The NASA Gateway to Astronaut Photography of Earth is the first new source of free satellite data that I have reported this year. This site is huge, claiming 546,548 images in total including 112,819 from the International Space Station. Although there may be some overlap with other NASA databases, for example EarthKam, this is clearly the largest compilation of Shuttle and Space Station Imagery anywhere on the internet. The site claims astronaut-acquired imagery dating to back 1961. Moreover, the data is conveniently catalogued with important metadata included.

The first challenge is to get into the site. At the time of writing, the link to access the data is a small one at the upper right of the web page that says merely "find photos" in microscopic font. Selecting this link opens the type of clickable map user interface that is becoming standard and should be quite familiar to users of this type of data. It took only two clicks to reach the index. The index is also conveniently arranged with browse images to the left. To order, click on the image index number link. You will be asked to fill out a short form and then download directions will be emailed to you. (This is probably a device to prevent automatic bots from tying up the bandwidth by repeatedly downloading large lists of images.)

After a few minutes, download directions will arrive by email. You will be able to either download using your web browser or else by ftp. Note: the ftp directions are a little confusing. You will want to connect to eol.jsc.nasa.gov using user name "anonymous" and password your email address. The email will instruct you to CD LargeImagesTemp but this did not work for me. I instead found my image listed in the main directory and downloaded it without problem.

I found that there were two advantages to ftp as opposed to web browser. Downloading from the browser gave me a .bmp image instead of the .jpg format that the file name indicated was the native format. Secondly, opening the main directory via ftp apparently gives you immediate access to the current list of requested images. You may find something that interests you, especially if you know what index number you are looking for.

The image quality for the data is similar to that from other NASA imagery sites: dicey. A search of the region that I explored in the Chilean Andes near the Bolivian border yielded about five useless images (100% cloud coverage) three so-so images (muddy, high obliquity) and two outstanding images, which are shown at the right. These seem to cover an area approximately 50km square each.

Considerable interesting metadata is supplied on the web page. This includes information on the origin of the image, camera obliquity, cloud cover, coordinates, camera information, footprint area, sun angle, sun azimuth and much more. However, I did not find a metadata file where all this information can be downloaded.

Another interesting feature of the website is the image transformation tutorial presented by Bill Innanen. This creative piece presents a "poor man's" approach to color correction and "orthorectification". While professional image analysts may be appalled, the results are impressive and quite good enough for many amateur applications.