We describe theoretically and numerically the interaction of a laser- or LINAC-accelerated beam of relativistic electrons with a high intensity optical lattice, resulting from the superposition of two transverse laser pulses. The bunch is trapped and guided within the potential channels of the optical lattice, leading to betatron oscillations. We describe the emission from individual particles and from the bunch, and analyze its spectrum, considering the dominant incoherent radiation as well as possible effects of partial coherency. Analysis of the emitted radiation should provide useful information on the characteristics of the electron beam, and its interaction with the optical lattice.