Obtaining Landsat 7 images

Landsat 7 was launched successfully on 15 April 1999. More details are available on:

http://geo.arc.nasa.gov/sge/landsat/l7status.html

The following information on obtaining Landsat 7 data was recently circulated by: Serge Andrefouet, Frank Muller-Karger and Chuanmin Hu

Landsat 7 images are now available. The test period of Landsat 7 and the ETM+ sensor was completed in early July 1999. Since then, around 20,000 images have been acquired, and a significant number of scenes include coral reef areas. The useful web sites if you are interested in these images are:

Documentation on Landsat sensors:

http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_toc.html

Landsat project:

http://landsat7.usgs.gov/

http://landsat.gsfc.nasa.gov/

Main Landsat data gateway:

http://edcimswww.cr.usgs.gov/pub/imswelcome/

http://harp.gsfc.nasa.gov/~imswww/pub/imswelcome/plain.html

Other gateways (US and international):

http://harp.gsfc.nasa.gov/~imswww/pub/imswelcome/imswwwsites.html

Landsat 7 data ordering tutorial via main gateway:

http://edcwww.cr.usgs.gov/landdaac/tutorial/

Tool to retrieve browse products (i.e. quicklook):

http://edcwww.cr.usgs.gov/landdaac/convert/hdfconvert.html

Useful ordering info:

http://harp.gsfc.nasa.gov/~imswww/pub/imswelcome/imswww.faq.html

http://edcwww.cr.usgs.gov/landdaac/tutorial/tips.html

Current coverage since beginning July 1999:

http://landsat7.usgs.gov/currentcov.html

Landsat software:

http://ltpwww.gsfc.nasa.gov/LANDSAT/CAMPAIGN_DOCS/MAIN/Software.html

Image processing handbook:

http://rst.gsfc.nasa.gov/TofC/Coverpage.html

If you want to browse, visualize and order Landsat 7 images, you need to do the following (sounds complicated but is not):

  1. Check out one of the gateways. You can enter as a guest or registered user.
  2. You must select the Data Set Catalog you want (Keyword: Landsat or visible imagery). This is on the Simple form.
  3. Select the Dataset you want: for Landsat 7, you have L0R (raw images) or L1R (radiometrically corrected images). You will be able to order L1G (L1R images geometrically corrected) as far as you have identified the L0R or L1R in which you are interested.
  4. Select your research criteria. For this I recommend to switch to the Advanced Form. You can enter your region of interest (lat/long, or Path/row i.e. coordinates in World Reference System 2, or draw of box on a map), date, maximum cloud cover, etc...
  5. Launch the search and wait.
  6. If successful, the search provides for each Data Set the number of granules found. A granule is actually just an image.
  7. List your data granules (or images)
  8. At this stage, you can select individually each granule and ask for a sample (i.e. quicklook) to check if the images really cover your area and the cloud cover. When you request a sample, you have to fill a form and send it ("Start FTP browse request"). Few minutes later, you will receive an e-mail with the instructions to visualize your file. This e-mail contains a line with "FTPDIR:" and a number such as: FTPDIR: 1452716838

    To visualize your file, I recommend you not to follow the instruction of the e-mail but to open a new browser at:

    http://edcwww.cr.usgs.gov/landdaac/convert/hdfconvert.html

    You just have to input the number right to the FTPDIR to see your quicklook.

  9. Take a break
  10. If you are satisfied by the quicklook, have a credit card number in hand and between 400 to 650 US$, you can follow the next step to complete your order. Tests show that you will receive your image (CD or tape) in a few days (for USA). You can also download (FTP) your image.

Quicklooks:

We have put some quicklooks over coral reef areas at:

http://paria.marine.usf.edu/ftp/Serge/L7

The quicklooks are resampled images (ratio ~1/100) and do not reflect at all the information provided by the real images. They are of variable quality (e.g. Chrismas1 and Chrismas2) and they are not optimized for reef detection. As a reminder, Landsat-7 image swath is 180 km, the spatial resolution is 30 metres for the bands in the visible and 15 metres for the panchromatic band.

A txt file, Word doc file and Endnote file (.enl) including a (non-exhaustive) bibliography on remote sensing/coral reefs and related subjects (spectrometry, optics, image processing, ...) are also posted at: http://paria.marine.usf.edu/ftp/Serge/Biblio.

The Landsat Project must be acknowledged for their effort in integrating a significant number of coral reef sites into the Landsat-7 Long-Term Acquisition Plan (LTAP). According to NASA Headquarters, 8725 reef sites (reference ReefBase) have been integrated in the LTAP, and ~7500 have been surveyed during the first months of operation. There is still a priority setting for coverage among these reefs, from two images per year (most of the reefs) to 12 images per year for very high priority reefs or for special events (hurricanes, bleaching, ...). Images are not of course entirely cloud free but the process of acquisition is well in progress.

Feel free to ask any questions or make comments to:

serge@carbon.marine.usf.edu