you can see what events are running locally. Down here in Plymouth, the events include Ocean Science at The National Marine Aquarium, tomorrow at Museum & Art Gallery learn about the science behind the headlines and on Saturday, also at the Museum, an animal themed day including some real mini-beasts from Dartmoor Zoo – the place that inspired the 2011 film ‘We Bought A Zoo’, which starred Matt Damon and Scarlett Johnansson.

If you can’t get to any of the events in your local area, British Science Week is also promoting two citizen’s science projects:

  • Nature’s Calendar run by the Woodland Trust, asking everyone to look out for up to six common natural events to see how fast spring is arriving this year. They want to be informed of your first sightings of the orange tipped butterfly, the 7-spot ladybird, frog spawn, oak leaves, Hawthorn leaves, and Hawthorn flowers. This will continue a dataset which began in 1736, and we thought the Landsat archive was doing well.
  • Worm Watch Lab – A project to help scientists better understand how our brain works by observing the egg laying behaviour of nematode worms. You watch a 30 second video, and click a key if you see a worm lay an egg. We’ve watched a few and are yet to see the egg laying moment, but all the video watching is developing a lot of datasets for the scientists.

If you are interested in Citizen Science and go to sea, why not get involved in the citizen science work we support, by taking part in the Secchi Disk Project. Phytoplankton underpin the marine food chain and is particularly sensitive to changes in sea-surface temperatures, so this project aims to better understand their current global phytoplankton abundance. You do this by lowering a Secchi disk, a plain white disk attached to a tape measure, over the side of a boat and then recording the depth below the surface where it disappears from sight. This measurement is uploaded to the website and helps develop a global dataset of seawater clarity, which turn indicates the amount of phytoplankton at the sea surface. All the details on how to get involved are on the website.

On Friday, nature is getting involved by providing a partial solar eclipse over the UK. Starting at around 8.30am the moon will take about an hour to get to the maximum effect where the partial eclipse will be visible to the majority of the country – although the level of cloud will determine exactly what you see. Plymouth will be amongst the first places in the country to see the maximum effect around 9.23am – 9.25am, however the country’s best views will be on the Isle of Lewis in Scotland with a 98% eclipse predicted. The only two landmasses who will see a total eclipse will be the Faroe Islands and the Norwegian arctic archipelago of Svalbard. The last total eclipse in the UK was on the 24th August 1999, and the next one isn’t due until 23 September 2090!

Although the eclipse is a spectacular natural event, remember not to look directly at the sun, as this can damage your eyes. To view the eclipse wear a pair of special eclipse glasses, use a pinhole camera or watch it on the television!

We fully support British Science Week, it’s a great idea and we hope it will inspire more people to get involved in science.

What do colours mean in satellite imagery?

False colour image of phytoplankton blooming off the coast of Patagonia. Acquired 2nd Dec 2014. Image Courtesy of NASA/NASA's Earth Observatory

Phytoplankton blooming off the coast of Patagonia on 2nd Dec 2014.
Image Courtesy of NASA/NASA’s Earth Observatory

Satellite images are a kaleidoscope of colours, all vying for attention. It’s important to be clear what the colours are showing, and more importantly, what they may not be showing, to interpret the image correctly. For example, a patch of white on an image might indicate snow or ice, sunglint off the ocean, fog or it could just mean it was cloudy.

On the earth’s surface different colours represent different land types:

  • Vegetation appears as shades of green from pale for grasslands to dark for forests – although some forests will progress from green to orange to brown in autumn.
  • Ocean colour is significantly influenced by phytoplankton, which can produce a range of blue and green colours. A fantastic example of this can be seen in the image at the top of the blog showing phytoplankton blooming off the cost of Patagonia.
  • Snow and ice can appear white, grey, or slightly blue.

As noted in the opening, colours can also mislead with cloud cover being the natural nemesis of optical remote sensing. However, you also have to be careful with effects such as:

  • Smoke: ranges from brown to grey to black.
  • Haze: a pale grey or a dirty white.
  • Dust: can be brown, like bare ground, but also white, red and black.
  • Shadow: Clouds or mountain shadows can look like dark surface features.

There is a good article here from NASA’s Earth Observatory giving more details on the different colours of surface land types. So far, we’ve focussed on natural colour signatures; but man-made structures also appear on imagery. Generally, urban areas tend to be silver or grey in colour; although larger objects also show up in their own right such as the bright red roof of Ferrari World in the middle of the Abu Dhabi Grand Prix Circuit – as discussed in a previous blog.

Composite Google Earth image of the entrance to the Panama Canal: Data courtesy of DigitalGlobe

Composite Google Earth image of the entrance to the Panama Canal: Data courtesy of DigitalGlobe

We tried to repeat the identification of man-made objects for this blog using the coloured roofs of the Biomuseo building, located on the Amador Causeway – at the entrance to the Panama Canal in the Pacific Ocean. Sadly, Landsat 8 pixels are too coarse; and Google Earth has fallen prey to cloud cover preventing visibility, as shown in the image on the right. What you can see though is the buildings in Panama City and the yachts in the marinas and clustered around the four islands (Naos, Perico, Culebra and Flamenco) at the end of the Amador Causeway.

