Time Delay Integration Research Articles

侧摆成像交错拼接时间延迟积分CCD搭接像元数的匹配设计

侧摆成像交错拼接时间延迟积分CCD搭接像元数的匹配设计

Monte-Carlo simulation of a slot-scanning X-ray imaging system

We present a method for simulating slot-scanning X-ray imaging using the general-purpose Monte Carlo simulation package PENELOPE and penEasy Imaging. Different phantoms can be defined with the PENGEOM package, which defines bodies as combinations of volumes limited by quadric surfaces. The source-detector geometry, the position of the object, the collimator, the X-ray tube properties, the detector material and the pixel dimensions are defined. The output of the time-delay integration detector is simulated using sequential slot outputs derived from penEasy Imaging. The simulations are validated using tungsten and aluminium test objects, which are both simulated and imaged. The simulations are compared to the X-ray images using standard image quality metrics. The MTF, NPS and DQE curves show that the real and simulated X-ray images are comparable in terms of spatial resolution, noise and frequency information. The implementation can be modified to suit alterations in the system being simulated.

Studies on dynamic motion compensation and positioning accuracy on star tracker.

Error from motion is the dominant restriction on the improvement of dynamic performance on a star tracker. As a remarkable motion error, the degree of nonuniformity of the star image velocity field on the detector is studied, and thus a general model for the moving star spot is built. To minimize velocity nonuniformity, a novel general method is proposed to derive the proper motion compensation and location accuracy in cases of both uniform velocity and acceleration. Using this method, a theoretic analysis on the accuracy of time-delayed integration and similar techniques, which are thought of as state-of-the-art approaches to reduce error from motion, is conducted. The simulations and experimental results validate the proposed method. Our method shows a more steady performance than the dynamic binning algorithm. The positional error could be neglected when the smear length is far less than 3.464 times the scale of star spot, which suggests accuracy can be maintained by changing frame-integration time inverse proportional to the velocity on the focal plane. It also shows that the acceleration effect must be compensated to achieve accuracy close to the Cramér-Rao lower bound.

Computational imaging from non-uniform degradation of staggered TDI thermal infrared imager.

For the Time Delay Integration (TDI) staggered line-scanning thermal infrared imager, a Computational Imaging (CI) approach is developed to achieve higher spatial resolution images. After a thorough analysis of the causes of non-uniform image displacement and degradation for multi-channel staggered TDI arrays, the study aims to approach one-dimensional (1D) sub-pixel displacement estimation and superposition of images from time-division multiplexing scanning lines. Under the assumption that a thermal image is 2D piecewise C(2) smooth, a sparse-and-smooth deconvolution algorithm with L1-norm regularization terms combining the first and second order derivative operators is proposed to restore high frequency components and to suppress aliasing simultaneously. It is theoretically and experimentally demonstrated, with simulation and airborne thermal infrared images, that this is a state-of-the-art practical CI method to reconstruct clear images with higher frequency components from raw thermal images that are subject to instantaneous distortion and blurring.

Acquisition of cross-polarized diffraction images and study of blurring effect by one time-delay-integration camera.

Blurred diffraction images acquired from flowing particles affect the measurement of fringe patterns and subsequent analysis. An imaging unit with one time-delay-integration (TDI) camera has been developed to acquire two cross-polarized diffraction images. It was shown that selected elements of Mueller matrix of single scatters can be imaged with pixel matching precision in this configuration. With the TDI camera, the effect of blurring on imaging of scattered light propagating along the side directions was found to be much more significant for biological cells than microspheres. Despite blurring, classification of MCF-7 and K562 cells is feasible since the effect has similar influence on extracted image parameters. Furthermore, image blurring can be useful for analysis of the correlations among texture parameters for characterization of diffraction images from single cells. The results demonstrate that with one TDI camera the polarization diffraction imaging flow cytometry can be significantly improved and angular distribution of selected Mueller matrix elements can be accurately measured for rapid and morphology-based assay of particles and cells without fluorescent labeling.

Multi-pulse time delay integration method for flexible 3D super-resolution range-gated imaging.

Constructing flexible regular-shaped range-intensity profiles by the convolution of illuminator laser pulse and sensor gate pulse is crucial for 3D super-resolution range-gated imaging. However, ns-scale rectangular-shaped laser pulse with tunable pulse width is difficult to be obtained, especially for pulsed solid-stated lasers. In this paper we propose a multi-pulse time delay integration (MPTDI) method to reshape range-intensity profiles (RIP) free from the above limitation of pulsed lasers. An equivalent laser pulse temporal shaping model is established to evaluate and optimize the MPTDI method. By using MPTDI, the RIP shape and depth of viewing can both be flexibly changed as desired. Here typical triangular and trapezoidal RIPs are established for 3D imaging under triangular and trapezoidal range-intensity correlation algorithms. In addition, a prototype experiment is demonstrated to prove the feasibility of MPTDI.

