Posted on July 12th, 2012

Our Changing Landscape – The Black Sea

In this monthly feature, we span the globe to examine Our Changing Landscape with time series of medium resolution RapidEye satellite imagery. The RapidEye archive dates back to late 2008 and already contains more than 3 billion square kilometers of data. This month, we travel to Eastern Europe and explore changes in water conditions of the Black Sea.

The RapidEye Constellation

RapidEye is a constellation of five 5-meter medium resolution satellites each offering five spectral bands of information. The RapidEye constellation offers a daily revisit time to every location on the planet with a huge footprint that is 77-km wide. The data is priced competitively with a base price of $1.28 per square kilometer for all five spectral bands – academics receive a discount on this price. RapidEye adds a fifth band, the red edge, to the ‘traditional’ multispectral set of blue, green, red and near-infrared (NIR). The additional spectral data available in the red edge band allows users to extract more useful land ‘information’ than can be from traditional 4-band imagery sources. When RapidEye imagery is ordered as a Level 3A Orthorectified product, images from multiple dates are extremely well registered, making it the ideal data source for Our Changing Landscape.

The Black Sea

Since the 1960s, intense human development along the shores of the Black Sea and the rivers that feed it has resulted in significant increases in the annual input of dissolved nutrients such as nitrogen and phosphorus. When there are excessive nutrients present in the water column, algal blooms can intensify. These blooms can absorb most (or all) of the dissolved oxygen from the water column for their metabolic processes, which has a devastating effect on local ecosystems, for instance suffocating fish and plant populations. The Danube River is the largest contributor of dissolved nutrients to the Black Sea as it is transports more nutrients than any other major river in Europe, dumping some 826,000 tons of nitrogen and phosphorous into the ecosystem per year.

 

Starting in the 1990s, the nations of Europe and many international and local non-profits have focused much attention on reducing nutrient loads in the Danube River. When I started this exploration, I had intended to show changes in the Danube River’s nutrient load as it poured into the Black Sea on the border of the Ukraine and Romania from 2009 to 2012. But what I quickly discovered is that seasonal changes in algal blooms were far more apparent than were changes through the years.

When I ordered imagery to support this analysis, the best available datasets from 2009, 2010, 2011 and 2012 were spread across the year, spanning both the wet season (i.e. May to September) and the dry season. During the wet spring and summer seasons, when nutrients flow into the Black Sea, algal blooms spring up across the large body of water. These blooms die back in the dry fall and winter months when nutrient inputs decline. Algae use a similar process (i.e. photosynthesis) as do plants to create the sugars they need to live. Hence, well-known remote sensing techniques such as a Normalized Difference Vegetation Index (NDVI) should be effective in determining the spatial extents of these blooms. The animation below was created by calculating a red edge NDVI for each date of RapidEye imagery; color coding the outputs with the same 3-class light red to dark red ramp; and then overlaying these NDVI calculations on a base map.

 


black_sea_anime

Click on the image above to see an animation of an algal bloom spread across the surface of the Black Sea and then retract as the seasons progress. Less vigorous plants and algal blooms are in light red; moderately vigorous plants and algae are in medium red; and the most vigorous plants and algae are in dark red. Pixels with red edge NDVI values less than 0.10 have been filtered out. This 5-meter RapidEye imagery comes from the mouth of the Danube River where it empties into the Black Sea close to Sulina, Romania (Images Courtesy: RapidEye)

The results of this analysis with 5-meter RapidEye imagery suggest that this medium resolution data is an effective, low-cost means to monitor widespread algal blooms on the surface of any water body.

If you would like to find out more about using RapidEye for your academic studies, engineering projects or any landscape analysis, let us know at sales@apollomapping.com or (303) 993-3863.

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