Spectropolarimeter for Planetary EXploration (SPEX) is an innovative, single channel, high precision polarimeter for the characterization of planetary atmospheres. It can measure the flux and the degree and direction of linear polarization of sunlight that has been scattered within a planetary atmosphere from 350 to 800 nm with 2 nm (flux) to 20 nm (polarization) spectral resolution.

SPEX spectropolarimetry works by encoding the degree and angle of linear polarization of the incoming light in a sinusoidal modulation of the flux spectrum. A single modulated flux spectrum thus provides the degree and angle of linear polarization as functions of the wavelength. SPEX measures two flux spectra with different modulation phases, and from these two spectra, the total flux spectrum itself can be obtained. The modulation of the flux spectra is done with birefringent crystals. With its 1-liter volume, SPEX is capable of full linear spectropolarimetry, without moving parts.

SPEX novel polarimetry method has successfully been tested with a breadboard model, both in laboratory conditions and outside, looking at the Earth' zenith sky. An airborne version has also been integrated on the NASA ER-2 aircraft, and will be flown in the ACEPOL field campaign.

More information:

https://www.sron.nl/earth-instrument-development/spex

Data

Calibration

Uncertainty

References
Spectral modulation for full linear spectroscopy
Prototyping for the Spectropolarimeter for Planetary EXploration (SPEX): Calibration and sky measurement
SPEX: A highly accurate spectropolarimeter for atmospheric aerosol characterization