of Smooth Water at 19.24 and 22.43 GHz as Measured with a Free-Wave Microwave Reflectometer

The first phase of the work reported here deals with the establishment of the temperature dependence of smooth water reflectivity at 19.24 and 22.43 GHz. Previous mea- surements (10) have been made of this property using both a free space technique and later a more accurate absorption cell technique (11 ). Using the analysis of Saxton (12) these results can be compared at 19 GHz and a significant dis- crepancy of 1.4 percent is noted. This raises the question of whether the free space reflectometer technique is an accu- rate means of measuring the reflection coefficient. It is the purpose of this paper to show that the reflectometer tech- nique can yield results of accuracy comparable to the ab- sorption cell technique and to point out some errors made in the earlier reflectometer measurements ( 10). Our interest in the reliability of the reflectometer method is prompted by the fact that the absorption cell technique cannot be applied to the measurement of rough surfaces. The frequency of 19.24 GHz was chosen to allow direct comparison of our results with the measurements of Saxton and Lane. The other frequency, 22.43 GHz, is the frequency of a microwave radiometer being constructed for later use in our experimental program and is close to a water vapor absorption line.