. "3 From Satellite Observations to Earth Information." Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. Washington, DC: The National Academies Press, 2007.
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to climate change. Such sustained observations allow scientists to document changes, to determine the processes responsible for changes, and to develop predictions. They also are often needed to allow resource managers to assess the ongoing effects of changes on society.
Data from a new technology mission sometimes prove critical for an operational system. Wind speed and direction measurements from NASA’s QuikSCAT mission and precipitation measurements from NASA’s Tropical Rainfall Measurement Mission (TRMM), for example, are used in weather forecasting. The need for such measurements to become part of an operational system and to be sustained for many years is a recognized and well-studied challenge, but the record of moving new technology into operational systems is, at best, mixed.1
Another aspect of the connectivity between sustained research observations and operational systems is that the observations and products from those systems, such as the observations used in weather forecasts, are also useful for many research purposes. Likewise, sustained observations, although focused on research questions, clearly include an aspect of monitoring and may be used operationally. Exploratory, sustained, and operational measurements often share the need for new technology, careful calibration, and long-term stability, but there are also important differences among them.
The ability to reach across the overlapping categories of exploratory, sustained, and operational Earth observations has not proved very successful, and the recent experience with the National Polar-orbiting Environmental Satellite System (NPOESS) is particularly problematic and revealing with respect to sustained measurements (Box 3.1).
Climate data records (CDRs) are time series of measurements of sufficient length and accuracy to document climate variability and change.2 Such records are invaluable because an examination of the causes of changes in Earth processes often requires long, stable, accurate records of several variables. For example, to investigate links between hurricane intensity and global warming (Emanuel, 2005; Webster et al., 2005) by determining whether there is a connection between the power of hurricanes and a warming ocean, it is necessary to have long and accurate records of both hurricane wind speeds and ocean temperatures; Box 3.2 provides additional examples.
In addition to an observation system that routinely makes critical measurements, obtaining CDRs requires a substantial commitment by a team of experts to support data reprocessing, the resolution of differences in sensor characteristics, and evaluation of data for research and applications. For example, measurements of sea-surface temperature were improved through several joint agency efforts (such as the NOAA-NASA Pathfinder program and the Global Ocean Data Assimilation Experiment (GODAE) of the National Oceanographic Partnership Program) and, more recently, by combining infrared measurements with those from a microwave radiometer that can measure through the ubiquitous cloud cover (the GODAE High Resolution Sea Surface Temperature Pilot Project, GHRSST-PP3).
Calibration and validation in the context of CDRs can be considered a process that encompasses the entire system, from sensor to data product (NRC, 2004b). The objective is to develop a quantitative understanding and characterization of the measurement system and its biases in time and space; this involves a wide array of strategies that depend on the type of sensor and data product. For example, for ocean color,
Transition failures have been exhaustively described in previous reports (NRC, 2000a, 2003b), and this committee supports their analyses and recommendations.
Characterization of many Earth processes requires sustained and carefully calibrated data, including a history of continuous and consistent measurements, and so the challenge extends beyond the issue of climate. The distinction between CDRs and the NPOESS EDRs is discussed in NRC (2004a).