Average Cloud Cover Map and Map Projections

We recently came across this article about a recently released map of average cloud cover for the last 13 years produced by NASA.

The map is provided in the form of an image and a high resolution version can be downloaded from NASA. It would have been nice to view it Google Earth. However, it is provided with a different map projection than is used by Google Earth image overlays. This is usually not much of a problem for small image overlays, but for global maps it is critical. Google Earth image overlays need to be in the Equirectangular Projection. The NASA cloud cover map is provided in the Hammer Projection.

Do any of our readers know of an easy way to convert global images from one projection to another? NASA provides this tool to convert from the Equirectangular Projection to a wide variety of other projections, but it doesn’t convert the other way.

NASA does provide daily and monthly images of cloud cover maps in the Equirectangular Projection. NASA includes the option to download them as KMZ files ready to be viewed in Google Earth.

NASA’s average cloud cover map for April, 2015 as seen in Google Earth. To see it for yourself download this KMZ file

Antarctica is of particular interest. It appears to have three distinct zones of cloud density. We guess that these correspond to:

• A region offshore with pack ice.
• The coastal ice shelves.
• The actual land, which is higher than the ice shelves.

Can any of our readers give a more scientific explanation?

About Timothy Whitehead

Timothy has been using Google Earth since 2004 when it was still called Keyhole before it was renamed Google Earth in 2005 and has been a huge fan ever since. He is a programmer working for Red Wing Aerobatx and lives in Cape Town, South Africa.

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