Eighty-five percent of our nation's energy results from the burning of fossil fuels from vast reservoirs of coal, oil, and natural gas. These processes add carbon to the atmosphere, principally in the form of carbon dioxide (CO2). It is important to understand the fate of this excess CO2 in the global carbon cycle in order to assess contemporary terrestrial carbon sinks, the sensitivity of climate to atmospheric CO2, and future potentials for sequestration of carbon in terrestrial systems. Therefore, improved measurement approaches are needed to quantify the change of CO2 in atmospheric components of the global carbon cycle. There is also interest in innovative approaches for flux and concentration measurements of methane and other greenhouse gas constituents associated with terrestrial systems as well as quantifying root associated belowground processes relevant to carbon cycling. The First State of the Carbon Cycle Report (SOCCR) (Reference 1) and the Carbon Cycling and Biosequestration Report: (Reference 2) provides rough estimates of terrestrial carbon sinks for North America. Numerous working papers on carbon sequestration science and technology also describes research needs and technology requirements for sequestering carbon by terrestrial systems(References 3-5). Both documents call for advanced sensor technology and measurement approaches for detecting changes of atmospheric CO2 properties and of carbon quantities of terrestrial systems (including biotic, microbial, and soil components). Such measurement technology would improve the quantification of CO2, as well as carbon stock and flux, in the major sinks identified by the SOCCR report (see Figure ES.1 therein). Furthermore, the report, A U.S. Carbon Cycle Science Plan (Reference 6) provides additional background on critical, overarching research needs related to carbon cycling in terrestrial ecosystems. Grant applications submitted to this topic should (1) demonstrate performance characteristics of proposed measurement systems, and (2) show a capability for deployment at field scales ranging from experimental plot size (meters to hectares of land) to nominal dimensions of ecosystems (hectares to square kilometers). Phase I projects must perform feasibility and-or field tests of proposed measurement systems to assure a high degree of reliability and robustness. Combinations of stationary, remote, and in situ approaches will be considered, and priority will be given to ideas-approaches for verifying biosphere carbon changes. Measurements using aircraft or balloon platforms must be explicitly linked to real-time ground-based measurements. Grant applications based on satellite remote sensing platforms are beyond the scope of this topic and will be declined.