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"The three 100-m resolution Proba-V images shown here were acquired on 27 April 2014, 20 July 2015 and 22 January 2016 respectively." "But the lake’s shallow n

"The three 100-m resolution Proba-V images shown here were acquired on 27 April 2014, 20 July 2015 and 22 January 2016 respectively." "But the lake’s shallow nature, with an average depth of just 3 m, coupled with its arid highland surroundings, means that it is very sensitive to fluctuations in climate." These quotes leave me wondering; why did they chose to take these images in vastly different times of year?

wavefunction 11y ago
It may correspond to availability of the satellite to take the photos of the area. First the satellite has to be over the area. Second the satellite has to be free from other tasks to take photos of the area. From Wikipedia, the satellite's mission involves: Proba-V will support applications such as land use, worldwide vegetation classification, crop monitoring, famine prediction, food security, disaster monitoring and biosphere studies. Taking photos of a single lake in Bolivia may not be high on that list of priorities.
- mturmon 11y ago
  Interesting speculations, but that's not how these environmental monitoring satellites work. They are set up to get global coverage with this instrument every 5 days. The orbit is chosen so that this happens, to enable long-term time series of vegetation, land cover, etc., as you note. It's a successor to other satellites like SPOT, and a competitor/complement to NASA satellites like MODIS.
mturmon 11y ago
They appear to have, in essence, two imaging modes. They are showing the higher-resolution-mode, with 100 meter pixels, which are made every 5 days. (They get global coverage every 5 days.) I'll bet there are very few clouds there, so almost all the images (~66 per year) will be OK. It turns out (http://www.tandfonline.com/doi/pdf/10.1623/hysj.51.1.98 http://www.tandfonline.com/doi/pdf/10.1623/hysj.51.1.98) that the lake is fed by a river which is in turn fed by Lake Titicaca (made famous by Beavis and Butthead). Almost all rain there falls from December to March, so the first two images would be fairly "wet" while the last one (from January) might be rather "dry". Of course, in December 2015, the lake totally dried up. Besides the climate sensitivity, they also have a water management problem, because the level in the downstream Popoo is controlled somewhat by releases from Titicaca. One more thing: this set of visual images finds lake extent by measuring the retreat of the shoreline. Another approach is to use radar to find the elevation of water bodies, directly, to high accuracy. That should happen in a couple of years when SWOT launches (https://en.wikipedia.org/wiki/Surface_Water_Ocean_Topography_Mission https://en.wikipedia.org/wiki/Surface_Water_Ocean_Topography...).

wavefunction 11y ago

It may correspond to availability of the satellite to take the photos of the area. First the satellite has to be over the area. Second the satellite has to be free from other tasks to take photos of the area. From Wikipedia, the satellite's mission involves: Proba-V will support applications such as land use, worldwide vegetation classification, crop monitoring, famine prediction, food security, disaster monitoring and biosphere studies. Taking photos of a single lake in Bolivia may not be high on that list of priorities.

mturmon 11y ago
Interesting speculations, but that's not how these environmental monitoring satellites work. They are set up to get global coverage with this instrument every 5 days. The orbit is chosen so that this happens, to enable long-term time series of vegetation, land cover, etc., as you note. It's a successor to other satellites like SPOT, and a competitor/complement to NASA satellites like MODIS.

mturmon 11y ago

They appear to have, in essence, two imaging modes. They are showing the higher-resolution-mode, with 100 meter pixels, which are made every 5 days. (They get global coverage every 5 days.) I'll bet there are very few clouds there, so almost all the images (~66 per year) will be OK. It turns out (http://www.tandfonline.com/doi/pdf/10.1623/hysj.51.1.98 http://www.tandfonline.com/doi/pdf/10.1623/hysj.51.1.98) that the lake is fed by a river which is in turn fed by Lake Titicaca (made famous by Beavis and Butthead). Almost all rain there falls from December to March, so the first two images would be fairly "wet" while the last one (from January) might be rather "dry". Of course, in December 2015, the lake totally dried up. Besides the climate sensitivity, they also have a water management problem, because the level in the downstream Popoo is controlled somewhat by releases from Titicaca. One more thing: this set of visual images finds lake extent by measuring the retreat of the shoreline. Another approach is to use radar to find the elevation of water bodies, directly, to high accuracy. That should happen in a couple of years when SWOT launches (https://en.wikipedia.org/wiki/Surface_Water_Ocean_Topography_Mission https://en.wikipedia.org/wiki/Surface_Water_Ocean_Topography...).