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.