To overcome the limitations of CdZnTe substrates for large-format, low-cost HgCdTe infrared focal plane arrays (IRFPAs), the epitaxial growth of HgCdTe films on alternative substrates (e.g., GaAs and Si) has become an important research focus. The lattice mismatch of approximately 14% between the GaAs alternative substrate and the HgCdTe material generates a high density of interfacial defects, such as dislocations and twins. These defects induce a high density of interface states within the near-interface bandgap, resulting in interfacial recombination and consequently limiting device performance. This paper proposes an optimization method for the HgCdTe/GaAs interface that involves substrate removal and surface passivation after the fabrication of GaAs-based HgCdTe infrared (IR) detectors. The GaAs substrate was removed without damage through chemical mechanical polishing (CMP) and selective wet chemical etching. A bromine-based solution (Br2–HBr) was employed to eliminate the surface damage layer for interfacial optimization, and a composite dielectric film was deposited to achieve simultaneous surface passivation and optical antireflection. Experimental results on n-on-p devices operating at 80 K demonstrate that after interfacial optimization, the average quantum efficiency across the 3.5–6.1 μm wavelength range increased from 58% to 84% and the blackbody responsivity improved from 8.7 × 106 V/W to 1.6 × 107 V/W. Both quantum efficiency and blackbody responsivity reached levels comparable to those of CdZnTe-based detectors. Numerical fitting based on the carrier diffusion model indicated that interfacial optimization reduced the surface potential by approximately two orders of magnitude, effectively suppressing interfacial recombination.

An electrical potential difference emerges between the central and edge regions of the p-region in focal plane arrays (FPAs), particularly pronounced in HgCdTe FPAs, characterized by a higher potential in the center and a lower potential at the edges. This may lead to an uneven spatial distribution of the pixel current. In order to analyze this phenomenon, one-dimensional and two-dimensional models were established in this paper, and the Newton-Raphson method was employed to calculate. A simplified relationship between the center-edge potential difference and the array size as well as the current was derived. The elevation of the potential at the center of the array is attributed to the current loop within the array, which becomes more pronounced with increased FPA format. The FPAs current was calculated under conditions of non-uniform diode characteristics across pixels, and the simulation results agree well with the measured data. Finally, three methods were discussed to reduce the impact of this potential difference. Among them, increasing the bias voltage and introducing threaded electrodes have been verified to yield certain improvements.

Compared to the traditional flip-chip bonded focal plane array, in high-density vertically integrated photodiode (HDVIP) focal plane technology, the thickness of the mercury cadmium telluride (MCT or Hg1-xCdxTe) layer serves as a more critical parameter. This parameter not only influences the efficiency of photon energy absorption but also defines the pn junction area, thereby affecting the magnitude of the dark current. Furthermore, it significantly impacts the manufacturability of via-hole etching and formation processes. This paper investigated the photonic crystal resonances and coherent perfect absorption (CPA) effect of a thin MCT layer in HDVIP by using COMSOL Multiphysics® 4.3b and optimized the structure of the loop-hole photodiode device. The CPA, which is formed by this structure, achieves high absorption of illumination in a very thin MCT film. It is demonstrated that an absorption rate of infrared radiation of more than 95% with a wavelength during the 8 µm-10 µm range can be achieved in Hg1-xCdxTe (x = 0.225) with a thickness of only 1.5 µm-3 µm. The benefit of thinner MCT film is that it decreases the dark current of pn junction and reduces the technical difficulty of etching and metallization of the loop-hole photodiode.

This paper presents an extended short-wave infrared (eSWIR) image sensor, a large format infrared focal plane array (IRFPA), applied in advanced hyperspectral imager (AHSI) aboard China’s three GaoFen-5 satellites and two more followed ZY-1 satellites. Hyperspectral imaging has been emerged as a very important application in Earth observation instruments, for the spectral detection provides the spectrum information of ground objects except for the spatial imaging of the objects. AHSI has a 60-km swath width and a 30-m spatial resolution, and has high signal-to-noise ratio (SNR) in spectrum of interest. Large format infrared focal plane arrays which are ordinarily used in staring infrared imaging have some special performance requirements when applied in hyperspectral imaging, such as higher quantum efficiency, lower dark current, lower noise and selectable current conversion gain to match the different radiation flux of different subdivided spectral bands. We developed a format of 2048×512 HgCdTe/Si IRFPA sensor (equivalent 2012×256 after pixel overlapping and binning) in which 2012 pixels meet the demands of 60km swath width and 256 pixels line meet the 200 spectral bands. The sensor has 8-level gains selectable by spectral bands, and array dark current densities on an order of 10 -10 A/cm 2 , quantum efficiency exceeding 80%, and the operability of 99.5% at operating temperature of around 110K. The SNR of this FPA achieved 150 when illuminated under 5×10 4 photons/pixel.

