Reanalysis of the observations of Mars made at the Hida Observatory in 1975 with a new image processing method is reported. Red filter images taken in the period before vernal equinox (areocentric longitude of the sun Ls=0°) revealed dark surface features at the northern high latitudes, while blue filter images taken at the same time showed the extensive polar hood. The latitude of the northernmost feature observed was about 67°N. An extensive north polar cap, which is predicted by most of the existing models and observed with Viking, did not exist in our reanalyzed images obtained at the Hida Observatory in 1975.

• KYOSUKE IWASAKI(Kyoto Gakuen University)
• TOKUHIDE AKABANE(Hida Observatory, Kyoto University)
• YOSHIO TOMITA(Department of Astronomy, Kyoto University)