An astronaut aboard the International Space Station (ISS) took this photograph highlighting the water surface in the southeast corner of the Caspian Sea. The tight angle of the coastline, close to the point where Iran and Turkmenistan meet, is a readily recognizable landmark for ISS crews. The region has a generally arid climate, but thick forests blanket the rain-catching slopes of the Elburz Mountains that fringe the sea.
The image shows patterns of swirls on the sea surface as revealed by reflected sunlight, or sunglint. This circulation has been studied through both remote sensing and in situ techniques—in this case floating drifters that take direct measurements in the water column as their movements are tracked by GPS.
Thanks to such data, scientists now know that the water in this corner of the Caspian Sea circulates slowly in a counterclockwise direction, making a broad current pattern termed a gyre. This flow appears to astronauts as a complicated pattern of smaller eddies or swirls; they are larger where the water is deeper (top center) and much smaller near the shoreline, where the water is shallower.
Astronaut photograph ISS061-E-6914 was acquired on October 18, 2019, with a Nikon D5 digital camera using a 240 millimeter lens and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 61 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by Justin Wilkinson, Texas State University, JETS Contract at NASA-JSC.