Measuring and Correcting Wind-Induced Pointing Errors of the Green Bank Telescope Using an Optical Quadrant Detector

TL;DR

This paper presents an optical quadrant detector system for the Green Bank Telescope to detect and correct wind-induced pointing errors, significantly improving observational accuracy and sensitivity.

Contribution

Introduction of an optical quadrant detector instrument and correction methods for wind-induced pointing errors in large radio telescopes.

Findings

Corrected ~70% of sensitivity loss due to wind errors.

Wind-induced errors mainly caused by feedarm displacement along wind direction.

Preliminary real-time correction tests show promising results.

Abstract

Wind-induced pointing errors are a serious concern for large-aperture high-frequency radio telescopes. In this paper, we describe the implementation of an optical quadrant detector instrument that can detect and provide a correction signal for wind-induced pointing errors on the 100m diameter Green Bank Telescope (GBT). The instrument was calibrated using a combination of astronomical measurements and metrology. We find that the main wind-induced pointing errors on time scales of minutes are caused by the feedarm being blown along the direction of the wind vector. We also find that wind-induced structural excitation is virtually non-existent. We have implemented offline software to apply pointing corrections to the data from imaging instruments such as the MUSTANG 3.3 mm bolometer array, which can recover ~70% of sensitivity lost due to wind-induced pointing errors. We have also performed preliminary tests that show great promise for correcting these pointing errors in real-time using the telescope's subreflector servo system in combination with the quadrant detector signal.