Aerosol optical depth (AOD) is an important indicator for air pollution monitoring. We obtain AOD from the GF-6 satellite, which was launched on June 2, 2018 by China. Beijing is selected as the study area. Based on the deep blue algorithm, the moderate-resolution imaging spectroradiometer surface reflectance product is used to correct and establish the surface reflectance library, and the AOD is retrieved from the GF-6 wide field of view (WFV) blue band. So, the application of the deep blue algorithm in a GF-6 WFV camera is realized. The aerosol is divided into three models: a custom model, a continental model, and an urban model in second simulation of the satellite signal in the solar spectrum model. To improve the accuracy of retrieval results, we recalculated the aerosol component concentration ratio based on GF-6 WFV data and ground observation as the custom model. The retrieval results of the three aerosol models show that the central and southern urban areas are higher than the mountainous areas in the northwest, indicating that human emission is the main source of air pollution in Beijing. The retrieval results of the custom model, continental model, and urban model are compared with the ground observation. The error of urban model retrieval is large, and the determination coefficient R2 is only 0.3671. The results of the custom model and continental model are similar. The R2 of the custom is 0.8942, which is higher than that of the continental (0.8872). We analyze the relationship between the retrieved AOD of the three aerosol models and top of atmosphere (TOA) reflectance and find that the custom AOD has the best sensitivity to TOA reflectance, whereas the urban AOD has the worst sensitivity. So, the custom aerosol model is closer to the real aerosol situation in Beijing.
With the rapid development of modern agriculture, LEDs as artificial light sources are playing an increasingly important role in modern agriculture. However, the uneven lighting of LEDs will cause the uneven quality of agricultural products. For requirements of plant light source on highly uniform illumination distribution, we put up an improved Pigeon- Inspired Optimization algorithm to design uniform light of the LED array. Using this method, we designed four different shapes of LED arrays. Through optimizations on MATLAB and simulation analysis on optical software TracePro, we obtained the illumination uniformity of 91.03%, 91.64%, and 92.89% for hexagonal, circular, and rectangular LED arrays, respectively, and the illumination uniformity of freely arranged LED array is up to 93.64%. The results show that LED arrays with near-optimal illumination uniformity on the target plane were obtained by this method. In addition, based on these LED arrays obtained, we investigated the relationship between the uniformity of the target plane and the vertical distance of the LED array. It is concluded that as the vertical distance increases, the illumination uniformity of the target plane increases, but the average illumination value decreases. The improved algorithm proposed in this paper lay a solid foundation for the uniform lighting design of LEDs.
KEYWORDS: Magnetic sensors, Magnetism, Sensing systems, Sensors, Interferometry, Thermal effects, Temperature metrology, Data acquisition, Bragg cells, Optical fibers, Fiber in the loop, Temperature sensors
A fiber loop ring-down (FLRD) magnetic field sensing system combined with frequency-shifted interferometry (FSI) was proposed and the effect of temperature on its performance was experimentally demonstrated. The FSI-FLRD technique measures the light intensity decay rate (called the ring-down distance) in the space domain instead of in the time domain. Compared with conventional time domain FLRD scheme, FSI-FLRD technique greatly reduces the cost due to only need of inexpensive continuous-wave laser and slow detection. The tapered single mode fiber surrounded by magnetic fluid (MF) was utilized to construct the sensor head for temperature measurement. Different temperature was generated due to the thermal effect of MF and the temperature was obtained by measuring the ring-down distance. The experimental results indicated that a sensitivity of 0.31 /(mm·°C) was achieved.
We proposed a novel multipoint sensing method for large strain measurement combined fiber loop ringdown (FLRD) and frequency-shifted interferometry (FSI). Using this method, a biconical tapered multimode fiber was used as a sensor head for large strain measurement and a serial dual-point strain sensing system was experimentally validated. By measuring the ringdown distance of each FSI-FLRD strain sensor, the strain and position of each sensor can be simultaneously obtained. Using such strain sensors, the strain sensitivities of 0.51337 km-1·mε-1 and 0.8667 km-1·mε-1 within a large measurement range of up to 6 mε were achieved.
We demonstrate fast power and wavelength control of a monolithic sampled grating distributed Bragg reflector (SGDBR) laser integrated with semiconductor optical amplifier (SOA). Optical power leveling for different channels can be achieved by tuning SOA driving current. Wavelength switching transients are analyzed experimentally. An appropriate shuttering operation of SOA sections during the channel switching process is implemented to eliminate the impact of transient emitting modes, and greatly improved dynamic performance of the SGDBR laser can be observed. With our design, output power of the laser can be precisely controlled within 0.1 dB and rapidly shuttered within 2 ns.
A high-speed current driver circuit board for wavelength control of SG-DBR laser has been designed. Experiments have
been performed to show performances of the driver circuit board and characteristics of wavelength switching of the SGDBR
laser.
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