Spectral modulation polarization technology is a snapshot spectral polarization measurement technique without moving parts, offering high accuracy. Anhui Institute of Optics and Fine Mechanics has developed a prototype Ultraviolet-visible Imaging Spectropolarimeter. Prototype consists of a spectral modulation module, a telescope, and an Offner spectrometer, enabling dual-channel polarization imaging. The spectral modulation module uses Wollaston prisms for beam splitting, which has the disadvantage of asymmetric splitting angles, reducing the matching accuracy of the dual-channel polarized images. Therefore, it is necessary to analyze the imaging asymmetry caused by the prism wedge angle and determine the range for the wedge angle. To converge the dual-channel polarized beams after Wollaston prisms at the spectrometer slit, a telescope with F-number of 5 was designed. To verify the dual-channel imaging performance of the system, an overall analysis was conducted with the spectrometer, ensuring a modulation transfer function greater than 0.4 for each spectral and the specifications met the design requirements.
The InGaAs infrared detector, as the core component of photoelectric conversion in the Synchronization Monitoring Atmospheric Corrector (SMAC), is responsible for measuring short-wave infrared spectral and polarization information. Among them, the service life of the thermoelectric cooler (TEC) poses a bottleneck for the overall lifespan of the infrared detector, and its reliability directly affects the normal operation of the detector. A thorough analysis is conducted for the working mechanism of the infrared detector utilized by SMAC and the failure mechanism of the TEC, and the lifetime characteristic of the product is comprehensively evaluated and analyzed through lifespan testing. To minimize time costs, an innovative accelerated lifetime test method is proposed, which utilizes temperature change rate as the accelerated stress. A lifetime test system is developed. Meanwhile, the dark current, relative spectral response, and cooling current of the infrared detector have been measured before and after the lifetime test based on the segmented uniform illumination light source. The experimental results reveal that after a cumulative lifetime test of approximately 120 days, the infrared detector underwent approximately 170,000 temperature cycles. The maximum delta value in the relative spectral responsivity of the infrared detector pre and post the life test is -1.86%, and the maximum increase in the TEC refrigeration drive current is 8.6%. The service life and performance changes of the detector could satisfy the requirements of space payloads. Moreover, the lifetime test system significantly improves test efficiency and exhibits excellent stability and scalability, fully capable of meeting the needs of lifetime tests under different temperature stress levels.
The space radiometric benchmark enables in-orbit traceable to SI system, calibrates in-orbit loads, improves data consistency across different space radiometric remote sensing missions, and facilitates long-term high-precision monitoring of global climate and environment. The transferring detector becomes an absolute power detector by quantum optical radiation measurement in the self-calibration mode, and is used to measure solar radiation in the observation mode. Si photodiode is used as transferring detector in the visible band, which requires high-precision radiometric detection at the photon level. Therefore, Si photodiode and its amplifying circuit need to have low noise. To expand the detection dynamic range of Si photodiode under low radiation condition, the noise sources of Si photodiode and its amplifier circuit are analyzed, and cooling of Si photodiode is proposed to reduce the noise. Vacuum cryogenic experiment was conducted to study the temperature characteristics of Si photodiode at 223K to 263K, and the temperature control design requirements were obtained. A sealed package Si photodiode based on two-stages TEC was developed, and a high-precision temperature control circuit with -40 °C ± 0.01 °C was designed. The shunt resistance of the cooled Si photodiode at -40°C was tested to be 8.5 TΩ, and the dark current was 1.2 fA. A wide dynamic range low-light-level irradiance source with adjustable radiation intensity is used to test the cooled Si photodiode with a low-noise transimpedance amplifier, the measurement signal-to-noise ratio was 1158 when the photocurrent was about 1pA.
The division of focal plane (DoFP) polarimeters gradually become the mainstream technology in the field of polarization imaging. In this paper, the multispectral DoFP polarimeter is implemented using commercial off-the-shelf technology, and an information model of which is established. Due to the unavoidable nonuniformity of the response of different pixels and the need to ensure data accuracy in quantitative applications, we describe the calibration method to complete the system-level polarimetric calibration of the multispectral DoFP polarimeter. Finally, the validity of the calibration method was verified by testing in the laboratory with high-precision polarizing glass piles with an adjustable polarization degree.
