Since the 1960s, the United States has operated two separate operational polar-orbiting meteorological satellite systems. These systems are known as the Polar-orbiting Operational Environmental Satellites (POES), managed by the National Oceanic and Atmospheric Administration’s (NOAA) National Environmental Satellite, Data, and Information Service (NESDIS), and the Defense Meteorological Satellite Program (DMSP), managed by the Department of Defense (DOD). These satellites obtain environmental data that are processed to provide graphical weather images and specialized weather products, and that are the predominant input to numerical weather prediction models—all used by weather forecasters, the military, and the public. Polar satellites also provide data used to monitor environmental phenomena, such as ozone depletion and drought conditions, as well as data sets that are used by researchers for a variety of studies, such as climate monitoring. Unlike geostationary satellites, which maintain a fixed position above the earth, polar-orbiting satellites constantly circle the earth in an almost north-south orbit, providing global coverage of conditions that affect the weather and climate. Each satellite makes about 14 orbits a day. As the earth rotates beneath it, each satellite views the entire earth’s surface twice a day. Today, there are two operational POES satellites and two operational DMSP satellites that are positioned so that they can observe the earth in early morning, mid-morning, and early afternoon polar orbits. Together, they ensure that for any region of the earth, the data provided to users are generally no more than 6 hours old. Figure 1 illustrates the current operational polar satellite configuration. Besides the four operational satellites, there are five older satellites in orbit that still collect some data and are available to provide some limited backup to the operational satellites should they degrade or fail. In the future, both NOAA and DOD plan to continue to launch additional POES and DMSP satellites every few years, with final launches scheduled for 2008 and 2010, respectively. Each of the polar satellites carries a suite of sensors designed to detect environmental data either reflected or emitted from the earth, the atmosphere, and space. The satellites store these data and then transmit the data to NOAA and Air Force ground stations when the satellites pass overhead. The ground stations then relay the data via communications satellites to the appropriate meteorological centers for processing. Under a shared processing agreement among the four processing centers—NESDIS, the Air Force Weather Agency, Navy’s Fleet Numerical Meteorology and Oceanography Center, and the Naval Oceanographic Office—different centers are responsible for producing and distributing different environmental data sets, specialized weather and oceanographic products, and weather prediction model outputs via a shared network. Each of the four processing centers is also responsible for distributing the data to its respective users. For the DOD centers, the users include regional meteorology and oceanography centers as well as meteorology and oceanography staff on military bases. NESDIS forwards the data to NOAA’s National Weather Service for distribution and use by forecasters. The processing centers also use the Internet to distribute data to the general public. NESDIS is responsible for the long-term archiving of data and derived products from POES and DMSP. In addition to the infrastructure supporting satellite data processing noted above, properly equipped field terminals that are within a direct line of sight of the satellites can receive real-time data directly from the polar- orbiting satellites. There are an estimated 150 such field terminals operated by the U.S. government, many by DOD. Field terminals can be taken into areas with little or no data communications infrastructure— such as on a battlefield or ship—and enable the receipt of weather data directly from the polar-orbiting satellites. These terminals have their own software and processing capability to decode and display a subset of the satellite data to the user. Figure 2 depicts a generic data relay pattern from the polar-orbiting satellites to the data processing centers and field terminals. Polar satellites gather a broad range of data that are transformed into a variety of products for many different uses. When first received, satellite data are considered raw data. To make them usable, the processing centers format the data so that they are time-sequenced and include earth location and calibration information. After formatting, these data are called raw data records. The centers further process these raw data records into data sets, called sensor data records and temperature data records. These data records are then used to derive weather products called environmental data records (EDR). EDRs range from atmospheric products detailing cloud coverage, temperature, humidity, and ozone distribution; to land surface products showing snow cover, vegetation, and land use; to ocean products depicting sea surface temperatures, sea ice, and wave height; to characterizations of the space environment. Combinations of these data records (raw, sensor, temperature, and environmental data records) are also used to derive more sophisticated products, including outputs from numerical weather models and assessments