Experimental results were studied to determine the relationships between positioning precision of a differential global positioning system (DGPS) and forest type, antenna height, and season, and to clarify the relationship between sampling number and the convergence of positioning precision. Observation was carried out for 24 h. Mean circular area probability (CEP 95 ) was 2.80 m for deciduous broadleaved trees, and 4.99 m for conifers. The mean CEP 95 taken at 7 m height (3.14 m) was higher than that at 1 m height (3.92 m) at all sites. The mean CEP 95 taken during the defoliation season (2.65 m) was slightly better than during the foliation season (2.96 m). There were significant differences between forest types (P Ͻ 0.001) and antenna heights (P Ͻ 0.05). Positioning precision was not noticeably improved if the sampling number was around ten or less. A sampling number of 100-1000 or more is required before substantial improvements can be expected. As long as high positioning precision is not required, it is acceptable to use 2D & 3D modes and relatively few samples to take measurements.

This study investigated the relationship between the quantity of the shielding effect by wood material and the lowering of the signal to noise ratio (SNR) of global positioning system (GPS), signals. Three types of wood materials, namely, Japanese cedar board (JCB), Japanese cedar needle (JCN), and deciduous broadleaf (DBL), were prepared. We performed analysis by quantification I to clarify the factors that affect SNR. Approximately 60% of SNR could be explained by wood resistance quantity (Wrq) and satellite elevation angle SEA. The order of the factors that effect SNR was SEA > Wrq > experimental date > type of wood material > permeation distance through wood material (Dwm). We could formulate the relationship between Wrq and SNR. The Monte Carlo simulation was used to confirm the relationship between SNR and Wrq. The results of the positioning fix ratio by the simulation showed an excessive value in the coniferous forest that almost corresponded with that of the deciduous broad-leaved forest.

This study examines a method for designing an optimum profile of a forest road in a short matter of time. In this method, a genetic algorithm (GA) searches for points where the gradient changes and dynamic programing (DP) designs the longitudinal slope. This method can be applied to the ground heights of an actual forest road. The evaluation function of the DP assesses the total expenditure. The inverse of this function is the fitness function. Crossover and mutation are operators of an evolution simulation of a GA. They are each repeated 20 times and 420 profiles are designed and assessed, all within about 10 min. A comparison of the profile designed by the GA with that of an actual forest road shows only one section where the formation level differed substantially. Overall, both profiles seem to show a high degree of correspondence. From this result, we believe that the profile designed by the GA is best, or the one of the best. A conventional method takes about 65 h to calculate all changing points of gradients. However, by using the GA, the calculation time was reduced to about 1/389 that of the covcntional method, showing that the method which uses the GA through the profile design is very useful.

No abstract

This study was performed to investigate the factors responsible for the reduction in the signal-to-noise ratio (SNR) of a global positioning system (GPS) when used in a forest. We investigated the relationship between the SNR values of GPS signals and the moisture in wood materials and clarified this relationship through experimentation and simulation. Although the wood material itself had a minimal effect on SNR reduction, moisture in the wood had an obvious effect. It is noteworthy that wood material with a moisture resistance quantity (Mw) of 2 g/cm 2 caused a reduction of more than *10 dB in the SNR. This Mw value corresponds to Japanese cedar with a green stem thickness of *7 cm. Under unobstructed sky conditions, SNR is less than *20 dB, so a reduction of 10 dB has a marked effect on GPS reception. The reduced SNR under canopies resulted from moisture in stems and the canopy. Furthermore, a simulation performed in a Japanese cedar forest revealed that 77.8% of the SNR reduction was caused by stems, 8.1% by branches, and 14.1% by needles.