Browsing by Subject "PRM"

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  • Nykänen, Mikko (Helsingfors universitet, 2011)
    In Finland collation of data needed in forest planning is changing from traditional standwise field inventory to area-based airborne laser scanning and aerial photography inventorying. The aim of this study was to compare prediction accuracy of stand total volume and diameter distribution using following methods: MSN, PRM, ML, FMM and Weibull-distribution. Results were calculated separately for pine, spruce, birch and other tree species. In addition need of calculation time and storage space was established. Sampling plot and stand information used in this study were collected in the vicinity of Evo, Finland. Total of 249 sampling plots were measured. 12 clear-cutting areas measured by logging machine were used as reference data. In addition area-based laser scanning and aerial photographbased features were used in estimation of variables of interest. Results were calculated in all 12 stands and stands which area was over 0,5 hectares (8 pcs). Number of grid neighbours differed between 1 and 10. Depending on method and number of neighbours the relative RMSE and bias of stand total volume varied between 20,76 – 52,86 % and -12,04 – 46,54 % respectively in all stands and between 6,74 – 59,41 % and -8,04 – 49,59 % respectively in stands which area was over 0,5 hectares. Calculation time varied strongly depending on method and number of neighbours. With more developed programming and programs calculation times could decrease substantially. Storage space needed in saving information is not an issue in tested methods even in large-scale applications. According to diameter distribution PRM-method predicts narrow distribution if sampling plot consists of only few trees nearly same size. This affected results especially in PRM2.