红外探测器的光谱响应一致性影响高光谱成像仪器的动态范围,研究高光谱成像用拼接型短波红外探测器在同一光谱维的响应均匀性对提高高光谱成像性能有重要意义.通过测量相对光谱响应和窄带响应,对响应波段为 1.0～2.5 μm、规格为 2000×256 的碲镉汞短波红外探测器光谱响应率进行测量和分析,提出用光谱响应非均匀性定量化分析光谱响应一致性.分析了在 80℃和 140℃不同的黑体温度下,窄带滤光片的中心波长和半带宽不同时,带外截止深度为OD3 时,带外信号对窄带性能测试误差的影响.通过测量探测器模块的光谱响应率,计算拼接的 2000×256 探测器在 1 μm、1.9 μm和 2.5 μm处的响应非均匀性分别为 6.23%、6.06%和 4.07%.光谱响应率的准确测量实现了拼接型短波红外探测器的光谱响应一致性的定量化评价,有利于探测器在高光谱成像中的合理应用.

This letter focuses on the detection of subtle human activity, from multipass airborne interferometric synthetic aperture radar (InSAR) images, of such activities causing absolute decorrelation between two acquisitions. These activities can be vehicle track, footprint, grazing, and human construction. The millimetric sensitivity of the interferometric phase makes it valuable for detecting such activities. It can bring a large value to civil and military applications. However, there are always high false alarms in the conventional detection method. To solve this problem, a human activity detection method based on the coherence matrix is approached in this letter. In the final part of this letter, a preliminary validation of the method is provided by processing actual multipass airborne InSAR data stacks acquired by the Aerospace Information Research Institute, Chinese Academy of Sciences. It is noted that the proposed method reaches reliable results in comparison with the ground truth.

Infrared photon detection technology usually works in the passive sensing mode and contains the advantages of long acting-distance, good anti-interference, excellent penetration of smoke and haze, and all-day operation, which has been widely used in space remote sensing, military equipment, astronomical detection and other aspects. So far, the second-generation and the third-generation infrared photon detectors have been deployed widely. The high-end third-generation infrared photon detectors have been gradually promoted to practical application. The fourth generation and more forward-looking research including new concept, new technology, and new device has been proposed. This paper focuses on the research status of infrared technology at home and abroad, emphatically introducing the hotspots and development trends of infrared photon detectors. Firstly, the concept of SWaP(3) is introduced due to tactical ubiquity and strategic high performance. Secondly, the high-end third-generation infrared photon detectors with ultra-high spatial resolution, ultra-high energy resolution, ultra-high time resolution and ultra-high spectral resolution are reviewed. Technical characteristics and implementation methods of ultimate-performance infrared detectors are analyzed. Then, the fourth-generation infrared photon detector based on the artificial micro-structure is discussed. The realization approaches and technical challenges of multi-dimensional information fusion such as polarization, spectrum and phase are mainly introduced. Lastly, highly innovative trends of future detectors are discussed according to upgradation from on-chip digitization to on-chip intelligence.

When Interferometric Synthetic Aperture Radar (InSAR) is used to obtain the Digital Elevation Model (DEM), highly sloped terrains will make interferometric fringes dense and increase the difficulty of phase unwrapping, which will affect the accuracy of phase unwrapping and elevation inversion. To solve this problem, an InSAR elevation inversion method based on BackProjection (BP) model with an external DEM is proposed. This model achieves imaging and InSAR DEM inversion in a uniform BP geographic space and introduces an external DEM as auxiliary information. These processes, in turn, can remove most phases of the terrain and reduce the density of interferometric fringes and phase wrapping. Additionally, the proposed method can avoid the procedures of image registration and phase unwrapping in most cases, which simplifies traditional InSAR processing and achieves high processing accuracy. A simulation experiment and X-band InSAR data processing were performed to verify the effectiveness of the proposed method.

