The Robustness of Least-Squares Frequency Switching (LSFS)

TL;DR

This paper investigates the stability and robustness of the Least-Squares Frequency Switching (LSFS) method for spectral line observations, demonstrating its effectiveness and limitations under various observational challenges.

Contribution

The paper provides a detailed statistical analysis of LSFS stability and introduces solutions to mitigate its failures caused by RFI and strong line emissions.

Findings

LSFS is robust against gain instabilities and continuum sources.

LSFS fails in the presence of RFI or strong line emission.

Flagging and remapping improve LSFS performance.

Abstract

Least-squares frequency switching (LSFS) is a new method to reconstruct signal and gain function (known as bandpass or baseline) from spectral line observations using the frequency switching method. LSFS utilizes not only two but a set of three or more local oscillator (LO) frequencies. The reconstruction is based on a least squares fitting scheme. Here we present a detailed investigation on the stability of the LSFS method in a statistical sense and test the robustness against radio frequency interference (RFI), receiver gain instabilities and continuum sources. It turns out, that the LSFS method is indeed a very powerful method and is robust against most of these problems. Nevertheless, LSFS fails in presence of RFI signals or strong line emission. We present solutions to overcome these limitations using a flagging mechanism or remapping of measured signals, respectively.