A Baseline Correction Algorithm for FAST

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) is the most sensitive ground-based, singledish radio telescope on Earth. However, the original H Ⅰ spectra produced by FAST are affected by standing waves.To maximize the power of FAST for high-sensitivity observations, we proposed an algorithm that combines fast Fourier transforms and extreme envelope curves to automatically correct the baselines of FAST H Ⅰ spectra and remove standing waves from the baselines. This algorithm can reduce the amplified noise level caused by standing waves to a near-ideal level without losing signals or introducing false signals. The root mean square of the average baseline reaches ～8 mK, approaching the theoretical sensitivity of an H Ⅰ spectrum produced by FAST for an integration time of 335 minutes, i.e., ～6 m K.