Landsat-7 Long-Term Acquisition Plan: Development and Validation

Terry Arvidson, Lockheed Martin

Samuel Goward, University of Maryland College Park

John Gasch, Emalico LLC

Darrel Williams, NASA Goddard Space Flight Center

 

Photogrammetric Engineering & Remote Sensing, vol. 72, no. 10, pp: 1137–1146.

The long-term acquisition plan (LTAP) was developed to enable the Landsat-7 (L7) mission to build and seasonally refresh an archive of global, essentially cloud-free, sunlit, land scenes. The LTAP has been recognized as a key achievement of the L7 mission. By incorporating seasonality (what scenes to take when) and cloud avoidance into the decision-making process for scheduling image acquisitions, the L7 data in the U.S. Landsat archive is more complete and of higher quality than has ever been previously achieved in the Landsat program. The LTAP acquisition goals and rules enable the mission to acquire meaningful global coverage by focusing the limited resources on regions likely to be in demand. These goals are based upon expected seasonal land cover change, as well as the history of user interest Consequently, specific requests for image acquisitions from the user community are minimized; the data they need is already in the archive, having been scheduled for acquisition by the LTAP. On a daily basis, the LTAP directs the automated process of acquisition planning and scheduling that would otherwise be an insurmountable task if attempted manually, given the volume of candidate scenes and dynamic weather conditions.

The LTAP system evolved over more than a decade, starting in 1995. This paper reports on the results of the validation of the LTAP elements, which was conducted from 2002 to 2004. We found Landsat 7 has surpassed the original expectations and goals for the LTAP. We have acquired relatively cloud-free images for the world’s landmasses on at least an annual basis, and the availability of cloud-free imagery from our archive is better than ever. This is a tremendous resource for global climate change researchers. During validation we identified some seasonal and geographic acquisition shortcomings of the implementation, including how we interpreted a vegetation index to determine seasonality and how cloud climatology varies on a regional and seasonal basis. Some of these issues have already been at least partially addressed in the L7 LTAP, while others will wait further attention in the adaptation of the LTAP for the Landsat Data Continuity Mission (LDCM), the next satellite in the Landsat program.

The LTAP encapsulates a knowledge base built upon 34 years of managing Landsat assets, and the LTAP continues to evolve to this day. The lessons learned from a decade of work on the L7 LTAP provide a solid foundation upon which to formulate LTAPs for future Landsat missions, including the LDCM.