What does Density Altitude measure?

Density altitude is a critical concept in aviation that measures the density of air. It is defined as the pressure altitude corrected for non-standard temperature. When the air is less dense—due to higher temperatures or higher humidity—it affects aircraft performance because less dense air can result in decreased lift, engine performance, and propeller efficiency. Therefore, understanding density altitude is essential for pilots, including those operating unmanned aircraft, to ensure safe flight operations.

The other options, while they relate to certain aspects of atmospheric science, do not accurately describe density altitude. For instance, distance from the Earth's surface pertains to geographic elevation rather than the properties of air. The weight of water vapor in the air relates more to humidity and does not directly measure air density. Lastly, while atmospheric pressure is an important factor in understanding altitude and density, it is not an indicator of density altitude itself. Instead, density altitude is specifically a measure reflecting how air density impacts aircraft performance.