Folded HRS 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 obtained on UT 1.5 September 2010. The fitted baselines are obtained using the same method as for the WBS data. 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.