The Origin of Sensors: Evolutionary Considerations for Next Generation Satellite Programs

The process of defining instrument requirements for environmental satellites is governed by science requirements driven by operational needs, program budgets, and ultimately, politics. Attaining optimal observing system performance in this instrument specification phase requires big-picture vision, correct interpretation of user needs, and above all, program agility. Given the limited resources of any specific program, an emphasis on one capability inevitably leads to unavoidable concessions or omissions in another. In many cases, however, shortcomings of the end-design observing systems arise not from careful trade-space considerations but from unforeseen and potentially addressable issues. For example, sometimes a new discovery/technique/capability emerges, while at other times a previously established physical linkage is simply overlooked. In still other cases the requirements process itself fails to capture the full scope of actual user needs.

The United States next generation polar (National Polar-orbiting Operational Environmental Satellite System—NPOESS) and geostationary (Geostationary Operational Environmental Satellite R-Series—GOES-R) satellite programs include mechanisms for gathering research and operational community input (e.g., via the NPOESS Joint Agency and Senior User Advisory Groups and the GOES-R Users Conference series). Based on guidance and recommendations emerging from these activities, the Pre-Planned Product Improvements (P3I) initiative provides a vehicle for evolving sensor design during the active-phase of these satellite programs. However, even under these well thought-out programs, several potentially important sensor capabilities have slipped through (or were otherwise de-selected/de-scoped during) the requirements process. This paper examines the merits of several potential changes/additions associated with the NPOESS and GOES-R programs, listed in no particular order as follows:

1) Including a 6.7-μm water vapor channel NPOESS Visible/Infrared Imager/Radiometer Suite (VIIRS) for polar wind vector retrievals.

2) Adjusting the dynamic range (or implementing dual-gain) and including a sub-pixel element saturation flag on the NPOESS VIIRS 11.0-μm band aggregate pixelfor active fire characterization.

3) Shifting the DNB spectral response function to improve detection of certain forms of marine bioluminescence, and selective overriding of on-board sub-pixel element aggregation on the NPOESS VIIRS Day/Night Band (DNB) for tactical applications.

4) Including a 0.55-μm (green) channel on GOES-R Advanced Baseline Imager (ABI) to enable natural color capabilities from geostationary orbit.

5) Adding a microwave imager to the GOES-R sensor suite for improved quantitative precipitation estimation, tropical cyclone tracking, and soil moisture characterization.

These items serve as a reminder that the “Three-Pillar Partnership” envisioned by the Committee on Environmental Satellite Data Utilization (CESDA; formed under the auspices of the National Academy of Sciences), in which government, academia, and industry work hand-in-hand to realize optimal advances in remote sensing, faces numerous fundamental challenges. To what extent are user requirements lost in translation (e.g., do the end-users comprehend what their requirements are, and if not, who interprets this on their behalf)? How can the window of opportunity for sensor modifications leading up to the actual “bending of metal” be widened in the pre-selection phase and left ajar in the post-selection phase? In a competitive contract paradigm, how realistic is it to expect significant changes given the inertia inherent to a large program, particularly after the contract has been awarded? How should the responsibility of algorithm development and hand-off be shared such that innovation, lines of interdisciplinary communication, and the peer review process are optimized? Instead of attempting to answer these difficult questions, we focus in this paper on describing the P3I topics currently on the table, and how they translate to end-user needs. Understanding the limitations of the contemporary process-driven requirements system is the first step toward improving our ability to “read between the spectral lines” of user needs and formulating truly agile and evolutionary satellite programs.