Coherent imaging systems, such as synthetic aperture radar (SAR), often suffer from granular speckle noise due to inherent defects, which can make interpretation challenging. Although numerous despeckling methods have been proposed in the past three decades, SAR image despeckling remains a challenging task. With the extensive use of non-local self-similarity, despeckling methods under the non-local framework have become increasingly mature. However, effectively utilizing patch similarities remains a key problem in SAR image despeckling. This paper proposes a three-dimensional (3D) SAR image despeckling method based on searching for similar patches and applying the high-order singular value decomposition (HOSVD) theory to better utilize the high-dimensional information of similar patches. Specifically, the proposed method extends two-dimensional (2D) to 3D for SAR image despeckling using tensor patches. A new, non-local similar patch-searching measure criterion is used to classify the patches, and similar patches are stacked into 3D tensors. Lastly, the iterative adaptive weighted tensor cyclic approximation is used for SAR image despeckling based on the HOSVD method. Experimental results demonstrate that the proposed method not only effectively reduces speckle noise but also preserves fine details.

This paper examines the effects of temperature and humidity on the absorption spectrum and concentration of nitrous oxide (${\mathrm{N}}_2\mathrm{O}$) using a compact, portable open optical-path gas detection sensor system. We obtained the absorption coefficient and widened the linear function of the ${\mathrm{N}}_2\mathrm{O}$ absorption spectrum related to temperature by theoretical analysis and the high-resolution transmission molecular absorption database (HITRAN). Afterward, we conducted real-time monitoring of ${\mathrm{N}}_2\mathrm{O}$ in both campus and laboratory environments using lasers for a duration of 32 h and 6 h, respectively, and the results were compared and analyzed with the theoretical derivation. The results show that the concentration of ${\mathrm{N}}_2\mathrm{O}$ increased with increasing environmental temperature but decreased with increasing humidity. Furthermore, the variations in temperature and humidity significantly affected the peak values of the second-harmonic (2f) and first-harmonic (1f) signals. Finally, the temperature ${\mathrm{N}}_2\mathrm{O}$ concentration and humidity ${\mathrm{N}}_2\mathrm{O}$ curves were calibrated separately, and temperature changes were positively correlated with the ${\mathrm{N}}_2\mathrm{O}$ concentration, while humidity changes were negatively correlated with the ${\mathrm{N}}_2\mathrm{O}$ concentration. The experimental results indicate that the concentration of ${\mathrm{N}}_2\mathrm{O}$ and its absorption spectra are influenced by humidity and temperature, which has a significant reference value in the absorption and measurement of ${\mathrm{N}}_2\mathrm{O}$ in practical applications.