Altimeter: What is it, what is it for, types and how it works

An altimeter is a instrument used to measure altitude between a specific point and sea level. This device is commonly used in aviation, mountaineering and other activities where it is important to know the height at which a person or vehicle is.

An altimeter serves mainly to know the altitude in which a person or an object is at a given time. This is useful in several situations and activities:

• Aviation: In airplanes, altimeters are fundamental to security. The pilots use these devices to maintain an adequate height during the flight, avoid collisions with the ground or with other airplanes and follow pre -established air routes. In addition, it is crucial in landings and takeoffs, when they need to know the distance precise to the ground.
• Mountaineering and hiking: Excress and mountaineers use altimeters to monitor their progress and plan their route.
• Skydiving: Paracharidists trust the altimeters to know when to open the parachute.
• Outdoor sports: In activities such as mountain cycling, skiing or trail running, the altimeter allows athletes to know the height gained or lost during their route, which helps them plan their performance and measure their progress.
• Meteorology: Altimeters are also used in weather studies to measure atmospheric pressure at different altitudes, which contributes to climate prediction and the analysis of atmospheric conditions.

There are several types of altimeters, each with specific characteristics according to the method they use to measure altitude. The main types of altimeters are:

• Barometric altimeter: It is the most common type and is based on the measurement of atmospheric pressure. As one ascends, air pressure decreases, and the altimeter turns this difference into altitude. This type of altimeter should be regularly calibrated to take into account the changes in atmospheric pressure that can be caused by the weather.
• GPS altimeter: Use satellite signals to calculate the geographical position, including altitude. Unlike the barometric, this type is not affected by variations in atmospheric pressure. The devices that use GPS often combine this function with the measurement of length and latitude.
• Radar altimeter: This type of altimeter emits radio waves towards the ground and measures the time it takes to return to the device. Use this time to calculate the distance to the ground, that is, the altitude. It is very precise at low altitudes, so it is used in airplanes and helicopters, especially during landing and takeoff maneuvers.
• Laser altimeter: It works by sending laser light pulses to the ground and measuring the time it takes for the reflection to return. Like the radar altimeter, it measures the altitude with great precision, but in this case using light instead of radio waves.
• Acoustic altimeter: It is less common and uses the sound to measure the distance to the ground. It is more used in underwater applications, such as submarines or unmanned vehicles, to measure the distance to the surface of the water or to the seabed.

The operation of an altimeter varies according to the type. Let’s see how the main types of altimeters work:

Barometric altimeter

The barometric altimeter works measuring changes in atmospheric pressure. Within the altimeter there is a sensor that detects the current atmospheric pressure. This sensor can be a mechanical barometer or an electronic sensor, depending on the device. We recommend reading this article about the barometer: what is it, what it is for, how it works and types.

In mechanical altimeters, metal capsules are used that expand or contract with pressure changes, moving a needle that indicates altitude. On the other hand, in the digital ones, a pressure sensor converts the readings into data that are then processed by a microchip to show the altitude on a digital screen.

This type of altimeter requires being calibrated periodicallysince atmospheric pressure can change due to climatic factors. For example, one day with low atmospheric pressure can cause the altimeter to show an incorrect altitude if it is not adjusted.

GPS altimeter

The GPS altimeter is based on satellite signals to determine the exact positionincluding altitude. Use a technique called trilateration: GPS devices receive signals from at least four satellites and calculate their position in three dimensions (latitude, length 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 and with this information, calculate the distance to the satellite and, by trilateration, determines the altitude.

Radar altimeter

The radar altimeter measures the altitude sending radio waves to the ground and measuring the time it takes to receive the echo of those waves when they bounce. The time that the waves take to return to the altimeter becomes a measure of the distance to the ground, which is the altitude. The device emits radio waves towards the earth’s surface. The waves bounce on the floor and return to the altimeter. The device measures the time that the waves took to make that route and use the speed of radio waves (which is constant) to calculate the distance, that is, the altitude.

Laser altimeter

The laser altimeter follows a principle similar to that of the radar, but instead of radio waves, Use laser light pulses. 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

The acoustic altimeter works underwaterusing sound waves instead of light or radio. These waves spread underwater and bounce in the seabed or in an object. The device measures the time it takes for the sound to return and, based on the speed of sound in the water, calculates the distance.

Now that you know what an altimeter is, you may also be interested in reading this article on atmospheric general circulation: what is and how it occurs.

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