Utilization of GNSS at forest mapping | Využitie GNSS pri lesníckom mapovaní

Utilization of the GNSS technology is current topic. This technology appears to be as the most advantageous at densifying of the geodetic points in open areas, forest rides and forest stands borders with following measurement under the forest stand canopy by classic terrestrial methods (measurement with total stations, electronic tachymeters, compass measurement with the Field-map hardware and so on). Results of the GNSS measurements are dependent on the method of measurement, length of the observation, satellite system, number, type and position of the satellites. At forest mapping as the most advantageous appears the Static method of the GNSS. In the forest stands conditions at the kinematics (RTK) and also at the Stop and Go method of the GNSS is coming to higher fluctuations of the errors in position (tenths of centimeters), hence there is no possibility of utilization of these methods at point fields creation, at property boundaries surveying with the fourth class of the mapping accuracy, which is required as the minimum (mxy = 0.26m). But there is possibility of utilization of these methods at surveying of the boundaries of forest management distribution units, which are not property boundaries and the other forest detail, where horizontal accuracy at the GNSS measurement methods is sufficient (mxy = 1.50m). Also next factors have an influence on the measurement, for example type of the forest stand, mean thickness, canopy, crop density. Influence has also season and location of the measured points in terrain. Here takes a role terrain configuration, exposure, appearance of shading trees close to measured point. At point fields densifying it is important to pay an attention on the optimal point arrangement. Points should be placed in open areas (borders of the forest stands, forest rides), to have secured an optimal signal receiving, but also with the optimal possibility of the projected point field utilization for next terrestrial measurements. Projected points should be placed in the range of 1 km from the reference station. While there will not be secured the sufficient number of the satellites (six and more), there is not desirable to realize the measurement, because even though the length of the observation is extended, there is not secured solving of the ambiguities. At present is known, that the two-frequency GNSS receivers could determine position of the points with required accuracy. Also one-frequency GNSS receivers need to be reflected (e. g. LOCUS), which at Static methods have reached relatively good results in the deciduous and coniferous forest stands. At utilization of today two-frequency GNSS receivers, which are able to receive not only signals from the American satellites NAVSTAR (GPS) but also from the Russian satellites GLONASS and in the near future also from the GALILEO satellites, are much higher possibilities of the GNSS technologies utilization, also in less favorable measurement conditions like forest rides and forest stands have.