Next generation radar (NEXRAD) is used to obtain weather information like precipitation and wind, according to the National Oceanic and Atmospheric Administration. NEXRAD radar satellites emit energy, and if the energy hits an object like a rain drop, the energy gets scattered in every direction. Small amounts of the scattered energy make their way back to the satellite, which is then used to produce weather maps. The satellite only sends out energy seven seconds out of an entire hour and spends most of its time waiting for energy to come back. NEXRAD is a type of Doppler radar, which was named after Christian Doppler, an Austrian physicist.
Radiosondes have been used by the National Weather Service to make upper atmosphere air observations for more than 60 years, according to the National Oceanic and Atmospheric Administration. Radiosondes are small instrument packages that are attached to a 6-foot wide balloon filled with helium or hydrogen. As the radiosonde ascends into the atmosphere, it takes measurements for temperature, pressure and relative humidity. Sensors on the radiosonde are linked to a 300-milliwatt radio transmitter that sends data to a ground receiver with a radio frequency ranging from 1668.4 to 1700.0 MHz. Radiosondes only stay in flight for about two hours and can travel up to 115,000 feet. Approximately 75,000 radiosondes are released by the National Weather Service each year, and only about 20 percent of them are found, returned and used again.
According to the United States Department of Energy, air pressure is measured in inches of mercury or millibars (mb). Weather forecasters use barometers to measure air pressure, which helps them predict weather patterns. Before a hurricane, and rain storms in general, air pressure drops significantly. Low pressure systems in the Midwest can be a sign of a tornado coming. Mercury barometers are one of the most basic types of weather technology and have been used since Torricelli, a student of Galileo, invented them in 1643, according to Barometerfair.com.
