ECOSYSTEM PROPERTIES FOR WHICH SATELLITE DATA ARE REQUIRED
measurement of canopy height with lidar. Others are derived from the statistics of direct measurements, such as estimates of landscape heterogeneity used in conservation biology and ecosystem management and the inference of surface sources and sinks of CO2 from space-based measurements of column-integrated atmospheric CO2. A third category includes quantities that result from using direct observations as inputs in physical, biological, or statistical models; an example is the estimation of carbon uptake and release through photosynthesis and respiration in marine or terrestrial systems, which are inferred from space-based estimates of photosynthetic light absorption. A final category includes quantities estimated from time series of measurements, which by their rate of change define some other process (for example, the integral of photosynthesis over time can define biological productivity).
The currently available long-term record of ecosystem dynamics from a variety of sensors is critical for understanding and managing ecosystems in the coming decades. The panel places high priority on maintaining and enhancing this record. The role of multiyear time series in understanding ecological dynamics has long been recognized. From classic examples like the scientific exploitation of the Canadian Lynx-Hare data set through the establishment of the Long Term Ecological Research (LTER) network and newer classic papers that used decadal eddy covariance record, long time series have shaped the field. Understanding of global-scale processes has been substantially advanced through long time series, including the ice-core records, the Keeling record of atmospheric CO2, the CZCS-SeaWiFS-MODIS records of ocean color, and the AVHRR and Landsat records of photosynthesis and land-cover change. Long-term records of photosynthetic activity have enabled forecasts of impending food shortages, pest outbreaks, and other key ecological linkages with human health. To meet the challenges for understanding and managing ecosystems in the coming decade, the maintenance and extension of long-term ecosystem records are paramount. Here, the panel briefly reviews critical applications, problems, requirements, and opportunities.
There are three fundamental long-term satellite records of ecosystem dynamics, and each addresses a separate issue. First is ocean color, which began with the Coastal Zone Color Scanner and continues with