Abstract:As an important emitter of terahertz radiation, the traditional antenna has limited flexibility due to its fixed polarization state. In response to this issue, we have designed and studied a polarization-adjustable four-element terahertz gallium arsenide photoconductive antenna array, aiming to enhance its versatility and applicability in various applications. By precisely controlling the excitation of each element, the antenna array can achieve precise control of linearly and circularly polarized terahertz waves through in-phase unequal amplitude excitation and phase difference excitation. The results show that with in-phase unequal amplitude excitation, flexible control of linearly polarized terahertz waves within a 360-degree range can be achieved. With a 90-degree phase difference excitation, circularly polarized terahertz waves are generated, with a -10 dB impedance bandwidth range of 0.057 THz to 1.013 THz and a relative bandwidth of 178.69%. The axial ratio bandwidth range is 0.815 THz to 0.947 THz, with a relative bandwidth of 14.98%.

Abstract:To address the issues of low detection rate and high false alarm rate caused by complex background during sub-pixel aerial aircraft detection in hyperspectral remote sensing image, an aerial aircraft detection method was proposed based on contrails cloud proposal. Firstly, a hyperspectral semantic segmentation model was used to search for the contrails cloud, and ROIs of aircraft were proposed to reduce invalid search ranges and suppress false alarms based on the contrails cloud; Secondly, an endmember extraction algorithm based on dictionary learning and semi-blind non-negative matrix factorization was proposed to improve the accuracy of aircraft endmember extraction for hyperspectral subpixels; Finally, verification experiments were carried out on the hyperspectral remote sensing image dataset of gaofen-5 satellite, and the results demonstrated that the algorithm proposed in this paper can effectively suppress false alarms in complex scenes, and significantly improve the detection rate and detection accuracy of sub-pixel aerial vehicles.

Abstract:Aiming at the problem that infrared small target detection faces low contrast between the background and the target and insufficient noise suppression ability under the complex cloud background, an infrared small target detection method based on the tensor nuclear norm and direction residual weighting is proposed. Based on converting the infrared image into an infrared patch tensor model, from the perspective of the low-rank nature of the background tensor, and taking advantage of the difference in contrast between the background and the target in different directions, we design a double-neighborhood local contrast based on direction residual weighting method (DNLCDRW) combined with the partial sum of tensor nuclear norm (PSTNN) to achieve effective background suppression and recovery of infrared small targets. Experiments show that the algorithm is effective in suppressing the background and improving the detection ability of the target.

Abstract:Smooth objects such as metals， optical mirrors， and silicon wafers generally have extremely low emissivity and high reflectivity， and are called low emissivity objects.The extremely weak radiation from low emissivity objects will be submerged by the environmental radiation reflected from their surface. Infrared temperature measurement of low emissivity objects has always been a challenge in the field of infrared temperature measurement. Due to the continuously growing demand for non-contact temperature measurement of low emissivity objects in fields such as metal smelting， solar telescope thermal control， and semiconductor production， a large number of infrared temperature measurement methods for low emissivity objects have been proposed. First， this paper elaborates on the difficulties of the infrared temperature measurement of low emissivity objects and summarizes the temperature measurement methods currently used for low emissivity objects into five categories. Then， the basic principles and technical routes of each temperature measurement method were summarized， and the advantages and disadvantages of each temperature measurement method were analyzed in detail. Finally， the possible development directions of temperature measurement for low emissivity objects were discussed.

Abstract:Lasers near the wavelength of 2 μm are located in the atmospheric transmission window and the strong absorption peak of water， and have important applications in medicine， LIDAR， material processing， and as pump sources for mid-infrared lasers. The thulium-doped fiber laser （TDFL） stands out as a critical light source capable of delivering high power outputs at this wavelength. In this paper， to address the problems of relaxation oscillation and inter-modal four-wave mixing in quasi-continuous wave （QCW） TDFL， the time and frequency-domain output characteristics of the laser are optimized by increasing the bias current， optimizing the length of the gain fiber， and changing the diameter of the fiber coiling， etc. The effects of different gain fiber structures on the fiber transmission modes are also investigated. The developed QCW-TDFL achieves a peak power of 894 W and an average power of 89.4 W at a central wavelength of 1939.2 nm with a pulse width of 100 μs， a repetition frequency of 1 kHz and a duty cycle of 10%， and obtains stable and controllable pulse output waveforms and spectral characteristics.

Abstract:Small target detection has been a classic research topic in the field of infrared image processing, and the objects are usually brighter than the local background. However, in some scenarios, the target brightness may be lower than the background brightness. For example, the civil airplanes usually have low-temperature skin when cruising, appearing as dark points on medium spatial resolution thermal infrared satellite images. There are few features of these objects, so the current detection networks are redundant. Hence, authors proposed a lightweight dark object detection network, AirFormer. It only has 37.1K parameters and 46.2M floating-point operations on a 256×256 image. Considering the lack of infrared dark object detection dataset, authors analyzed the characteristics of airplanes on thermal infrared satellite images, and then developed a simulated flying aircraft detection dataset called IRAir. AirFormer achieves 71.0% at recall and 82.6% at detection precision on the IRAir dataset. In addition, after training on simulated data, AirFormer has achieved detection of real flying airplanes on the thermal infrared satellite images.

Abstract:The acquisition of aircraft altitude information is crucial for aviation safety and traffic control applications. Infrared remote sensing technology can accurately measure the thermal radiation information of targets, which means there is potential for quantitative observation of certain characteristics of aircraft target. A method for estimating the altitude of airborne targets based on infrared multi-channel feature matching is proposed in this paper. Firstly, a thermal infrared radiation characteristic observation model of aircraft is established, which based on the thermal infrared radiation characteristics of large aircraft and atmospheric radiative transfer models. Secondly, based on the observation model, a spectral database of aircraft方 at different altitudes and flight states under different atmospheric condition can be obtained by simulating. Thirdly, target spectral information can be extracted from remote sensing images and the altitude information can be estimated with using spectral angle matching (SAM). Finally, verification and analysis were completed using simulation data and SDGSAT-1 in-orbit data. The results indicate that the proposed method can achieve kilometer-level estimation accuracy for aircraft at cruising altitude. This method provides a new solution for estimating the altitude of aircraft and has important application potential.