Less than a year ago, we noted in a previous commentary for Space News [“Landsat 2005: Lost in the Wilderness Again?” Jan. 17, 2005, page 20], that the Landsat mission on the National Polar-orbiting Operational Environmental Satellite System (NPOESS) was rumored to be in trouble. Please do not shoot the messenger, but Space News has now reported that the Landsat Operational Land Imager will likely be removed from the manifest of the first series of satellites launched by the much troubled NPOESS program.
So where does this leave us with respect to Landsat?
The commitment to move ahead on an operational implementation of the next Landsat mission is still as strong as ever, reinforced by what we have learned about disaster monitoring over the last several months. The recent National Academy of Sciences review identified Landsat continuity as a near-term priority for NASA.
This observatory is a critical component in our societal capabilities to monitor and respond to natural and man-made disruptions of our day-to-day lives as well as keeping track of ongoing trends in land cover change, agriculture, forestry and related land dynamics.
The rumor mill once again is cranking out many alternatives of what might come next. The possibilities include:
– A government-designed and -procured mission, following the Landsat 7 model
– A science data buy approach, following the Landsat Data Continuity Mission/Resource21 model
– A government/industry collaboration derived from lessons learned from the above
At this juncture it is critically important to note that, so far, we have wasted more than half a decade exploring possible alternative approaches to continue Landsat into the future. Curiously, the anticipated engineering mission life of Landsat 7, which was launched in 1999, was only five years.
Landsat 5, which was launched in March 1984 and must hold some record for engineering duration, is about to expire. The Landsat 7 ETM+ Scan Line problem persists and Landsat 7 could quit at any time. Current Landsat 7 data quality falls short of what is needed. Many users have returned to the acquired Landsat 5 Thematic Mapper (TM) data rather than use degraded Landsat 7 data.
In the meantime our experience in working with large volumes of Landsat data, through the Landsat 7 long-term acquisition plan and projects such as tropical deforestation and the North American Carbon program, have quickly taught us that one sensor of this class (30-meter spatial resolution, 16-day repeat views) simply is not enough, particularly when we need to know as quickly as possible the human impacts of major hurricanes, fire, earthquakes and other potential disasters.
At the end of the day, we really do not simply want another Landsat. As a community, we need to begin a new discourse that does not continue to complain about the failure of NASA and its government partners to continue the Landsat series. The recent disasters created by the Indian Ocean tsunami and hurricanes Katrina, Rita and Wilma show clearly the need for operational land observing systems.
The cost of recovery far exceeds the cost of any land observation system. Moreover, many of the most critical problems facing humanity in the coming decades require land-based decision support. Paramount among these concerns are land use change, climate change, food security and clean water — all critical public domain issues that require routine observations. We need new and creative thinking on a new mission to solve several of these most important problems, with U.S. science and technology leadership that is thinking ahead to a simple, cost-effective system that continues the Landsat heritage but is not just another Landsat.
We are increasingly aware that we need at least six-day repeat temporal coverage with similar or better geographic coverage to that of Landsat 7, simply to keep track of the seasonal dynamics of the Earth’s surface and respond to disasters, such as the recent hurricanes.
Following from our last commentary, there is a rapidly evolving technology in microsatellites (aka microsats or smallsats), which is currently being developed for Landsat-class observations, mostly in Europe and Asia. Not surprisingly, five years ago the National Research Council conducted a study of the potential use of smallsat technologies within the NASA program and found such an approach promising, particularly for this type of application.
The use of smallsat technologies for continuation of the Landsat mission offers some significant advantages, not the least of which is that system costs for individual satellites are well below that experienced for previous Landsat missions, such as Landsat 7. This cost factor is particularly important if we are to increase the temporal resolution of the observations by a factor of three to four.
There are however many significant technical challenges to be overcome, if a smallsat technology is to provide an adequate replacement for previous Landsat missions. The state of sensor, platform, telemetry and cross-platform communications, as well as mass volume ground processing and distribution systems, all present interesting challenges for our current generations of engineers and scientists.
Pushing the space technology envelope is a primary goal for NASA and one thing that it does extremely well. In many ways, addressing such challenges is the hallmark of the U.S. society. An Earth-observing Landsat system that provides global, 15-meter to 30-meter resolution coverage every four to six days would provide a major technological breakthrough for land studies and provide an important contribution to the emerging international Global Earth Observing System of Systems program. At this time when we increasingly need such national earth observation technologies, we repeatedly find ourselves seriously wanting.
So let’s get going. There is no time to waste. Best estimates are that a first, science-quality smallsat land imager could be in orbit in one to two years with a full observation system in operation within two to three years. Now is the time to act.
Samuel N. Goward is a professor in the geography department at the University of Maryland, College Park. David L. Skole is a professor at the Center for Global Change and Earth Observations at Michigan State University in East Lansing.