  We propose a method for measuring the temperature of fermionic atoms in an
optical lattice potential from the intensity of the scattered light in the
far-field diffraction pattern. We consider a single-component gas in a
tightly-confined two-dimensional lattice, illuminated by far off-resonant light
driving a cycling transition. Our calculations show that thermal correlations
of the fermionic atoms generate fluctuations in the intensity of the
diffraction pattern of light scattered from the atomic lattice array and that
this signal can be accurately detected above the shot noise using a lens to
collect photons scattered in a forward direction (with the diffraction maxima
blocked). The sensitivity of the thermometer is enhanced by an additional
harmonic trapping potential.
