Tag: satellite image

Meeting Without Mixing
When bodies of water meet, they don’t always mix right away. Here we see the confluence of the Back and Hayes Rivers in the Canadian Arctic. The Back River appears as a darker blue-green color compared to the light turquoise Hayes River. The different colors reflect the levels of algae and sediment carried in their waters. As seen in both the aerial and satellite photos here, there’s a distinct line where the two waters meet without mixing, and that line persists for kilometers beyond their initial confluence. Typically, this lack of mixing between bodies of water is caused by differences in temperature, salinity, and turbidity (amount of sediment) that make the density of each river’s water different. (Image credit: top – R. Macdonald/Univ. of Manitoba, bottom – J. Stevens/USGS; via NASA Earth Observatory)
May 5, 2021
Sea Swirls by the Shore
Water and sediments swirl in these enhanced satellite photos of China’s Leizhou Peninsula. Color-filtering algorithms have drawn out the details of the flows, but the patterns themselves are real. Tides, currents, sediment, and human activity combine to form these complex flows along the peninsula’s shores. The straight parallel lines seen off Liusha Bay, for example, are likely the result of a traditional fishing method using nets suspended off poles anchored into the seabed. (Image credit: N. Kuring; via NASA Earth Observatory)
April 23, 2021
Strings of Swirls
Von Karman vortex streets are the rows of alternating vortices shed off isolated objects interrupting a flow. Here, the volcanic peaks of Cabo Verde disrupt an atmospheric flow accustomed to an empty ocean. In a steady wind, air wraps around the volcanoes and detaches first on one side, creating a vortex, then from the other side, making a vortex of the opposite rotation. Although these structures are always present, we only see them when they stir up the cloud layer, leaving these strings of swirls for hundreds of kilometers behind the islands. (Image credit: L. Dauphin/NASA; via NASA Earth Observatory)
February 15, 2021
High Tide
Broad Sound, in eastern Australia, is home to some of the most extreme tidal swings in the world, with more than ten meters difference between high and low tides. The bay’s peculiar geography, along with the topography of nearby reefs, combine to cause the large tides. This color-enhanced satellite image shows the bay at high tide, as phytoplankton and suspended sediments are swept into the bay and around its many islands. The level of detail is just stunning. I particularly love all the von Karman vortex streets visible in the wakes of islands. I count more than a dozen of them! (Image credit: N. Kuring/NASA/USGS; via NASA Earth Observatory)
January 13, 2021
Curls Past the Canaries
When winds flow past a solitary peak, like an island in the ocean, they’re disrupted into a series of counter-rotating curls. That’s what we see here stretching to the southwest of Madeira Island. The official name for this flow is a von Karman vortex street, and it can be found anywhere from a soap film to a starship. (Image credit: J. Stevens; via NASA Earth Observatory)
December 14, 2020
Meandering
The banks of rivers are in constant flux, a pattern most easily captured from above. This satellite image shows a section of the Ivalo River in Finland, swollen with snowmelt after a winter of historic snowfalls. From above we see some of the river’s previous paths. This meandering is a natural result of secondary flows where rivers bend. The water carves away sediment from the outer bank and deposits it on the inner one, exaggerating every curve until the river cuts itself off, leaving behind a sinuous lake detached from the river’s new course. For an interesting (though non-physical) look at meandering, check out this procedural system for generating maps of rivers (thanks to Kam-Yung Soh for sharing). (Image credit: J. Stevens; via NASA Earth Observatory)
November 30, 2020
Hudson Bay Watercolors
Rivers sweep fresh water and sediment into the Hudson Bay in this satellite image. Dark brown plumes mark the mouths of several coastal rivers as they add to the cyclonic sediment flow around the bay and out the Hudson Strait. Paler swirls, like strokes of watercolors, mark turbulent mixing between the sediment-filled shallows and the deep blue waters of the bay. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)
November 23, 2020
Green Swirls and Dark Streaks
Green phytoplankton blooms swirl through the currents of the Baltic Sea in this satellite image. Individual phytoplankton are microscopic, which makes them excellent tracer particles in the flow; together, they make the ocean’s motion visible. Look closely and you’ll see dark streaks across the images showing where ships’ wakes are disrupting the bloom. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)
October 30, 2020
A Colorful Portrait of Flow
This gorgeous, natural-color image shows Lake Balkhash in southeastern Kazakhstan. In early March, the ice on the lake was beginning to break up, revealing glimpses of swirling sediment below the water’s surface. In contrast, the smaller lakes and ponds of the surrounding area remained frozen amidst the wintery browns of the nearby desert and wetlands. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)
October 15, 2020
Two Views of Ocean Eddies
Colorful, sediment-laden eddies swirl off the Italian coast in this satellite image. These small-scale eddies — less than 10 km in diameter — can be short-lived and are often difficult to capture in numerical models, but remote sensing can help scientists better understand their impact on oceanic mixing, especially when we capture more than one view of the same event.
The image below shows the same eddies in an infrared (thermal) view. The resolution on this instrument is not as fine as the natural color one, but we can still make out some of the same swirling motions. It’s also worth comparing the features we don’t see in both images. For example, the Cornia River discharges in infrared as a bright, white plume of cooler water, but it’s barely visible in the color-image, suggesting that the river is not contributing much sediment to the bay. (Image credit: USGS; via NASA Earth Observatory)
September 8, 2020