This project proposes a new theoretical method to measure non-invasively the key characteristics of a two dimensional dynamically rough free surface of a turbulent open channel flow using airborne acoustic waves. The research of this project will cover both numerical simulation and analytical derivation of the approximated solutions based on extending the Kirchhoff approximation technique to the case of rough surface containing multiple scales. This will be used to develop a technique of recovering water surface profile based on the data recorded on array of microphones. The method will provide sub-millimetre accuracy required to identify various scales of gravity-capillary waves present on the surface of shallow water flow. This information can potentially be linked to underwater conditions and flow velocity profile. The project outcomes will provide a virtual environment to prove the concept of non-invasive measurements as well as a tool to interpret the collected data. The numerical simulations will be adapted to open source software (i.e. GNU Octave and Scilab). For dissemination of the results and further developments, the software will be realised to acoustic and hydraulic communities as open source. The key novelty of this project is that the proposed method will be able to work reliably with a broad range of flows typically found in rivers, estuaries and partially filled pipes (sewers), which are the key components of water infrastructure and are critical in the water circulation process. This work will enable the development of non-invasive instrumentation which can determine flow rates and sediment transport in natural and man-made channels. This will enhance our capability for flood risk assessment and pollution monitoring.