The robust detection of infrared small targets plays an important role in infrared early warning systems. However, the high-brightness interference present in the background makes it challenging. To solve this problem, we propose a weighted improved double local contrast measure (WIDLCM) algorithm in this paper. Firstly, we utilize a fixed-scale three-layer window to compute the double neighborhood gray difference to screen candidate target pixels and estimate the target size. Then, according to the size information of each candidate target pixel, an improved double local contrast measure (IDLCM) based on the gray difference is designed to enhance the target and suppress the background. Next, considering the structural characteristics of the target edge, we propose the variance-based weighting coefficient to eliminate clutter further. Finally, the targets are detected by an adaptive threshold. Extensive experimental results demonstrate that our method outperforms several state-of-the-art methods.

Monitoring global greenhouse gas concentration information via satellite remote sensing has become a critical area of research to support the further understanding of global carbon emissions. The Greenhouse-gases Absorption Spectrometer-2 (GAS-2) is being developed as the primary payload of the Fengyun-3H (FY-3H), which will be launched in 2024. Achieving high-precision mesurements of greenhouse gases requires precise spectral calibration. However, currently, there is no method for assessing the detection accuracy of GAS-2 using spectral calibration light sources, and quantitative studies are lacking. In this study, the influence model of calibration light sources on spectral calibration accuracy is established, and the spectral radiance acquired via GAS-2 is simulated using the line-by-line radiative transfer model (LBLRTM). We investigated the impact of different linewidths and wavelength stabilities of the calibration light source on its accuracy in four wavelength bands. This study is the first to examine the effects of the linewidth and wavelength stability of a calibration light source on the spectral radiance acquired via GAS-2. The initial results demonstrate that if the linewidth of the calibration light source is approximately 100 MHz and the wavelength stability is in the order of subpicometers, the radiance error obtained by GAS-2 is less than 10%. Among the four bands, the 2.06 $\mathsf{\mu }$m (strong-$C{O}_2$) band is more affected by the calibration light source than the other three bands. In addition, the wavelength stability of the light source has a greater influence on the error than the linewidth of the light source under the same error condition. The research findings can be used to guide and reference the selection of light sources in the laboratory spectral calibration of GAS-2, ultimately contributing to the instrument’s quantitative development level.

Satellite-based monitoring of atmospheric greenhouse gas (GHG) concentrations has emerged as a prominent and globally recognized field of research. With the imminent launch of the Greenhouse-Gases Absorption Spectrometer-2 (GAS-2) on the FengYun3-H (FY3-H) satellite in 2024, there is a promising prospect for substantial advancements in GHG detection capabilities. Crucially, the accurate acquisition of spectral information by GAS-2 is heavily reliant on its instrument parameters. However, the existing body of research predominantly emphasizes the examination of atmospheric parameters and their impact on GHG detection accuracy, thereby leaving a discernible gap in the comprehensive evaluation of instrument parameters specifically concerning the acquisition of atmospheric greenhouse gas concentration data by GAS-2. To address this knowledge gap, our study employs a radiation transfer model grounded in radiation transfer theory. This comprehensive investigation aims to quantitatively analyze the effects of various instrument parameters, encompassing crucial aspects such as spectral resolution, spectral sampling rate, signal-to-noise ratio, radiometric resolution, and spectral calibration accuracy (including instrument line shape function, central wavelength shift, and spectral resolution broadening). Based on our preliminary findings, it is evident that GAS-2 has the necessary spectral resolution, spectral sampling rate, and signal-to-noise ratio, slightly surpassing existing international instruments and enabling a significant detection accuracy level of 1 part per million (ppm). Moreover, it is essential to recognize the critical impact of instrument spectral calibration accuracy on overall detection precision. Among the five commonly used instrument line shape functions, the sinc function has the least impact on detection accuracy. Additionally, GAS-2’s radiance quantization depth is 14 bits, which is comparable to similar international payloads and maintains a root mean squared error below 0.1 ppm, thus ensuring a high level of precision. This study provides a comprehensive evaluation of the influence of GAS-2’s instrument parameters on detection accuracy, offering valuable insights for the future development of spectral calibration, the optimization of similar payload instrument parameters, and the overall improvement of instrument quantification capabilities.

Context . The radiation pattern of a radio telescope antenna, particularly in terms of the pointing deviation (PD) and peak gain loss (PGL), is critical for determining the telescope’s front-end sensitivity and angular resolution. These performance indices are highly susceptible to deformations of the primary reflector induced by external loads such as gravity and wind. Active optics, which involves adjusting actuators mounted on the backup structure of the primary reflector, offers a promising solution. However, the underlying mechanism linking actuator adjustment to variations in the radiation pattern is not well understood. Aims . This research aims to uncover the relationship between actuator adjustment and key performance indicators of a radiation pattern (i.e., PD and PGL) by establishing a reliable analytical framework that enables the precise optimization of the antenna’s electromagnetic characteristics. Methods . We investigated the radiation pattern of the 10.4 m Leighton Chajnantor Telescope (LCT) antenna under various actuator configurations using the aperture integration method for segmented reflectors (AIMSR). Based on the simulation results, we propose a superposition principle (SP) that approximates the cumulative effect of multi-actuator adjustment as the linear combination of their individual contributions. The mathematical model we developed on the basis of this principle is aimed at describing the functional relationship between actuator displacements and the resulting PD and PGL. Results . Numerical experiments confirm the accuracy of the SP in capturing the effects of actuator-induced deformation on the radiation pattern. Furthermore, the SP-based mathematical model is validated by its successful application in optimizing actuator configurations to minimize the PD and PGL of LCT’s antenna, thereby enhancing the radiation performance under external loads. Conclusions . Our findings demonstrate that the proposed SP method provides a physically interpretable and computationally efficient approach to model and optimize the active control of large segmented reflectors. This approach lays the groundwork for high-precision pointing correction for future submillimeter radio telescopes.

The primary reflector of the Leighton Chajnantor Telescope (LCT) is usually affected by various environmental loads and panel misalignments, both of which can significantly degrade its radiation pattern performances. To address these effects, this paper focuses on optimizing actuator adjustments and proposes a Mixed-Integer Nonlinear Programming (MINLP) model that takes key radiation pattern performance indicators as the optimization objective. Recognizing the limitations of traditional optimization methods, which are prone to falling into local optima due to high-dimensional and complex nonlinear constraints, and struggle to optimize both actuator positions and adjustment values simultaneously, we introduce an enhanced genetic algorithm combined with a heuristic actuator selection rule, which efficiently solves the beam performance optimization problem by regulating part of the actuators. Notably, the approach demonstrates a significant reduction in the magnitude of the pointing deviation (PD), achieving approximately 80% of decrease when utilizing 20 actuators. Furthermore, with the application of 40 actuators, the method successfully reduces the RMS surface error induced by gravitational deformation to below 12 µm across all zenith angles. The proposed method is applied to typical deformation scenarios caused by environmental loads and panel misalignments, resulting in actuator adjustment schemes for varying numbers of actuators. A systematic evaluation of each scheme’s impact on beam performances is provided, and further analysis reveals the relationship between actuator position distribution, adjustment values, and surface error. Additionally, the influence of surface error distributions on the selection of key actuators is systematically revealed.