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Spectropolarimetry is the measurement of EMR polarization by wavelength. Light that is not monochromatic (i.e., has a mix of wavelengths) may have one kind and amount of polarization at one wavelength and at some other wavelength have another kind/amount. A spectropolarimeter, an instrument that measures this, is often a spectrograph feeding into a polarimeter that is capable of separating a line of an image into polarized components. A CCD's two dimensions can display the wavelength over one dimension and two components of polarization across the other, so the CCD image holds polarization data by wavelength for a point source. A Wollaston prism is one optical device to separate the light into components by polarization.
Spectropolarameters are used on ground telescopes, and spacecraft including telescopes and planet exploration missions. Applications include detecting and mapping magnetic fields (by working out the Faraday rotation) such as those around the Sun, and working out characteristics of the source of reflected or scattered EMR, such as from a planetary nebula, or an active galactic nucleus.