Many scientific goals for DES require calibration of broadband grizY photometry that is stable in time and uniform over the sky to better than 1%. It is also necessary to limit systematic uncertainty in the calibrated broadband magnitudes due to the spectrum of the source. I present details on the Forward Global Calibration Method (FGCM), which combines data taken with auxiliary instrumentation with data from the survey imaging itself and models of the instrument and atmosphere to estimate the spatial- and time-dependence of the passbands of individual DES exposures. The passband of individual observations is combined with the source spectral shape to compute chromatic corrections to the standard system which is necessary to achieve sub-percent calibrations.
Eli RYKOFF (SLAC National Accelerator Laboratory)