In 2017, the US Geological Survey released 72.57 kg of Rhodamine WT dye into Idaho’s Kootenai River over 90 seconds to study how a tracer moves through flowing water. Researchers tracked the dye using instruments in the river and hyperspectral images captured from an aircraft flying 1,000 metres above the ground, with images recorded in 0.5-metre pixels across 48 spectral bands.