Archive for the ‘Ground to Space’ Category

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Photo by Adam Voiland. Taken from Rodeo Beach in Marin County, California, in the evening on December 14, 2015.

If you have ever stood on a beach before sunset and gawked at a gleaming line of light extending toward the horizon, you have seen a glitter path.

What causes this spectacular optical phenomenon? Glitter paths are made up of many bright points of light reflecting off tiny ripples, waves, and undulations on the water surface and back at a sensor (for instance, a camera or human eye). Together, these points of light make up areas of sunglint. The appearance of glitter paths on water varies depending on the height of the Sun above the horizon, the height of the surface waves, and the position of the observer.

For instance, if the Sun had been directly overhead and above perfectly calm water, I would have seen a circular reflection that looked much like the Sun in the sky. However, when I took this photograph from Rodeo Beach near sunset in December 2015, the reflection appeared as a long elliptical line of light because the Sun was quite low in the sky. Note how much the roughness of the water surface affected the glitter path. Near the shore, where waves had just broken and the water surface was filled with foam, the glitter path was significantly wider than it was in the smoother waters farther off shore.

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NASA image acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite on the morning of June 22, 2015.

Sunglint is visible from space as well. In the satellite image of California above, which the Terra satellite captured on the morning of June 22, 2015, notice the line of light running over the Pacific Ocean. This line of sunglint traces the track of Terra’s orbit. If the ocean surface had been completely smooth, a sequence of perfect reflections of the Sun would have appeared in a line along the track of the satellite’s orbit. In reality, ocean surfaces are chaotic and often in motion due to the constant churn of waves and winds. As a result, light reflecting off the surface was scattered in many directions. This left the blurred, washed out line of light along the satellite’s orbital track that you see here instead.

You can learn more about sunglint and glitter paths from stories by Darryn Schneider, Atmospheric Optics, Joseph Shaw, Richard Fleet, NASA Earth Observatory, and Earth Science Picture of the Day.

Editor’s Note: Ground to Space is a recurring series of posts on NASA Earth Observatory’s Earth Matters blog that pairs ground photography and satellite imagery of the same feature or phenomenon. If you have a photograph that you think would be a good candidate, please email Adam Voiland.

Ground to Space: Antelope Island, Utah

February 9th, 2016 by Adam Voiland
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Photo by Ray Boren. Image first published by Earth Science Picture of the Day.

Technically, there are not any antelope on Utah’s Antelope Island, the largest island in the Great Salt Lake. Rather, some 200 pronghorn (which fill a similar ecological niche as their Old World counterparts) and 300 mule deer live on the island in the southern part of the lake.

Despite the name (attributed to explorers John Frémont and Kit Carson), Antelope Island is perhaps best known for its free-ranging bison herd. Four breeding pairs were introduced to the island in 1893, a period when hunters had pushed bison toward extinction across much of North America. The lack of trees and abundant grass made the 24 kilometer (15 mile) long and 8 kilometer (5 mile) wide island ideal habitat for the largest land animal in North America. Now, park managers have to remove a few hundred bison every year to keep the population at sustainable levels (between about 500 and 800). See the video below, produced by the Salt Lake Tribune, to learn more about the island’s annual bison roundup.

The landscape and geology of Antelope Island offers much of interest as well. The island is comprised of several different rock formations that represent a range of geological processes. The oldest rocks on the island—gneiss, a coarse-grained, irregularly banded metamorphic rock—formed between two and three billion years ago when sedimentary rocks such as claystone and siltstone were squeezed under extremely high temperatures and pressures. The island’s youngest rocks (tufa limestone) formed when calcium carbonate precipitated from Lake Bonneville about 10,000 to 15,000 years ago.

Ray Boren, a photographer and retired journalist, stopped by the island on December 23, 2015. “I love to go there when I’m out and about,” Boren said in an email. “It is a wonderful rural setting within shouting distance (well, not quite) of the millions of people living along Utah’s Wasatch Front.”

It was a chilly, windy day. “I’ve come to see what’s happening on the island,” Boren told a worker at the park entrance. “You mean, besides the wind?” she replied. Indeed, strong prevailing winds out of the northwest and west were whipping loose snow across the causeway and the island roads, creating intermittent drifts and icy conditions. Even more dramatic was the effect on the island’s shores, benches, plains and mountainous central ridge.

In the photo at the top of the page, originally published by Earth Science Picture of the Day, snow streamed through a boulder field on the island’s northeast side. “The Sun is beginning to set, and the light’s low angle and longer wavelength colors help tint the scene. In the photograph below, snow is being stirred in ephemeral waves, swirls and columns off the jagged terrain of Frary Peak, the island’s highest point at 6,596 feet (2,010 meters).”

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Photo by Ray Boren. Image first published by Earth Science Picture of the Day.

For a different perspective on Antelope Island, I dug into the Earth Observatory archives for the images below. Acquired by the Multi-angle Imaging SpectroRadiometer in 2001, the pair offers a winter and summer view of the island. In addition to the obvious difference in snow cover, note the contrasting water color in the northern and southern part of Great Salt Lake. The different colors are the result of a rock-filled causeway built in 1953 to support a permanent railroad. The causeway decreased circulation between the two arms, producing higher salinity on the northern side. If you look closely at the full resolution image, you should be able to see the causeway connecting the island to the mainland.

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The winter image (left) was captured by the Multi-angle Imaging SpectroRadiometer on NASA’s Terra satellite on February 8, 2001. The summer image (right) was captured by the same sensor on June 16, 2001.