A depth sounder is calibrated assuming the speed of sound in seawater is 1450m s−1. If the actual temperature of the water rises so that the true speed becomes 1470m s−1, how will the depth indicated by the instrument compare with the true depth for the same measured echo time?
(a) Indicated depth equals true depth
(b) Indicated depth is about 1.4% greater than the true depth
(c) Indicated depth is about 1.4% smaller than the true depth
(d) Indicated depth may be smaller or greater depending on echo time