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Earth Observations from Space: The First 50 Years of Scientific Achievements
FIGURE 3.1 Locations of Integrated Global Radiosonde Archive stations. SOURCE: Data from the National Climatic Data Center, Durre et al. (2006). Reprinted with permission from the American Meteorological Society, copyright 2006.
developed the capability to fly satellites in sun-synchronous orbits,6 in which an instrument on a single satellite could view the entire Earth twice per day, once in daylight and once at night (Figure 3.2). Then meteorologists could tile the pictures together to form the long-sought global picture of Earth’s weather (Figure 3.3).
Also during the mid-1960s, the first geostationary satellites were launched. These satellites orbit Earth in the equatorial plane at the same angular velocity that Earth rotates on its axis; thus, they stay “stationary” over the same point on the equator. Although they do not view the entire Earth but only one hemisphere (Figure 3.4), they can make images frequently, not just twice per day. These images can be assembled into movies that allow forecasters to watch the weather in motion. This is an invaluable tool for weather analysis and forecasting (Box 3.1). Geostationary satellites rapidly became the choice of weather services worldwide, such that today they form a ring around the equator, providing coverage of the entire tropics and midlatitudes.
Many accomplishments in weather forecasting have been achieved using the imagery from weather satellites. Only a few can be mentioned in this document. Perhaps the most dramatic accomplishments relate to observing and predicting hurricanes and tropical storms. In 1900 a “surprise” hurricane roared out of the Gulf of Mexico over Galveston Island killing at least 8,000 people; it was the largest natural disaster in the United States (Blake et al. 2006). Since then an important scientific accomplishment occurred sometime in
FIGURE 3.2 One day’s orbits of a sun-synchronous satellite. A single instrument views the entire Earth. SOURCE: Kidder and Vonder Haar (1995). Copyright Elsevier, 1995.
the 1960s: with the continuous monitoring of weather by satellites, no tropical cyclone anywhere on Earth escapes detection (Figure 3.5). Indeed, Robert C. Sheets, former director of the National Hurricane Center (NHC), has written:
A circular, near-polar orbit in which the orbital plane keeps a constant relationship to the Sun-Earth line, such that the satellite passes over a point on the Earth near the same time every day.