The NOD3 software package: A graphical user interface-supported reduction package for single-dish radio continuum and polarisation observations

TL;DR

NOD3 is a Python-based, GUI-supported software package designed for the reduction and analysis of single-dish radio continuum and polarisation maps, improving distortion correction and data integration capabilities.

Contribution

It introduces a modern, extendable GUI tool for radio map reduction, including new methods for scanning effect correction and data combination, building on the legacy of NOD2.

Findings

Reduces scanning effects using orthogonal map combination.

Halves noise in dual-beam observations compared to NOD2.

Enables full flux recovery by combining single-dish and interferometer data.

Abstract

The venerable NOD2 data reduction software package for single-dish radio continuum observations, developed for use at the 100-m Effelsberg radio telescope, has been successfully applied over many decades. Modern computing facilities call for a new design. We aim to develop an interactive software tool with a graphical user interface (GUI) for the reduction of single-dish radio continuum maps. Special effort is given on the reduction of distortions along the scanning direction (scanning effects) by combining maps scanned in orthogonal directions or dual- or multiple-horn observations that need to be processed in a restoration procedure. The package should also process polarisation data and offer the possibility to include special tasks written by the individual user. Based on the ideas of the NOD2 package we developed NOD3, which includes all necessary tasks from the raw maps to the final maps in total intensity and linear polarisation. Furthermore, plot routines and several methods for map analysis are available. The NOD3 package is written in Python which allows to extend the package by additional tasks. The required data format for the input maps is FITS. NOD3 is a sophisticated tool to process and analyse maps from single-dish observations that are affected by 'scanning effects' due to clouds, receiver instabilities, or radio-frequency interference (RFI). The 'basket-weaving' tool combines orthogonally scanned maps to a final map that is almost free of scanning effects. The new restoration tool for dual-beam observations reduces the noise by a factor of about two compared to the NOD2 version. Combining single-dish with interferometer data in the map plane ensures the full recovery of the total flux density.