Pilot Balloons (PIBAL)

Pilot balloons are used for a wide variety of observations.  However, one area where these play an extremely important role is during fire fighting and fire weather forecasting. PIBALs are launched to determine wind speed and wind direction for effective dropping of flame retardants and aerial water drops, possible direction of the fire to alert fire fighters and relocate vehicles and personnel, warning residential areas of potential danger and other factors related to these dangerous situations.

When used with radiosondes, the information given regarding the temperature and humidity is entered into computations for fire danger rating, burn rate and factors effecting how fast a fire might advance.

Whereas the ceiling balloons are used to determine the altitude of a cloud base, pilot balloons (PIBAL) are used to determine wind speed and wind direction at altitudes from 15,000 feet (30 gram) to altitudes in excess of 20,000 feet (100 gram). PIBAL balloons are visually tracked with optical instrumentation. Altitude is derived from an assumed ascent rate, without any additional payload attached. Depending on sky and weather conditions, PIBAL’s can be tracked to altitudes in excess of 40,000 feet.

Wind speed and wind direction are determined by measuring the angular change over a specific time interval. High accuracy is obtained when using a dual theodolite set-up. The highest accuracy achieved is when using the largest balloon defined in the PIBAL category (100 gram) and attaching a radiosonde. A radiosonde is a small electronic package that will transmit essential upper data, pressure, temperature and humidity, plus transmit the position of the balloon via a GPS transmitter. The GPS information is converted to wind speed and wind direction. The pressure information will also provide altitude data.

PIBAL balloons are provided in different colors to provide better sighting depending on the sky background. White (natural) balloons are used when there is a clear sky, black balloons are used when there is a low overcast and red balloons are used when there is high overcast, or there is a white or gray background.