<P> Radiosondes may operate at a radio frequency of 403 MHz or 1680 MHz . A radiosonde whose position is tracked as it ascends to give wind speed and direction information is called a rawinsonde ("radar wind - sonde"). Most radiosondes have radar reflectors and are technically rawinsondes . A radiosonde that is dropped from an airplane and falls, rather than being carried by a balloon is called a dropsonde . Radiosondes are an essential source of meteorological data, and hundreds are launched all over the world daily . </P> <P> The first flights of aerological instruments were done in the second half of the 19th century with kites and meteographs, a recording device measuring pressure and temperature that was recuperated after the experiment . This proved to be difficult because the kites were linked to the ground and were very difficult to manoeuvre in gusty conditions . Furthermore, the sounding was limited to low altitudes because of the link to the ground . </P> <P> Gustave Hermite and Georges Besançon, from France, were the first in 1892 to use a balloon to fly the meteograph . In 1898, Léon Teisserenc de Bort organized at the Observatoire de Météorologie Dynamique de Trappes the first regular daily use of these balloons . Data from these launches showed that the temperature lowered with height up to a certain altitude, which varied with the season, and then stabilized above this altitude . De Bort's discovery of the tropopause and stratosphere was announced in 1902 at the French Academy of Sciences . Other researchers, like Richard Aßmann and William Henry Dines, were working at the same times with similar instruments . </P> <P> In 1924, Colonel William Blaire in the U.S. Signal Corps did the first primitive experiments with weather measurements from balloon, making use of the temperature dependence of radio circuits . The first true radiosonde that sent precise encoded telemetry from weather sensors was invented in France by Robert Bureau . Bureau coined the name "radiosonde" and flew the first instrument on January 7, 1929 . Developed independently a year later, Pavel Molchanov flew a radiosonde on January 30, 1930 . Molchanov's design became a popular standard because of its simplicity and because it converted sensor readings to Morse code, making it easy to use without special equipment or training . </P>

Which of the following is not true about rawinsondes (weather balloons)