Clouds play an important role in weather and climate-related investigations. However, they often influence the quality of images and waste resources of storage and bandwidth in remote sensing. So, it is critical to detect clouds for less cost of payload. In this paper, the design of a real-time cloud detection camera for small satellite platforms is proposed based on field programmable gate array (FPGA). Two MicroBlaze Soft Cores are embedded in the FPGA to accomplish the task without other chips assist. By using this way, the system is highly programmable and integrated, the weight of which also becomes lighter. We implemented the system on a Xilinx Virtex-4 FPGA. The test results show that the signal-to-noise ratio (SNR) is 128.1 at 80% of the saturated exposure. We select Arabian Peninsula-Pakistan-West India area to evaluate the cloud judgment accuracy. Compare with moderate resolution imaging spectroradiometer (MODIS) cloud mask products, the false alarm rate (FAR) is less than 3%. The application of the proposed approach in a simulation and engineering system indicates its effectiveness and practicability.
According to the demand of laser initiating device miniaturization and low power consumption of weapon system, research on the low power pulse laser detonation circuit with super capacitor. Established a dynamic model of laser output based on super capacitance storage capacity, discharge voltage and programmable output pulse width. The output performance of the super capacitor under different energy storage capacity and discharge voltage is obtained by simulation. The experimental test system was set up, and the laser diode of low power pulsed laser detonation circuit was tested and the laser output waveform of laser diode in different energy storage capacity and discharge voltage was collected. Experiments show that low power pulse laser detonation based on super capacitor energy storage circuit discharge with high efficiency, good transient performance, for a low power consumption requirement, for laser detonation system and low power consumption and provide reference light miniaturization of engineering practice.
According to the environmental requirement of detectors, we studied the characteristics of Si and InGaAs detectors irradiated by the Cobalt60-γray with the total dose of 5krad, 10 krad, 20 krad, 30krad respectively. We measured the dark current and relative spectral responsivity by the Relative Responsivity Measurement Apparatus before and after irradiation. The results suggest that the characteristics of Silicon and InGaAs detectors don't change obviously after different total dose irradiation, both detectors can work in the space irradiation environment due to its stability and reliability.
KEYWORDS: Sensors, Control systems, Infrared detectors, Control systems design, Signal detection, Infrared sensors, Detection and tracking algorithms, Interference (communication), Signal processing, Indium gallium arsenide
The InGaAs Short-wave infrared detector is a temperature-sensitive device. Accurate temperature control can effectively reduce the background signal and improve detection accuracy, detection sensitivity, and the SNR of the detection system. Firstly, the relationship between temperature and detection background, NEP is analyzed, the principle of TEC and formula between cooling power, cooling current and hot-cold interface temperature difference are introduced. Then, the high precision constant current drive circuit based on triode voltage control current, and an incremental algorithm model based on deviation tracking compensation and PID control are proposed, which effectively suppresses the temperature overshoot, overcomes the temperature inertia, and has strong robustness. Finally, the detector and temperature control system are tested. Results show that: the lower of detector temperature, the smaller the temperature fluctuation, the higher the detection accuracy and the detection sensitivity. The temperature control system achieves the high temperature control with the temperature control rate is 7~8°C/min and the temperature fluctuation is better than ±0. 04°C.
On-line customer research has been conducted for European and American markets by marketers and academics. Whilst
e-Commerce and tourism develop rapidly in China, and the fraud information in E-commerce market makes the
conditions of information asymmetry becoming more seriously, understanding of Chinese internet travelers is required.
This paper reviews current research on supply chain management (SCM) within the context of tourism. SCM in the
manufacturing industry has attracted widespread research interest over the past two decades, whereas studies of SCM in
the tourism e-commerce are very limited. The potential benefit of considering not only individual enterprises but also the
tourism value chain becomes evident. This paper presents the model e-market structure and process analysis of tourism
e-commerce, and also sets up tourism supply chain and tourism e-commerce system to probe how to apply tourism ecommerce
to promote the sustainable development of tourism. The paper also identifies key research questions in TSCM
worthy of future theoretical and empirical exploration.
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