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航摄象片50年代就开始应用于森林资源调查,但多数是独立的调查,即是说同一地区利用象片调查,尽管前后期象片拍摄时间不同,而调查资料没有有机联系。近年来有的学者利用成数抽样方法,在试验总体中按予先计算的样本单元数,布设成千上万个样点,在两期象片的同一点上进行土地资源判读,然后统计各类土地的点数,按照一定的公式计算出各类土地成数的估计值及误差,并换算成面积,比较两期各类土地面积,可以得出各类土地面积总的动态变化。但有关报导中没有说明同一地点土地资源的变化。
Aerial photos began to be applied to forest resources surveys in the 1950s, but most of them were independent surveys. That is, they used image surveys in the same area. There was no organic link between the survey materials despite the different filming times of the previous and later photographs. In recent years, some scholars use the number of sampling methods, in the total test in accordance with the pre-calculated number of sample units, laying thousands of sample points, the same period in the two films for land resources interpretation, and then statistics According to a certain formula, the estimated value and error of each type of land are calculated and converted into the area. The total dynamic change of various types of land area can be obtained by comparing the two types of land area. However, the report did not explain the change of land resources in the same place.