Time Delay Integration Research Articles

A novel approach to separate absorption, refraction and scattering in analyzer based lung imaging

In analyzer based imaging (ABI) scattering can be efficiently separated from refraction and absorption effects by acquiring three images of the sample. In the scattering image the lungs appear as areas of high intensity signal (area contrast), which is modulated by the local thickness of the scattering tissue intersecting the X-ray path. The scattering signal is also included in the so-called apparent absorption image, where it adds to the absorption contrast thanks to the extinction of rays which are deviated outside the analyzer crystal's acceptance window. The presence of scattering can be emphasized in the ratio between two images acquired with a strongly detuned and a perfectly tuned analyzer crystal, respectively: we name this ratio as the amplified scatter image. In this paper we present ABI scattering methods applied to postmortem mouse lung imaging to assess their diagnostic value. For this purpose images have been acquired at the SYRMEP beamline of the ELETTRA synchrotron in Trieste (Italy) with the Argus time delay integration CCD detector at a photon energy of 25 keV . Subsequently the parametric images, including the amplified scatter image have been obtained, and contrast and signal-to-noise ratio have been evaluated. It is noteworthy that images have been acquired with a radiation dose of some mGy, thus are compatible with dose restricted medical imaging settings such as mammography.

Luximos: A 768×64 900-fps Tileable Pipelined X-Ray CMOS Image Sensor for Dental Imaging With 2.6 LSB/nGy Sensitivity

In this letter, a stitched array of $768\times 64$ pixels for X-ray dental imaging is presented. The sensor architecture allows to increase the frame rate up to 900 fps thanks to a pipeline approach that minimizes the deadtime between consecutive frames. A column-based ADC converts pixel values in digital form while an external FPGA performs the operation of time-delay integration accumulation, thus increasing the signal-to-noise ratio. Internal programmable gain allows to achieve a maximum sensitivity of 2.6 LSB/nGy and, at the same time, to extend the dynamic range of the sensor in case of high intensity. The final system consists of two sensors each one having a size of $74.5\times 9$ mm, assembled in a PCB and coupled with a high sensitive columnar thallium-doped cesium iodide (CsI(Tl)) scintillator for X-ray conversion. The sensor, fabricated in a standard CMOS 0.15- $\mu \text{m}$ technology with a stitching approach, shows a pixel size of 97 $\mu \text{m}$ .

Removal of Large-Scale Stripes Via Unidirectional Multiscale Decomposition

Stripes are common in remote sensing imaging systems equipped with multichannel time delay integration charge-coupled devices (TDI CCDs) and have different scale characteristics depending on their causes. Large-scale stripes appearing between channels are difficult to process by most current methods. The framework of column-by-column nonuniformity correction (CCNUC) is introduced to eliminate large-scale stripes. However, the worst problem of CCNUC is the unavoidable cumulative error, which will cause an overall color cast. To eliminate large-scale stripes and suppress the cumulative error, we proposed a destriping method via unidirectional multiscale decomposition (DUMD). The striped image was decomposed by constructing a unidirectional pyramid and making difference maps layer by layer. The highest layer of the pyramid was processed by CCNUC to eliminate large-scale stripes, and multiple cumulative error suppression measures were performed to reduce overall color cast. The difference maps of the pyramid were processed by a designed filter to eliminate small-scale stripes. Experiments showed that DUMD had good destriping performance and was robust with respect to different terrains.

Attitude Maneuver Planning of Agile Satellites for Time Delay Integration Imaging

In the prevailing operations of agile satellites for time delay integration (TDI) imaging tasks, two degrees of freedom (DOFs) in the attitude maneuver are determined by tracking the transient target point, whereas the third DOF is used in the control of the drift angle, which is calculated within the sensor focal plane as a feedback. However, optimal attitude maneuver planning is rarely considered during a TDI imaging mission to improve the efficiency of agile satellites. In this paper, a general attitude maneuver planning for agile satellites in the TDI imaging of an arbitrary target strip is formulated, where the energy consumption is minimized while the TDI imaging quality is guaranteed. Coupled with the attitude dynamics, the highly nonlinear constraints required by the TDI imaging principal make this planning hard to solve. By introducing a parameterized time-mapping technique and a compact approach to the attitude maneuver that ensures zero drift angle, the problem is relieved in both complexity and computational burden. The validity of this approach is verified by various imaging simulations.