Spatial Resolution in Scanning Direction in Detectors Based on Signal Accumulation with Time Delay

The goal of this work is to discuss the influence of spatial and temporal quantization on the modulation transfer function of the X-ray image in digital scanning X-ray machines designed based on matrix linear receivers operating in the TDI (Time Delay Integration) mode.

时间延迟积分CCD空间相机信噪比的影响因素

To quantitatively assess factors affecting the Signal to Ratio(SNR)of a Time Delay Integration(TDI)CCD camera,the imaging principle and noise sources of the TDICCD space camera were researched and a SNR model was established.The effects of the radiance lightness,integration stages,line transfer frequency and the system gain(analog gain)on the SNR were analyzed.A laboratory radiation calibration system was established to simulate the on-orbit radiance conditions of the camera.The relationship between the SNR and different working parameters were verified by radiation calibration.The calibration results show that the photon shot noise,dark current noise and the fixed pattern noise play a major role in all kinds of noise.The output signal and the SNR of the camera increase with the raises of the radiance,integration stages and the system gain and decrease with the raise of the line transfer frequency.The varieties of these factors have different influences on the SNR.Specifically,when the variations of the radiance,integration stages and the line transfer frequency are respectively Ltimes,Mtimes andτtimes,the variations of the SNR are slightly larger than L1/2 times,M1/2 times,τ-1/2 times,respectively.Moreover,the influence of the system gain on the SNR is in a relatively small range and the variation of the SNR decreases gradually with the raise of the system gain.

Application of the time-delay integration method: Survey observations of geosynchronous orbit objects and short-term variability observations

Abstract “Time-Delay Integration (TDI)” readout technique has been adopted to a mosaic CCD camera equipped with four fully-depleted CCDs. Optical distortion and image deformation due to the TDI operation are discussed. The manner and advantages of the TDI method in survey observations of geosynchronous orbit objects are summarized. We propose a new TDI application method of getting short-term light curves of artificial space objects. This method of detecting a short-term variability can be applied for a variety of objects, ranging from satellites to stars. It can also be used for the light-curve observations of transient objects which might show short-term variability and of which the precise time information is needed.

A 12-bit high-speed column-parallel two-step single-slope analog-to-digital converter (ADC) for CMOS image sensors.

A 12-bit high-speed column-parallel two-step single-slope (SS) analog-to-digital converter (ADC) for CMOS image sensors is proposed. The proposed ADC employs a single ramp voltage and multiple reference voltages, and the conversion is divided into coarse phase and fine phase to improve the conversion rate. An error calibration scheme is proposed to correct errors caused by offsets among the reference voltages. The digital-to-analog converter (DAC) used for the ramp generator is based on the split-capacitor array with an attenuation capacitor. Analysis of the DAC's linearity performance versus capacitor mismatch and parasitic capacitance is presented. A prototype 1024 × 32 Time Delay Integration (TDI) CMOS image sensor with the proposed ADC architecture has been fabricated in a standard 0.18 μm CMOS process. The proposed ADC has average power consumption of 128 μW and a conventional rate 6 times higher than the conventional SS ADC. A high-quality image, captured at the line rate of 15.5 k lines/s, shows that the proposed ADC is suitable for high-speed CMOS image sensors.

Thirty Two-Stage CMOS TDI Image Sensor With On-Chip Analog Accumulator

This brief presents a 32-stage CMOS time delay integration image sensor with on-chip column parallel analog accumulator. Temporal oversampling technique is applied in the sensor to realize synchronous signal capturing. A column parallel analog accumulator with layout size of 0.09 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is integrated at both sides of pixel array. Through adopting input-offset storing technique, a column fixed pattern noise because of the amplifier's offset variations is reduced by the accumulator. The accumulator also acts as a pixel noise canceller. The fabricated chip in 0.18- μm one-poly four-metal 1.8/3.3-V CMOS technology achieves the maximum line rate of 3875 lines/s. The measured signal-to-noise ratio of the fabricated sensor is improved on average by 11.9 dB at 16 stages and 14.2 dB at 32 stages. The presented sensor is suitable for application in low illumination, high scanning speed, and remote sensing systems.

