  Specularly reflected light, or glint, from an ocean surface may provide a
useful observational tool for studying extrasolar terrestrial planets.
Detection of sea-surface glints would differentiate ocean-bearing terrestrial
planets, i.e. those similar to Earth, from other terrestrial extrasolar
planets. The brightness and degree of polarization of both sea-surface glints
and atmospheric Rayleigh scattering are strong functions of the phase angle of
the extrasolar planet. We modify analytic expressions for the bi-directional
reflectances previously validated by satellite imagery of the Earth to account
for the fractional linear polarization of sea-surface reflections and of
Rayleigh scattering in the atmosphere. We compare our models with Earth's total
visual light and degree of linear polarization as observed in the ashen light
of the Moon, or Earthshine. We predict the spatially-integrated reflected light
and its degree of polarization as functions of the diurnal cycle and orbital
phase of Earth and Earth-like planets of various imagined types. The difference
in polarized reflectances of Earth-like planets may increase greatly the
detectability of such planets in the glare of their host star. Finally,
sea-surface glints potentially may provide a practical means to map the
boundaries between oceans and continents on extrasolar planets.
