Precision Agriculture makes use of quantitative measurements as input to sophisticated farm management software. For management of grazing animals, such as dairy cows, a key input is pasture biomass, so that pasture is not over-grazed nor have too much or too little application of fertilizer. Aside from destructively cutting, drying, and weighing the pasture, current measurement methods are slow and/or unreliable. We describe a new ultrasonic sensor which is compact and low-power, and which

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... es pasture properties remotely from a moving farm bike or UAV. The sensor comprises co-located log-spiral arrays of transmitters and receivers, giving high spatial resolution transverse to the propagation direction without excessive component counts. A pulsed, radar-like linear-FM chirp and matched filter gives high along-axis spatial resolution. With CLEAN image deconvolution, mm resolution is obtained through the pasture layer. This methodology allows detailed profiles of pasture density to be obtained at rates of 100 profiles per second. We present results retrieved via modelling of the complex acoustic scattering occurring in the pasture layer.