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A barometer altimeter, also known as a barometric or pressure altimeter, is used to measure air pressure, which can help the user forecast short-term weather changes and altitude. These devices are commonly used by hikers, pilots, and the operators of weather stations, who need both types of information. Barometer altimeter technology can be found in watches, global positioning system (GPS) devices, aircraft cockpit instrumentation, and weather balloons using radiosonde equipment, which take measurements in the Earth's atmosphere.
Hikers and climbers often use barometer altimeters with topographical maps to determine their location using the altimeter setting. As a person moves higher above sea level, the air pressure falls; the barometer in the device can measure these changes and provide the user's altitude based on a reference point, usually sea level. Changes in the weather can also cause air pressure to rise or fall, however, so altitude measurements are really only accurate when the weather is consistent.
When the user is not changing his or her altitude, a barometer altimeter can be used to predict the weather. A rapid drop in air pressure, for example, indicates that a low pressure system is approaching. This type of change is often associated with rain and other bad weather, so a pressure drop indicates that a hiker or camper should find shelter.
Barometer altimeters are commonly found in sports watches, hand-held GPS devices, and similar tools. Hybrid GPS/barometer altimeters are a popular choice for outdoor activities because, unlike watches with similar functions, hand-held models often allow users to display both altitude and weather functions at the same time. GPS is not always accurate when it comes to the user's altitude, and it requires a clear line of sight to the sky to receive information, so in the event of poor reception, the barometer provides back-up altitude readings. Such devices often allow users to maintain a log of their routes or at least periodically record altitudes.
Despite the technological advantages of larger GPS devices, sports watches with altimeter technology also have their perks. For one, they are lightweight and hands free, so hikers or climbers may find them more convenient. Most are also durable enough to withstand exposure to water and other elements common in outdoor settings. Besides being used in hiking and other ground-level outdoor activities, hang gliders, skydivers, and paragliders also frequently use wrist barometer altimeters.
Flight regulations require many aircraft to have an instrument that provides the plane's altitude at any given time, and barometer altimeters are typically used because GPS readings are not accurate enough. Altimeter readings are usually based on the barometric pressure of the outside air in comparison to a set reference point at sea level. Changes in weather conditions require pilots to adjust their altimeter, since low or high pressure air masses can affect the readings. Commercial and military aircraft have radar altimeters which monitor altitude by emitting radio signals that bounce off the ground and back to the aircraft's receiver, which gives the distance between the plane and the surface of the ground rather than the height above sea level.
The National Oceanic and Atmospheric Administration (NOAA), a US government agency that operates weather stations around the world, uses radiosonde equipment in weather balloons. These are instruments that record and transmit temperature, humidity, air pressure, and altitude readings. Barometer altimeters are often included with such devices to take readings at specific altitudes.
There are various product models available for those looking to purchase their own barometer altimeter, and the wide range of features can be a bit daunting. Factors to consider when making a purchase may include the altitude range the device can measure, the increments at which it takes measurements, weather forecast alarms, and the style or materials of the device. People who plan to use the device for hiking or orienteering may want one that also includes a compass, thermometer, GPS or other features. Some models can be linked to a computer, so that measurements can be downloaded and saved.
Since there is a learning curve when using altimeters and other navigation devices, it's a good idea for someone using one for the first time to practice in a familiar area before taking a trip where it's more important that the readings are accurate and properly interpreted. New users should practice setting and calibrating the device, and using any additional features they may need. When taking longer trips, it's always a good idea to bring a conventional compass along for basic directional information.
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