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.  

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.

Downloading 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.

So 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:

ecosystems_map

                        el_salvador

                                        images

                                                    18_51_2009_11_25

                                                    19_50_2008_10_30

                                        dem

                                                    astgtm_n13w088

                                                    astgtm_n14w091

                                        vector_maps

                                                            elevation_lines

                                                            roads

                                                            hydrology

                                                            ecosystem_map

Available images

A very large volume of low costs is available; the links below will help you find it.
Also...here is an update on the three Landsat datasets that NASA is in the process of releasing. There is one each from the '70s, 1990, and 2000. These satellite cover virtually the entire earth, are available at no cost, are as cloud-free as possible, and are ortho-rectified (geometrically excellent). These are/will be available at the first two websites (the first one may apply a nominal handling charge). A large number of scenes are available now and others are forthcoming. The release of this huge volume of free very high quality data at no cost is truly a fantastic thing.

Lastly, with so many free data, and with some fairly friendly search tools now available to help find it, the limiting factor for many conservation people now seems to be in actually viewing and using these satellite images. Special formats and sophisticated and expensive tools can make this difficult. We are hoping to try to fix that, and the ASTER Protected Area Archive should be a good start once it becomes available. APAA will allow users with no experience in remote sensing to view ASTER (and hopefully other) images and perform some basic functions. For more information on APAA or to download a demonstration go to http://asterweb.jpl.nasa.gov/APAA/default.htm

Some Options for Obtaining low-cost or free Satellite images:
1. http://lpdaac.usgs.gov. An archive that includes ASTER and Landsat data (and MODIS--see below). ASTER is available at US$60 per scene, or at no cost, depending on the type of product you order (all "higher-level" products are free and this should work well for most people, especially the Surface Radiance product--see the Custom ASTER Data link). 

Landsat satellite images is about US$600 per scene.
Recommend you use the "GloVis tool" (also called the Browse Viewer) for locating the scenes of interest as it is much friendlier than the alternative.
The steps are:
a) Find the scenes of interest using GloVis (Browse Viewer). Be sure to select ASTER or Landsat as appropriate b) Order them--follow instructions
c) For ftp orders...wait for the order to be filled (usually within 24 hours...note this option requires a very fast network connection)
d) Download the data or wait until they come in the mail
2. http://glcf.umiacs.umd.edu/index.shtml 

Before buying any image, always search here first and see if you can get an appropriate image for free. This link may lead directly to the ESDI database: 3. http://glcfapp.umiacs.umd.edu:8080/esdi/index.jsp

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. (US$25-50)

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.

When comparing costs between ASTER  and Landsat, one must take in consideration that Aster cover 60 X 60 km, while Landsat covers an area of 180 X 180 km, which is 9 time larger. As a result, the difference in price per area covered is rather small. But if you just need a specific small location, you would be better off buying that location from ASTER.

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.

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:
http://science.nature.nps.gov/im/monitor/lulc_rs.htm

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 

Other important sites to visit:

Thanks Dr. Gary N. Geller for helping us all with access to completely free and low cost satellite images and other tools and sources for data acquisition. 

For the USA:

This site links per state, the possibilities to download maps and aerial photographs. The page is from 2005, so many links are dead. But with a bit of searching in the link domains you may still find what you are looking for. Good luck!

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