Surface characterization from doubly scattered light

When a translucent diffuser is illuminated by a speckle pattern, a new speckle pattern is produced. We show that the decorrelation of this intensity pattern by displacement of the diffusing surface is related to the standard deviation of the slope's distribution when the illuminating speckle grain is chosen appropriately small. The experimental results are compared with those obtained by measuring the angular distribution of the mean scattered intensity, and they show good agreement with each other.