Is This The Worst Global Coral Bleaching Event Ever?

Great Barrier Reef off the east coast of Australia where currents swirl in the water around corals. Image acquired by Landsat-8 on 23 August 2013. Image Courtesy of USGS/ESA.

Great Barrier Reef off the east coast of Australia where currents swirl in the water around corals. Image acquired by Landsat-8 on 23 August 2013. Image Courtesy of USGS/ESA.

It was announced last week that 93% of the Great Barrier Reef has been hit by coral bleaching due to rising sea temperatures from El Niño and climate change. We first wrote about the third worldwide coral bleaching in October 2015, noting this year’s event could be bad. Those fears would appear to be coming true with the results of Australia’s National Coral Bleaching Task Force aerial survey of 911 coral reefs which found 93% had suffered from bleaching; of which 55% had suffered severe bleaching.

Coral bleaching occurs when water stresses cause coral to expel the photosynthetic algae, which give coral their colours, exposing the skeleton and turning them white. The stress is mostly due to higher seawater temperatures; although cold water stresses, run-off, pollution and high solar irradiance can also cause bleaching.

Bleaching does not kill coral immediately, but puts them at a greater risk of mortality. Recovery is also possible if the water stress reduces and normal conditions return, which is what is hoped for in the Northern Sector of the reef above Port Douglas, where around 81% of corals had suffered severe bleaching – the water quality in this area is good, which should also aid recovery. The reefs fared better further south. Within the Central Sector, between Port Douglas and Mackay, 75 of the 226 reefs suffered from severe bleaching. Whilst in the Southern Sector below MacKay only 2 reefs suffered severe bleaching and 25% had no bleaching.

The news is not all bad. A survey of the coral reefs of the Andaman and Nicobar Islands, a territory of India that marks the dividing line between the Bay of Bengal & Andaman Sea, also published this week shows no evidence of coral bleaching. This survey is interesting for remote sensors as it was undertaken by a remotely operated vehicle, PROVe, developed by India’s National Institute of Ocean Technology. As well as mapping the coral reefs, PROVe has a radiometer attached and is measuring the spectral signatures of the coral in the area, which could be used to support the monitoring of corals from satellites.

Monitoring coral bleaching from space has been done before. For example, Envisat’s MERIS sensor was determined to be able to detect coral bleaching down to a depth of ten metres, or the Coral Bleaching Index (Ziskin et al, 2011) which uses the red, green and blue bands to measure increases in spectral reflectance in bleached corals. Given the size, geographical area and oceanic nature of corals, satellite remote sensing should be able to offer valuable support to the monitoring of their health.

Following the second global bleaching event, in 1997/98, research confirmed that 16 percent of the world’s coral died. Who knows what the outcome of the current event will be?

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.

Home from Hawaii

I got back to a ‘cold’ UK on Saturday afternoon after spending last week at Ocean Sciences 2014.  It was a fantastic conference with over 5,600 attendees.  My scientific highlights were:

The Surface Ocean Layer Atmosphere Study (SOLAS) session on Monday where speakers presented research on the sea surface microlayer (the top 1 mm of the ocean); this layer is important so we can understand the transfer of compounds, such as carbon dioxide, and particles from the ocean to the atmosphere and vice versa that are critical to our interpretation of the climate.

On Tuesday afternoon it was the Optics and Light in the Particle-Laden Coastal Ocean session, with presentations focused on understanding the acoustic and optical signatures of particles, including their shape, from multi-angular measurements and Lidar (laser) profiling of a phytoplankton bloom.

My key session was obviously Optical Remote Sensing of Freshwater, Estuarine and Coastal Environments on Wednesday. I gave a presentation on Multi-Sensor Ocean Colour Atmospheric Correction for Time-Series Data.  Atmospheric correction is the removal of the atmosphere’s signal from data so only the water-leaving radiance signal is left; it allows data to be compared between days irrespective of the weather conditions of that day – so an image taken on a hazy day will look like it was taken on a clear day.

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

Other interesting talks from this session included Tiit Kutser’s presentation on comparing in-situ measurements with MERIS data for dissolved organic carbon and iron concentrates in Lake Malaren in Sweden, Keping Du’s retrieval algorithm for phycocanian, a pigment within cyanobacteria, within Taithu lake in China, Heidi Dierssen’s optics of seagrass for remote sensing and I also really enjoyed my mentee Guangming Zheng’s presentation on suspended sediment within Chesapeake Bay, off the west coast of America – this took me back to my PhD that focussed on the suspended sediment plume from the River Humber.

Finally, there were great presentations by Curt Davis and Nick Tufillaro on the Hyperspectral Imager for the Coastal Ocean (HICO) mission. It’s an experimental mission that’s designed to sample the coastal ocean; one 50 x 200 km scene per orbit at a spatial resolution of around 90 m. The image on the right shows a HICO example.

