Weather surveillance can serve biosurveillance in a number of ways. Predicting the spread of a bioaerosol could help governmental public health contain an organism's release in air. Changes in weather can improve or hamper the reproduction and spread of virulent organisms in the environment.
Weather and climate data currently used in epidemiological analysis include temperature, wind direction and speed (for bioaerosol related analyses), and precipitation. Of possible value, but not used according to our experts, might be barometric pressure and ultraviolet exposure.
In the United States, weather data are already highly available. The specific data available include temperature, wind speed, wind direction, and precipitation. Up-to-the-minute information for the entire nation is available because data are collected in real time, in standard formats, and integrated in a central location that is publicly available without any technical or administrative barriers (http://weather.noaa.gov/). We note that the weather system—in addition to a mature source of data for public health surveillance and early warning of bioterrorism—represents a good case study in how to integrate data from many sources and independent monitoring stations using communication networks and standards to achieve a national surveillance capability.
The space-based weather satellites most interesting and relevant to public health authorities are those that measure water temperature and ecological conditions, such as floods, fires, and conditions of vegetation, which have been used for epidemic prediction. These ecological factors are often predictive of changes in intermediate host and vector activity that are, in turn, predictive of outbreaks of human disease.
In the United States, satellite data are already highly available. As with reconnaissance satellites, data for the entire U.S. are usually constantly available, so long as enough satellites are in orbit. There have been occasions when the United States has not launched a satellite in time to replace a failing "bird,'' resulting in temporary gaps in coverage.
The raw data are of various types ranging from numeric to image. We have begun to develop the ability to extract useful information for public health purposes from these images; researchers at Johns Hopkins used satellite imagery (mediumresolution spectroradiometer) to assess a Canadian forest fire's impact on Baltimore's particulate air pollution (Sapkota et al., 2005). Another example is a joint venture formed by the U.S. Department of Defense and the NASA Goddard Space Flight Center, called the GEIS Rift Valley Information System. This project uses satellite near-real-time data, such as vegetation measurements, cloud cover measurements and sea surface temperatures to predict the appearance of Rift Valley fever in Kenya; a virus in the bunyaviridae family causes this disease, which affects primarily sheep and cattle but can also afflict humans who work with these animals. Rift Valley fever is actually endemic in many African countries, including Sudan, Egypt, Mauritania, and Senegal. The outbreaks are usually preceded by heavy and persistent rainfall in geographic regions accustomed to relative drought, and can result in heavy losses of livestock, leading to famine conditions (U.S. Department of Defense, 2005). We have yet to uncover other factors that determine availability and utility, such as the extent to which they are available in standard formats, and integrated in a central location that is publicly available without any barriers.
The National Oceanographic and Atmospheric Administration (NOAA) operates geostationary environmental satellites, parked in either equatorial or polar orbits 22,300 miles above the Earth's surface; these satellites observe weather patterns, measure winds, detect ash plumes from volcanic eruptions, help assess ground moisture, and provide 99% of the observations that NOAA requires to make climate predictions (Ray, 2005). The most recent program is called the National Polar-Orbiting Environmental Satellite System (NPOESS), a new family of spacecraft managed jointly by the Departments of Defense and Commerce and by NASA, which collect and disseminate data on weather, atmosphere, bodies of water and land (National Oceanographic and Atmospheric Administration, 2005). Government, agricultural, and other uses will access high-quality real-time data.
Spacecraft, such as Ikonos, as well as government spacecraft, can image the ground and help interpreters assess the condition of vegetation, moisture, the presence of fires, and so on, with the help of multispectral imaging as well as false color overlays.
The European Space Agency's Remote Sensing Satellite (ERS) measures atmospheric and surface properties using radar. Measurements include sea-surface wind-speed/ direction, sea-surface height, wave height, sea-surface temperature, cloud-top temperature, and atmospheric water vapor; these are in addition to photography offering 30-m resolution (U.S. Air Force 2005).
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