|
|
The Planetary Society Blog
By Emily Lakdawalla
An embarassment of riches from HiRISE
Jun. 8, 2007 | 05:55 EDT | 09:55 UTC
Earlier this week, the HiRISE team announced the release of 1,200 images to NASA's Planetary Data System, which is the public repository for data from planetary missions. Actually, the sheer number of images is the least newsworthy aspect of this announcment. Space missions make releases to the PDS all the time, usually once a quarter, and there are usually many hundreds or thousands of images involved; 1,200, while a lot, isn't all that unusual. Here's the unusual number: 1.7 Terabytes. For those of you who are a little rusty with your little-used metric prefixes, "Tera-" is 1,000 times "Giga-", which is 1,000 times "Mega-". A Terabyte is a million Megabytes. That's a mind-boggling amount of data.
To put this in perspective, consider how that data is going to be delivered to scientists. Originally, planetary data was archived on the ground on gigantic magnetic tape reels; images were printed out on large-format photographs and stored at Planetary Data Centers around the country, where researchers could go, as to a library, and study them, or request copies (at not insignificant expense) from the PDS. CD-ROMs came as a huge relief; storing 600 to 700 Megabytes of data apiece, an entire mission's worth of data could be kept on a bookshelf, and more importantly, shared fairly cheaply to scientists. You can browse these CDs online through the PDS's various data nodes, like the Imaging Node. The Voyager mission's entire image data collection -- two spacecraft and six planetary encounters over 10 years -- fit on 38 CDs (with some duplication). Galileo's image data fit on 24 CDs, of which only seven contained data from the Jupiter system. To date, Cassini has filled 32 CDs with imaging data, of which 23 are from Saturn. This is all just image data -- of course all these spacecraft had other instruments, many of which have comparable or even larger data volumes than the cameras.
Mars missions produce more data, because the shorter distance between Mars and Earth makes higher data rates possible. The startlingly long-lived Mars Global Surveyor mission produced nearly 600 CDs worth of data from the high-resolution Mars Orbiter Camera, and from my browsing around on the PDS Imaging Node, that seems to be the last Mars mission that used the CD-by-CD format for delivery of images. How many CDs would HiRISE's first data release fill? 1.7 Terabytes, divided by 700 Megabytes per CD, is 2,500 CDs. I can conceive of a professional researcher's library containing 600 CDs for a complete Mars mission, but 2,500 for just the first release of many is clearly an impossibility. What to do?
Various Mars missions have come up with different answers to this problem. Mars Global Surveyor, the rovers, Odyssey THEMIS, and Mars Express HRSC each have searchable (or at least browseable) online data catalogs. The real news from yesterday's announcement from the Mars Reconnaissance Orbiter HiRISE team is the launch of their new website for finding, browsing, and saving image data. And it's absolutely fabulous, because it permits anyone to browse these huge images -- some of them are upwards of 2 Gigabytes on disk -- without actually downloading the whole image to your computer. There's a Java applet that downloads just the data necessary to fill your view window; and if you find a view you like and want to keep, you can save that part of the view to your disk. The home page has links to the week's most recent releases, but also has useful links to images cataloged by science theme (like volcanic features or fluvial processes) and a box to search by keyword (for instance, "Spirit"). It doesn't take very long for the Java viewer to download the necessary data -- especially when you compare it to the hours it took to download entire images before this new website came along.
Rather than put in screen caps here, I'm just going to encourage all of you to go visit the website and have a look around for yourselves!
|
|
[ what is this? ]