Matt Wronkiewicz’s Weblog

I’ve finished my first Google Gadget. It’s an up-to date map of the Earth using satellite imagery from the Aqua and Terra observation satellites. The satellite data gets downloaded from NASA GSFC and turned into tiles which work with the Google Maps API. No images older than 36 hours are used. There are other satellite maps available online which are more up to date or more complete, but not both.

Add it to your iGoogle homepage or use the interactive map page.I’ve been working on mapping satellite images off and on for about two years. I have a virtual globe program that downloads the images on the fly and lets you spin and zoom around, but it was never in a state that I could distribute it. The biggest problem was that it makes heavy use of NASA’s web server, and I didn’t think they could take the load if lots of people were using it at the same time. The gadget gets around that problem by hosting a reduced resolution map on my own server. If the load gets too much for my web host, I can make use of Google caching, but that has its own problems. There are some defects in the map stitching. MODIS Rapid Response serves the images as JPEGs, with stuff drawn on them. Also, absent data and heavy cloud cover look exactly the same in the images, so picking them apart is a difficult problem. That’s why there’s some occasional white noise or white regions in the map. Finally, NASA doesn’t publish the geolocated satellite images until about a day after the image is taken, so I had to do it myself using the orbital elements of the satellites. I don’t think the orbital elements are exact enough for this, and I think I have some errors in the algorithm. This means that some parts of the map are shifted slightly from the correct locations.

Still, I think the resulting map came out really good. It’s fun to watch as clouds swirl around, dust blows off the Sahara, snow covers New England, and fires consume my home state.