The interferometric synthetic aperture radar (InSAR) elevation inversion method based on the backprojection (BP) imaging model simplifies the interferometric processing chain where image registration and phase unwrapping are not required. Meanwhile, BP algorithm is suitable for radar with different imaging modes and geometry. However, the existing calibration methods are all aimed at traditional InSAR which adopts frequency domain imaging algorithm, but the calibration method for backprojection InSAR elevation inversion model has not been published. In this paper, we propose a novel InSAR calibration method which combines Fast Fourier Transform (FFT) estimation method with sensitivity equation method based on backprojection imaging model. FFT is used to process the interferometric phase which has removed the terrain phase of external digital elevation model (DEM) under BP imaging, and the estimation of interferometric parameters is realized through the phase fringe frequency. In the calibration method based on sensitivity equations, the deviations of interferometric parameters are calculated by solving sensitivity equations according to the three-dimensional information of ground control points. FFT estimation method not only generates the initial baseline parameters for sensitivity equation method, which is conducive to obtaining the global optimal solution, but also separates the calibration of phase offset and baseline parameters, which makes it possible to minimize the condition number of sensitivity matrix in sensitivity equation method. Finally, we obtain the calibrated interferometric parameters through iteration of sensitivity equation method and realize high accuracy DEM inversion. Both simulation experiment and airborne dual-antenna InSAR data processing are performed to verify the effectiveness of this method.

Human activity detection plays an important role in social security monitoring. Since human activity is very weak, it is necessary to employ the repeat-pass Interferometric Synthetic Aperture Radar (InSAR) technique to detect the potential activity between two data acquisitions; a high level of coherence is required for detection. With the object of detecting human activity of interest, this paper presents a coherence improvement approach based on sub-aperture InSAR for human activity detection. Different sub-apertures contain different scattering information of the target, as they represent the backscatter of the target from a different range of angles. Integrating corresponding sub-aperture interferometric results can improve the coherence between two complex images compared to the entire synthetic aperture, as well as removing a little disturbance in some circumstances. To validate the method presented in this paper, the actual airborne Ka-band frequency modulated continuous wave (FMCW) InSAR data acquired by the Aerospace Information Research Institute, Chinese Academy of Sciences (AIRCAS) are utilized. The experimental results demonstrate that the proposed method can effectively improve the coherence between two complex SAR images and can validly detect human activity of interest.

The Advanced Hyperspectral Imager (AHSI) is a visible/short-wave infrared hyperspectral imager on China’s GaoFen-5 satellite, which was launched on May 9th, 2018. The AHSI is the first spaceborne hyperspectral sensor that utilizes both the convex grating spectrophotometry and an improved three concentric-mirror (Offner) configuration. It has 60 km swath width, 30 m spatial resolution, 5-10 nm spectral resolution, and 330 spectral bands. Instrument performance was evaluated and validated through well-designed experiments on orbit. Results show that the performance of AHSI has met or exceeded predictions. The AHSI has outstanding capability of detecting and identifying different ground objects and in ecological environment monitoring and natural resource exploration.

本文介绍了高分五号（GF-5）卫星上的主载荷之一—可见短波红外高光谱相机AHSI （the Advanced Hyperspectral Imager）的基本结构、成像原理、系统组成、关键技术和系统性能。该相机是国际上首个采用改进型Offner结构凸面光栅分光的星载高光谱相机,具有60 km的幅宽、30 m的空间分辨率和5/10 nm的光谱分辨率,同时获取地表地物在400—2500 nm范围内330个谱段的空间、辐射与光谱信息,具有突出的地物探测和识别能力。相比国际上经典的高光谱相机Hyperion,该相机幅宽提高8倍,谱段数增加近百个,信噪比提升近4倍;与德国、日本、意大利、印度等国际上当前发展的高光谱相机比较,该相机在幅宽和光谱通道数等方面具有明显优势,其综合性能处于国际领先水平。

This article introduces the design and imaging principles of the Advanced Hyperspectral Imager (AHSI) aboard China's GaoFen-5 satellite. The AHSI is a visible and nearinfrared (VNIR)/short-wave infrared (SWIR) HSI. It is the first spaceborne hyperspectral sensor that utilizes both a convex-grating spectrophotometry and an improved three-concentric-mirror (Offner) configuration. It has 330 spectral...

In this paper, a calculation method for the response spectrum of a mercury cadmium telluride (MCT) infrared focal plane detector was proposed. A calculation approach of the spectrum in the short-wavelength region was proposed considering the relationship between surface recombination and response spectrum. A MCT focal plane infrared detector was fabricated, and the response spectrum was characterized. The experimental results were consistent with the expected results.

