Atmospheric Turbulence Profiling for Optical Astronomy

Atmospheric turbulence profiling underpins the performance of ground-based optical telescopes by characterising the refractive disturbances that degrade image clarity. Turbulent eddies across a range of altitudes introduce wavefront aberrations, limiting angular resolution and contrast. Precise profiling informs the design and operation of adaptive optics systems, which apply real-time corrections to restore diffraction-limited performance. Techniques span direct wavefront sensing, scintillation analysis and remote sensing via radiosondes or numerical weather models. Recent advances exploit wide-field video-rate sensors and machine learning to resolve fine-scale structure and temporal evolution at frame rates surpassing conventional methods. High-resolution vertical profiles of refractive index structure constant, coherence time and isoplanatic angle are now within reach for observatories situated in diverse climatic regimes, from the high Antarctic plateau to arid mountain summits. By integrating in situ measurements with satellite data and atmospheric models, researchers achieve global site characterisation and predictive scheduling, enabling more efficient use of large telescopes and informing the selection of future observatory sites.

Research from Nature Portfolio

Direct observation of atmospheric turbulence has been achieved with a video-rate wide-field wavefront sensor capable of sampling a 1,100 arcsec field at 30 Hz. This instrument resolves three distinct turbulent layers up to 750 m altitude and yields high-resolution aberration-corrected imaging without additional deformable mirrors. A convolutional recurrent neural network predicts turbulence evolution over 33 ms, facilitating pre-compensation in free-space optical links. In a complementary study of a high-altitude plateau, three years of site monitoring at over 4,200 m elevation reveal 70 per cent clear nights, a median seeing of 0.75 arcseconds and low precipitable water vapour. The remarkably stable temperature and aridity underscore the plateau’s suitability for next-generation optical facilities, demonstrating the vital role of long-term profiling in site selection.

Atmospheric Turbulence Profiling for Optical Astronomy publication trend

The graph below shows the total number of articles in atmospheric turbulence profiling for optical astronomy across all publications each year (not limited to Nature Index journals).

Technical terms

Optical turbulence: Random refractive-index fluctuations in the atmosphere that distort incoming starlight and degrade image quality.

Wavefront sensor: An instrument that measures the shape of the optical wavefront to detect phase distortions caused by turbulence.

Adaptive optics (AO): A technology that corrects wavefront aberrations in real time, restoring high-resolution imaging through turbulence.

Seeing: A measure of atmospheric turbulence strength, expressed as the full-width at half-maximum of a stellar point spread function.

Isoplanatic angle: The angular separation over which the turbulence-induced wavefront distortions remain highly correlated.

Coherence time: The temporal scale over which atmospheric turbulence remains effectively constant for adaptive corrections.

Refractive index structure constant (Cn2): A parameter quantifying the intensity of refractive-index fluctuations as a function of altitude.

Richardson number (Ri): A dimensionless ratio indicating the stability of atmospheric layers and propensity for turbulence generation.

References

1. Direct observation of atmospheric turbulence with a video-rate wide-field wavefront sensor. Nature Photonics (2024).
2. Lenghu on the Tibetan Plateau as an astronomical observing site. Nature (2021).
3. A comparison of next-generation turbulence profiling instruments at Paranal. Monthly Notices of the Royal Astronomical Society (2024).
4. Antarctic atmospheric Richardson number from radiosonde measurements and AMPS. Atmospheric Chemistry and Physics (2023).