One of the oldest and one of the most crowded cities in the world. thumbnail: http://svs.gsfc.nasa.gov/vis/a000000/a003700/a003791/beijing_2010.1020_gal.png

Above the Earth, Below the Surface: Landsat’s Role in Monitoring Water Quality
Safeguarding freshwater resources is crucial, and while scientists use a variety of ground-based techniques to gauge water quality, the Landsat program has provided water quality data from orbit for decades.