The performance of a sonar system operating in shallow water is closely linked to the properties of the seabed. At the same time the sensitivity of the acoustic signal (or background) to sediment properties gives an acoustic sensor the potential to measure precisely those properties that are needed to estimate sonar performance. Of particular interest in this context is reverberation from low frequency active sonar (LFAS), because of its wide area potential, and the single beam echo sounder, because of its almost universal availability. The potential of these two instruments to provide the necessary data for the purpose of LFAS performance prediction is explored. Particular emphasis is placed on exploiting their complementary nature. Relevant questions include: The echo sounder measures properties of the uppermost few centimetres of sediment. How can this be made relevant to LFAS, which is sensitive to properties on a depth scale of metres rather than centimetres? The echo sounder measures properties directly beneath the ship, and at normal incidence. How can this information be used when the LFAS attention is focussed on sound travelling several kilometres, at angles close to grazing incidence? The information content of signals from the two sensors is discussed, with a view to answering these and related questions.