A baseline correction algorithm for FAST

TL;DR

This paper presents a novel algorithm combining Fourier transforms and envelope curves to automatically correct baselines in FAST HI spectra, effectively removing standing waves and approaching theoretical sensitivity.

Contribution

The proposed algorithm is the first to automatically correct FAST HI spectra baselines, significantly reducing noise caused by standing waves without signal loss.

Findings

Reduces baseline noise to ~8 mK, close to theoretical sensitivity.

Effectively removes standing waves from FAST HI spectra.

Maintains signal integrity without false signals.

Abstract

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive ground-based, single-dish radio telescope on Earth. However, the original HI 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 HI 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 $\sim$ 8 mK, approaching the theoretical sensitivity of an HI spectrum produced by FAST for an integration time of 335 minutes, i.e., $\sim$ 6 mK.