The final thing to remember when considering colours, is the format of the image itself. Some images use true-colours from the red, green and blue wavelengths, which produce colours as if you were looking at the scene directly, so trees are green, sea is blue, etc. However, other images incorporate infrared light to enhance the detection of features not easily distinguished on a true-colour image; this means colours aren’t what you would expect, for example, the ocean may appear red.

Colour is central to use of satellite imagery, but you need to know the properties of the rainbow you are looking at or you may never find the pot of satellite gold.

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.

Looking Deeper At Phytoplankton from Space

NASA is currently in the middle of a joint airborne and sea campaign to study the ocean and atmosphere in preparation for developing instruments for future spaceborne missions. The Ship-Aircraft Bio-Optical Research (SABOR) campaign has brought together experts from a variety of disciples to focus on the issue of the polarization of light in the ocean; it runs from 17th July to 7th August and will co-ordinate ocean measurements with overflights.

One of the instruments on SABOR is an airborne Lidar-Polarimeter aimed at overcoming the limitation of vertically integrated surface measurements as captured by many existing Earth Observation satellites. These traditional satellites measure the water-leaving radiance, which is the signal returned from an area of water; the problem is that the signal is returned from a variety of different depths and it’s then aggregated to provide a single vertically integrated measurement for that area.

Diffuse attenuation depth at 490 nm, Kd(490), created from the SeaWiFS mission climatological data; data products retrieved from http://oceancolor.gsfc.nasa.gov/

Diffuse attenuation depth at 490 nm, Kd(490), created from the SeaWiFS mission climatological data; data products retrieved from http://oceancolor.gsfc.nasa.gov/

In effect, this means that a phytoplankon bloom at the surface will show up as a strong concentration on an image, however the same bloom at a deeper depth will show as having lower concentrations. The figure on the right shows the diffuse attenuation depth at 490 nm, blue light, created from the SeaWiFS mission climatological data collected between 1997 and 2010; the higher the value the shallower the depth of maximum passive light penetration. So, in summary, the light penetrates further within the open ocean than in many coastal waters that are more turbid.

The SABOR Lidar is based on lasers and will provide depth-resolved profiles, so instead of having a single value for an area of water, the measurements will be separable for different depths; expected to penetrate to around 50m. This will enable a much more detailed analysis of what’s happening within the water column. Satellite Lidar measurements have already been used to provide initial insights into the scattering of light resulting from phytoplankton through the CALIPSO satellite, an atmospheric focused Lidar mission launched in 2006.

In addition, the polarimeter element of SABOR will improve the quantification of the in-water constituents, such as the concentration of Chlorophyll-a (the primary pigment in most phytoplankton as well as land based plants) plus an understanding of the marine aerosols and clouds. Polarimeters have been launched before with the POLDER/PARASOL missions being examples.

The SABOR campaign will provide valuable information to support a proposal to have an Ocean Profiling Atmospheric Lidar (OPAL) deployed from the International Space Station (ISS) in 2015. If successful, it will join the existing Earth Observation mission on the ISS, called the Hyperspectral Imager for the Coastal Ocean (HICO), which I discussed in an earlier blog.

The potential offered by depth profiled oceanic measurements is exciting and will offer much more granularity beyond the ocean’s surface. I’m looking forward to the campaign’s results.

The Science Behind Springwatch

Last Wednesday Pixalytics made it’s TV debut on the BBC2 Springwatch programme, where they showed a video we’d made on phytoplankton blooms.  The video was based on NASA MODIS-Aqua daily images. MODIS, or the Moderate-Resolution Imaging Spectroradiometer, is an optical sensor that’s used for mapping the both land and the oceans. It can be thought of as a digital camera that operates at a number of different wavelengths of light.

Spring 2014 phytoplankton image

Spring 2014 phytoplankton image, MODIS data from NASA with movie animation by Pixalytics Ltd.

As an ocean colour sensor it detects the change in colour of the ocean caused by what’s both dissolved and suspended in the water, e.g. the microscopic plants of the sea that are called phytoplankton. The chlorophyll pigments in plants (both on land and in the oceans) absorb light at blue and red wavelengths making waters high in phytoplankton appear green in colour. This colour change is picked up by chlorophyll algorithms (mathematical equations) and equated to changes in concentration that are displayed using a rainbow colour palette, which goes from purple to blue, green, yellow and red as the concentrations go from low to high values. Black on the imagery is where there’s no data, which for optical imagery is primarily due to cloud cover.

MODIS is on both the Aqua (travels south to north over the equator in the afternoon) and Terra (north to south across the equator in the morning) satellites, which orbit the Earth several times a day collecting strips of imagery 2330 km wide at a spatial resolution of around 1 km. The strips from a day are combined to create a daily composite image, and by looking at images over time we can see the changes in the phytoplankton concentrations as we as we move out of the winter through months into spring. The ‘spring bloom’ is an increase in phytoplankton concentrations as the days become lighter and the phytoplankton make use of the nutrients mixed into the surface waters over the winter.