Frequently Asked Questions
- What is GLCF?
- What does the GLCF research?
- Who funds GLCF?
Data Product Information
- What data does GLCF have?
- What derived products does GLCF offer?
- I am new to remote sensing and GIS. What can I use this data for?
- Do I have to pay for the data I find on your web site?
- What media can you provide data on?
- I don't see the data I am interested in on your site. Can I still get it from you?
- How long before I get my order?
- I would like to share my data with the Earth science community through GLCF. How do I do this?
- How to order Landsat-7 (ETM+) data through the GLCF?
- What are the Landsat7 band ranges?
- I downloaded a file with an L1G extension. What does this mean?
- What is Orthorectification?
- What is this Citation?
- I am having difficulties downloading data from your site. What should I do?
- Do you provide support for your products?
- How large are the data sets you offer?
- I have downloaded data from GLCF but cannot open it with my image processing program. How do I do this?
- I am using ArcView, how do I import your imagery?
- I am using ArcInfo, how do I import your imagery?
- What is my Workspace?
- I am doing a MS Power Point presentation and need visuals. How do I get these from my Workspace?
- I came across band files that seemed to be infected with a virus.
- How do I open imagery in IDRISI software?
1. What is GLCF?
The Global Land Cover Facility (GLCF) provides earth science data and products to help everyone to better understand
global environmental systems. In particular, the GLCF develops and distributes remotely sensed satellite data and
products that explain land cover from the local to global scales.
2. What does the GLCF research?
GLCF research focuses on determining land cover and land cover change around the world. Land cover is the discernible
vegetation, geologic, hydrologic or anthropogenic features on the planet's land surface. These features, such as
forests, urban area, croplands and sand dunes, can be measured and categorized using satellite imagery. Land cover
change can be assessed by comparing one area with two images taken at different dates. Determining where, when, how much
and why change occurs with land cover is a crucial scientific concern. It is imperative that appropriate tools be made
available to better manage and adapt to change.
3. Who funds GLCF?
The Global Land Cover Facility though primarily funded by NASA has received funding from other federal agencies such
as National Science Foundation and the United States Geological Survey. We have also received funds from foundations
and private organizations.
Data Product Information
4. What data does GLCF have?
GLCF currently holds over 50 terabytes of raw and derived remotely sensed products. Our composite holdings are listed at
5. What derived products does GLCF offer?
GLCF offers land cover, percent tree cover, forest change, radiative flux and other derived products. All are available
6. I am new to remote sensing and GIS. What can I use this data for?
The data provided by GLCF can prove useful in global, regional and even local analyses of the earth's surface. Many of
our derived products, such as our 1km global land cover product can be particularly useful when combined with higher
resolution data types such as Landsat TM, ETM+ and MSS.
7. Do I have to pay for the data I find on your web site?
Not currently. The GLCF has taken extraordinary measures to ensure that users of our data are not charged when they
download from our web site. If individuals require a hard copy, for small orders, we request a $25 + shipping fee per
item ordered for the cost of media, postage and labor.
8. What media can you provide data on?
For small orders the GLCF primarily provides data on CD-ROM. For large orders please
9. I don't see the data I am interested in on your site. Can I still get it from you?
In addition to our partnerships, GLCF has a team of remote sensing and computer science professionals who have designed
a suite of in-house processing utilities. These tools allow us to purchase raw data at a cheaper price than standard market.
After we process the data, the savings always translates back to our users. Data is never degraded in quality.
10. How long before I get my order?
That depends on whether the requested data is in-house or not. In-house media duplication has a very short turnaround
period. Most orders are processed and shipped within five working days. If imagery is being purchased or needs to be
pulled from deep archive media, expect an extended delivery period; less than two weeks is usually possible.. For
individuals who have more stringent time requirements, rush service may be negotiated. This will be at a significantly
higher cost, however.
11. I would like to share my data with the Earth
science community through GLCF. How do I do this?
The GLCF has received valuable data contribution from its users, and is thankful for their contribution to the free
Landsat archive, available at GLCF. Contributions to the GLCF can be transferred either via FTP or mail. Please
contact us prior to sending the data, so that we can make proper arrangements and give the proper credit to the
person(s)/ organization that sent the data.
Please Contact us
and we will make arrangements. Also, please keep in mind that we share our
data, we do not profit from it. Reciprocity on the part of the user community is greatly appreciated.
12. How to order Landsat-7 (ETM+) data through the GLCF?
In order to purchase data through GLCF we request users to provide us with the following information:
- Number of scenes
- List of scenes path/row/acquisition date.
