Comment on "The microwave reflective properties of water surfaces - 1: The reflectivity of smooth water at 19.24 and 22.43 GHz as measured with a free-wave microwave reflectometer" [with authors' reply]

The commentors (J.A. Saxton and J.A. Lane) have read the above paper [ibid., vol. MTT-16, pp. 938-943, November 1968] which makes extensive references to their earlier work. Several comments are provided. The method followed by Thompson, Silberberg, Gray, and Hardy (the authors of the above-named work), although identical in principle Saxton & Lane's free-wave method, incorporated several features of microwave measurement technique developed in recent years; whereas the original experiments were carried out in 1944 to 1945 with relatively simple equipment. The commentors agree that, with modern techniques, the free-wave method may with care be as accurate as the absorption-cell method for deriving reflection coefficients, and of course the former can provide data for rough surfaces. On the other hand, the cell technique requires a relatively small quantity of liquid which is a considerable advantage in that the temperature of the liquid can be varied rapidly and conveniently. In replying, the authors note that they believe that Saxton and Lane's sensitivity on this matter is due to the fact that they missed the basic point of our work which was, as clearly stated in our paper, to refine the freewave method to make it suitable for the precision measurements of reflectivities of roughened water surfaces. The authors have examined carefully Saxton and Lane's information, which includes their antenna patterns, and we must conclude that it is highly unlikely that the direct coupled component is significant in their experiment and, furthermore, that it is very likely that the standing wave between horns and target is in fact present in their system, given that our geometry was made to correspond as closely as possible to theirs. The authors note that in the commentors' paper, Saxton and Lane also express surprise that such a direct coupled component could exist in view of the observed radiation patterns of their antennas.