Development of unmanned airboat for water-quality mapping

We have developed an unmanned airboat for mapping the water quality of shallow (<1 m) mire pools where aquatic weeds flourish. A differential global positioning system receiver and a global positioning system compass were used as navigation sensors. The airboat was designed for automatic operation. Using the boat, we measured parameters such as temperature, pH, dissolved oxygen, electrical conductivity, turbidity and chlorophyll-a of the water in a 26-ha mire pool in Hokkaido, Japan. To determine the appropriate sampling-grid size, the water was sampled along lines spaced 10 m apart, and the spatial variability of the mire pool characteristics was determined using a semivariogram. Results from the spherical model fit to the empirical semivariogram revealed spatial fluctuations in the water-quality parameters on the scale of 100 to 140 m. Because the size of the grid must be smaller than this scale, a second survey of water samples in the pool was carried out using a grid size of 40 m × 40 m. At each target point, a water-quality sensor unit was lowered from the boat. The survey of the entire grid area took approximately 231 min, during which time 130 points were sampled. The precision of the sampling points was within 2.6 m. The maximum speed and yaw rate of the airboat were 1.2 m s^[-1] and 48 deg s^[-1], respectively. The resulting maps showed the fine-scale distribution of water quality