High-resolution electromagnetic altimetry over the ocean

A pair of coils acting as transmitter and receiver of a harmonic electromagnetic (EM) wave is found to be an excellent high-resolution altimeter at low altitudes over ocean regions. Due to high seawater conductivity, the altimetric determination from a received signal is computationally simple. Experimental results obtained from the Cape Cod Bay area indicate that an EM altimeter may be superior in resolution to a radar altimeter. Because of its wide beamwidth, the EM altimeter measures the distance to the instantaneous mean sea level and ignores ripples and waves. This may be considered an advantage over a laser altimeter which, despite its high resolution, is susceptible to noise caused by small surface fluctuations (due to its small beamwidth). The method has potential application to determining the sea-ice thickness.