Altitude refers to the vertical distance of an object or point above a specified reference level. This concept is fundamental to understanding everything from mountain heights to aircraft flight paths. It is important in fields like geography, aviation, and atmospheric science, impacting weather patterns and the biology of living organisms.
What is Altitude?
Altitude is a measurement of vertical distance from a defined starting point. The most common reference is Mean Sea Level (MSL), the average height of the ocean’s surface, providing a consistent global baseline. Another common reference is Above Ground Level (AGL), which measures height directly above the terrain.
While often used interchangeably, altitude and elevation have distinctions. Elevation typically refers to the height of a point on Earth’s solid surface above MSL, such as a mountain peak. Altitude, in contrast, generally describes the vertical distance of an object not connected to the ground, like an aircraft or satellite.
How Altitude is Measured
Measuring altitude involves various instruments and methods. The barometric altimeter operates on the principle that atmospheric pressure decreases predictably with increasing altitude. Inside, sealed aneroid wafers expand or contract with air pressure changes, translating into an altitude reading calibrated to Mean Sea Level.
Global Positioning System (GPS) technology also determines altitude using signals from orbiting satellites. GPS receivers calculate vertical distance by measuring signal reception time from multiple satellites. GPS readings can differ from barometric altimeters due to atmospheric variations or geoid models.
For precise height above immediate terrain, especially in aviation, radar altimeters are used. These devices transmit radio waves downwards, measuring the time for reflection from the ground. Knowing wave speed allows calculation of the exact distance between the aircraft and the surface. Unlike barometric altimeters, radar altimeters provide true height above ground level, which is important for landing.
Altitude and Atmospheric Changes
As altitude increases, changes occur within the Earth’s atmosphere, impacting environmental conditions. Atmospheric pressure decreases because there is less air mass pressing down from above. At sea level, pressure is approximately 101,325 Pascals, but it drops substantially with altitude.
Air density also decreases, meaning less oxygen is available, contributing to the feeling of “thin air.” Temperature generally decreases with increasing altitude in the troposphere, the lowest layer of Earth’s atmosphere, at an average rate of about 6.5 degrees Celsius per kilometer. This is known as the environmental lapse rate.
These atmospheric changes have noticeable effects. Lower atmospheric pressure means water boils at a lower temperature, requiring longer cooking times. Reduced oxygen can lead to physical discomfort for unacclimatized individuals. These changes in pressure, density, and temperature define the high-altitude environment.
Altitude’s Effect on Living Organisms
Altered atmospheric conditions at higher altitudes, particularly reduced oxygen and lower temperatures, present considerable challenges for living organisms. Humans exhibit both short-term physiological responses and long-term adaptations to cope with reduced oxygen availability. Initial responses include an increased breathing rate and a faster heart rate to compensate for less oxygen per breath. Over time, the body can produce more red blood cells, which enhances the blood’s capacity to carry oxygen to tissues.
Populations that have lived at high altitudes for generations, such as Tibetans and Andeans, have developed distinct genetic adaptations that allow them to thrive in these environments. Animals inhabiting high-altitude regions display specialized adaptations to survive these conditions. Many species have evolved larger lungs and higher concentrations of hemoglobin, the protein responsible for oxygen transport, allowing them to absorb and utilize oxygen more efficiently.
Some high-altitude animals, like deer mice, possess more efficient aerobic muscles with a higher number of mitochondria, cellular structures that generate energy. Tibetan yaks, for example, have proportionately larger lungs and hearts compared to other cattle, enabling them to transport oxygen more effectively through their blood.
Plants also demonstrate remarkable adaptations to high-altitude environments, which often feature low temperatures, strong winds, intense ultraviolet radiation, and shorter growing seasons. Many high-altitude plants exhibit compact or prostrate growth forms, staying low to the ground to minimize exposure to harsh winds and cold. Their leaves may be smaller, thicker, or covered in a waxy coating or fine hairs, which helps reduce water loss and offers protection from UV radiation. Some plants have developed specialized root systems to anchor themselves in unstable, rocky soils and to efficiently absorb nutrients and water.