|Figure 1. Yellowstone National
Park. 1989 image (above) showing
the fire scars, 2002 image (below)
showing the re-growth.
Dr. Bruce Quirk
Program Coordinator, Land Remote Sensing Program
U.S. Geological Survey
Introduction and Background
On July 23, 1972, the National Aeronautics and Space Administration (NASA) launched the Earth Resources Technology Satellite (ERTS-1) a satellite designed to acquire global coverage of the landmass of the planet, data which would be used to monitor ‘Earth Resources.’ The satellite was the brainchild of Dr. William Pecora, former Director of the U.S. Geological Survey (USGS) and Assistant Secretary of the Department of the Interior.åÊ Pecora had noticed that photos from the early manned space program had given scientists a fresh perspective on the land features and he felt a dedicated satellite series would be useful for monitoring the dynamics of the Earth’s surface.åÊ ERTS-1, soon to be changed to Landsat, was the first of a series of satellites, which, to this day, offer scientists, educators, resource managers, and the general public an important ‘photo album’ of decades of Earth observations.åÊ It is the responsibility of the USGS to collect the data, make it available to interested parties and to continue the success of the satellite series into the next decades.
Today, Landsats 5 and 7 continue to collect data. The Landsat series offers a remarkable record of observations at a fairly consistent scale (resolution has increased from 79m to as high as 15m) in a consistent format and area of coverage. The data are measured in wavelengths of energy from the visible to the thermal portions of the electromagnetic spectrum.åÊ That, in itself, has proven a valuable tool as certain features show more prominently in certain bands.åÊ Healthy vegetation can be measured through subtle comparisons of ‘bands’ of recorded reflected light; certain geological features are identified using other bands.åÊ A data file from 1972 over, for example Yellowstone National Park, can reasonably be matched with an image acquired in 2009 (Figure 1). The 2.4 million scenes in the USGS archive represent the largest civilian collection available of global coverage at a compatible scale and format.
The Value of the Data
There is a basic principle involved in the data collection. Think in terms of a family photo album. Why collect pictures? Because we welcome a permanent record of people and ‘conditions’ at a particular time. And, while children grow, others pass away or move. We have a record of what they looked like at that point in time. The same applies to the planet. We can examine the vegetation patterns before the Chernobyl incident and compare the changes over a period of time. For example, cultivated crops were replaced by large forests as agricultural production moved to other regions. A number of Landsat images have been placed on a USGS ‘Image Gallery’ (http://landsat.usgs.gov/gallery.php) to demonstrate the variety of images available (Figure 2).
In the Shanghai area of China major population shifts have taken place in the past decades (Figure 3). Landsat data record the growing urban expansion and the loss of agricultural land as the population grew, causing, as well, additional stress on water supplies.
In tropical zones clear cutting of forests has impacted soil conditions, erosion potential and changed the dynamics of agricultural production. The thirty + years of Landsat observations have proven invaluable for measuring the alteration of land use worldwide.
At the same time, Landsat data are useful when more immediate changes happen. The USGS is a member of the International Charter for Disaster Relief. When the tsunami devastated portions of Southeast Asia, Landsat data were combined with other government and commercial data to record the level of devastation.
|Figure 3. Shanghai, China region
1984 (above) and 2005 (below).
When events, natural or anthropogenic, call for moderate resolution observations Landsat data, compatible with previous observations, have proven to be important for evaluating the breadth and dimension of the area affected.
Accessing the Data
An important role for the USGS is to make the data easily available. To that end the USGS has developed an efficient system which will have a profound effect on data users and providers in the years to come. Images can be previewed and downloaded at no cost from two search engines (http://earthexplorer.usgs.gov/ and http://glovis.usgs.gov/).
Beginning in mid 2008, through stages, the entire Landsat archive was made accessible through the Internet at no-cost and without restriction. As of late 2009 global users have downloaded over 1 million scenes.
What does this mean? First, the demand for data will only grow. Secondly, no-cost data makes the data available to a much wider audience and with those new users new applications, based on increased familiarity, are likely.
Educators have long tried to use the Landsat data and have made progress in developing innovative applications. However, until recently educators have had limited access because of the cost of data. With the no-cost access the ‘door to the archive’ is open. One can foresee new interest and uses of the data as a new generation of students have access to the data and their growing familiarity can only increase their Û÷comfort’ with the data.
Landsat data have been a solid foundation for Earth observations since 1972 and have proven important for studying the dynamics of global change. The next generation of users will have more immediate access and understanding of the data and will be more likely to apply the data to future resource challenges.
Landsat 5 was designed to last only three years. It has completed over twenty-five. Landsat 7, with a five year design life, has been providing data for over ten years. While both satellites have developed problems, they continue to extend the observation record started by Landsat 1.
The USGS and NASA are involved in the construction of the Landsat Data Continuity Mission (LDCM), a mission to provide the next generation of Landsat like observations. Scheduled for launch in December of 2012, LDCM will provide a consistent, compatible set of observations of the world (Figure 4).
NASA and the USGS are also starting to investigate a follow-on mission to LDCM, consistent with the recommendations of the National Science and Technology Council’s report, a Plan for a U.S. National Land Imaging Program that, if implemented, will assure the global science community of U.S. interest in continuing the remarkable record of Landsat type Earth observations.