JPSS-1/NOAA-20 VIIRS Day-Night Band Prelaunch Radiometric Calibration and Performance

The Visible Infrared Imaging Radiometer Suite (VIIRS) on board the first Joint Polar-Orbiting Satellite System series 1 (JPSS-1) has a panchromatic, three gain stage, day-night band (DNB) capable of imaging the Earth under illumination conditions ranging from reflected moonlight to daytime scenes. The DNB has four charged-coupled devices (CCDs) with 32 different modes of time-delay integration and subpixel aggregation to achieve high SNR in low light conditions while maintaining roughly constant spatial resolution across scan. During the prelaunch testing phase, these 32 different aggregation modes are separately calibrated over a large dynamic range (covering seven orders of magnitude) through a series of radiometric tests designed to generate initial calibration coefficients for the sensor data record (SDR) operational algorithm, assess radiometric performance, and determine compliance with the sensor design requirements. Early in the environmental testing at the Raytheon El Segundo facility, nonlinear behavior was discovered in some DNB edge of scan aggregation modes at low signal levels. In response to this nonlinearity, the test program was altered to characterize the radiometric performance both in the baseline configuration and with a modified aggregation scheme that eliminates the modes used at the end of scan, replacing them with an unaffected adjacent mode and trading off spatial resolution for improved linearity. Presented in this paper is the radiometric performance under both sensor configurations including dynamic range, sensitivity, radiometric uncertainty, and nonlinearity along with a discussion of the potential impact to DNB on-orbit calibration and SDR performance.

High-resolution dynamic inversion imaging with motion-aberrations-free using optical flow learning networks

Dynamic optical imaging (e.g. time delay integration imaging) is troubled by the motion blur fundamentally arising from mismatching between photo-induced charge transfer and optical image movements. Motion aberrations from the forward dynamic imaging link impede the acquiring of high-quality images. Here, we propose a high-resolution dynamic inversion imaging method based on optical flow neural learning networks. Optical flow is reconstructed via a multilayer neural learning network. The optical flow is able to construct the motion spread function that enables computational reconstruction of captured images with a single digital filter. This works construct the complete dynamic imaging link, involving the backward and forward imaging link, and demonstrates the capability of the back-ward imaging by reducing motion aberrations.

Serendipitous detection and size estimation of space debris using a survey zenith-pointing telescope

The size distribution of space debris constitutes an important input to risk analysis for current and future space missions. In preparation for future observations with the zenith-pointing 4-m International Liquid Mirror Telescope (ILMT), the 1.3-m Devasthal Fast Optical Telescope (DFOT) was used to gain experience with zenith-pointing observations and, serendipitously, to detect, identify and characterize orbital debris. Observational data were acquired on 11 nights in May 2015 using a 2048 × 2048-pixel CCD detector operating in time-delay integration mode. Thirteen debris streaks were detected, mostly during dawn and twilight. All were identified by correlation with available two-line element sets. By modelling each of the objects as a diffuse-specular Lambertian sphere with an albedo ρ= 0.175, their effective diameters were estimated from the observed apparent magnitudes, altitudes, velocities and solar phase angles. Seven objects were found to be in low Earth orbits and five in mid-Earth or geo-transfer orbits. The apparent Gaia magnitudes of the identified objects range from 5.6 to 12.0 and their estimated effective diameters from 0.8 to 7.6 m. The detection size limit of DFOT is found to be 50 cm for objects orbiting at an altitude of 1000 km. Images from the future ILMT photometric survey are expected to provide detections of space debris having diameters as small as 5 cm at this altitude.

A 10 bit Fully Differential Dual Slope Analog-to-digital Converter for Time Delay Integration CMOS Image Sensors

A 10 bit fully differential dual slope Analog-to-Digital Converter (ADC) for Time Delay Integration (TDI) CMOS image sensors is realized based on column-parallel single-slope ADC. Top plates of the two capacitors are used for sampling differential inputs, and the bottom plates are connected to ramp generator for conversion. Current steering is used to generate the rising and falling ramp with the same step voltage simultaneously. The proposed ADC is fabricated in SMIC 0.18 μm CMOS process. Simulated spurious free dynamic range and effective number of bits are 87.92 dB and 9.84 bit with the input frequency of 1.32 kHz at 19.49 kS/s sampling rate, respectively. Measured results show that the ADC has a differential nonlinearity of –0.7/+0.6 LSB and integral nonlinearity of –2.6/+2.1 LSB.

Time-Delayed Integration-Spectral Flow Cytometer (TDI-SFC) for Low-Abundance-Cell Immunophenotyping.

