Tuesday, January 15, 2008

Google Earth does Clouds!

As indicated in a previous post, I love Google Earth. It's educational, it's easy to use, it's just fun!

So, I was checking it out on my lunch break today and I noticed a weather section in the "Layers" toolbar on the right-hand side. One of the options is to be able to view cloud coverage. Look under Primary Database\Weather\Clouds. Select the option, and you will receive a current cloud situation as well as the ability to animate the image.

Here's the scoop from the Google Earth help file:

"Since the 1960s, the capability to view Earth's cloud patterns from space has been made possible from two main types of environmental satellites, geostationary Earth-orbiting and low Earth-orbiting satellites. At least five geostationary satellites positioned around the equator are capable of providing depictions of global weather patterns, updated every hour. From their vantage point 36,000 km above the equator, the sensors onboard geostationary satellites can't quite 'see'the very high latitudes near the north and south poles. Since their orbit flies over the high latitude regions over the north and south poles typically every 90 minutes, low Earth-orbiting satellite imagery is well-suited to complement the geostationary imagery and thereby provide total global coverage. Even so, such satellite data merging is complicated by the fact that each individual satellite observation represents a single 'snapshot' of the cloud patterns, each taken at slightly different times, whereas the underlying clouds themselves are constantly moving and evolving.

In this depiction of global clouds, these satellite data are processed to discriminate clear (transparent) and cloudy areas. For cloudy areas, the brightness is approximated based upon the cloud top temperature relative to the surface temperature, as a proxy for the height of each cloud pixel. Due their location near the Earth's surface, low level clouds such as stratocumulus and stratus (fog) clouds may be poorly represented. For more information, visit the Naval Research Laboratory (NRL) Marine Meteorology Division."

The image that is produced is quite interesting and useful. Check out the example to the left (click on it for full scale image). As you would expect, you get a close-to-real-time view of cloud activity over the selected area. At quick glance, it looks like you get coverage over most of the globe, although the animated feature is a bit quirky and seems to only work for the USA (?).

Anyway, this could be a useful tool for planning your astronomical observing sessions, coupled perhaps with local weather forecasts and the Skyclock website.

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