Excerpt from A Survey of the Techniques for Measuring the Radio Refractive Index The radio refractive index can be measured either directly or indirectly. The former method is utilized by radio frequency refrac tometers; the latter method involves measurement of temperature, pressure and humidity and conversion to refractive index. In terms of convenience and accuracy the direct method is superlor; however, lack of the umversal use of refractometers requires the use of weather service type of data for the bulk of refractive index structures. Meteor ological sensing is limited mainly by the inaccuracy in measuring humidity Which under ideal conditions appears to limit the accuracy to i N. Gradient measurements utilizing radiosondes reflects an accuracy no better than zt 3 N units. Radio frequency refractometers are capable of accuracies as much as an order of magnitude better than that achieved by meteorological sensors. Lightweight refracto meters have been devised for balloon-borne and dropsonde measure ments reflecting accuracies inferior to the conventional refractorneter but superior to the radiosonde. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.