HARMONI at ELT: An evolvable software architecture for the instrument pointing model

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. To achieve its optimal image quality, an accurate measurement of the telescope’s instrumental pointing error is necessary. These measurements are affected both by systematic and random error contributions. To characterise the impact of the latter (as well as the performance of any necessary corrective model), simulations of the pointing error measurement process are required.

We introduce harmoni-pm: a Python-based prototype which, departing from a geometric optics modelisation of the instrument, attempts to reproduce the main drivers of the instrumental pointing error. harmoni-pm features a software architecture that is resilient to instrument model refinements and enables performance analyses of corrective models based on simulated calibrations. Results showed that the relay optics are the main drivers of the instrumental pointing error (order 100 µm).

The current simulator has been also critical in the design of a corrective model that not only takes noisy measurements into account, but also error distributions thereof. This motivated the development of a Bayesian corrective model that is able to integrate the incertitude of noisy measurements into the posterior knowledge of the final corrective model parameters.