Continuity of NASA Earth Observations from Space A Value Framework (2015) / Chapter Skim
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3 A Decision Framework for NASA Earth Science Continuity Measurements
3 A Decision Framework for NASA Earth Science Continuity Measurements
Pages 30-45
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Chapter 4 provides examples of applications of the methodology. Within NASA, choosing among Earth science continuity measurements competing for funding naturally involves weighing risks and benefits under uncertain technical and financial conditions.
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Finding: A value-based approach can enable more objective decisions regarding continuity measurements. Recommendation: NASA's Earth Science Division should establish a value-based decision approach that includes clear evaluation methods for the recommended framework characteristics and well-defined summary methods leading to a value assessment.
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Recommendation: Proposed space-based continuity measurements should be evaluated in the context of the quantified science objectives that they are addressing. As stated in Chapter 1, the committee chose to illustrate the framework with science objectives and not societal-benefit objectives, primarily because of the perceived difficulty in adequately comparing large numbers of possible applications.
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The following are sample quantified objectives for continuity measurements in Earth system science. It is important to recognize that this list is meant for illustration purposes only; it is not a complete list, and the entries are in no particular order.
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Recommendation: NASA, which is anticipated to be a principal sponsor of the next decadal survey in Earth science and applications from space, might task the decadal survey committee with the iden tification, and possible prioritization, of the quantified Earth science objectives associated with the recommended science goals. 3.2.2 Benefit: Utility The utility metric gauges the contribution that an intended geophysical variable record makes to a specified quantified science objective.
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Finding: The benefit of a measurement is valued by the degree of contribution that the derived geo physical variable record makes to a targeted quantified objective. Recommendation: NASA should foster a consistent methodology to evaluate the utility of geophysical variables for achieving quantified science objectives.
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A full Bayesian approach to the value characteristics for continuity in this report would be an ideal long-term quantitative strategy, but practical challenges as discussed in ARCM may limit its full application. These challenges arise due to the large number of parameters and measurements that would be used for many quantified objectives (see examples in the appendixes of this report)
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Those measurements whose calibration is sufficiently certain to meet global change requirements will have high quality rating, and their success probability rating will also be high due to smaller impacts of data gaps.8 As a result, gap impact on quality, gap risk of occurrence, and gap effects on observing system costs can all be accounted for in the current framework. Finding: Success probability is assessed by evaluating the maturity of the measurement instrumentation and algorithms, the risk-posture of the mission implementation approach, the resilience of the geo physical variable record to measurement gaps, and the degree to which alternate approaches, including those from national and international partners, can provide acceptable bridging measurements.
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Thus, cost shares a number of cross-cutting characteristics with utility, quality, and success probability that must be quantified and implemented in the value metric. Finding: Assessing affordability requires comprehensive cost analysis from measurement to geophysical variable record and includes risk mitigation.
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All of these factors in the observing system design will affect the success probability of achieving a geophysical variable record of desired quality (Loeb et al., 2009)
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3.6 DETERMINING CONTINUITY MEASUREMENT VALUE Having identified the key value characteristics in the previous sections, the committee sought a robust approach for rating the value of a continuity measurement based on evaluations of its key characteristics. To be useful, the framework must successfully differentiate among the hundred or more climate-related geophysical variables of interest (e.g., there are approximately 50 Global Climate Observing System (GCOS)
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1 Regarding 3b and "relative fraction": In this report, the committee notes that its evaluation methods for the impor tance and utility characteristics are subjective; however, it recommends (in Chapter 3) that the sum of the utility ratings of all observations needed by the quantified objective be equal to 1.0.
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• valuation of the measurement's success probability includes consideration of the heritage and E maturity of the proposed instrument and its associated data algorithms, the likelihood of leveraging similar or complementary measurements, and the likelihood of data gaps that would adversely affect the quality of the measurement. • valuation of the affordability of a proposed continuity measurement includes consideration of the E total cost of developing, producing, and maintaining the sought-after data record.
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, where I = importance of the quantified objective = maximum potential benefit, U = percentage of the quantified objective achieved by obtaining targeted geophysical variable record, Q = percentage of required geophysical variable record obtained by proposed measurement, and S = probability that proposed measurement will be successfully achieved. In Chapter 4, the committee describes its examination of various methods for defining and quantifying characteristic ratings and for calculating the cost-benefit value.
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Given an appropriate objective, a new measurement would be handled within the decision framework in a manner identical to that of an existing measurement. Addressing questions 2 and 3 can be readily accomplished within the recommended framework by repetitive application of the methodology to each of the measurements contributing to a single objective or to each of the objectives pertaining to a single measurement, respectively.
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Chapter 3 in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Stocker, T.F., D
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