Area Array Detector Research Articles

Compact broadband high-resolution real-time four-dimensional imaging spectrometer

A broadband high-resolution real-time four-dimensional imaging spectrometer (HRRFDIS) is presented, which can acquire both broadband fine spectra and high-resolution three-dimensional (3D) spatial images of a 3D object in real time. The HRRFDIS consists of a first microlens array arranged in a plane to achieve orthographic view spatial imaging, a second microlens array arranged on a conical surface to measure the depth and to achieve 360-degree side-view spatial imaging, multiple optical fibers, a collimating microlens array arranged in a straight line, a parallel planar transmission grating pair to obtain high spectral resolution over a broadband spectral range, and an area-array detector. Compared with the scanning four-dimensional imaging spectrometer (FDIS), the HRRFDIS can obtain a broadband high-resolution four-dimensional dataset using only one frame of data, and it is more stable, compact, small-sized, and lightweight. Compared to the staring FDIS using a liquid crystal filter and requiring at least one modulation period of liquid crystal to acquire a complete hyperspectral image, the HRRFDIS can acquire a complete broadband hyperspectral image in real time. Compared to existing snapshot FDIS, the HRRFDIS can achieve much higher spectral resolution, especially over a broadband spectral range. The HRRFDIS is a unique concept that is the first to obtain both high-resolution broadband spectral information and high-resolution 3D spatial information in real time, to the best of our knowledge. The HRRFDIS will be suitable for real-time measurement of 3D objects in the ultraviolet to infrared spectral range.

Calibration method of relative spectral response function of indirect imaging spectrometer

In imaging spectrometers, area array detectors are usually used as photoelectric conversion devices, but the inconsistency of the spectral response among pixels can distort the collected target spectra. To improve the spectral radiometric accuracy of imaging spectrometers, calibrating and correcting the inconsistency of the spectral response among pixels is essential. The signal received by each pixel of area array detector of the indirect imaging spectrometer is usually the superposition of the target multi-spectral radiation signals or full-spectral radiation signals. Therefore, its relative spectral radiometric calibration requires measuring the spectral response of each pixel at different wavelengths on the array detector. Under the ideal conditions, the response values of each pixel in the area array detector are different, so the indirect imaging spectrometer cannot simply calibrate the relative spectral response (RSR) function between pixels by using the method of “monochromator + integrating sphere”. In this work, taking the interferometric imaging spectrometer for example, we analyze the influence of the inconsistency of the RSR among pixels on the target spectral radiation measurement accuracy, and propose a system-level RSR function measurement method for the indirect imaging spectrometer based on the Fourier transform modulation calibration source. In addition, we establish a mathematical model for calibrating the RSR function,and provide guidelines for selecting calibration system parameters such as light source, spectral resolution, and OPD sampling interval. The simulation results show that under the ideal noise-free condition, the 1% spectral response inconsistency among pixels results in a relative error of 1.02% to the recovered spectra. After RSR correction, the relative error of the recovered spectra of different rows decreases to 0.08%. Furthermore, in this work we simulate and analyse the influence of spectral signal-to-noise ratio on the calibration accuracy of the RSR function, and point out that increasing the brightness of the calibration light source, extending exposure time, and combining multi-frame interferograms can enhance RSR function calibration accuracy in practical applications. The research result can provide a theoretical basis for realizing the relative spectral radiometric calibration of indirect imaging spectrometer, which is of great significance in promoting quantitative spectral remote sensing.

Aircraft Target Detection in Low Signal-to-Noise Ratio Visible Remote Sensing Images

With the increasing demand for the wide-area refined detection of aircraft targets, remote sensing cameras have adopted an ultra-large area-array detector as a new imaging mode to obtain broad width remote sensing images (RSIs) with higher resolution. However, this imaging technology introduces new special image degradation characteristics, especially the weak target energy and the low signal-to-noise ratio (SNR) of the image, which seriously affect the target detection capability. To address the aforementioned issues, we propose an aircraft detection method for RSIs with low SNR, termed L-SNR-YOLO. In particular, the backbone is built blending a swin-transformer and convolutional neural network (CNN), which obtains multiscale global and local RSI information to enhance the algorithm’s robustness. Moreover, we design an effective feature enhancement (EFE) block integrating the concept of nonlocal means filtering to make the aircraft features significant. In addition, we utilize a novel loss function to optimize the detection accuracy. The experimental results demonstrate that our L-SNR-YOLO achieves better detection performance in RSIs than several existing advanced methods.

