The SOUSY-VHF-Radar has been used to study the diurnal variation of the echo power received from mesospheric structures in different seasons. For the first time phase coding techniques have been applied to such measurements with a height resolution of 300 m during 6 days in summer, 5 days in autumn and 3 days in winter 1978 within the height range between 51 and 118 km. The various structures observed are classified according to characteristic features such as thickness and apparent lifetime. The results indicate the existence of four main types of mesospheric structures--blobs, sheets, thin and thick layers. Their spatial and temporal occurrence, which depends on season, is discussed.