Various examples are provided related to autonomous unmanned drone-tethered sonar systems. In one embodiment, a bathy-drone system includes an unmanned payload vessel and an unmanned drone tethered to the payload vessel through the tether attachment point. The unmanned payload vessel can include a sensor or sensor suite coupled to a bottom of the payload vessel and a tether attachment point through which propulsive force can be applied to the payload vessel. The drone can autonomously transport the payload vessel to and from a survey location and autonomously propel the payload vessel along a survey path at the survey location.

The present invention relates to a method (10) to control weeds comprising the steps of: a) acquiring geopositional information of planted crop seeds on an agricultural field and generating a crop seed map, b) acquiring soil elevation data and the corresponding geopositional information of the soil elevation on the agricultural field where the crop seeds have been planted or are being planted at at least two different time points and generating soil surface profile maps of the agricultural field, the soil surface profile maps showing the soil surface profiles at the at least two different time points, c) comparing the soil surface profile maps and the crop seed map to identify differences in the soil elevation profile that are not associated with seed growth of the planted seeds on the agricultural field, d) generating a weed control agent spray map on the basis of the differences in the identified soil elevations on the agricultural field that are not associated with seed growth of the planted crop seeds on the agricultural field.