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  • Rights: The University of Waikato Te Whare Wānanga o Waikato
    Published 25 July 2022 Referencing Hub media

    Dr Moritz Lehmann is a freshwater scientist specialising in lake water quality and remote sensing. He uses data from Earth observation satellites to gain more information about cyanobacteria blooms in New Zealand lakes.

    Moritz references the Eye on Lakes project, a multi-year MBIE Smart Ideas -funded project run from the University of Waikato.

    Questions for discussion:

    • What are the advantages of using Earth observation satellites to monitor lakes?
    • What is a disadvantage of using satellites to monitor lakes?
    • What do you think Moritz means when he refers to manually checking a lake?


    Dr Moritz Lehmann

    Aquatic remote sensing scientist
    Senior Scientist, Xerra Earth Observation Institute
    Adjunct Senior Research Fellow, University of Waikato

    Eye on Lakes project is specifically looking for algal blooms or cyanobacteria blooms in lakes. Cyanobacteria are tiny microscopic bacterial cells that photosynthesise, and under the right conditions, they can proliferate and they can completely smother a lake.

    There is evidence that these blooms are increasing. And it’s important to know the scale of this problem so that we can study the lakes and find the reasons why this happened, and mitigate the expansion of the cyanobacteria.

    We like to identify a bloom, not when it’s already there and established, but on the way of happening, of ramping up. So we like to see the first signs, the first greening essentially of the lake that might lead to a severe bloom.

    The objective of the Eye on Lakes project is to develop models to allow us to look at an image and say, “OK, so here we have a cyanobacterial bloom” or “Here’s a bloom in development.” The advantages of using this Earth observation remote sensing system is that we get this data coming in all the time from the same places in New Zealand. And so this allows us to create a monitoring system that, cloud cover permitting, looks at the planet every 5 days to get the cyanobacteria and the algal concentration in those lakes.

    You have to build some kind of software, some kind of automated system to do this. It’s very well possible for anybody now to download a satellite image and do those calculations as well. But to do this over and over and over again would take too much time, and computers are really good at that. So we would like to implement these calculations in the software system that then monitors and tells the authorities and the citizens whether a lake is safe to swim in or whether a lake needs manual checking.

    Dr Moritz Lehmann, Xerra Earth Observation Institute and University of Waikato Te Whare Wānanga o Waikato
    Algae images, timelapse of Sentinel-2 imagery showing changing water colour, Lake Waikare, The colour of 1,486 New Zealand Lakes: Clean, green and pristine? Poster, Landsat satellite overpass of North Island, toxic algae indication sign, Dr Moritz Lehmann and Xerra Earth Observation Institute
    Sentinel-2 global coverage animation, European Space Agency (ESA)

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