An accurate knowledge of lower atmosphere is essential in many RF
applications such as radar and communication systems. Variations is
atmospheric temperature, humidity and pressure will create changes in the
atmospheric index of refraction. Especially at low altitudes, this change
can vary considerably with both height and range,
heavily affecting the propagation characteristics. One important
example is the formation of an electromagnetic duct. A signal sent from a
surface or low altitude source, such as a ship or low-flying object, can
be totally trapped inside the duct. This will result in multiple
reflections from the surface and they will appear as
clutter rings in the radar plan position indicator (PPI) screen.
Trident Warrior 2013 was conducted off the coast of Norfolk, VA from
July 12-18, 2013. Passive RF measurements were made between 80-700 MHz
using antennas mounted on the R/V Knorr. These were coupled with
ScanEagle, balloon, radiosonde, kite, surface wave glider
measurements in addition to the MET stations aboard R/V Knorr.
Accuracy of these measurements and Numerical Wether Prediction (NWP) codes
such as Coupled Ocean Atmospheric Mesoscale Prediction System (COAMPS) are
tested via the measured RF data using passive
measurements of sources of opportunity such as FM and TV stations
located around the coastal regions.