Interferometric synthetic aperture radar (InSAR) can be used to extract digital elevation model (DEM) with high accuracy. However, the side looking geometry of synthetic aperture radar (SAR) may cause geometric distortions such as shadow and layover in the mountainous terrain, which will reduce the quality of generated DEM. Fusion of two or more different aspects of InSAR data can deal with this problem. We propose an InSAR DEM reconstruction method based on backprojection (BP) algorithm in two converse flights. This method utilizes the feature of BP algorithm that geocoding has been realized in imaging process to simplify the fusion process of multi-aspect InSAR data. In addition, an iterative DEM extraction method is introduced to improve DEM accuracy. Experimental results verify the effectiveness of the proposed method.

为生成基准干涉相位图用于干涉合成孔径雷达(interferometric synthetic aperture radar,InSAR)辅助惯导系统导航,提出了一种基于数字高程模型(digital elevation model,DEM)的机载干涉相位生成算法.该算法利用惯性测量单元(IMU)得到轨迹信息,根据SAR成像参数确定成像区域,并对成像区域内的基准DEM数据按斜距进行重采样,然后将重采样后的DEM结合InSAR成像几何模型来生成基准干涉相位.最后利用山地区域的仿真数据和存在斜视角情况的实际InSAR数据,通过将本文提出的相位生成方法与InSAR系统获取的相位进行对比,仿真数据相位误差在0.000 5 rad左右,实测数据相位误差在0.001 4 rad左右,进而验证了提出的相位生成算法的有效性.

After removing the Hg1-xCdxTe infrared focal plane device substrate, the response bandwidth can be extended to the visible light band, which can significantly reduce the size and weight of the system in the application of hyperspectral imaging, and miniaturize the photoelectric detection system. Miniaturization has important practical value. The determination of the optical constants of HgCdTe materials in the visible near-infrared region is of great significance for the performance of HgCdTe devices in this response band. The ellipsometric spectra of different compositions of HgCdTe materials were measured and their optical constants in the band from 400 to 1 600 nm were fitted. The obtained optical constants were verified by using the reflectance spectra. Using these measured values, and using ZnS and YF3 as the high and low refractive index anti-reflective coating materials respectively, HgCdTe focal plane devices responding to different widths of back-incident near-infrared light have been designed. Spectroscopic AR coatings have an average transmission rate in the range of the response band of more than 90%.

To measure the global atmospheric three-dimensional distribution and change of temperature and humidity is one of the key areas in atmospheric remote sensing detection; it is also a new research and development direction in the field of meteorological satellite application. As a main element of China second generation of geostationary meteorological satellite Fengyun 4 (FY-4), which was launched on Dec. 11, 2016, the Geostationary Interferometric Infrared Sounder (GIIRS) is the first interferometric infrared sounder working on geostationary orbit internationally. It is used for vertical atmospheric sounding and gains atmospheric temperature, humidity, and disturbances. The combination of Fourier transform spectrometer technology and infrared detectors makes GIIRS have high spectral resolution and large coverage over spatial areas. With this kind of instrument, meteorological satellites can improve the capabilities for severe weather event monitoring and numerical weather prediction. Here a concise review of the GIIRS development project, including its history, missions and functions, technical design, key technologies, system integration, calibration and in-orbit operation status, etc., is presented.

This paper reports the development of 2000×256 format SWIR HgCdTe/Si FPA with multiple-choice gain (i.e. multiple-choice charge handling capacity) for hyperspectral detection. The spectral resolution is about 8nm. To meet the demands of variable low flux detection within each spectral band in the short wave infrared range, low dark current, low noise, variable conversion gains and high SNR (Signal to Noise Ratio) of FPA are needed. In this paper, we fabricate 512×512 pixel 30μm pitch SWIR HgCdTe diode array on Si by using a novel stress-release construction of HgCdTe chip on Si. Moreover, we design low noise, variable conversion gain and large dynamic range read-out integrated circuit (ROIC) and hybridized the ROIC on the HgCdTe diode array on Si substrate. There are 8-choice gains which can be selected locally according to the incident flux to meet high SNR detection demand. By high-accuracy splicing 4 512×512 HgCdTe/Si FPA we get mosaic 2000×512 FPA, and characterizations have been carried out and reveal that the array dark current densities on an order of 10-10A/cm2, quantum efficiency exceeding 70%, and the operability of 99.5% at operating temperature of around 110K. The SNR of this FPA achieved 120 when illuminated under 5×104photons/pixel.