樹冠下降雨量の標本調査に就いて
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概要
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樹冠下の積算降雨量を標本調査によつて推定する場合、雨量計の分布が疎ならば、降雨毎に此をat randomに配置換えするがよい。雨量計の分布密度が大きくなるに從つて配置換えの奴果は減少する。雨量計を移動すべきか、或は移動を行わず、その數を増すことによつて同一精度の達成を狙うべきかは、両者の要する勢力、經費の比較考量によつて決定さるべきである。A 4m x 4 m plot under an isolated pine (Pinus Thumbergii) was divided into 16 squares each 1㎡ in area, and a standard rain gage was installed at the centre of each square. With these gages daily rainfall under the different parts of the crown was measured during the period May-July, 1952, the arithmetical mean of the measurements being assumed to represent the average value. With a view to ascertaining the relative merits of sampling methods for determining the cumulative rainfall for the stated period, the standard error of the estimator for the average was computed for two different methods of procedure. In one of them (method A) the sample gages were selected at random before each storm, while in the other (method B) random selection was made once for all at the start. It was found that the increase of the standard error with the number of rainfalls was less rapid in the former procedure than in the latter, the divergence of the two standard errors decreasing with the increase of the sample size. The minimum number m of additional gages necessary to attain by method B at the end of the period the same or higher degree of precision than by method A depends upon the number of sample gages n used, as shown in the following table. It would appear that the advantage of method A over method B is greatest when one gage or six gages are used, according as it is measured by the difference between the two standard errors or by the minimum additional number of gages required by method B to attain the same or less standard error. Economic considerations may provide still another criterion for the relative merits of both methods.
- 九州大学の論文
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