| This analysis addressed a number of remote sensing policy issues in the context of the NASA Earth Observing System, (EOS). Repeated redesign of EOS in response to budgetary restrictions has highlighted the need for comprehensive analysis of the interdependencies of space-based instruments and their integration with air and ground-based measurements, as well as a methodology for accommodating further budget restrictions. In the context of the case study chosen for this analysis, characterization of methane sources, three sets of questions were addressed. The first set of questions pertained to the importance of simultaneity in space-based observations. The second set of questions pertained to orbital selection for space-based observation of methane relative to the current EOS configuration. The final set pertained to the spatial resolution appropriate for observation of methane sources, the relative capabilities of different measurement methods, and comparative costs.;The second portion of the analysis pertained to orbital choice and the suitability of the EOS sun-synchronous orbit for methane source observation relative to a diurnal sampling alternative. This portion used current estimates of the global methane source distribution and global mean cloud cover observations to evaluate orbital choices with regard to latitudinal coverage and revisit time. The analysis concluded that the EOS AM-1 orbit will provide approximately 25% less methane coverage than would be provided by a lower inclination orbit.;The third portion of the analysis examined the spatial resolution and accuracy of various measurement approaches, evaluating them with respect to anticipated sources. This analysis concluded that few source areas will be of sufficient strength to be observable from space. Sources averaging 100 mg m;The questions discussed here in the context of methane characterization recur for other remote sensing objectives throughout EOS. Examinations of the evolving capabilities of EOS like this case study provide a starting point for subsequent investigation of the decision making process that has guided the program, the evolving mission of the program, and the implicit attitudes of the decision-makers toward risk.;FASCODE radiative transfer code was used to simulate MOPITT signals under a number of scenarios of methane enhancement, temperature, and relative humidity profiles. Uncertainty on the Maximum Likelihood Estimator (MLE) of the methane mixing ratio was used as a measure of system performance subject to assumptions of surface albedo and calculated photon counting noise. Separation of MOPITT and AIRS+, and the resulting degradation of knowledge of the temperature and humidity profile was found to increase the minimum detectable methane mixing ratio enhancement by a factor of four. |