A dynamic range extension scheme applied to a TDI CMOS image sensor

A dynamic range extension scheme applied to a time delay integration (TDI) CMOS image sensor (CIS) is presented. Two types of pixels with higher and lower conversion gain are adopted in the pixel array, which are suitable for capturing images in low and high illumination respectively. By fusing the two kinds of pixels' output signals in the process of TDI accumulation, a high dynamic range image can be achieved. Compared with the traditional multiple integration technique, no photoelectrons generated during the exposure time are discarded by the reset operation, and thus a higher level of signal-to-noise ratio (SNR) can be retained. A prototype chip with an 8 × 8 pixel array is implemented in a 0.18 μm CIS process, and the pixel size is 15 × 15 μm2. Test results show that a 76 dB dynamic range can be achieved in 8-stage TDI mode, when the SNR boost can reach 7.26 dB at 90.8 lux.

ASSET: a software tool for the evaluation of manoeuvre capabilities of highly agile satellites

The new generation of agile earth observation satellites provides much higher observation capabilities than their non-agile predecessors. From a kinematic point of view, these capabilities result in more complex guidance laws for the spacecraft’s attitude control system. The computation of these guidance laws is driven by a number of factors. For instance, the Earth’s curved shape and its rotation in combination with the possible scan path geometries lead to a highly nonlinear relation between the motion of the satellite and the line-of-sight projection onto Earth. In this paper ASSET (Agile Satellites Scenario Evaluation Tool) is presented. ASSET is a modular MATLAB command line tool developed at Astrium GmbH, Germany, to asses the manoeuvre capabilities of agile satellites carrying time-delayed integration instruments. Each single scenario may consist of one or several ground scans, linked by suitable spacecraft slews. Once the entire scenario is defined, ASSET will analyse whether the kinematic and dynamic constraints of a specific satellite allow this scenario to be performed and will then generate the related guidance profile (angles and angular rates). The satellites’ ground track, the projection of the instruments line-of-sight, and the projection of the instruments field of view onto the earth can be plotted for a visual inspection. ASSET can perform the analysis of scenarios with several different scan modes usually performed by this type of satellite.

基于空间相机时间延迟积分传感器拼接区图像的像移测量

In order to measure the wide-frequency-range image motion caused by spacecraft attitude instability or residual vibration of the vibration isolation devices, image motion measurement method using images taken from time delayed integration (TDI) sensors, overlapped area is proposed. Offset coefficient is defined to measure the mismatch between image motion velocity and integration time. The relationship between mismatch and image quality using modulation transfer function (MTF) as image quality evaluation index is analyzed. The image motion measuring accuracy range is determined. By taking full advantage of features of the images taken from TDI sensors, overlapped area that have the same content but are taken at the different time, the theory of image motion measurement method based on images taken from TDI sensors, overlapped area is elaborated. Experimental results show that the measurement precision can reach 0.2377 pixel, and the measurement bandwidth can reach 228 Hz, proving that this method can effectively achieve wide-frequency-range, high-precision measurement of image motion.

TDI-CCD全景航空相机的像移速度场计算模型研究

Image motion compensation of aerial panoramic camera can be accomplished by employing scan head rotation and charge coupled device (CCD) time delay integration (TDI), whereas residual still remains. Therefore, based on the structure and the image motion compensation (IMC) mechanism of aerial panoramic camera, a rigor mathematical model of image motion velocity filed is derived from imaging geometry, which is built by coordinate transformation and collinear equation. Numerical analysis indicates that the closer image coordinate locates to the rear edge of CCD focal plane, the larger scan angle and forward motion compensation (FMC) angel are, and the faster the image motion velocity is. For an aerial panoramic camera with 14000 CCD pixel and 100 TDI stages, when scan angle and FMC angle is smaller than -1.5and 4.16, respectively, the maximum of image motion is less than 1 pixel pitch. Dynamic imaging experiments validate the rationality of the model which provides a theoretical basis for the quantitative analysis of image motion compensation residual.

高速TDI CCD空间相机焦平面设计与实验

Time delay integration (TDI) CCD focal plane assembly is one of the most important components for a space camera, which mainly fulfill photoelectric conversion and output video signal of analog CCD. Due to the hard condition resulted from the transportation and launch of a space camera, it is difficult to keep a TDI CCD with high interleaving precision. Therefore, in this work, we design a TDI CCD focal plane assembly with a good performance based on the optimization both on structural control and thermal control. According to the analysis of the factors that affect the interleaving precision of a TDI CCD focal plane assembly and the maximal error of three axes theoretically, we design an especial structure for a TDI CCD focal plane assembly to keep the high interleaving precision of a TDI CCD which can fit the hard condition for the transportation and launch of a camera and the harsh on-orbit operating temperature. The effectiveness of the modified TDI CCD focal plane assembly is supported by the results obtained from dynamic test and thermal vacuum test. For the dynamic test, the response result shows that the assembly can conquer the interference of dynamic environment and keep a high interleaving precision of TDI CCD. For the thermal vacuum test, thermal balance test indicates that the highest temperature of TDI CCD is 30 in 1.5 min, which can work properly. The interleaving precision of focal plane is done after the dynamic environment and thermal vacuum tests. The linearity error of the TDI CCD is 3.5 m, the interleaving error is 4 m, the parallelism error between two lines of the TDI CCD is 3.5 m, and the coplanar error of 4 TDI CCD is 5 m. These results satisfy the optical design very well. Therefore, the aforementioned course proves that this design is feasible and precise, and it can achieve a high interleaving precision for a TDI CCD.

