Ocean colour, an essential climate variable

Earth observation from space is a fundamental part of the second Copernicus revolution. During the first Copernicus revolution, Man has given up its egocentrism to assume he’s just an improbable small peace floating in the great Universe. Today, the second Copernican revolution force us to admit something even more difficult: without proper concern, our own survival is at risk.

Climate change is real, and satellites have been a valuable tool to measure the effects of rising global temperatures. Additionally, the United Nations UNFCCC has defined a set of multiple variables measurable from space thus gathering great amounts of data. One of these variables is Ocean Colour, which allows us to estimate phytoplankton concentrations in water bodies. Phytoplankton contains chlorophyll, making satellite images of the water surface slightly greener.

Plants are extremely sensitive to changes in temperature patterns. Just like land plants, phytoplankton cycles are sentinels for change. In high-altitude areas, where the temperature is increasing at double the rate of the global average, this is even more dramatic. Phytoplankton provides the basis of the oceanic food web, and its window of opportunity for exponential growth is narrow. These periods of fast algae growth are called blooms. In polar regions, these blooms occur in perfect harmony between ice melt, and greater availability of sunlight.

Previous research has shown that especially in the Arctic blooms occurred up to 50 days earlier in 2009 than in 1997 – the year SeaWiFS started sending the first data. This brings harmful consequences for marine life and carbon dioxide uptake from the atmosphere.

To better monitor phytoplankton from space, is it indispensable to validate ocean colour images with in-situ chlorophyll concentrations. Our research is focusing on Finnish lakes ( Figure 3 ), where we have collected samples from 19 lakes and compared the values with images from satellites that have flown overhead on the same day.

Stars represent the locations where in-situ sampling was carried.

The result of this method is a model from which to estimate chlorophyll concentrations in each satellite pass. These satellites orbit the Planet every 90 minutes, proving to be a fundamental resource to study how climate is changing and its impact on phytoplankton.

Result of the model that allow estimating the abundance of phytoplankton in Finnish lakes based on satellite images.

There are only two life forms seen from space: land and marine plants, and humans, with their great ingenuity — cities, pollution and deforestation. Although we are not the centre of the Universe, we are responsible for our future, and Earth Observation can help us make better decisions for the future.



H. Schellnhuber, Earth system’analysis and the second Copernican revolution, Nature, vol. 402,

no.December, pp. 19–22, 1999.

M. Kahru et al. 2011, Are phytoplankton blooms occurring earlier in the Arctic?, Global Change

Biology (2011) 17, 1733–1739, doi: 10.1111/j.1365-2486.2010.02312.x.

Lisboa et al. 2018, Spatial variability and detection levels in Chlorophyll-a estimates using Landsat imagery, submitted.

Author: Filipe Lisboa


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