What Is an Altimeter and How Does It Work?
An altimeter is a device that measures altitude, meaning the vertical distance between a given point and certain fixed level. In most practical uses, this fixed level is sea level. Its use is essential in various activities such as aviation, mountaineering and outdoor sports. In these capacities, accurate information about height is necessary for safety and planning. In this article from thedailyECO we explain more about how this device works and its uses by asking what is an altimeter and what does it measure?
What is an altimeter?
An altimeter is an instrument used to measure the altitude between a specific point and a fixed level. This device is commonly used in aviation, mountaineering and other activities where it is important to know the altitude at which a person, vehicle or geological point is located.
What is an altimeter used for?
An altimeter is primarily used to determine the altitude of a person or object at a given time. This is useful in several situations and activities:
- Aviation: in airplanes, altimeters are essential for safety. Pilots use these devices to maintain a proper altitude during flight, as well as to avoid collisions with the ground or other aircraft. It also allows them to follow pre-established air routes. It is especially crucial during landings and takeoffs, when they need to know the precise distance to the ground.
- Mountaineering and hiking: hikers and mountaineers use altimeters to monitor their progress and plan their route.
- Skydiving: skydivers rely on altimeters to know when to open their parachute. Doing so at the incorrect altitude can be fatal.
- Outdoor sports: in activities such as mountain biking, skiing or trail running, the altimeter allows athletes to know the altitude gained or lost during their journey. This helps them to both plan their actions and assess their performance.
- Meteorology: altimeters are also used in meteorological studies to measure atmospheric pressure at different altitudes, contributing to weather prediction and analysis of atmospheric conditions.
Types of altimeters
While they all carry out the basic function of measuring altitude, there are different types of altimeter designed for for specific needs. These include the following:
- Barometric altimeter: this is the most common type of altimeter and is based on the measurement of atmospheric pressure. As an object ascends, the air pressure decreases and the altimeter converts this difference into altitude. This type of altimeter must be calibrated regularly to account for changes in atmospheric pressure that can be caused by the weather.
- GPS altimeter: uses satellite signals to calculate geographic position, including altitude. Unlike barometric altimeters, this type is not affected by variations in atmospheric pressure. Devices that use GPS often combine this function with longitude and latitude measurement.
- Radar altimeter: this type of altimeter emits radio waves towards the ground and measures the time it takes for the waves to return to the device. It uses this time to calculate the distance to the ground, i.e. the altitude. It is very accurate at low altitudes, which is why it is used in airplanes and helicopters, especially during landing and takeoff maneuvers.
- Laser altimeter: this type of altimeter works by sending pulses of laser light towards the ground and measuring the time it takes for the reflection to return. Like the radar altimeter, it measures altitude with great precision, but in this case using light instead of radio waves.
- Acoustic altimeter: this is less common and uses sound to measure distance to the ground. It is most commonly used in underwater applications, such as in submarines or unmanned vehicles, to measure distance to the water surface or seabed.
Learn about another device which uses atmospheric pressure to predict weather with our article on what is a barometer and what does it measure?
How does an altimeter work?
The operation of an altimeter varies depending on the type. We look at how these different types of altimeters work:
Barometric altimeter
The barometric altimeter works by measuring changes in atmospheric pressure. There is a sensor inside the altimeter that detects the current atmospheric pressure. This sensor can be a mechanical barometer or an electronic sensor, depending on the type of device.
In mechanical barometric altimeters, metal capsules are used that expand or contract with changes in pressure. When they so do, they move a needle that indicates the altitude measurement. In digital barometric altimeters a pressure sensor converts the readings into data that is then processed by a microchip to display the altitude on a digital screen.
Mechanical altimeters require periodic calibration as atmospheric pressure can change due to weather factors. For example, a day with low atmospheric pressure can cause the altimeter to display an incorrect altitude if it is not adjusted accordingly.
GPS altimeter
The GPS altimeter relies on satellite signals to determine an exact position. This provides the altitude, but it can also be used to determine latitude and longitude. To do so, it uses a technique called trilateration. GPS devices receive signals from at least four satellites and calculate their position in space in three dimensions (latitude, longitude and altitude).
The GPS altimeter receives signals from several satellites. It measures the time it takes for the signal to travel from the satellite to the device. From this information, it calculates the distance to the satellite and determines the altitude using this trilateration method.
Radar altimeter
The radar altimeter measures altitude by sending radio waves toward the ground and measuring the time it takes for the waves to return. This time duration is converted into a measure of the distance from the ground, which provides the altitude.
A radar altimeter device sends radio waves toward the Earth's surface. The waves bounce off the ground and return to the altimeter. The device measures the time it takes for the waves to make that trip and uses the speed of the radio waves (which is constant) to calculate the distance, i.e. the altitude.
Laser altimeter
The laser altimeter follows a similar principle to a radar altimeter, but uses pulses of laser light instead of radio waves. It measures the time it takes for the light to travel from the device to the ground and back to calculate the distance.
Acoustic altimeter
An acoustic altimeter works underwater, using sound waves instead of light or radio waves. These waves travel underwater and bounce off the seabed or an object. The device measures the time it takes for the sound to return and calculates the distance based on the speed of sound in water.
Now you know what an altimeter is and how it works, you may want to learn more with our related article asking what is general atmospheric circulation?
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- LARRABE. (2022). What is a barometric altimeter. Available at: https://www.larrabe.com/Blog/what-is-a-barometric-altimeter/
- Florida Flyers. Altimeter: The #1 Ultimate Guide to Use and Setup. Available at: https://www.flightschoolusa.com/altimeter-the-ultimate-guide-to-use/