On top of these oral sessions, I also spent time in the exhibition, poster sessions and some of the evening events.  My last event on the Thursday evening was about getting involved in the European Commission’s Horizon 2020 Research programme – so if anyone needs an Earth Observation specialist partner for their bid, get in touch!

An EO conference roundup: RSPSoc 2013 and the ESA Living Planet Symposium

It’s conference season! I’m at my 2nd conference in 2 weeks, both in Scotland.

Last week was the Remote Sensing & Photogrammetry Society Annual Conference, #RSPSoc2013, hosted in Glasgow. It included a broad range of sessions and scientific output within the ‘family’ atmosphere that you find within societies.

The conference started off with a keynote from Dr. Stewart Walker (BAE Systems and President-Elect of the American Society for Photogrammetry and Remote Sensing)
reviewing the history and innovations in photogrammetry. I was fascinated to find out that in the early days of remote sensing (1960’s) US military satellites ejected cans of photographic film, picked up by aircraft as they fell to Earth, to get high resolution data.

He also showed that since then the number of high resolution optical satellites and the capacity of those satellites to capture information has continuing to increase; in addition to the speed at which an end user can receive captured data. Today Autonomous Unmanned Vehicles (AUVs) have the capability to take very high resolution video that can see objects as small as a songbird.

For me the most incisive comment he made was when he was summarising his own career, where he said that leaders don’t only develop science, but also develop people who develop science. Something worth remembering by every scientific business.

The second keynote was by provided by Craig Clark MBE (Clyde Space), which showcased the growth of the company that is leading the UK Space Agency’s programme to design and launch a cubesat; UKube-1 which is due for launch in December.

Cubesats are small satellites, built in units of 10 cm cubes, with Ukube-1 being 3u i.e. 3 cubes in size (length). These are not the smallest satellites to be launched, but offer the potential to provide scientific quality missions at a much lower cost than conventional satellites; allowing developers to be more innovative with technologies and off the potential for constellation, rather than single, missions. This won’t be the end of conventional larger satellites, as they are still needed for the capture of complex high quality data sets. But these two technologies will give greater flexibility for data capture.

This week I’m at European Space Agency’s Living Planet Symposium http://www.livingplanet2013.org/. Still a ‘family’ atmosphere, but a much larger family with around 1,700 attendees in Edinburgh. The conference has showcased ESA’s historical, current and future missions including SWARM that will be launched in November and the first Copernicus mission (Sentinel 1) that will launch in 2014.

The SWARM constellation (3 satellites) will measure the Earth’s magnetic field which protects us from cosmic radiation and charged particles arriving from the Sun. Whereas Sentinel 1 is a radar mission, which has many different applications as it provides a view of the surface roughness – a rough surface will reflect strongly while a smooth surface will reflect weakly – which is available during the day and night irrespective of cloud cover. Examples include tracking vessel movements at sea, monitoring forests and looking at the growth of mega-cities.

The last week has reminded me that remote sensing and photogrammetry are changing and fast moving fields; new technologies are offering us greater opportunities and flexibilities. But as Dr Walker reminded us, behind all these developments are some amazing people.

Completing the PhD publication triple

Some great news this week! Dr Susan Kay’s third paper from her PhD has been accepted for publication by Applied Optics. Entitled “Sun glint estimation in marine satellite images: a comparison of results from calculation and radiative transfer modeling”, it nicely shows the impact of choosing different models for the sea surface elevation and slope when predicting sun glint. In response to the notice of publication Sue said “It’s great to see that last bit of PhD work finished. Now I’d better get writing about marine ecosystem modelling!” which is her current research at Plymouth Marine Laboratory.

I’ve been one of Sue’s PhD supervisors, alongside Dr John Hedley, and it’s wonderful that she’s had three papers published. There is always an expectation that PhD students will produce papers during their studies, on top of writing up their PhD. However peer-reviewed publications aren’t easy to achieve, more and more papers are being produced but scientists only have limited time to act as reviewers. The consequence is that journals are tending more towards a straight forward acceptance or rejection, rather than longer supported revisions processes. Over the 20+ years I’ve supervised students, some have published several peer-reviewed papers whilst others have not managed to get one accepted. I never achieved a first-authored one during for my own PhD.

I think the differentiating success factors in getting publications are writing up research that is novel (rather than incremental), maintaining self-belief in your work plus a small measure of luck. Many times has a paper been rejected, only to be accepted by another journal after revisions, but for a PhD student the rejection can be a very disheartening process; especially if it’s their first paper.

Therefore if you get rejected, don’t be down-hearted. Use the valuable reviewer feedback to look at the paper with fresh eyes, and give careful thought on where to submit. A lower-ranked journal can be better for a first PhD submission; especially if the research is still in the initial stages of development. Believe in your work, believe in yourself and send the paper out again and do this over and over until you get it accepted. You never know you might get three papers published like Sue!