• Coverage and repeat cycle
— Ability to acquire and make available imagery anywhere on Earth, except perhaps for areas very near the poles, at approximately weekly frequency. (This frequency is desired not necessarily to acquire weekly data but rather to acquire cloud-free images.) The 705-km Landsat orbit, at 98 degrees inclination, provides 16-day frequency.
— Increased temporal frequency could be achieved with a slightly larger swath and consequently slightly larger off-nadir view angles at the edge (the users queried did not object to this).
• Data management and distribution
— A free data policy, as is currently in place, provides huge benefits to the nation as well as the international user community by supplying imagery to operational programs critical to U.S. needs as well as spurring innovation in the private sector.
— The USGS data distribution system is successful and effective but could continue to make technological advances and to streamline methods for managing Landsat imagery and derived products.
This set of requirements could be met by implementing the system as a series of satellite platforms, possibly with smaller satellites, whereby all capabilities may not reside on a single spacecraft. Many applications do not require precise simultaneity of all spectral bands, so that satellites flying in formation with nodes adjusted so that multiple spectral bands are acquired within hours could suffice.
The top priorities for the Sustained and Enhanced Land Imaging Program (SELIP) should be to ensure that the core program provides for continuity of Landsat products and coverage on a secure and sustainable path.
The SELIP should take advantage of technological innovation in sensors, spacecraft, and data management and analysis to improve system performance, allow for new analyses that better exploit the data and meet future needs. Because future measurements will derive from both current and new technologies, new implementations of existing data products derived from a multispectral sensor should be cross-calibrateable with Landsat legacy products and be essentially interchangeable for scientific and operational purposes.
To better meet these primary goals, the committee recommends that the program should
• Systematically monitor users and uses of Landsat data so that the program can evolve with changing user requirements and
• Consider alternative implementations that continue to enable the collection of global, moderate-resolution data with the full range of spectral capabilities.