Analysis of image motion for optical remote sensing satellites staring imaging with area-array detectors.

In this paper, the image motion introduced by the staring action itself during optical remote sensing satellites staring imaging with area-array detectors is studied. The image motion is decomposed into the angle-rotation image motion caused by the change of observation angle, the size-scaling image motion caused by the change of observation distance, and the Earth-rotation image motion caused by the rotation of the ground object with the Earth. The theoretical derivation of the angle-rotation image motion and size-scaling image motion is conducted, and the numerical analysis of the Earth-rotation image motion is carried out. Based on the comparison among the characteristics of the three types of image motions, the conclusion is drawn that, for general staring imaging scenes, the angle-rotation image motion is dominant, followed by the size-scaling image motion and the ignorable Earth-rotation image motion. On the condition that the image motion does not exceed 1 pixel, the allowed maximum exposure time for area-array staring imaging is analyzed. It is found that the large-array satellite is not suitable for long-exposure imaging, as its allowed exposure time decreases rapidly with the increase of roll angle. A satellite with a 12k×12k area-array detector and 500km orbit is taken as an example. The allowed exposure time is 0.88s when roll angle of the satellite is 0°; it decreases to 0.02s when the roll angle increases to 28°.

Optical Design of an Integrated Paschen–Runge Spectrometer by Using a Multigrating Structure

An integrated direct-reading spectrometer scheme using seven concave gratings is proposed. At present, the optical design simulation has been completed, and the subsequent physical design may be carried out according to the simulation results. Ray-tracing software (Zemax) is used to divide the spectrum on the grating into seven bands, and an area array detector is used to receive the spectral signals simultaneously, which reduces the volume of the spectrometer and improves the spectral consistency. Using this method, a spectrometer covering 230–440 nm is designed, and the spectral resolution of the center wavelength corresponding to the seven grating windows of 230–260 nm, 260–290 nm, 290–320 nm, 320–350 nm, 350–380 nm, 380–410 nm, and 410–440 nm can reach 0.0974 nm, 0.0652 nm, 0.0361 nm, 0.0157 nm, 0.0838 nm, 0.0872 nm, and 0.1471 nm.

Advances on terahertz single-pixel imaging

Single-pixel imaging is a novel imaging technique that can obtain image information through a single-pixel detector. It can effectively avoid the problem of lack of high-quality area array detectors in the terahertz band, and has attracted the attention of a large number of researchers in recent years. In this paper, the basic imaging principles, terahertz beam modulation methods and typical image reconstruction algorithms for terahertz single-pixel imaging are introduced and discussed, as well as its research progresses and developing trends.

Energy Transfer Assisted Fast X-ray Detection in Direct/Indirect Hybrid Perovskite Wafer.

Metal halide perovskite scintillators encounter unprecedented opportunities in indirect ionizing radiation detection due to their high quantum yields. However, the long scintillation lifetime of microseconds upon irradiation, known as the afterglow phenomenon, obviously limits their fast development. Here, a new type of hybrid X‐ray detector wafer combining direct methylamine lead iodide (MAPbI3) semiconductor and indirect zero‐dimensional cesium copper iodide (Cs3Cu2I5) scintillator through low‐cost fast tableting processes is reported. Due to the fast energy transfer from Cs3Cu2I5 to MAPbI3, the device response time to X‐rays is dramatically reduced by nearly 30 times to 36.6 ns, which enables fast X‐ray detection capability by a large area detector arrays within 1 s. Moreover, Cs3Cu2I5 exists at the grain boundaries of MAPbI3 crystals, and blocks the paths of mobile ions of perovskite, leading to the lowest detectable dose rate of hybrid X‐ray detector is thus reduced by 1.5 times compared with control MAPbI3 direct‐type semiconductor, and 10 times compared with the Cs3Cu2I5 indirect‐type scintillator. The direct/indirect hybrid wafer also exhibits improved operation stability at ambient conditions without any encapsulation. This new kind of hybrid X‐ray detectors provides strong competitiveness by combining the advantages of both direct perovskite semiconductors and indirect perovskite scintillators for next‐generation products.

