Abstract: This paper describes a key stage in the process for developing a new device for the measurement of gas bubbles in sediment. The device is designed to measure gas bubble populations within the top 2 m of marine sediments, and has been deployed at inter-tidal sites along the South coast of England. Acoustic techniques are particularly attractive for such purposes because they can be minimally invasive. However they suffer from the limitation that their results can be ambiguous. Therefore it is good practice to deploy more than one acoustic technique at a time. The new device does just this, but it is designed with the practical economy that the task is accomplished with the minimum number of transducers. One of the measurement techniques relies on insonifying the sediment with two frequencies. This paper outlines how the bubble size distribution is inferred through inversion of the signals detected when two frequencies are projected into the sediment. The high attenuation of the sediment makes this interpretation far more difficult than it would be in water. This paper outlines these difficulties and describes how they can be overcome.