In the sense of radar systems, this implies that the representation of a signal or data file needs both magnitude and phase measures. For any complex number a, the relationships are , where , and . For coherent systems such as SAR, the role of complex numbers is an essential part of the signal, since signal phase is used in the processor to obtain high resolution . For natural surfaces, conductivity in general is increased with increased moisture content. One expression of this rule is that the product of the range and the azimuth resolution divided by the number of statistically independent looks is a constant, which serves as a figure of merit of the system.
Strongest reflection is obtained when the materials are good conductors .
Measurement of signal strength, properly applied to a ratio of powers. For a signal power P compared by ratio to a reference power , the formal definition is . DeciBels often are used in radar, such as in measures of reflectivity , for which the dynamic range may span several factors of ten. The unit is named in honour of Alexander Graham Bell, inventor of the telephone. For image interpretation, use of the term is not recommended because it does not account for the effects of Earth curvature, and it does not conveniently include effects of local slope in the scene.