We describe a unique flow cytometer (TDI-SFC) for the immunophenotyping of low-abundance cells, particularly when cell counts are sample-limited and operationally difficult for analysis by fluorescence microscopy (>100 cells) or multiparameter flow cytometry (MFC, <10 000 cells). TDI-SFC combines the high spectral resolution of spectral flow cytometry (SFC) with a CCD operated in time-delayed integration (TDI) for improved duty cycle and sensitivity. Cells were focused with a 1D-sheathing microfluidic device, and fluorescence emission generated from a 488 nm laser was collected by epi-illumination and dispersed along one axis of a CCD by a spectrograph. Along the other axis, the CCD's shift rate was clocked at a rate that closely matched the cells' velocity through the field of view. This TDI-SFC format allowed the CCD shutter to remain open during signal acquisition, providing a duty cycle ∼100% and assurance that ∼95% cells were interrogated. We used fluorescent beads to optimize synchronization of TDI clocking with the sheathed-cell velocity and to improve sensitivity via the excitation intensity, epi-illumination numerical aperture, and integration time. TDI achieved integrated signals of 106 counts at a signal-to-noise ratio (SNR) of 610 for beads corresponding to a load of 4 × 105 antibodies. We also evaluated multiplexing capabilities by spectral deconvolution and undertook a proof-of-concept application to immunophenotype low-abundance cells; the demonstration consisted of immunophenotyping a model cell line, in this case SUP-B15 cells representing B-cell acute lymphoblastic leukemia (B-ALL). The B-ALL cell line was stained against a leukemic marker (terminal deoxynucleotidyl transferase, TdT), and we successfully used spectral unmixing to discriminate TdT(+) cells from TdT(-) cells even at low cell counts (∼100 cells). The TDI-SFC could potentially be used in any application requiring the immunophenotyping of low-abundance cells, such as in monitoring measurable residual disease in acute leukemias following affinity enrichment of circulating leukemia cells from peripheral blood.

Lessons from the curious case of the ‘fastest’ star in Gaia DR2

Abstract Gaia DR2 5932173855446728064 was recently proposed to be unbound from the Milky Way based on the $-614.3\pm 2.5\, \mathrm{km}\, \mathrm{s}^{-1}$ median radial velocity given in Gaia DR2. We obtained eight epochs of spectroscopic follow-up and find a very different median radial velocity of $-56.5 \pm 5.3\, \mathrm{km}\, \mathrm{s}^{-1}$. If this difference were to be explained by binarity, then the unseen companion would be an intermediate-mass black hole; we therefore argue that the Gaia DR2 radial velocity must be in error. We find it likely that the spectra obtained by Gaia were dominated by the light from a star $4.3\, \mathrm{arcsec}$ away, and that, due to the slitless, time delay integration nature of Gaia spectroscopy, this angular offset corresponded to a spurious $620\, \mathrm{km}\, \mathrm{s}^{-1}$ shift in the calcium triplet of the second star. We argue that such unanticipated alignments between stars may account for 105 of the 202 stars with radial velocities faster than $500\, \mathrm{km}\, \mathrm{s}^{-1}$ in Gaia DR2 and propose a quality cut to exclude stars that are susceptible. We propose further cuts to remove stars where the colour photometry is suspect and stars where the radial velocity measurement is based on fewer than four transits, and thus produce an unprecedentedly clean selection of Gaia radial velocities for use in studies of Galactic dynamics.

红外时间延迟积分点目标探测系统中速度失配影响研究

红外时间延迟积分点目标探测系统中速度失配影响研究

Area targets observation mission planning of agile satellite considering the drift angle constraint

The generation of agile satellites has better flexible three-axis maneuverability, which makes dynamic imaging possible. A mission planning algorithm is proposed to deal with the area target observation problems of agile satellites, which takes the drift angle constraint of the observation instrument into account. First, an area target observation path planning algorithm is presented based on the dynamic imaging mode and the grid discretization approach. Second, the constraint of drift angle is introduced into the mission planning to account for the effect of image motion on time delay integration charge coupled device imaging. Third, an improved ant colony algorithm based on sensational and consciousness strategy is developed to solve the travelling salesman problem with constraints. Finally, the computer simulation results show that the proposed algorithm can effectively solve the area target mission planning problem.

