Ionosondes and VHF radars have been employed to simultaneously observe the sporadic E (Es) layer. In previous studies, an absence of correlation was found between the height of field-aligned irregularities (FAI) observed by the radars and the virtual height of the Es layer (h'Es) by their colocated ionosondes. A careful study shows that the low correlation results from the beam broadening effect of the ionosonde. In this paper, the investigation shows a better correlation between the heights of the FAI bottom-side (hFAlb) observed by the VHF radar and the h'Es by ionosondes in Chung-Li. It is found that the h'Es is greater than the hFAlb by about 5--10 km. Meanwhile, we demonstrate that h'Es observed by two nearby ionosondes (and/or radars) can be employed to evaluate the velocity of waves in the Es layer. ¿ 2000 American Geophysical Union