An ionosonde is a special HF radio transmitter that periodically transmits a signal that sweeps across a large portion or the entire HF spectrum to identify the propagation of radio signal in the ionosphere, currently they are operated by various institutions around the world.
To my knowledge, in order to legally operate a radio transmitter at a frequency/band, the frequency must be allocated by regulatory agencies for use by the type of service that the transmitter belongs to. Ultimately, all radio transmissions must be legal under the ITU Radio Regulations.
How does the ITU Radio Regulations apply to an ionosonde? Why is it legal for an ionosonde to use a huge portion of the spectrum, which otherwise wouldn't be possible for conventional radio communication services?