Broadband high-spatial-resolution high-spectral-resolution flexible imaging spectrometer design study.

A broadband high-spatial-resolution high-spectral-resolution flexible imaging spectrometer (B-2HSR-FIS) is presented, which includes two microlens arrays (MLAs), multiple fiber bundles, a scanning Fabry-Perot interferometer (FPI), a reflection grating, a cylindrical lens, and an area-array detector. The first MLA is arranged in a circular arc to obtain a field angle between 8° and 60° in the horizontal plane. The second MLA is arranged in a straight line. Each fiber bundle containing seven optical fibers is coupled to a separate microlens of the first MLA, subdividing the field angle of each microlens into seven smaller field angles to improve spatial resolution. The combination of a scanning FPI and a reflection grating enables the B-2HSR-FIS to obtain both high spectral resolution and broadband spectral range in the ultraviolet to near-infrared spectral region. Compared with all existing imaging spectrometers, the B-2HSR-FIS is the first to simultaneously obtain high spatial resolution, high spectral resolution, broadband spectral range, and moderate field angle, to the best of our knowledge. The B-2HSR-FIS has great potential for vision intelligence (e.g., as an eye of a robot).

Digital micromirror device and spatial heterodyne spectroscopy combined modulation interference spectroscopy

Spatial heterodyne spectroscopy (SHS) has advantages of hyperspectral, high luminous flux, and high stability. However, its main performance indexes, such as spectral resolution, bandwidth, dynamic range and signal-to-noise ratio (SNR) are all limited by the performance parameters of the area array detector. In this paper, a digital micromirror device (DMD) is applied to the interference spectroscopy, and DMD and SHS combined modulation interference spectroscopy (DMD–SHS) is proposed. On the basis of retaining advantages of SHS such as high stability and hyperspectral resolution, DMD–SHS uses the linear array detector, eliminating high-performance area-array detector dependence and dramatically reducing the cost of the instrument. It can also improve the instrument’s SNR and dynamic range, and enhance weak signals’ detection capability. DMD–SHS theory is analyzed theoretically and further verified by simulation in this paper. The combined modulation method proposed in the paper can also be applied to other interference spectroscopy, and the related research has important scientific significance and application prospect.

Defect detection system for silicon solar panels under all-day irradiation.

In terms of the shortcomings of defect detection based on the electroluminescence of conventional silicon solar panels, which can only be performed under darkroom conditions, a defect detection system that can work under the Sun with any irradiance in all weather is designed. The system electrifies solar panels through a modulated current source, uses high frame rate InGaAs area array detectors for image data acquisition, and transmits images via CameraLink. Using these image data as data sources, a defect display algorithm model is designed. Through experiments, it can effectively collect the defect information of solar panels within the range of 0.2 to 1300W/m2 of sunlight irradiance. Based on this, according to the relationship of the modulated phase difference between the defective points and the nondefective points found in the experiment, an enhancing algorithm for image saliency is proposed. The results show that this algorithm can reduce background interference in an effective way and improve the contrast of defects displayed under high irradiance.

Snapshot spectroscopic microscopy with double spherical slicer mirrors.

Snapshot hyperspectral microscopic imaging can obtain the morphological characteristics and chemical specificity of samples simultaneously and instantaneously. We demonstrate a double-slicer spectroscopic microscopy (DSSM) that uses two spherical slicer mirrors to magnify the target image and slice it. These slits are lined up and dispersed, then mapped onto an area-array detector. An anamorphosis unit optimizes the capacity of the limited pixels. With a single shot and image recombination, a data cube can be constructed for sample analysis, and a model of DSSM is simulated. The system covers the spectral range from 500 nm to 642.5 nm with 20 spectral channels. The spatial resolution is 417 nm, and the spectral resolution is 7.5 nm.

