DATA ACQUISITION / FREE SATELLITE IMAGES
At the World Parks Congress in Durban, Gary N. Geller, Ph.D., SDSIO Contract Technical Manager of the ASTER Science Project with NASA informed the delegates that very low cost satellite images are available for downloading. On our request he prepared an overview of sites and links so that you may have easily accessible imagery that can serve for many conservation management purposes. Over the years, this page has been updates with findings of my own and new information from Gary.
Now, before we go any further, I recommend that you start your project in a very organized fashion, which usually starts out with receiving and downloading files and images. GIS projects may get quite messy when one works with a variety of maps and images.
The images are usually heavily compressed into .tar.gz files, which can be decompressed with " 7Zip ", a great free open source programme. These compressed files may contain a variety of file by wavelength or colour. Each of those files are quite large, so I would suggest to only extract the wavelength that you need. I prefer to work with .tif files but formats may vary by provider.
I highly recommend that before downloading and receiving files, you make a directory system with a folder for each image that you download and name them after path number, row number, year, month, day. If you do that consistently, your images will be automatically organized in the directory of your project. Only a very clean and well-organized directory structure will allow you to keep track of all the files in your project. A project directory may look like this:
A very large volume of free images is available; the links below will help you find them.
http://glovis.usgs.gov/ This is the official USGS distribution website for Landsat 4+5 and 7, as well as for ASTER. The website has tons of free images and it is always worth checking if thereare free image available for your area of interest. It runs the so called "GloVis tool" (also called the Browse Viewer) for locating the scenes of interest. You need Java installed in your browser but the site directs you there if your browser does not have it. Moreover, you must have "pop" enabled for the Glovis tool to function.
Landsat satellite images
Landsat covers an area of 180 X 180 km and has a 30X30 m pixel.
The difference between Landsat 5 and Landsat 7 is that
Landsat 5 however has far fewer images available but the recent ones available are far better because from 2003 onward, the Landsat 7 images show linear gaps: annoying black lines without information.
There seems to be a method to complete those gaps, but anybody I talked to never got it to work. For visual data interpretation though, it is a workable choice because there are many images per year and the gaps are never at the same place, so by switching back and forth, one can still digitize landuse, landcover, ecosystems, etc. This systematic historical availability is important, because one can search for cloud-free images during the season of choise (wet, dry, winter, summer, etc.) In the tropics, one wants the wet season to recognize the forests.
I recommend you use the GloVis
tool first. Register with your email address.
ASTER comes in 60 X 60 km images with a 15X15 m pixel. The ASTER satellite orbits Earth 14 times a day, but it does not systematically take pictures. The taking of pictures must be requested, but that is free for conservation purposes. So it is a great instrument for monitoring, but for acquiring historical data, it is less reliable, because it is difficult to find an image for each season for your area of interest over the last 5 or 10 years, something which is readily available for Landsat.
A lower-spatial-resolution alternative (250 m pixels, compared to 15 or 30 for ASTER and Landsat) would be MODIS satellite images, available at the first two websites for free. MODIS goes back to 2000. A strong point for MODIS is its frequent repeat coverage--it now covers the entire earth every day (which is pretty incredible). MODIS also has special support for monitoring fires--and can send you an email if a fire is detected in your area of interest. For fire data it is useful to consult http://www.nrlmry.navy.mil/flambe/ where you can see current fires on line.
Another site with a search tool is:
The Global Land Cover Facility, University of Maryland. It provides free (and also other products, including MODIS): http://glcf.umiacs.umd.edu/data/ The pages gives you and overview of the different available image types. The site particularly specializes in the Americas.
The real data are at Earth Science Data Interface (ESDI). Click on the ESDI icon on that site: . There you will find several convenient search modules:
Some other sites to check are:http://lpdaac.usgs.gov
Tropical Rain Forest Information Center, University of Michigan. Low cost and free Landsat satellite images, including very recent scenes. Focus is on tropical areas but some others are included. Some radar data are also available. http://www.trfic.msu.edu/
Finally, for those of you with lots of time on your hands, and a good Internet connection...if you are looking for a nice portal to many useful remote sensing sites, you might try this one:
TerraLook and ASTER
Gary continues to be a great supporter of protected areas and has worked hard at facilitating what he called the Protected Area Archive. Its purpose is to make recent and historical satellite images available at no charge in a simple "jpg" format. A user-friendly software tool to view and work with these images as well as with overlays such as park boundaries and vegetation maps is also provided. This often is needed for quick consults of materials. The news is that this system is now called TerraLook. It is fully operational and available for use. Images in "jpg" format and "TerraLook Viewer" can be downloaded from http://www.terralook.cr.usgs.gov. This material is also great for high schools and all students making their first exploring steps into the fascinating world of maps and satellite images. We feel that every field biologist and protected areas manager should have the "TerraLook Viewer" on his/her computer, along of course with the free open source user-friendly raster and vector GIS software "ILWIS", which is available from the Nature Worldwide Website http://www.ilwis.org
A new development is that New ASTER data acquisitions can be requested that will command the ASTER instrument to take pictures of a site of your choosing, at no cost. JPEG versions of those images are then available for free using TerraLook. So, by combining ASTER acquisitions with TerraLook, you can, for free, monitor any site on Earth on a periodic (perhaps annual) basis.
There are two types of requests for ASTER data. Larger requests use a “STAR”, in which case you send the information to Gary and he submits it on your behalf. Smaller requests (about 10 scenes or less) use a “DAR”, in which case, once approved, you use a website to submit the request (or requests) yourself. Both work well, and are described on the ASTER website at http://asterweb.jpl.nasa.gov/NewReq.asp
Note that approval is very easy, and if you need a lot of data, go ahead and ask for it. The ASTER team loves to provide data to conservation users, who are one of our heaviest users. Before submitting a request be sure that the existing archive does not contain images that fulfill your needs.
Thanks to Gary for providing such tireless support to the conservation community and many other users of satellite images.
Gary N. Geller, Ph.D. - Deputy Manager, NASA Ecological Forecasting Program - Conservation Liaison, ASTER Science Project Jet Propulsion Laboratory MS171-264, 4800 Oak Grove Drive Pasadena, CA 91109-8099 USA +1 818-354-0133 FAX: +1 818-393-1370 GMT -8 http://terralook.cr.usgs.gov
So, as a result of all those free data and the free ILWIS GIS and TerraLook Viewer, in less than a decade, GIS has become a completely cost free science available to anybody who wants to invest a bit of time to learn the GIS basics
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