EMI is a nadir-viewing wide-field imaging spectrometer aiming to quantify the global distribution of tropospheric and stratospheric trace gases. The spectral range is 240–710 nm, with the spectral resolution 0.3–0.5 nm. The preflight accuracy of wavelength calibration is less than 0.05 nm; the accuracy of radiance calibration is less than 5 %. The obtained calibration key data are used for the L1b processor. In-orbit wavelength/radiometric calibration is used to monitor performance changes.