The amplitude of ground backscatter at high frequency (HF) recorded with oblique sounding equipment that utilizes azimuthal antenna beamwidths of about 6° and effective pulse lengths of about 50 μsec is characterized by sharp spikes that rise 10 to 20 db above the diffuse background clutter and have a range extent as short as the pulse length. These spikes suggest that the backscattering efficiency of the ground is highly nonuniform as a result of the occasional presence of a localized surface feature with a backscatter cross section one or two orders of magnitude larger than any object in the surrounding countryside. When short-pulse ground backscatter echoes are displayed as intensity modulated range versus azimuth records, these sharp spikes produce discrete echoes with an azimuthal extent approximately equal to the effective beamwidth of the antenna. The sources of many of these discrete echoes have been identified with specific topographic and geographic features, including cities and mountains in the western United States and islands in the Caribbean Sea.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.