Precision of micro-elevation map in agricultural fields using RTK-GPS

Micro-elevation maps were generated by mounting a single-carrier RTK-GPS receiver on a combine harvester, and were compared with others surveyed with a laser level. Under a favorable satellite arrangement (PDOP2.0), minimum standard errors were 5.1 mm in a concrete open space and 7.7mm in a paddy field after harvest. Periodical fluctuation was observed as PDOP increased, resulting in the maximum standard error of 16.9mm and 13.6mm, respectively (PDOP near equal 3.0). The moving average of the elevations taken more broadly across the paths of the vehicle lowered the standard errors by up to 47% in the open space and 34% in the paddy fields. However, loss of information of micro-topography of the fields should be taken into account in the paddy fields. The ratio of standard error to altitudinal variation was considered as a criterion, and the optimal area of the moving average was 6.0mx6.0 m to minimize it. In the open space, renewing a reference elevation every 3 to 4 minutes compensated for the fluctuation and lowered the standard error by 17% while a high PDOP was observed.