We explore the complementarity between two tomographic probes of the universe: baryon acoustic oscillations (in the galaxy power spectrum) and weak gravitational lensing. The galaxy power spectrum characterizes the density fluctuations, whereas the weak lensing shear power spectrum is a direct measure of the potential fluctuations. We find that photometric measurements of baryon oscillations alone do not provide very tight constraints on the dark energy equation of state parameters, partially due to our uncertain knowledge of the galaxy clustering bias. Weak lensing, on the other hand, is adversely impacted by the uncertainties of the probability distribution of photometric redshift errors. A joint analysis of the two, however, is more robust to these uncertainties and leads to a remarkable improvement over the results from either probe alone.

Forecasts of cosmological constraints with baryon oscillations and weak lensing are provided for four proposed multiband imaging surveys in combination with measurements of the cosmic microwave background from Planck. In particular, we find that the joint analysis of galaxy and shear power spectra with the Large Synoptic Survey Telescope can tighten the 1σ error bounds on the dark energy equation of state (at the pivot expansion factor a_p = 0.63) and its rate of change, respectively, to 0.016 and 0.16 (marginalized over 131 other parameters). With supernovae and cluster counting as well as higher-order statistics of the same galaxy and shear data, one can further improve the constraints.