Andrew K. Johnston

Mapping net primary production and related biophysical variables with remote sensing: Application to the BOREAS region

Maps of net and gross primary production, autotrophic respiration, biomass, and other biophysical variables were generated for 106 km2 of boreal forest in central Canada (the Boreal Ecosystem-Atmosphere (BOREAS) region) using a production efficiency model (PEM) driven with remotely sensed observations at 1 km2 spatial resolution. The PEM was based on carbon yields of absorbed photosynthetically active radiation for both gross and net primary production (GPP and NPP), accounting for environmental stress and autotrophic respiration (Ra). Physiological control was modeled using remotely sensed maps of air temperature, vapor pressure deficit, and soil moisture. The accuracy of the inferred variables was generally within 10–30% of point measurements at the surface and independent model results (both at the stand level). Biomass maps were derived from visible reflectance measurements and were also compared to independently derived maps. Area-averaged GPP was 604 g C m−2 yr−1 compared with average canopy respiration of 428 g C m−2 yr−1 and NPP of 235 g C m−2 yr−1. Net annual carbon uptake in net primary production for the region totaled 175 teragrams. Canopy carbon exchange (GPP and Ra) differed widely between land cover types even though the model does not use land cover information. Extensive areas of the least productive cover types (e.g., lowland needleleaf species) accounted for the greatest amount of NPP.

Spaceflight: The Development of Science, Surveillance, and Commerce in Space

To commemorate the centennial of the Proceedings of the IEEE, several authors from diverse areas of expertise examine space exploration from its beginnings in the middle of the last century and look onward to half a century in the future. Beginning by examining the reasons why the two 20th century superpowers believed that space exploration was an important investment, the chronological review of early developments includes discussions on science, commerce, and national security; the evolution of space-related technologies; progress and advancements in launch vehicles, spacecraft, and spacecraft payloads; and improvements in space communications and tracking. With the subjects of robotic solar system exploration and crewed missions to space discussed in some detail, the great advances of the last 60 years establish a foundation for addressing the challenges of future human flight beyond Earths vicinity-challenges that are technical, political, social, and economic in nature. The authors take a pragmatic view in making forecasts for the future of spaceflight: they limit their conjecture, for the most part, to the next 50 years. While it is very difficult to make realistic predictions for longer periods, the authors are confident that space exploration continues to grasp the publics imagination and desire to know more about the universe, and that it continues to build on many of the same questions that inspired the space program in the mid-20th century.