Managed by PML.
Collaborating with AMT.
Funded by the EU and ESA
Funded by the European Commission European Space Agency logo Copernicus Logo

Discrepancies in satellite chlorophyll are half what we previously thought

James Clark Ross Research ship at sea Image courtesy of C Gilbert, BAS
Accurate chlorophyll measurements in the ocean are crucial for understanding environmental change.

It is impossible to take enough samples of the global ocean in situ to obtain a comprehensive map of chlorophyll measurements for a given week or month, therefore satellites are vitally important because they can observe vast areas of the ocean in a matter of days that are difficult to access and sample using traditional methods. Satellite data therefore offers a cost-effective means of providing a global overview of oceanic conditions. However, in order for these observations to be meaningful they need to be corroborated by measurements taken in the field.

Our current understanding of the accuracy and precision of satellite ocean-colour chlorophyll data is impeded by the limited number and geographical coverage of in situ data coincident with the satellite data. In addition the distribution of existing observations is often biased towards coastal waters, with limited data in the remote oligotrophic waters, despite these constituting the majority of the surface ocean.

Recent work by AMT4SentinelFRM scientists measured chlorophyll on two Atlantic Meridional Transect (AMT) cruises using a relatively new technique that uses spectrophotometry to measure the optical properties of particles sampled by the flow-through system of the moving ship. This provides continuous highly accurate measurements of chlorophyll meaning that there are more match-ups with the satellite overhead, giving multiple in situ reference measurements matched to each satellite pixel. Compared to previous work where the difference in scale from a single in situ measurement to a 4km square pixel is immense, this method has proved to be better suited for validating satellite data.

Bob Brewin, the lead author on the paper, said “What is really important to note about this work is that by using this new technique, we found the errors in satellite chlorophyll measurements are half of what we previously thought, so the data can be used with greater confidence to help understand the dynamics of the ocean and predict how it may change in the future.”

The AMT transect is of particular value as it covers a vast range of environments from the productive coastal regions to the desert-like gyres in the centre of the ocean, which are rarely accessed by research ships, thus enabling the satellite data to be validated under a wide range of conditions.

The paper highlights the benefits of using these underway spectrophotometric systems for evaluating satellite ocean colour data and underlines the importance of in situ observatories, particularly in the oligotrophic gyres. This method will be utilised as part of the AMT4SentinelFRM project to validate satellite data during the AMT26 cruise.


Share this with others:


Other news articles

Atlantic Meridional Transect 27 scientists and crew of RRS Discovery.

The south subtropic convergence zone to South Georgia

02 November 2017

Hold onto your hats folks, we are entering the South Subtropical Convergence Zone!! From the deep blue waters between 10 and 35 South, one crosses...
Chlorophyll map with ship's track overlaid

Expanding ocean deserts

02 November 2017

After crossing the equator we sampled a...
A fish-eye camera looks upwards to produce a photographic log of the condition of the sky

Comparing measurements with measurements

26 October 2017

The inter-comparison of measurements between laboratories, who work on the accuracy of Copernicus Sentinel Ocean Colour and Sea Surface Temperature...

Launching balloons

16 October 2017

Most of the data that we collect on AMT4SentinelFRM are water profiles or continuous surface water measurements. However, every day at midday we...
Flying fish in the North Atlantic Gyre. (Credits: Ian Brown, Plymouth Marine Laboratory, UK).

Life on the edge

09 October 2017

We are transiting the deep ocean gyres, where life survives on the edge. From the surface of these deep blue waters there seems to be little life...
The Conductivity, Temperature and Density (CTD) device

A day in the life of an ocean-going scientist

09 October 2017

When you mention to friends back home that you are going on a research cruise, most people think of Jacques Cousteau or The Life Aquatic, or...
RRS Discovery

The second voyage

22 September 2017

Last year, the AMT4SentinelFRM Research Voyage set sail from Immingham on 20 September 2016 aboard the British Antarctic Survey ship, the Royal...
Bow of research ship with ice capped mountains of south giorgia in the background

The 27th AMT cruise embarks

21 September 2017

The 27th AMT cruise has now departed from Southampton in the UK on board the RRS Discovery and will spend the next 6 weeks...
Presentation slide for Fiducial Reference Measurements

AMT4SentinelFRM Workshop a great success

23 June 2017

A successful two-day workshop was held in Plymouth focussing on validating the performance of Sentinel-1, -2 and -3 at retrieving ocean colour, sea...
Sentinel 2 ocean colour, September 2016, English Channel

News from the AMT cruise

06 January 2017

On 20 September 2016 scientists from Plymouth Marine Laboratory, the University of Southampton and IFREMER collectively embarked on a 7000 mile...
Copernicus Sentinel-1 satellite and C-band radar on-board the RRS James Clark Ross

C-band radar test data

07 November 2016

A dedicated C-band radar is deployed on AMT26 to validate Sentinel-1 Synthetic Aperture Radar (SAR) imager products to investigate sea surface...
Radiosones attached to helium balloon

Getting technical with SST instrumentation

06 October 2016

An important part of the AMT4SentinelFRM project is the validation of the SLSTR (Sea and Land Surface Temperature Radiometer) sensor on Sentinel...
RRS James Clark Ross leaves Portsmouth

Bon voyage to AMT26

23 September 2016

The British Antarctic Survey ship, the Royal Research Ship James Clark Ross, has left the UK and set sail on a voyage that will traverse almost...
Sentinel 3 satellite

AMT4SentinelFRM kicks off

13 July 2016

The ESA funded AMT4SentinelFRM project has now launched, focusing on validating Sentinel satellite data by using measurements taken on the...