瑞典在南部一片7,600公顷林地上进行了用直升飞机调查森林的试验。事先用1:20,000一30,000的航空像片进行了判读,共划了90个调查小班。用《Hughes一300》直升飞机飞行,时速30一60公里,高度10一30米。共有四个人参加调查工作。以在小班上的全林检尺或抽样材料比较了直升飞机调查的结果。一个调查员确定的龄级 Sweden conducted a helicopter survey of forests in a forest area of ​​7,600 hectares in the south. Interpreted in advance with aerial photographs of 1: 20,000-30,000, a total of 90 surveyed small classes were drawn up. Flying with the “Hughes-300” helicopter at a speed of 30-60 kilometers per hour and at a height of 10-30 meters. Four people participated in the survey. The results of the helicopter survey were compared on a full scale or sampling material in small classes. An investigator determines the age class