Lakes seen from space

23 August 2018

Research at Lake Tekapo. Photo credit: Warrick Powrie.

A team led by senior research fellow Dr Moritz Lehmann at the University of Waikato has published the first comprehensive assessment of lake water colour in New Zealand based on four years of satellite observations. The researchers found the lakes span close to the full global range of possible water colours; some lakes have a stable blue or yellow colour, while others vary strongly through the seasons, or because of the impact of agriculture, forestry, invasive species and climate change.

The development of the space-based methodology is timely as water colour has recently been added to the New Zealand national environmental monitoring standards for lakes.

Dr Lehmann says that while clear and pristine lakes are blue, a non-blue colour does not necessarily mean that the water is polluted. “The colour of water is related to the amount of algae, suspended sediments and tannins (brown soil-derived organic material). These substances are naturally present, but may also be enhanced by pollution.”

The researchers believe that in the near future water-colour earth observation data will be complemented by observations made by a simple smartphone app created by fellow researchers at Vrije Universiteit Amsterdam. The aim is to foster environmental stewardship more widely.

Colour of 1486 lakes determined from satellite images taken in August 2016. The colour is expressed as dominant wavelength, an intensification of the colour as perceived by the human eye.

Space-based technology and applications are globally growing at a tremendous rate as access to vast libraries of satellite images and processing systems is free. Dr Lehmann says the research is a good demonstration of the application and potential of space technology. From next month he will be continuing his research as a senior scientist at the recently formed Centre for Space Science Technology.

The team is part of LERNZ (Lake Ecosystem Research New Zealand) and the data can be explored by logging into New Zealand’s lakes information system Takiwa via

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