 Solution

Gravitational radiation admits polarization: general relativity has two transverse tensor modes, plus polarization and cross polarization, whose relative amplitudes and phase give linear, elliptical or circular gravitational-wave polarization. Their axes transform through twice a rotation of the transverse coordinate frame, unlike the vector polarization of electromagnetic radiation. Measuring these modes is physically plausible with several differently oriented detectors; a single detector generally measures only one projected combination.