Error tolerance and effects analysis of satellite vibration characteristics and measurement error on TDICCD image restoration

Satellite vibrations during exposure time could lead to image motion degradation, and image restoration methods are commonly used to compensate for such degradation. However, effects of space-variant image degradation characteristics due to the vibrations for time delayed integration (TDI) camera and real-time measurement errors of the vibration motion are rarely taken into account during the restoration process, which will bring final restored image processing error. In this paper, the analytical model of vibration motion is first deduced mathematically and then the space-variant modulation transfer function (MTF) degradation and corresponding influence factors are analyzed. Meanwhile, the effect of measurement errors is theoretically explained on that basis of high-performance restoration model. Then the effects of the space-variant MTF and measurement errors for different frequencies, amplitudes and sampling rate on image restoration performance are further presented. Finally, influences of above factors affecting restoration quality are verified and the relationships between them are established experimentally. Subsequently, the error tolerance of satellite vibration itself and measurement specifications are quantitatively generated from the practical application point of view, which can provide a valuable reference for future satellite platform design and the specifications determining of TDICCD camera.

An Improved Electronic Image Motion Compensation (IMC) Method of Aerial Full-Frame-Type Area Array CCD Camera Based on the CCD Multiphase Structure and Hardware Implementation.

In this paper, the performance of the electronic conventional image motion compensation (IMC) method based on the time delay integration (TDI) mode was analyzed using the optical injection formula of charge coupled devices (CCDs). The result shows that the non-synchronous effect of charge packet transfer caused by line-by-line transfer during exposure makes the compensated image dissatisfying. Then an improved electronic IMC method based on the CCD multiphase structure was proposed. In this method, a series of proper driving clocks were applied to drive the charge packet to move electrode-by-electrode during the exposure time, which results in a minimum non-synchronous effect of charge packet transfer. The mismatch of velocity between charge packet transfer and image motion was decreased. The performance of the improved electronic IMC method was also analyzed using the optical injection formula. The modulation degrees of the two methods were compared. The average value of the modulation degree of the improved electronic IMC method was 47/96, greater than the conventional electronic IMC method, which was 1/3. To achieve the improved electronic IMC, the driver timing diagram of the improved electronic IMC method was proposed. This paper presented an improved hardware implementation method for the improved electronic IMC method. Based on the basic FTF4052M drive circuit system, an IMC pulse pattern generator that worked together with the main pulse pattern generator (SAA8103) was added to achieve the improved electronic IMC. Then, the internal structure of the IMC pulse pattern generator was given. A dual pulse pattern generator drive circuit system was proposed. After computer simulation and indoor real shot verification, the compensation effect of the improved electronic IMC method was better than the compensation effect of the conventional electronic IMC method.

Staring array infrared search and track performance with dither and stare step

Operationally significant infrared search and track (IRST) systems have been primarily second-generation thermal imager technology with scanned time-delay-integration (TDI) detector operation. The benefit of the scanned technology provides for large aperture, gimbal-scanned sensors with extremely wide field of regard, but with low revisit rates. Dramatic progress in large format staring arrays has provided the possibility of higher performance systems with lower complexity. These large format infrared staring arrays may be able to provide systems with higher performance (due to detector count) with less complexity (fewer gimbal scan limitations). In fact, lower performance IRST systems may satisfy operational requirements without scanning or stare-step operation in a “strap-down” architecture. The first step in a full capability staring system IRST design requires a thorough knowledge of staring array IRST performance. This knowledge includes a basic understanding of signal to noise (SNR) in both undersampled and well-sampled systems, with and without a matched filter. For undersampled systems, unresolved targets result in low SNR in both the average case and worst-case scenarios. We assess (using SNR as our primary metric) how the staring IRST system benefits from typical staring operations, such as dither and stare step. We provide a comparison of staring IRST system performance in the midwave infrared (MWIR) and longwave infrared (LWIR) with three modes of operation: basic staring (no sensor movement), dither, and stare step. In addition, we introduce a metric that allows comparison of different types of IRST systems. We use this metric to compare the performance of MWIR and LWIR as well as staring, dither, and stare-step systems. In the future, we will compare scanned systems to staring IRST systems.

Updating Absolute Radiometric Characteristics for KOMPSAT-3 and KOMPSAT-3A Multispectral Imaging Sensors Using Well-Characterized Pseudo-Invariant Tarps and Microtops II

Radiometric calibration of satellite imaging sensors should be performed periodically to account for the effect of sensor degradation in the space environment on image accuracy. In this study, we performed vicarious radiometric calibrations (relying on in situ data) of multispectral imaging sensors on the Korea multi-purpose satellite-3 and -3A (KOMPSAT-3 and -3A) to adjust the existing radiometric conversion coefficients according to time delay integration (TDI) adjustments and sensor degradation over time. The Second Simulation of a Satellite Signal in the Solar Spectrum (6S) radiative transfer model was used to obtain theoretical top of atmosphere radiances for both satellites. As input parameters for the 6S model, surface reflectance values of well-characterized pseudo-invariant tarps were measured using dual ASD FieldSpec® 3 hyperspectral radiometers, and atmospheric conditions were measured using Microtops II® Sunphotometer and Ozonometer. We updated the digital number (DN) of the radiance coefficients of the satellites; these had been used to calibrate the sensors during in-orbit test periods in 2013 and 2015. The coefficients of determination, R2, values between observed DNs of the sensors, and simulated radiances for the tarps were more than 0.999. The calibration errors were approximately 5.7% based on manifested error sources. We expect that the updated coefficients will be an important reference for KOMPSAT-3 and -3A users.

