Mesospheric studies using the EISCAT UHF and VHF radars: a review of principles and experimental results

Studies of the mesosphere and ionospheric D-region are carried out with the incoherent scatter as well as with the MST radar technique. We briefly describe the principal differences between these techniques and the corresponding scattering mechanisms. Particular emphasis is placed on the observation of the coherent echoes from the summer mesosphere, which the EISCAT VHF and UHF radars have recently also detected. We present an overview of the historical development of EISCAT observations and results in these areas, and suggest possible directions of progress which would make the EISCAT radar systems even more suitable for mesosphere measurements.