of climate trends. Figure 3 is a simplified depiction of the various stages of data processing. EDRs can be either images or quantitative data products. Image EDRs provide graphical depictions of the weather and are used to observe meteorological and oceanographic phenomena to track operationally significant events (such as tropical storms, volcanic ash, and icebergs), and to provide quality assurance for weather prediction models. The following figures demonstrate polar-orbiting satellite images. Figure 4 is an image from a DMSP satellite showing an infrared picture taken over the west Atlantic Ocean. Figure 5 is a POES image of Hurricane Floyd, which struck the southern Atlantic coastline in 1999. Figure 6 is a polar- satellite image used to detect volcanic ash clouds, in particular the ash cloud resulting from the eruption of Mount Etna in 2001. Figure 7 shows the location of icebergs near Antarctica in February 2002. Quantitative EDRs are specialized weather products that can be used to assess the environment and climate or to derive other products. These EDRs can also be depicted graphically. Figures 8 and 9 are graphic depictions of quantitative data on sea surface temperature and ozone measurements, respectively. An example of a product that was derived from EDRs is provided in figure 10. This product shows how long a person could survive in the ocean—information used in military as well as search and rescue operations—and was based on sea surface temperature EDRs from polar-orbiting satellites. Another use of quantitative satellite data is in numerical weather prediction models. Based predominantly on observations from polar- orbiting satellites and supplemented by data from other sources such as geostationary satellites, radar, weather balloons, and surface observing systems, numerical weather prediction models are used in producing hourly, daily, weekly, and monthly forecasts of atmospheric, land, and ocean conditions. These models require quantitative satellite data to update their analysis of weather and to produce new forecasts. Table 1 provides examples of models run by the processing centers. Figure 11 depicts the output of one common model. All this information—satellite data, imagery, derived products, and model output—is used in mapping and monitoring changes in weather, climate, the ocean, and the environment. These data and products are provided to weather forecasters for use in issuing weather forecasts and warnings to the public and to support our nation’s aviation, agriculture, and maritime communities. Also, weather data and products are used by climatologists and meteorologists to monitor the environment. Within the military, these data and products allow military planners and tactical users to focus on anticipating and exploiting atmospheric and space environmental conditions. For example, Air Force Weather Agency officials told us that accurate wind and temperature forecasts are critical to any decision to launch an aircraft that will need mid-flight refueling. In addition to these operational uses of satellite data, there is also a substantial need for polar satellite data for research. According to experts in climate research, the research community requires long-term, consistent sets of satellite data collected sequentially, usually at fixed intervals of time, in order to study many critical climate processes. Examples of research topics include long- term trends in temperature, precipitation, and snow cover. Given the expectation that merging the POES and DMSP programs would reduce duplication and result in sizable cost savings, a May 1994 Presidential Decision Directive required NOAA and DOD to converge the two satellite programs into a single satellite program capable of satisfying both civilian and military requirements. The converged program is called the National Polar-orbiting Operational Environmental Satellite System (NPOESS), and it is considered critical to the United States’ ability to maintain the continuity of data required for weather forecasting and global climate monitoring. To manage this program, DOD, NOAA, and the National Aeronautics and Space Administration (NASA) have formed a tri- agency Integrated Program Office, located within NOAA. Within the program office, each agency has the lead on certain activities. NOAA has overall responsibility for the converged system, as well as satellite operations; DOD has the lead on the acquisition; and NASA has primary responsibility for facilitating the development and incorporation of new technologies into the converged system. NOAA and DOD share the costs of funding NPOESS, while NASA funds specific technology projects and studies. NPOESS is a major system acquisition estimated to cost almost $7 billion over the 24-year period from the inception of the program in 1995 through 2018. The program is to provide satellite development, satellite launch and operation, and integrated data processing. These deliverables are grouped into four main categories: (1) the launch segment, which includes the launch vehicle and supporting equipment, (2) the space segment, which includes the satellites and sensors, (3) the interface data processing segment, which includes the data processing system to be located at the four processing centers, and (4) the command, control, and communications segment, which includes the equipment and services needed to track and control satellites.