How is the height of different places on earth measured from the sea level? The height of different places on earth is measured with the help of the ‘altimeter’. The instrument used for measuring the height at a place is basically a barometer. At sea level, the height of the barometric liquid (mercury) is 76 cm.
When we go to higher altitudes, the barometric height goes on decreasing, and right on top, where the atmospheric pressure is zero, the mercury column also dips to zero. This decrease is not uniform. At different ranges, the rate of decrease too is different. In modern barometers, mercury is not used. Such dial-type barometers are called ‘Aneroid barometers’. When such barometers are manufactured, instead of the pressure graduating, the corresponding height graduates. This instrument is called the ‘Altimeter’ and is used in aircraft by skydivers, mountaineers etc.
An altimeter is a device that measures altitude, the distance of a point above sea level. Altimeters are important navigation instruments for aircraft and spacecraft pilots who monitor their height above the Earth’s surface. Skydivers and mountaineers also use altimeters to pinpoint their location in the sky or on the ground.
The most common types of altimeters are barometric. They determine altitude by measuring air pressure. As altitude increases, air pressure decreases. This is because the density of air is lower (thinner) at high altitudes. It exerts less pressure on the Earth below.
An altimeter’s readings change as elevation changes. The atmospheric pressure on Denali, Alaska, is about half that of Honolulu, Hawai’i. Denali, also known as Mount McKinley, is the highest peak in North America. Honolulu is a city at sea level.
Altitude readings can also change due to weather, as air pressure decreases during storms.
A simple barometric altimeter includes a sealed metal chamber, a spring, and a pointer that shows altitude in meters or feet. The chamber expands as air pressure decreases and contracts as it increases, bending the spring and moving the pointer. An altimeter can be mounted on an aircraft’s instrument panel or worn on a person’s wrist.