Design study of a compact ultra-wide-angle high-spatial-resolution high-spectral-resolution snapshot imaging spectrometer

An ultra-wide-angle high-spatial-resolution high-spectral-resolution snapshot imaging spectrometer (UWA-2HSR-SIS) is presented, which comprises a microlens array (MLA), multiple fiber bundles, a micro-cylindrical-lens array (MCLA), a cylindrical lens, a static grating interferometer (SGI), and an area-array detector. The MLA is arranged in a circular arc of 120° or more. The MCLA is arranged in a straight line. The SGI includes a fixed reflection grating in Littrow configuration, a beam splitter, and a fixed plane mirror. Each fiber bundle containing multiple optical fibers is coupled to a separate microlens of the MLA, subdividing the field angle of each microlens into multiple smaller field angles. The light passing through each subdivided smaller field angle of each microlens of the MLA is received by a separate part of the detector. The UWA-2HSR-SIS is a new concept that not only obtains both high spatial resolution and high spectral resolution based on a single sensor for the first time, but also has an ultra-wide field angle in the horizontal plane, can obtain spectral information covering the full spectral range of interest in real time, and is very stable against various disturbances. The UWA-2HSR-SIS has great potential for remote sensing electro-optical reconnaissance sensors in the visible and near-infrared region.

Non-Scanning Three-Dimensional Imaging System with a Single-Pixel Detector: Simulation and Experimental Study

Existing scanning laser three-dimensional (3D) imaging technology has slow measurement speed. In addition, the measurement accuracy of non-scanning laser 3D imaging technology based on area array detectors is limited by the resolution and response frequency of area array detectors. As a result, applications of laser 3D imaging technology are limited. This paper completed simulations and experiments of a non-scanning 3D imaging system with a single-pixel detector. The single-pixel detector can be used to achieve 3D imaging of a target by compressed sensing to overcome the shortcomings of the existing laser 3D imaging technology. First, the effects of different sampling rates, sparse transform bases, measurement matrices, and reconstruction algorithms on the measurement results were compared through simulation experiments. Second, a non-scanning 3D imaging experimental platform was designed and constructed. Finally, an experiment was performed to compare the effects of different sampling rates and reconstruction algorithms on the reconstruction effect of 3D imaging to obtain a 3D image with a resolution of 8 × 8. The simulation results show that the reconstruction effect of the Hadamard measurement matrix and the minimum total variation reconstruction algorithm performed well.

The Design of Focal Plane Splitting Unit in a Hyperspectral Lidar System

A hyperspectral lidar system with focal plane splitting unit is proposed, including an off-axis receiving telescope, a grating spectrometer, and a single-tube detector array. The spectrum of the system covers 380-930nm, and is separated by grating spectrometer. The microlens-fiber coupling system guides the echo signal of 50 channels into each detector. The system solves the data processing problem of the bandwidth and gain the line array and area array detector in traditional hyperspectral lidar. And it also meets the requirement of the high efficiency splitting coupling and weak signal acquisition and detection.

空间遥感器线阵与面阵探测器共基板焦面组件设计

空间遥感器线阵与面阵探测器共基板焦面组件设计

Compressed sensing imaging system based on improved theoretical model and its weighted iterative strategy

Based on the characteristic analysis of the traditional block-based compressed sensing system, an improved compressed sensing theory model is proposed in this paper, and its hardware implementation scheme and the overall system workflow are specified according to the model requirements. Compared with the traditional block-based compressed sensing system, the linear array detector is used instead of the area array detector in the system, and the one-dimensional encoding is adopted instead of the two-dimensional encoding to simplify the encoding process. The experimental results show that the system proposed by this paper can significantly improve the image quality compared with the block-based compressed sensing system under the same system conditions, and eliminate the block effect that is common in the block-based compressed sensing system. On the basis of the proposed system, a weighted iterative restoration strategy based on frequency estimation is proposed. By adaptively adjusting the restoration process and optimizing the distribution of computing resources, the image quality is further improved.

Three-area-array coherent-dispersion stereo-imaging spectrometer.

