Reflection of Ultrasonic Wave on the Substrate‑Ice Layer‑Air Interface: The Role of Roughness Parameters

Ice accretion on transmission lines poses a severe threat to the safety of power grids. To achieve early icing warning and online ice thickness measurement， it is necessary to consider the effect of the rough ice layer on ultrasonic echo signals during the early icing stage. This study applied a sinusoidal equivalent roughness model to simplify the ice layer profile， and used PZFlex to numerically analyze the effects of the rough structure scale on the ultrasonic pulse-echo signals. The reflection coefficient of the ice-air layer interface was introduced to characterize small-scale roughness. It is found that the attenuation of pulse-echo signals is dominant by the height of rough structure. As the roughness upper ice layer increases， the interface reflection coefficient gradually decreases. When the roughness exceeds the critical value， the reflection coefficient shows independent with roughness. As the threshold of reflection coefficient is set as 0.25， the effective measurement range of roughness under different center frequencies of excitation signal sources is determined. The relationship between the reflection coefficient and roughness upper ice layer is established， enabling the quantitative identification of rough ice layer using the ultrasonic pulse-echo technique. The research can provide a technical basis for the accurate measurement of ice thickness above transmission lines.