Tag: ASTER

The topographic Earth

By Phil Plait | October 18, 2011 1:30 pm

This is pretty nifty: a new elevation map of the Earth has just been released by NASA and Japan. It’s a "significantly improved" version of one that came out in 2009.

It uses Japan’s ASTER, the Advanced Spaceborne Thermal Emission and Reflection Radiometer, an instrument on board NASA’s Terra satellite. Terra is an Earth-observer, with detectors on board used to study various properties of our planet. ASTER looks both straight down and slightly behind the satellite’s track on the Earth is it passes. Over time stereo image pairs are created, and these can be used to create very high-resolution elevation maps (called topographic maps) of the surface of the Earth.

The new images are higher-res than before, and cover the Earth better to the tune of 260,000 more images. As an example of what can be done, they used it to make this map of the Grand Canyon:

[Click to enmesanate.]

One thing that struck me as funny when I read it: the coverage of ASTER’s observations goes from the Equator to as far north and south as 83° latitude… and they say that this is 99% of the Earth! That sounds odd, doesn’t it? You’d think the north and south poles of the Earth from 90° to 83° would be more than that, but in fact it’s true.

The portion of a sphere above a certain latitude line is called a cap, and the area of that cap depends on the latitude in question, and the radius of the sphere. I drew myself a diagram, fiddled with the numbers a bit, and found that the area of the Earth north of 83° compared to the surface area of the northern hemisphere is about 0.75%! So in fact, ASTER covered a bit more than 99% of the Earth’s surface, even if it never got past that 83°latitude.

Math! Surprising people since the time of Pythagoras.

Anyway, if you want to download the ASTER data yourself, you can: it’s public. Japan has a copy, and so does the USGS. I imagine it won’t be long before it’s integrated into Google Earth and all that too. Living in the future is pretty cool.

Image credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team


Related posts:

- Staring down an active volcano’s throat
- The Earth’s lumpy gravity
- Satellite view of a volcanic pressure valve
- Volcano study in red

CATEGORIZED UNDER: Cool stuff, NASA, Pretty pictures

Volcano study in red

By Phil Plait | November 16, 2010 9:00 am

I focus a lot of attention on NASA images of space, from our Moon to distant quasars. But NASA has a fleet of satellites which don’t look out, they look down, studying our home planet. One of the most amazing and beautiful of their targets are active volcanoes, like Mount Merapi in Indonesia:

aster_merapi

[Click to hephaestenate.]

Merapi has been active for some time, blowing out hot ash and dust. This material can blast down the slope of the volcano in what’s called a pyroclastic flow, one of the most terrifying events I think the Earth can produce. It’s a wall of vaporized rock that can move very rapidly; Merapi’s flows have been clocked at 150 kph (90 mph).

In this image, taken with NASA’s Terra satellite on November 15, vegetation is shown in red (not green; the detector used by Terra can see light in the near-infrared, where plants are highly reflective, and this is colored red in the images). The ash and rock from the volcano appear gray. You can see where pyroclastic flows have flooded the forests on the volcano slope, destroying whatever plant life they touch. You can also see white clouds, and the gray plume of ash from the crater itself. Note that I have rotated the image so that north is to the left; I did this to make it fit better on the blog.

The long, feather-like finger to the right is the Gendol river, choked with mud flows called lahars which cascade down the mountain (much of the damage done by Mt. St Helens in 1980 was through lahars). Just below the river is a squiggly red region; that’s actually a golf course that’s been hit by a pyroclastic flow.

Images like this help scientists keep track of volcanoes in near-real time. While there is a chilling beauty to them, satellite images of volcanoes can be used to understand how they behave, and in a very literal sense help save lives. Yogyakarta, for example, is a city of nearly 400,000 people located not quite 30 km (18 miles) south of Mount Merapi. If I lived there, I imagine I’d be very happy indeed that people are keeping a close eye on the not-so-sleepy giant to the north.

Image courtesy NASA/GSFC/METI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team


Related posts:

- Satellite view of a volcanic pressure valve
- Blowin’ off some scream
- The one-dimensional volcano
- Plume and ash


CATEGORIZED UNDER: NASA, Pretty pictures

Terra spots a volcanic plume

By Phil Plait | December 9, 2009 7:39 am

On NASA’s Earth Observatory site, a picture was just posted that’s too pretty not to share. It’s a plume escaping from the Bezymianny Volcano in Kamchatka on November 25:

nasa_bezymianny

Cooool. It was taken by the Earth-observing satellite Terra, using ASTER: the Advanced Spaceborne Thermal Emission and Reflection Radiometer. The image is in false color; the white plume suggests it’s mostly steam, and not laden with the usual ash and dust (the brown you see in the image is the shadow of the plume on the terrain).

I highly recommend the Earth Observatory website Image of the Day if you like looking at beautiful imagery of our home planet. And if you have more suggestions for such sites, leave them in the comments below!

Image credit: Robert Simmon, based on data from the NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team.

CATEGORIZED UNDER: NASA, Pretty pictures
MORE ABOUT: ASTER, volcano
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