The main focus of the previous chapters has been on the optical methods of ocean sensing and monitoring, in part due to the fact that the only transmission window of seawater is in the visible range. However, longer wavelengths of the EM spectra are less sensitive to atmospheric influences, and approaches have been developed for sensing the ocean’s surface temperature, salinity, sea surface height, and roughness by both passive and active microwave sensors. Microwave radiation from thermal emissions is typically in the 1- to 100-GHz (3mm to 0.3 m) region of EM bands. Due to the longer wavelengths, there is little scattering effect from molecules and aerosols, including pollen, ash, and fog. Therefore, atmospheric influences are smaller and easier to correct, making microwave sensing one of the more attractive choices in ocean sensing with 24/7 coverage. Some excellent reviews on the applicability of microwave sensing of the ocean can be found in Swift (1980), with in-depth discussions in Robinson (1995) and Rees (2001). The key areas of sensing in both passive and active microwave methods are discussed in this chapter to provide the necessary background knowledge for further investigations.
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