Page "High Frequency Active Auroral Research Program" Paragraph 31

# Polar mesospheric summer echoes ( PMSE ) have been studied, probing the mesosphere using the IRI as a powerful radar, and with a 28 MHz radar, and two VHF radars at 49 MHz and 139 MHz.

The presence of multiple radars spanning both HF and VHF bands allows scientists to make comparative measurements that may someday lead to an understanding of the processes that form these elusive phenomena.