Comments to Figure 7.29 on ¡­

Comments to Figure 7.29 on page 429 in the text book: The receiver (Ar in the figure) receives backscattered signals over a time interval T, which is equal to c*H, where c is the speed of light and H the pulse length. It starts sampling when the first backscatter from the leading edge of the pulse ("Top" in the figure) arrives, and stops sampling (from this pulse) a time T later. Consequently, the sampling will start as soon as the backscattered signal from the leading edge hitting the bottom of the target arrives, and it will stop as soon as the backscattered signal from the trailing edge ("Bottom" in the figure) hitting the bottom of the target arrives. At the time when the trailing edge hits the bottom of the target, and becomes partly reflected, backscattering of the leading part of the beam (between "Top" and "Middle" in the figure) will also have arrived at the bottom of the target. This backscatter comes from that part of the target that lies between r and r + H/2, where r is the distance between the receiver and the bottom of the target. Hence, during time T the measurement covers a volume proportional to H/2, as shown on the right hand side of the figure. Backscattering from the next H/2 above will be captured by the subsequent time interval, etc. Hence, even though the pulse length is H, the vertical distance measured by each pulse within the time interval T is only H/2.