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Optical turbulence forecast for ground-based astronomy and free-space optical communication

Elena Masciadri, Alessio Turchi, Camilo Weinberger, Marlene De Sepibus, Luca Fini

TL;DR

The paper surveys the state of optical turbulence forecasting, focusing on non-hydrostatic mesoscale models (notably $C_N^2$ profiling) for ground-based astronomy and exploring extensions to free-space optical communication. It details the Astro-Meso-Nh framework, its calibration/validation workflow, and the development of operational systems (ALTA Center, FATE) that deliver long- and short-term forecasts. A key contribution is the autoregressive (AR) method that updates physics-based forecasts in real time, achieving significant reductions in RMSE at 1 h scales and outperforming persistence. The work argues for a hybrid forecasting paradigm and stresses daytime instrumentation to enable reliable OT forecasts for both astronomy and FOS.

Abstract

Forecasting optical turbulence in the Earth's atmosphere has been an ambitious challenge for the astronomical scientific community for several decades. While earlier research primarily focused on whether it was possible to predict optical turbulence and its vertical distribution, current efforts are more concentrated on the accuracy achievable at different timescales, the efficiency of various forecasting methods and the contributions of new statistical approaches, such as auto-regression and machine learning to this field. In this contribution, I will present the state of the art of the research conducted by our group, positioned within the international research scenery. Most of our past activity has been primarily focused on ground-based astronomy but recent advancements in space research opened new opportunities for applications in the free-space optical communication.

Optical turbulence forecast for ground-based astronomy and free-space optical communication

TL;DR

The paper surveys the state of optical turbulence forecasting, focusing on non-hydrostatic mesoscale models (notably profiling) for ground-based astronomy and exploring extensions to free-space optical communication. It details the Astro-Meso-Nh framework, its calibration/validation workflow, and the development of operational systems (ALTA Center, FATE) that deliver long- and short-term forecasts. A key contribution is the autoregressive (AR) method that updates physics-based forecasts in real time, achieving significant reductions in RMSE at 1 h scales and outperforming persistence. The work argues for a hybrid forecasting paradigm and stresses daytime instrumentation to enable reliable OT forecasts for both astronomy and FOS.

Abstract

Forecasting optical turbulence in the Earth's atmosphere has been an ambitious challenge for the astronomical scientific community for several decades. While earlier research primarily focused on whether it was possible to predict optical turbulence and its vertical distribution, current efforts are more concentrated on the accuracy achievable at different timescales, the efficiency of various forecasting methods and the contributions of new statistical approaches, such as auto-regression and machine learning to this field. In this contribution, I will present the state of the art of the research conducted by our group, positioned within the international research scenery. Most of our past activity has been primarily focused on ground-based astronomy but recent advancements in space research opened new opportunities for applications in the free-space optical communication.
Paper Structure (11 sections, 6 equations, 8 figures, 2 tables)

This paper contains 11 sections, 6 equations, 8 figures, 2 tables.

Table of Contents

  1. INTRODUCTION
  2. Non-hydrostatic atmospheric meso-scale models
  3. Model Calibration and model validation
  4. Automatic operational forecasts systems and hybrid methods
  5. ALTA Center at the Large Binocular Telescope
  6. The time scale in a forecast process
  7. The AR method
  8. FATE at the Very Large Telescope
  9. Machine Learning
  10. Free-space optical communication (FOS): challenges for OT forecasts
  11. CONCLUSIONS

Figures (8)

  • Figure 1: ALTA Center web page home: http://alta.arcetri.inaf.it.
  • Figure 2: Examples of outputs/products provided by ALTA Center - Top: temporal evolution between the dusk and dawn of the total seeing ($\varepsilon$), isoplanatic angle ($\theta_{0}$) and wavefront coherence time ($\tau_{0}$). Bottom: temporal evolution of the $\hbox{$C_N^2$}$ on the 20 km above the ground (left), average of the $\hbox{$C_N^2$}$ profile all along a night (centre), average all along one night of the wavefront coherence time extended on a surface of 60 km $\times$ 60 km (right).
  • Figure 3: Extracted from Masciadri et al. 2023masciadri2023. Toy model: model configuration related to the automatic forecast system of the Very Large Telescope (FATE project). See text in Section \ref{['fts_sec']}.
  • Figure 4: Temporal evolution of the seeing during one night: green line: real-time observations; black line: forecast of the seeing obtained with the atmospheric Astro-Meso-Nh model in standard configuration therefore the afternoon for the coming night; red line: forecast of the seeing obtained with the AR method calculated at a time scale of 1 hour.
  • Figure 5: Extracted from Masciadri et al. 2023masciadri2023: Top: scatters plots of forecast versus observations for seeing, wavefront coherence time, isoplanatic angle and GLF. Bottom: Density function maps for the same parameters shown on top.
  • ...and 3 more figures