The Ministry of Defense is seen in Tokyo's Shinjuku Ward. (Mainichi/Kazuo Motohashi)

TOKYO -- A Ministry of Defense official revealed on June 8 that data errors in an investigative report on possible candidate sites for hosting the Aegis Ashore missile defense system were attributable to the use of Google Earth in examining those sites.

The ministry's report in question had concluded that the Ground Self-Defense Force (GSDF)'s Araya Maneuver Area in the city of Akita in the Tohoku region was the only appropriate site in eastern Japan to deploy the land-based interceptor system, as opposed to 19 other spots in Aomori, Akita and Yamagata prefectures that were subject to the survey for possible candidate sites in northern Japan.

Takashi Gomi, head of the ministry's strategy planning division, told reporters in Akita that officials who examined the candidate spots used Google Earth virtual globe software to display a topographic cross section without realizing that the scale reductions of the distance and altitude were different.

Specifically, the elevation angle of a mountain peak that could stand in the way of radar waves was erroneously calculated for each of the nine sites in state-owned land and exercise areas in Aomori, Akita and Yamagata prefectures. Elevation angle is the angle between the horizontal plane and the line of sight. The ministry had concluded that all those nine sites were "inappropriate" to host the Aegis Ashore system, after calculating figures that were far larger than actual numbers.

The latest revelation has shaken public confidence in the legitimacy of the ministry's selection of the Araya Maneuver Area as the rightful host site.

According to Gomi, ministry officials calculated the elevation angle of a mountain peak with trigonometric functions after measuring the altitude and horizontal distance with a ruler, even though the scale reduction of the altitude and horizontal distance differed in the topographic cross section displayed using Google Earth. The officials then confirmed the elevation angle using a protractor.

While Google Earth's topographic cross section shows actual figures for both distance and altitude with scale marks, Gomi said the officials used data without recognizing the gap between the scale reductions.

In the topographic cross section used in the ministry's survey, the scale reduction for altitude was larger than that for horizontal distance. As a result, the elevation angle calculated became larger than the actual figures. While the actual elevation angle of a mountain peak is roughly 4 degrees at a state-owned site in Oga, Akita Prefecture, ministry officials calculated the angle to be around 15 degrees.

With regard to why ministry officials did not conduct a field survey, Gomi said, "We can examine the figures as long as we have map data," before adding, "Our checking system was insufficient."

Prior to the press meeting, the Defense Ministry held a briefing session for local residents in Akita city. Participants blasted the ministry for the errors in the investigation report, with one saying, "I can't trust (the ministry's decision)," and another saying, "The plan to deploy the missile defense system in Araya should be reconsidered."

(Japanese original by Shun Kawaguchi, Akita Bureau)