Folded spectra for the horizontal polarization mixer (blue line), vertical polarization mixer (red line), and averaged spectrum (black line) of the ortho-water J_KaKc (1₁₀–1₀₁) line at 556.936 GHz acquired with the WBS on UT 1.5 September 2010. The fitted baselines are obtained by masking a (–1, 1) km s^-1 window around the rest frequency of the water line and using a linear combination of sine functions. The vertical axis is the calibrated main-beam brightness temperature, the upper horizontal axis is the lower sideband frequency, and the lower horizontal axis shows the Doppler velocity with respect to the nucleus rest frame.