Ionosonde
![Typical ionogram indicating foF2 of approximately 5.4 MHz.](/Images/godic/202501/20/Ionogramme4724.png")
![An example of an ionosonde system displaying an ionogram](/Images/godic/202501/20/Canadian_Advanced_Digital_Ionosonde4725.jpg")
An ionosonde, or chirpsounder, is a special radar for the examination of the ionosphere. The basic ionosonde technology was invented in 1925 by Gregory Breit and Merle A. Tuve and further developed in the late 1920s by a number of prominent physicists, including Edward Victor Appleton. The term ionosphere and hence, the etymology of its derivatives, was proposed by Robert Watson-Watt.