Detection of Saturation in High-Resolution Pushbroom Satellite Imagery

Over the last decade, DigitalGlobe has launched a series of commercial Earth imaging satellites. These high-resolution satellite imageries provide an increasingly abundant data source for remote mapping of the Earth surface and its temporal variability. Among the factors affecting image quality is saturation of the charge-coupled device due to improper setting of the time delay integration level for the imaged surface, which results in along-track striping over areas of high radiance. We present and demonstrate an algorithm for the local detection of saturation striping by a wavelet transform, used to detect periodic variations of brightness (i.e., striping) with varying frequencies at different locations, combined with the use of unidirectional brightness gradients. The algorithm is applicable to raw, orthorectified, and resampled imagery. We test the algorithm using panchromatic images acquired by the GeoEye-1 and WorldView 1–3 sensors over polar regions. Saturation area classification masks generated by the algorithm agree well with manually identified areas of saturation. Manual validation of the algorithm applied to over 6000 images in Iceland reveals a high (>80%) success rate when the saturation levels are 2% or higher. Our general methodology may be widely applicable to periodic noise detection in imagery.

A Global Shutter High Speed TDI CMOS Image Sensor With Pipelined Charge Transfer Pixel

In this paper, a $120\,\times \, 45$ global shutter high speed time delay integration (TDI) CMOS image sensor with pipelined charge transfer pixel (PCT-pixel) is presented. Offset free and low noise pipelined signal accumulation are achieved by the PCT-pixel, and a novel layout is also proposed to increase the equivalent photosensitive area’s fill factor of the proposed pixel. Due to the parallelism of the proposed PCT-pixel, global shutter exposure method is applied in this sensor, which can eliminate nonsynchronous signal capturing problem. The proposed TDI sensor is implemented in a 0.11- $\mu \text{m}$ one-poly three-metal CMOS image sensor technology with a line rate of 100 KHz, a PCT-pixel size of $30\,\times \, 15 \,\,\mu \text{m}^{2}$ , and a fill factor of 43.5%. Measurement results show that the sensor can achieve a maximum sensitivity of 95 V/lux $\,\times \, $ sec and an energy consumption of 0.12 nJ/pixel. Measured signal-to-noise ratio boost value follows theoretical value well. The proposed sensor has the potential to achieve high scanning speed and high TDI stage while costing less power and silicon area.

Mitigating fringing in discrete frequency infrared imaging using time-delayed integration.

Infrared (IR) spectroscopic microscopes provide the potential for label-free quantitative molecular imaging of biological samples, which can be used to aid in histology, forensics, and pharmaceutical analysis. Most IR imaging systems use broadband illumination combined with a spectrometer to separate the signal into spectral components. This technique is currently too slow for many biomedical applications such as clinical diagnosis, primarily due to the availability of bright mid-infrared sources and sensitive MCT detectors. There has been a recent push to increase throughput using coherent light sources, such as synchrotron radiation and quantum cascade lasers. While these sources provide a significant increase in intensity, the coherence introduces fringing artifacts in the final image. We demonstrate that applying time-delayed integration in one dimension can dramatically reduce fringing artifacts with minimal alterations to the standard infrared imaging pipeline. The proposed technique also offers the potential for less expensive focal plane array detectors, since linear arrays can be more readily incorporated into the proposed framework.

An improved adaptive preprocessing method for TDI CCD images

In order to achieve high quality images with time-delayed integration (TDI) charge-coupled device (CCD) imaging system, an improved adaptive preprocessing method is proposed with functions of both denoising and edge enhancement. It is a weighted average filter integrating the average filter and the improved range filter. The weighted factors are deduced in terms of a cost function, which are adjustable to different images. To validate the proposed method, extensive tests are carried out on a developed TDI CCD imaging system. The experimental results confirm that this preprocessing method can fulfill the noise removal and edge sharpening simultaneously, which can play an important role in remote sensing field.