Gregg Walters
                                                                DSS
                                                                Oct. 1, 2001
DEFINITIONS OF RAOB, PIBAL, ETC.                            rev.Oct.25, 2001

There are potentially confusing variations in the terminology which
characterize upper air station observations.  For those who deem this
to be important, we attempt to reduce the confusion.  Unfortunately,
our data sources have not regularly tagged the observations, and even
our own procedures have not been consistent.

In our NCEP/NMC ADPUPA files, NCEP did not tag the soundings as raob, pibal,
etc.  The sounding reports have sections ("categories") of data which must
be analyzed to identify the type of sounding.  Such analysis is not simple.
Generally, DSS expects the presence of at least one temperature value
anywhere in a sounding to be the mark of a raob.  This is the case for the
basic file inventories for ds353.1 and ds353.4.  Other inventories may expect
more levels.  Others may tag a sounding as a raob when it contains any
non-wind data: a temperature, or a height and a pressure.

We are presently developing a super inventory where for each sounding
there is a table of flags that indicate the presence of values at each
level.  This super inventory will span a substantial portion of our upper
air station data archive.  For this purpose, we have defined:

  1) raob   Sounding report from a radiosonde, with non-wind (usually
              temperature) data on at least one pressure level.

  2) pibal  Sounding report from a pilot balloon, with wind data (but
              no non-wind data) reported at height levels.

  3) rabal  Sounding report from a radiosonde, with wind data (but
              no non-wind data) reported at height or pressure levels.

            We counted this as a pibal, or as an attachment to a raob
              or pibal (when it came from the same balloon).

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The following information was extracted from the AMS Glossary (1959).  It has
yet to be compared to the 2000 edition for any changes.


 pibal - (Or pibal observation)  Contraction for pilot-balloon observation

 pilot balloon - A small balloon whose ascent is followed by a theodolite in
   order to obtain data for the computation of the speed and direction of
   winds in the upper air.

 pilot balloon observation - (Commonly called pibal.)  A method of winds-aloft
   observation; that is, the determination of wind speeds and directions in the
   atmosphere above a station.  This is done by reading the elevation and
   azimuth angles of theodolite while visually tracking a pilot balloon.
     The ascension rate of the balloon is approximately determined by careful
   inflation to a given total lift.  After release fromthe ground, periodic
   readings (usually at one minute intervals) of elevation and azimuth angles
   of the balloon are recorded.  These data are transferred to a winds-aloft
   plotting board, and the wind speed and direction at selected levels are
   calculated by trigonometric methods.
     Compare rabal, rawin, rawinsonde...

 rabal - A method of winds-aloft observation; that is, the determination of wind
   speeds and directions in the atmosphere above a station.  It is accomplished
   by recording the elevation and azimuth angles of the balloon at specified
   time intervals while visually tracking a radiosonde balloon with a theodolite.
     A rabal is basically the same as a pilot-balloon observation, except that
   the height data are derived from the radiosonde observation rather than from
   an assumed balloon ascension rate.

 radiosonde - A balloon-borne instrument for the simultaneous measurement and
   transmission of meteorological data.  The instrument consists of transducers
   for the measurement of pressure, temperature and humidity; a modulator for
   the conversion of the output of the transducers to a quantity which controls
   a property of the radio frequency signal; a seledctor switch which determines
   the sequence in which the parameters are to be transmitted; and a transmitter
   which generate the radio-frequency carrier.
     Various types include: audio-modulated radiosonde, chronometric radiosonde,
   code-sending radiosonde, Diamond-Hinman radiosonde, pulse-time modulated
   radiosonde, and variable radio-frequency radiosonde.

 radiosonde balloon - A balloon used to carry a radiosonde aloft.  They are
   considerably larger than pilot balloons or ceiling balloons.  Currently,
   economically feasible radiosonde balloons have been developed which have
   daytime bursting altitudes of about 100,000 ft and nighttime bursting
   altitudes of about 80,000 ft above sea level.

 radiosonde commutator - A component of a radiosonde consisting of alternate
   electrically conducting and insulating strips.  As these are scanned by a
   contact the radiosonde transmits temperature and humidity signals alternately.
   The contact may be a baroswitch as int he Diamond-Hinman radiosonde, or may
   be motor-driven.

 radiosonde modulator - That part of an audio-modulated radiosonde consisting
   of the baroswitch, the sensing elements, the reference elements, and the
   relay.

 radiosonde-radiowind system - Apparatus consisting of (a) standard radiosonde
   and radiosonde ground equipment to obtain upper-air data on pressure,
   temperature, and humidity, and (b) a self-tracking radio direction-finder
   to provide the elevation and azimuth angles of the radiosonde so that the
   wind vectors may be obtained.  It is a type of rawinsonde system.

 radiosonde observation - (Commonly contracted raob.)  An evaluation in terms
   of temperature, relative humidity and pressure aloft, of radio signals from
   a balloon-borne radiosonde; the height of each mandatory and significant
   pressure level of the observation is computed from these data.

 rawin - A method of winds-aloft observation; that is, the determination of wind
   speeds and directions in the atmosphere above a station.  It is accomplished
   by tracking a balloon-borne radar target, responder, or radiosonde transmitter
   with either radar or a radio direction-finder.
     With a radio direction-finder, the height data must be supplied by other
   means, normally by concurrent radiosonde observation.  With radar, if height
   data are not otherwise supplied, the slant range must be recorded in addition
   to the angles of elevation and azimuth.

 rawin target - A special type of radar target tied beneath a free balloon, and
   designed to be an efficient reflector of radio energy.
     Such targets usually consist of a corner reflector and are made of some
   reflecting material stretched over light wooden or metal struts.