The acquiring entity must engage in a more collaborative relationship with the builder and be prepared to accept more perceived risk through less intrusive “light touch” oversight rather than the traditional very intrusive insight. While this seems unorthodox in light of several well-documented and high-profile acquisition failures over the past decade, it has been shown to work (for example, the Applied Physics Laboratory’s New Horizons mission, the University Corporation for Atmospheric Research’s COSMIC mission, the National Geospatial-Intelligence Agency’s (NGA’s) NextView and EnhancedView programs, the Air Force’s TACSAT-3 mission, NASA’s QuikScat mission, and so on), and it is particularly applicable to the block-buys-of-clones model that eschews new technology development for predictability.
The Landsat satellites are not the only source of Earth imaging data available today. By including other sources under the umbrella of the Sustained and Enhanced Land Imaging Project (SELIP), not only is it possible to mitigate risk (by having other sources to fall back on in the event of a premature satellite failure), but also it enables an even more cost-effective approach where the core program is not constrained to acquire all needed data on its own. The integration can create a more robust data set by using other existing or planned data sources.
Many of the possible options were exhaustively studied by the Landsat Data Gap Study Team from 2005 to 2007 after the scan corrector failure on the Landsat 7 ETM+ instrument.4 This excellent examination of the subject offers a framework for developing a robust and sustainable land imaging program that integrates sources of Landsat-type data from the international land imaging community. Although the United States started the Landsat series and has continued to exercise leadership over the past 40 years, leadership is not synonymous with going it alone. There is a long history of international partnering in other space endeavors. Burden sharing could take many forms: a foreign launch vehicle provided under a science-driven memorandum of understanding with no exchange of funds, instruments (such as thermal infrared, visible and near-infrared, or shortwave infrared) from an international partner, or a foreign satellite bus.
One example is the European Space Agency’s (ESA’s) Sentinel-2, which is planned to collect all but the thermal infrared bands of Landsat and does so in a wider swath for improved revisit.5 NASA is collaborating with ESA to calibrate the Landsat 8 and Sentinel-2 instruments to generate comparable data products. Such an arrangement could be complemented with data (also shared) from a U.S.-funded thermal-infrared-only small satellite. Other nations, such as India and Japan, operate their own remote sensing programs, which could potentially fill some Landsat user needs, and China is emerging as an Earth observing satellite operator in the coming decade. On the Suomi NPP satellite, the VIIRS instrument collects data at greater frequency though lower spatial resolution and may be suitable for some applications, particularly when sharpened by less frequently collected but finer resolution data to enable a degree of spectral unmixing.6 Finally, the EnhancedView contract, managed by NGA, collects commercial imagery that can be widely shared within federal government agencies, potentially satisfying some of their need for Landsat-type data, although the data from EnhancedView cannot be freely distributed to the public and, thus, does not offer the full value of a national land imaging program. None of these suggestions can replace a dedicated U.S. program for obtaining critical measurements; however, judicious use of other data sources may reduce risk, reduce cost in some cases, and enhance the SELIP.
A potential design modification, which applies to all other options, is to increase the swath width of the sensors, with the objective of shortening revisit time, a commonly sought characteristic of any new Landsat system. Historically, Landsat has acquired data over a 185-km swath, which, for a single satellite system, yields a 16-day
4 U.S. Geological Survey, Landsat Data Gap Studies, available at http://calval.cr.usgs.gov/satellite/landsat-data-gap-studies/.
5 European Space Agency, GMES Sentinel-2 Mission Requirements Document , available at http://esamultimedia.esa.int/docs/GMES/Sentinel-2_MRD.pdf.
6 B. Huang, Spatiotemporal reflectance fusion via sparse representation, IEEE Transactions on Geoscience and Remote Sensing 50:3707-3716, 2012.