OH 1665 (left) and 1667 MHz (right) lines observed with the GBT (top) and the NRT (bottom) on 24 July 2020 in solid black lines. The red dashed curves show the fitted trapeziums to the spectra based on the methodology of Bockelée-Morvan et al. (1990). For GBT (NRT), the half lower bases of the trapeziums are 2.32 ± 0.07 (2.30 ± 0.14) and 2.43 ± 0.03 (2.23 ± 0.11) km s⁻¹ for the 1665 and 1667 MHz lines, respectively.