Electron concentrations in the D and E regions of the ionosphere have been measured by incoherent scatter radar from 130-km altitude down to the D region ledge with an altitude resolution of 900 m. The results are displayed as consecutive 5-min altitude profiles including sunrise, afternoon, and sunset periods. The ledge is found to undergo systematic variations between 80 and 90 km. A comparison with theoretical models for electron concentrations at 90 and 110 km reveals generally good agreement. However, at 90 km for &khgr;≲60¿ the model values are high by a factor of 2, and at 110 km for &khgr;=90¿ (sunrise and sunset) they are high by a factor of 4. The incoherent scatter results are consistent with rocket measurements and display well-known patterns of sporadic E as well as the postsunset valley in the E region.