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航空象片是遥测森林资源的主要资料,森林调查航空象片的利用可使用各种方法和不同的工艺,所有这些方法具有各种优缺点,且获得林分必要的结构资料的精度是不同。在森林调查工作中象片森林测树判读是主要方法。现在存在的问题是拍摄的1∶15000比例尺航空象片与象片量测判读是相当矛盾。在实践中在象片上量测平均冠幅、树冠郁闭度存在某些困难,因为同样的树冠在航空象片上各个部位有不同的形状、大小和方向,根据试验可以说在上述比例尺航空象片上确定平均冠幅是很成问题,尽管放大照片形象,在小比例尺航片上量测精度仍不能保证。现实量测冠幅直径仅在放大比例尺的航空象片上,为了可靠的确定树冠郁闭度,用不少于400个量测点的方法,而在小比例尺象片上不是所有树冠之间都获有影象,这样降低了确定郁闭度的可靠性。实践中在判读经验的基础上,是借助于立体模型的分析确定林冠郁闭度,虽然这种方法不能认为是科学的,但它具有不坏的结果。当量测误差在立体量测仪精度范围内,量测立体模型中林木平均高的纵向视差较能在未纠正的象片上量测平均树
Aeronautical images are the main source of telemetry forest resources and forest surveys can utilize various methods and different processes for the utilization of aerial photographs, all of which have various advantages and disadvantages and differ in the accuracy with which the necessary structural information is obtained for stand. In the forest survey work, the picture forest tree interpretation is the main method. The problem now is that a shot of 1: 15000 scale footage is quite contradictory to a picture measurement. In practice, it is difficult to measure the average crowns on the photos and the canopy canopy, because the same canopy has different shapes, sizes and orientations in all parts of the aerial photograph, according to the experiment, it can be said that on the aerial photograph of the above scale Determining the average crown is problematic, although the magnification of the photo image can not be guaranteed on a small scale. Realistic measurements of crown diameter are only made on aerial photographs of enlarged scales. For reliable determination of canopy density, use not less than 400 measuring points, not all of the crown on small scale images Image, which reduces the reliability of the determination of canopy closure. In practice, on the basis of interpreting experience, forest crown closure is determined by means of analysis of a three-dimensional model. Although this method can not be considered as scientific, it has not bad results. When the measurement error is within the range of the stereo measuring instrument, the average height of the trees in the three-dimensional model is higher than that of the average tree measured on uncorrected images