Daytime HyWFS approach for daylight adaptive optics wavefront sensing.

Bright daylight photon noise and the saturation of wavefront sensors pose challenges to high-resolution daytime imaging. In this paper, a daytime hybrid wavefront sensor (HyWFS) approach for real-time wavefront sensing in daylight adaptive optics (AO) is described. The Shack-Hartmann wavefront sensor (SHWFS) algorithm is used to efficiently compensate large-scale wavefronts, while the pyramid wavefront sensor (PyWFS) algorithm offers highly sensitive correction of small wavefronts. Daylight closed-loop AO experiments were performed using the daytime HyWFS approach with both algorithms, respectively. The experiment results indicate that the proposed approach provides accurate daylight AO correction and allows for a simple switch between the two algorithms without increasing system complexity. The daytime HyWFS approach can serve as an alternative for daylight natural guide star AO, enabling high-resolution observation of resident space objects no longer limited to dawn and dusk.

Design and Parameter Identification for a Positioning Platform with a Large Stroke and High Precision for Segmented Mirrors.

An active optical system with three segmented mirrors was proposed to verify the co-focus and co-phase progress. In this system, a kind of large-stroke and high-precision parallel positioning platform was specially developed to help support the mirrors and reduce the error between them, which can move in three degrees of freedom out of plane. The positioning platform was composed of three flexible legs and three capacitive displacement sensors. For the flexible leg, a kind of forward-type amplification mechanism was specially designed to amplify the displacement of the piezoelectric actuator. The output stroke of the flexible leg was no less than 220 µm and the step resolution was up to 10 nm. Further, a linear model was established to identify the amplification ratio between the actuator and the flexible leg, which can increase the precision of the positioning platform. Moreover, three capacitive displacement sensors with a resolution of 2.5 nm were symmetrically installed in the platform to accurately measure the position and attitude of the platform. To improve the stability and precision of the platform, particle swarm optimization algorithm was applied to identify the control matrix, which can help the platform achieve ultra-high precision positioning. The results showed that the theoretical matrix parameters had a maximum deviation of 5.67% from the experimental ones. Finally, abundant experiments verified the excellent and stable performance of the platform. The results proved that while bearing the heavy mirror, which is no more than 5 kg, the platform can realize a 220 µm translation stroke and 2.0 mrad deflection stroke, with a high step resolution of 20 nm and 0.19 µrad. These indicators can perfectly cater to the requirements of the proposed segmented mirror system's co-focus and co-phase adjustment progress.

Satellite-based survey of extreme methane emissions in the Permian basin.

Industrial emissions play a major role in the global methane budget. The Permian basin is thought to be responsible for almost half of the methane emissions from all U.S. oil- and gas-producing regions, but little is known about individual contributors, a prerequisite for mitigation. We use a new class of satellite measurements acquired during several days in 2019 and 2020 to perform the first regional-scale and high-resolution survey of methane sources in the Permian. We find an unexpectedly large number of extreme point sources (37 plumes with emission rates >500 kg hour-1), which account for a range between 31 and 53% of the estimated emissions in the sampled area. Our analysis reveals that new facilities are major emitters in the area, often due to inefficient flaring operations (20% of detections). These results put current practices into question and are relevant to guide emission reduction efforts.

Measurement of internal stray radiation of a thermal infrared spectrometer based on temperature variation.

The level of internal stray radiation is an important criterion to evaluate the performance of a thermal infrared spectrometer. In this study, a novel method is proposed and evaluated to measure the internal stray radiation of a thermal infrared spectrometer based on temperature variation. The proposed method was used to measure the internal stray radiation values of an existing instrument. First, two output gray value curves were constructed for a single spectral channel in a cryogenic detector at two different spectrometer temperatures based on radiometric calibration measurements. Subsequently, the gray value and radiation flux of the internal stray radiation of the spectrometer were calculated. In addition, the internal stray radiation data measured at different spectral channels and different integration times were used to verify and evaluate the proposed method. Results show that the proposed method is valid, and the standard deviations of the various internal radiation values of the tested spectral channels and the various integration times are 3.47% and 1.46%, respectively. The proposed method is adaptable, flexible, and efficient.