基于空间相机TDI传感器重叠区图像的像移测量方法中的多解性研究

The multiplicity of solution in image motion estimation method based on images captured by overlapping time delay integration (TDI) imaging sensors is addressed, and a method to eliminate the multiplicity of solution by taking the optimum of smoothness evaluation function as the only solution of image motion is proposed. The existence of the multiplicity of solution is analyzed. An evaluation function is proposed to evaluate the smoothness of each solution, and the minimized evaluation function is taken as the optimal solution of image motion. The optimum is found by using the conjugate gradient method (CGM). A single-solution result is obtained with an error of 0.13 pixel, showing that the added smoothness evaluation function is feasible to solve the problem of multiplicity of solution in image motion measurement.

多TDICCD拼接遥感相机成像串扰分析与抑制

In order to solve the imaging crosstalk between charge coupled device (CCD) channels and improve the signal-to-noise ratio (SNR) and imaging quality of multi time delay integration (TDI) charge coupled device mosaic remote sensing camera, a mathematical model of imaging crosstalk is established based on Fourier series analysis of the periodic signal. According to the results of mathematical analysis, the root cause of multi-TDICCD imaging crosstalk between different channels is proposed to be the unsynchronized TDICCD imaging circuit working, which causes high-frequency disturbance on the power ground plane and eventually affects the effective video signals acquisition of neighboring TDICCD. Referring to practical project, isolated CCD power supply, shared unified system clock and other methods are adopted to optimize multi-TDICCD imaging circuit system to suppress the occurrence of imaging crosstalk. The imaging quality and SNR are tested after improvement. Experimental results indicate that the adopted methods which can prevent the occurrence on imaging crosstalk between different CCD channels are effective, and the SNR is improved significantly. When the radiance is 42.6 W/(m2Sr), the camera SNR increases 18.85 dB, reaching to 50.42 dB. The image quality of outside scene imaging is also improved significantly, which can meet the requirements of practical engineering of TDICCD remote sensing camera.

TDI CCD成像电路系统响应模型的研究

To establish accurate response model of time delay integration charge coupled device (TDI CCD) image system, the main parts are analyzed in detail, such as CCD sensor, amplifier circuits and video processing circuit, according to the flow of signal processing. The response model for the actual system is established in theory based on the flow processing. The noises of dark current, video processing circuit are tested on a spatial TDI CCD image system. And so is the radiometric calibration under conditions of different parameters and illuminations. The image data of experiments is analyzed. An approximate formula and a precise formula are achieved by linear polynomial and quadratic polynomial of the least square method. The goodness of fit for linear and quadratic polynomial shows that R2 reaches 0.992 and 0.9998, respectively. The radiation character of ground targets can be acquired by the response model. And the choice of reasonable working parameter can also be decided according to the model. The experimental results show that the response model of image system is accurate and the working parameters are reasonable, which meets the demand and improves the efficiency of on-orbit spatial camera.

600mm长焦平面时间延迟积分CCD的交错拼接

A method to assemble muti-chip CCD devices together for a long focal plane assembly was proposed to meet the need of a space wider format camera for large field of view. By using a long array Time Delay Integration CCD(TDICCD) mosaic apparatus, 17 TDICCD devices were stitched onto the focal plan board with an interleaving assembly method according to the accuracy requirements, and fixed by plugs,then an extra long focal plane with a length of 600 mm, pixels of 69 000 was obtained. The experiments on the completed focal plane assembly were performed by a temperature cycling test, a vacuum thermal test and a vibration test, and the results show that structure design and material selection of the focal plan assembly meet the mechanical and thermal requirements. The accuracy measurment result of focal plane shows that the stitching error is less than 3 m. The extra long focal plane was applied to a remote sensing camera, and the seamless wider format image was captured. These results testify that the 600 mm long focal plane assembly meets the application needs of wide format remote sensing cameras.