- Urgency of the purchase*
If we purchase data in bulk, i.e. 25 scenes, we get a discounted rate $380 USD per scene versus $475 USD for Level 0R
data**. This doesn't mean that you have to have 25 scenes, we have other users in the science community or other
projects that would like to purchase data, and we can combine all of the orders to add up to 25, to get the bulk rate
price. There is no certain time frame for this. However, this doesn't guarantee the fact that we will always be able to
provide you with the bulk rate price. If we don't have 25 scenes to order over a period of 3 months, we notify the user.
Once the order is placed and we receive the data, we process the Level OR data to Level 1G using the LPGS-Lite
software. Depending on the size of the order, it usually takes 3 - 5 business days to process the scenes. Then we make
the scenes available via ftp for free. If you would like a to get your Level 1G data on CD, there will be a $25 USD +
By purchasing data through us your are not only helping yourself, but you are also helping us provide data to other user
and projects in our science community that might need the same data. GLCF strives to provide free data to the science
community, and hope that you as a user will help us attain that goal.
*If you want to purchase Level 0R data immediately, with out the bulk rate, send the request in as urgent.
** We recommend our users to purchase Level 0R data, which cost $475 USD (non bulk rate) versus Level 1G data which is
for $600 USD. We can process Level 0R data to Level 1G and provide you via ftp for free.
13. What are the Landsat-7 band ranges?
||Spectral Range (microns)
||Ground Resolution (m)
||.45 to .515
||.525 to .605
||.63 to .690
||.75 to .90
||1.55 to 1.75
|6L (low gain)
||10.40 to 12.5
|6H (high gain)
||10.40 to 12.5
||2.09 to 2.35
||.52 to .90
14. I downloaded a file with an L1G extension. What does this mean?
"L1G" is indicative of "Level 1G", meaning the data has been process to level 1 and is radiometrically and geometrically
corrected. Note this is a systematic (automated correction) and does not mean that the pixels in the image are
georeferenced. However, NASA claims that the Landsat 7 data is accurate to within 3-4 pixels. This is usually the case,
if not better. In order to indicate processing level - not format - we have added the "L1G" extension.
The format of the L1G data is "Unwrapped HDF". This means that in some image processing packages, you may easily
download the _HDF.L1G file and load that, gaining access to all the HDF metadata, from corner point locations to sun
zenith angle. This can be very helpful, particularly if you would rather not enter the specifications of each and every
band by hand.
Other users may prefer to load each band individually or their software may lack support for HDF. In this case, you
need to load each band separately as a generic binary file. Most image processing packages will query for spatial data
information for the file, and this can be found in the *.MTL.L1G file.
15. What is Orthorectification?
Orthorectification is the process by which the geometric distortions of the image are modeled and accounted for, resulting
in a planimetricly correct image. To put it another way, our 3D world is imaged by most sensors in 2D and orthorectification
corrects for many of the anomalies resultant from this conversion. Orthorectified imagery is particularly useful in areas
of the world with exacerbated terrain features such as mountains, plateaus, etc.
The orthorectification process yields map-accurate images which can be highly
useful as base maps and may be easily incorporated into a GIS. The success of the orthorectification process depends on the
accuracy of the DEM and the correction formulae. In the case of the data provided by GLCF, the most accurate publicly available
DEM was used and an RMS error of 50 meters or better can be expected.
16. What is this Citation?
The use of the word 'citation' in this instance refers to the spatial data itself. The intellectual property rights for
this data set are specified in this reference. The spatial data itself is a property that must be cited on its own,
which this citation facilitates. Related publications are separate intellectual properties that are cited elsewhere,
usually under the 'Publications' heading on 'Description' pages. Please note this distinction when applying citation
information for this or any other product.
17. I am having difficulties downloading data from your site. What should I do?
If you are behind a firewall, your Web browser or FTP client must support and be configured to use passive transfer
mode. Most modern versions should switch to this mode automatically. If you are on a slow connection, try using an FTP
client instead of your web browser to download the files. When clicking on a scene in the "Preview & Download" screen, a
link to the FTP directory is available. Use that link in your FTP client. Our FTP servers support transfers that can be
resumed, so use an FTP client that supports this feature. You can also try downloading during non-peak hours (anytime on
the weekends or 03:00 UTC to 10:00 UTC on the weekdays).
18. Do you provide support for your products?
GLCF will attempt to accommodate all user requests. It is, however, assumed that users of our data do possess a modicum
of experience in remote sensing, image interpretation, GIS or the like. Please contact us
and we will address your issue as best we can.
19. How large are the data sets you offer?
Data sizes range from small ASCII files to raster files over .5GB
20. I have downloaded data from GLCF but cannot open it with my image processing program.
How do I do this?
