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Ideas For Exploiting NASA's SRTM Data
MaxTardiveau writes with an excerpt from an article where the pictures are worth clicking through for: "Ten years ago, in February 2000, NASA mapped the entire world in eleven days. It's true: the mission was called the Shuttle Radar Topography Mission (SRTM), and over the course of eleven days, it used a big radar attached to the space shuttle to get elevation data from the vast majority of solid Earth; practically all land between 60 degrees North and 56 degrees South was included, with a resolution of 30 meters (90 feet). Over 9 terabytes of data were captured. It then took two years to process that data and make it usable (and it is still being refined to this day). This data is freely available to anyone, and the number of possible applications is almost infinite. It's been used in GIS, cartography, environmental planning, weather modeling (weather patterns are enormously influenced by the topography), flight simulators, Google Earth, and the list goes on. In this short article, I would like to give you a quick tour of the kinds of things this data can reveal. My hope is to get you thinking about what else could be done with this incredible resource."
It's just perfect use for games, from flight simulators to city building and civilization series. It's a lot more fun to play on real terrain.
The raw data, as well as data from multiple other sources can be downloaded from NASA's Earth Explorer http://edcsns17.cr.usgs.gov/EarthExplorer/. The article doesn't really address the fact that the Google data has been cleaned up a lot. SRTM has a lot of voids and areas of poor quality, especially over mountains. The resolution of the data is worse for anywhere outside of the USA.
I know Americans like to equate meters with yards, and when dealing with a small number, this is a close enough approximation for most purposes. However, 30 meters is 98.4 feet, so a better approximation for the purposes of this post would have been 100 feet.
Didn't we learn our lesson regarding sloppy unit conversions during one of our recent multi-million dollar collisions with Mars? ;)
Proud member of the Weirdo-American community.
Actually it's lower resolution then many other maps, It does have very high coverage, The problem is trying to find a pass that doesn't have to much cloud cover. As someone who does GIS for a living, I can say we usually use this data til we can get a LIDAR Plane over the prospect.
As much as it would be useful to scan all the sea for height data I suspect that the vast majority of the sea is at sea level.
The Canadian RADARSAT-I and RADARSAT-2 satellites have better data. Resolution goes down to 3 meters if desired, and is 25 meters normally. That's much better than what NASA has. Here's Ottawa seen by RADARSAT-II. Here's Paris. They did it first, too; here's RADARSAT-I's first image from 1995. RADARSAT-I was launched from the US on a Delta booster back in 1995, but RADARSAT-II was launched from Kazakhstan on a Soyuz booster
They collect amplitude, phase, and range data, so they can do processing to get false-color images which bring out terrain features. Here's Washington after processing.
RADARSAT is a commercial service. You can order images. The base price for a custom image (taken at your request, not from the archive) is $5400CN. Wait time is a week or two. If you're in a real hurry, an additional $4,800CN rush charge gets your picture taken within about 12 hours. Archival data is much cheaper, and is available from MDA Corporation. MDA also has data from Ikonos, Quickbird, Landsat, etc. Much topo data comes from those archives already.
Unlike the NASA data, this data is good enough to easily tell land from water. Better radar systems return "first and last" returns, which, over wooded areas, return both ground height and tree height, so areas of vegetation can be detected. The Washington DC false-color image shows all this.
It doesn't take all the NASA overhead of putting people in space to do this. The private sector is doing it just fine.
OpenStreetMap uses this data to give the elevation contour lines on the cycle map rendering. Eventually, it'll be used to guide cyclists on a flatter, faster (but possibly slightly longer) route to avoid the steep stuff.
Furries make the internet go.
Hopefully this will spur more interest in some of the many tools that NASA provides for free on its website. There are many free Java applications (standalone or jnlp) to view the data or embed it within your own application. Though the documentation is not always the greatest, with a little tinkering you can make interactive websites for anything from planning your camping trip to searching for ancient meteor craters.
http://worldwind.arc.nasa.gov/java/
Though a lot of the sources are availble, many of the Linux distributions don't have an easy way of building them. It's a real pain to build, but the results are spectacular.
I suspect that the vast majority of the sea is at sea level.
The Earth's gravitational field is not purely radial, resulting in very significant deviations from mean sea level over much of the ocean's surface. I believe the deviations can be up to tens of metres--I may be recalling incorrectly but I think there's a big one in the South Pacific that is something like 60 m deep and is getting on for a thousand kilometres across.
Blasphemy is a human right. Blasphemophobia kills.
That's not a gravity anomaly. Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn!
First, a quick reaction to your post. Radarsat-1 and 2 data, in regards to DEMs, is far from being comparable. The SRTM mission was dual-antenna interferometry, with Radarsat (or Envisat), you must use two images at different times. DEMs from Radarsat can be good and better than SRTM, but it's pretty expensive and there are alternatives (in Canada: CDED1 data is free and in many cases much more reliable than Radarsat data).
If you ever want to use SRTM-DEM data, check the CSI-CGIAR version 4 version. It's the best out there, it's a *major* improvement over the original and previous versions. If you're in hydrography, look at HydroSHEDS SRTM-DEM data.
This year, the advent of the ASTER-GDEM (global DEM) diminished the interest of SRTM-DEM. ASTER-GDEM is still "research-grade", but offers higher spatial resolution, and most important, cover much more land than SRTM (northerm Canada and URSS).
On top of my mind, don't forget SRTM-DEM is available at a higher spatial resolution over the USA than elsewhere (1 arc-second vs 3). The 1-arc-second for the whole world is suppose to become available some time in the future, but that has not happened yet. Also, the X-band (the actual SRTM-DEM comes from the C-band data IIRC) is in the hands of the Germans, but to my knowledge, no public DEMs has come out of it yet (even after all those years). Still relying on my memory (I can be mistaken, see next paragraph), the TerraSAR-X in orbit should be able to give us an even better near global DEM than what's available at the moment.
Sorry for the lack of links. I'm still in my holiday break and you can simply google your way in. Or search SRTM on the site in my sig! have fun -
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