Radio Astronomy at Extremely Low Frequencies?

Question:
Dear Dr. Mangum.
Decades ago, I was a US Navy Communications Technician. One subject we were taught was ELF (Exteremely Low Frequeny) radio.
I do not know what processes could create ELF signals. Do you have radio telescopes which can study these frequencies. I suspect any radios operating in these frequencies would have to be operating away from the shear noise of the Earth’s environment.
Tks in advance,
Michael Bell
Extremely Low Frequency radio telescopes
Answer:
I believe that Extremely Low Frequencies (ELFs) are defined as frequencies from 3 to 30 Hz. The lowest frequencies used in radio astronomy measurements from the Earth’s surface that I am aware of are as low as 30 MHz. As you suggest, emission from everything in the Earth’s environment, such as lightning and other atmospheric effects, would likely be a major source of noise for any astronomical measurements at EFLs.