Polarimetric Portraits

Abstract “Fully polarimetric” in its original radio science usage denotes a receiving instrument's ability to measure the four‐parameter Stokes vector characterizing the polarimetric properties of an electro‐magnetic (EM) field. In contrast, radar remote sensing specialists use “fully polarimetric” to apply exclusively to radars that evaluate the four complex scattering matrix elements. To disambiguate, polarimetric portrait is suggested, defined to be the Stokes vector of an unbiased EM field. For a passive system, this new name applies without qualification to the four Stokes parameters seen through a passive dual‐channel receiver. For an active system, the scene's illumination must have equal weighting between any two orthogonal polarizations to generate a polarimetrically unbiased reflected EM field. The suggested terminology is applicable to a variety of disciplines, including radiometry, alternative polarimetric radar architectures, radar astronomy, weather radar, and GPS/GNSS reflectometry. Polarimetric portraits obtained by dual‐polarized and quadrature‐polarized radars are shown to be equal.