A coherent-dispersion stereo-imaging spectrometer is presented, which combines three-view stereo imaging, interferometric spectroscopy and dispersive spectroscopy. Three area-array detectors record three spectral images of each scene unit from three views. For each of the three views, each scene unit is imaged on a given column of one area-array detector, and different wavelengths are dispersed across different rows of that column. For each scene unit, multiple interferograms are simultaneously generated at each view, each interferogram covering a separate wavelength range and located in a separate pixel. The orthographic view image is used to create a two-dimensional orthophoto image. The front view and back view images are used to reconstruct the three-dimensional stereoscopic image. Preliminary theoretical calculations are given. The instrument is a unique concept to obtain three-dimensional spatial information and one-dimensional spectral information while achieving high spectral resolution measurement of an ultraviolet-visible broadband spectral range (e.g., 0.05 nm at 450 nm together with 0.1 nm at 700 nm). It will be suitable for ultraviolet-visible hyperspectral remote sensing.

Spectropolarimetric measurement based on a fast-axis-adjustable photoelastic modulator.

A fast-axis-adjustable photoelastic modulator (Faa-PEM) is developed and studied, and a spectropolarimetric imaging method using the Faa-PEM and an acousto-optic tunable filter is presented. The Faa-PEM modulation retardation amplitude and fast-axis direction of the Faa-PEM can be adjusted by adjusting the two drives with no mechanical rotation. The I, Q, and U of the Stokes parameters of the incident light can be obtained by adjusting the retardation amplitude and fast-axis direction of the Faa-PEM. This measurement method does not require high-frequency components, and thus a general area array detector can realize the measurement. Theoretical simulation analyses show that the relative errors ΔI/I, ΔQ/Q, ΔU/U, and ΔDoLP/DoLP are less than 5.6% and that the deviation error ΔAoLP is less than 0.2° (at I=1.00, Q=0.707, U=0.707, V=0.0, -0.1°≤Δθ0≤0.1°, and -0.05 rad≤Δδ0≤0.05 rad). A prototype was developed and tested. The test results show that the average absolute relative error of the degree of linear polarization is 0.36%, and the average absolute deviation error of the angle of linear polarization is 0.048°. The method has potential application value in spectropolarimetric imaging technology.

Broadband snapshot spectrometer based on spliced spectra

Wavelength scanning in broadband spectrometers has limitations on transient imaging and instrument size. We demonstrate a broadband snapshot spectrometer scheme by developing an integrated grating with n different blaze angles on one substrate and a slicer mirror to provide high diffraction intensities in a wide wavelength range. A slicer mirror divides the entire spectrum into n windows, with each window containing a blazed wavelength. The spectra can be spliced and detected by an area-array detector at one exposure. Using this method, we designed and optimized a snapshot spliced-spectrum spectrometer that numerically covers 200–1000 nm wavelength range with a spectral resolution of 0.27 nm.

Stereo topographic mapping concept for the upcoming Luna-Resurs-1 orbiter mission

We report on the Lunar Stereo Topographic Camera (LSTC), currently being developed for the upcoming Luna-Resurs-1 Orbiter mission, which will perform observations from an orbit with the altitude to be optimized in the range from 50 to 100 km. The LSTC is composed of two identical optical heads and a common data processing unit. Each optical head has a similar optical system and an area array detector of 5120 × 3840 pixels, covering an area of 14 × 10 km (cross-track x along-track) from a 50-km spacecraft orbit. One of the optical heads looks forward within the orbit plane and the other looks backwards. The mission will focus on mapping mid- and polar latitudes up to 80° north and south to derive cartographic/topographic data products needed to support navigating future Luna-Resurs lander missions in polar regions. Extensive image simulations were produced to study the effects of illumination conditions and shadows on surface coverage and the precision of digital image matching for stereo photogrammetric processing. Also we studied a variety of possible off-nadir angles of the two camera systems and how these might affect the point measurement accuracy. We found that off-nadir angles of ±12.5° is a reasonable compromise to maximize topographic accuracy in varying observation conditions over both flat and rugged lunar terrains. Also, we investigate data compression algorithms at different compression ratios to minimize the impact of compression artifacts upon the photogrammetric image processing. The LSTC will take up to 400 images per orbit, i.e., 4800 images per day. During one month, we expect to cover 20% of the lunar surface on average, including the northern or southern polar areas. Imaging schemes and operation schedules will be optimized to maximum stereo coverage while producing the best DTM quality. We propose to increase the orbit altitude from the minimum altitude of 50 km to 70 km to enhance both along and cross track image overlap, yielding more geometrically stable image blocks.