A Robust Geometric Distortion Solution for Main Survey Camera of CSST

TL;DR

This paper introduces a robust weighted polynomial distortion correction method for the CSST survey camera, significantly improving astrometric precision under various conditions, including high distortion and crowded fields.

Contribution

The paper presents a novel WPDC-2P method that enhances geometric distortion correction by combining weighted polynomial fitting and residual absorption, validated on simulated and real survey data.

Findings

Achieves astrometric standard deviation of 0.013 to 0.107 pixels across detectors.

Reduces positional scatter in survey data from ~20 mas to below 10 mas.

Effective in crowded fields, maintaining high precision in extreme conditions.

Abstract

The advancement in sensitivity and field of view of next-generation wide-field survey telescopes requires astrometric measurements with high precision, even in the presence of significant geometric distortions. To address this challenge, we develop a Weighted Polynomial Distortion Correction in 2-Phase (WPDC-2P) method. This approach enhances stellar cross-matching, incorporates distance-based weighting into the traditional polynomial fitting, and employs a look-up table to absorb the remaining distortion residuals. Validated on simulated data from the Main Survey Camera of the \emph{Chinese Space Station Survey Telescope} (CSST), incorporating geometric distortions up to approximately $200$ pixels, the method achieves astrometric standard deviation ranging from 0.013 to 0.107 pixels (0.03 pixels for the $g$-1 detector) across all 18 detectors. Under extreme crowding conditions (e.g., globular cluster NGC 2298), the astrometric precision for the $g$-1 detector reaches 0.05-pixel level within the central region ($r_d < 4000$), despite a centroiding precision of $\sim$0.04 pixels. When applied to the Beijing-Arizona Sky Survey data, for which the standard pipeline delivers an astrometric uncertainty of $\sim$20 mas, our method reduces the positional scatter to $ \sigma_{\Delta\alpha}=5.494$ mas (0.01 pixels) and $ \sigma_{\Delta\delta}=9.981$ mas (0.02 pixels) using only a weighted 3rd-order polynomial correction. The method has been integrated into the CSST data processing pipeline and is prepared for further refinement using on-orbit calibration data.