BOX 4.1

NPOESS, EOS, and the Search for Sustained Environmental Measurements

The NPOESS program was, at the outset, driven by a single imperative—convergence of weather measurements, which would eliminate duplication in observations in the early afternoon and still maintain the same temporal robustness that characterized the combination of the Polar-orbiting Operational Environmental Satellites and the Defense Meteorological Satellite Program. The cost savings from eliminating duplication could then be reallocated to improve weather observations and models.

By the mid-1990s, it was clear that NASA would not sustain a long-term, broad observation and information-processing program (like the Earth Observation System); therefore, the community developed a new strategy for obtaining climate measurements from NPOESS. That led to a second NPOESS program imperative—operationalizing a climate observing system, which would enable sustained, long-term measurements for climate studies and other environmental issues. However, that was done after consideration of optical designs, orbits, and data systems needed for weather forecasts; additional requirements for climate were then added, invoking very different objectives and thus requirements for optical designs, orbits, and other mission and instrument characteristics.

Attempting to satisfy the two imperatives simultaneously constituted a difficult challenge, both technically and programmatically. Part of the challenge arose from trying to balance the inherent mismatch of data requirements. Weather forecasts demand frequent observations and rapid data dissemination, whereas climate studies and research demand accurate and consistent long-term records. The added requirements for instrument stability and accuracy, driven by the more stringent climate requirements, placed additional challenges on the instruments. Moreover, the expanded mission’s requirements to address climate and other environmental issues established demands for additional observations such as ocean altimetry, which were not weather-related. That expanded the scope of the mission, increased its complexity, and added to the pressure for larger platforms. Finally, although the mission of one of the operational partners (the Department of Commerce’s NOAA) included climate and other broad environmental issues, the mission of the other (the Department of Defense’s Air Force) did not. That led to conflicting priorities between the two agencies, which by law were required to share program costs on a 50-50 basis.

SOURCE: Reprinted from Box 3.1 in Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (NRC, 2007), p. 63.

The situation from the perspective of both research and operational agencies was characterized in a previous NRC report (NRC, 2000c, p. 8):

Although the operational and the research approaches can appear to conflict, there are features of both that are essential for climate research and monitoring. However, the operational agencies are necessarily wary of assuming responsibility for new requirements that may be open ended in an environment that is cost constrained. The research agencies are similarly concerned about requirements for long-term, operational-style measuring systems that might inhibit their ability to pursue new technologies and new scientific directions. Despite their need for long-term commitments to measure many critical variables, they wonder about relying on operational programs that might decrease the level of scientific oversight as well as opportunities for innovation.

In some cases there is clear overlap between sustained and operational measurement objectives, and a single measurement can provide for both needs. However, the specific measurement requirements for each application can vary, leading to less synergism than was initially intended. The ALT instrument on NPOESS, for example, is a well-designed and very capable instrument; however, climate science clearly requires an orbit different from

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