Many of our files are served as binary files. This is due to the fact that support for binary raster files is relatively
standard across platforms and image processing packages. Usually one will need the pixels and lines and relevant
georeferencing information. This may be found in the metadata file issued with all data downloaded from one's Workspace.
If the data was served from a project-specific page, the metadata is either included in the download or is listed on the
21. I am using ArcView, how do I import your imagery?
22. I am using ArcInfo, how do I import your imagery?
23. What is my Workspace?
The Workspace is a virtual locale for storing search results. This way, AVHRR processing done in KRONOS or the results
of an extensive Landsat search may be saved and referenced thereafter. Occasionally we do clean out workspaces but
notification is sent to our mailing list first.
24. I am doing a MS Power Point presentation and
need visuals. How do I get these from my Workspace?
First, bring up the preview image. In the case of a Landsat scene, navigate to your Workspace then left click the link
to the image of interest. A preview of the scene and a list of associated files will appear to the right. Second, right
click the preview and select "Save Image As" from the drop down menu. This will give you a .jpg or .gif file to use with
your presentation. Note that the quality of previews is never as good as that obtained from the original image.
25. I came across band files that seemed to be infected
with a virus.
The band files are not infected with any virus. Occasionally this can happen when the file sizes are incorrect (i.e. you
may not have downloaded the whole file). You can try to download the file again (check all file sizes versus the sizes
given in your workspace).
26. How do I open imagery in IDRISI software?
To use Landsat imagery in L1G format in IDRISI 15.0, 'The Andes Edition', follow the steps below:
- Start IDRISI: In MS Windows this will require clicking either a desktop icon or an entry under the "Start -> Programs"
section of the Windows menu.
- Load the Bands:For purposes of this FAQ, the file may be loaded either as a generic raster file (Alternative 1, below) or as
an HDF file (if the file is from the GeoCover collection). Both alternatives utilize the IDRISI "IMPORT" function.
- Alternative 1 (Generic Raster): File/Import/General Conversion Tools/GENERICRASTER. For this alternative the user needs to download
the MTL metadata file from the GLCF Earth Science Data Interface. The file is a text file and needs to be opened in any text editor.
After the GENERICRASTER window is open, navigate to and select the image as the "Input File". Change the number of bands to "1"
(BSQ becomes the default file format). Consult the previously downloaded MTL file and enter the columns and rows. Do the same for
the minimum and maximum X and Y coordinates (these will correspond to the MTL file's "PRODUCT_UL_CORNER_LAT" field for minimum X,
"PRODUCT_UR_CORNER_LAT" for maximum X, etc.). The Reference System (UTM zone for Landsat), the reference unit and the unit distance
should also be entered. Click "OK" and the file will be imported. It will be added as a single band in the "Composer" window when the
import is complete.
- Alternative 2 (HDFEOS) (Landsat GeoCover Only): File/Import/Government/Data Provider Formats/HDFEOS. For this alternative, the user
will need to download the HDF metadata file from the GLCF Earth Science Data Interface. The HDF metadata file will have an extension
"*_HDF.L1G" e.g. L71116050_05019991004_HDF.L1G and will need to be saved in the same directory as the band file.
After the "HDFEOS to Idrisi Conversion" window is open, navigate to and select the "_HDF.L1G" file. Select the band to be imported by placing
a check mark next to the appropriate HDF Field displayed e.g. "_B10.L1G" would be band 1 and will appear in the Idrisi HDF list
as 1, L71116050_05019991004_B10 (x,y image dimensions). Click "Run" and the file will be imported. It will be added as a single band
in the "Composer" window when the import is complete.
- To Display Bands Separately (as gray scale): As a band is imported, a preview window is automatically displayed.
- To Display Bands as an RGB Composite: After at least 3 bands have been imported, in the Composer, select the option to "Add Layer".
Under "File Type" select "Raster", pick the band to be added and identify any additional options. Any of the individual bands (now three)
may be manipulated by using the colored buttons in the Composer.
A Note on Spatial Reference Data in IDRISI: In some instances the user may be required to enter spatial coordinates, pixels size, etc.
manually. This information is all contained in the *MTL_L1G file (Figure 1). More detailed information such as sun elevation, time of
acquisition, etc. is also available.
Figure 1: Contents of the MTL.L1G File
Please note that IDRISI is a product of Clark Labs (www.clarklabs.org) that is capable of using imagery for spatial analysis. For further
information, please contact Clark Labs.
We welcome users to provide similar FAQ materials to GLCF for this or other spatial data software.