Definition
A method of measuring upper-air winds by releasing a small, helium- or hydrogen-filled balloon and tracking its movement from the ground with an optical theodolite. By recording the balloon's elevation and azimuth angles at fixed time intervals, observers calculate wind speed and direction at successive altitudes as the balloon rises at a known rate.
Plain English
A way of measuring winds high above the ground by letting a small balloon go and watching where it drifts. Because the balloon climbs at a known speed, the way it moves through the sky tells observers how fast and in what direction the wind is blowing at different heights.
Context Anchor
Seen in weather reporting and flight planning when pilots need wind information above the ground, especially where direct instrument reports are limited.
Derivation
From 'pilot balloon' -- a balloon used to 'pilot' (guide or scout) the winds aloft, similar to how a pilot vessel scouts ahead for ships. The balloon itself doesn't carry instruments; it's the scout whose path reveals the wind.
Why Pilots Care
Supplies accurate winds-aloft information that helps select efficient altitudes and routes while avoiding unexpected headwinds or turbulence.
Grounding Statement
As the balloon rises, it moves with the air around it, so its path makes the invisible wind easier to see.
Intuition Check
Do not read “pilot balloon” as a balloon flown by a pilot. Here, the balloon is a tool used to reveal wind direction and speed above the ground.
Example Sentence 1
The weather station's morning pilot balloon observation showed a sharp wind shift at 5,000 feet.
Example Sentence 2
At remote fields without radar, a pilot balloon observation still provides reliable upper wind data for cross-country planning.