The effect of wind motion on cereal crops

Discusses the use of synthetic aperture radar (SAR) in remote sensing for agriculture. The monitoring of agricultural resources is time-critical and relies on the availability of good quality images acquired within specific time windows when there are marked differences in backscatter between and among particular crops. However, in addition to the variations produced by the changes in crop structure during a season there exist other environmental influences which may impact on our ability to interpret SAR imagery correctly. Wind motion is a very obvious meteorological effect, and whilst caution is often expressed, quantitative estimates of its consequences for SAR imagery are curiously lacking in the scientific literature. We present detailed computer simulations of the effects of wind-induced target motion on radar imagery, applied particularly to the case of a crop where wind can exert a very significant effect on the architecture of the plant canopy. Our field observations show that the plants are characterised by a resonant oscillation near 1 Hz. When the wind speed is low the response of a plant is characterised by a simple harmonic motion; with increasing wind speed the motion is increasingly complex and random. The effects are presented in terms of changes to the shape of the impulse response function for a point target, and through examination of the image statistics. Provision of such modelling results over a wide range of wind conditions and acquisition configurations allow us to make quantitative assessments of the limitations of different SAR platforms under different meteorological conditions, and the validity of the data interpretation