The radio occultation (RO) technique using signals from the global navigation satellite system, is widely used to observe the atmosphere for applications such as numerical weather prediction (NWP) and global climate monitoring. Since 1995, there have been turborogue sounder on board global positioning system/meteorology, black jack sounder on board challenging minisatellite payload and gravity recovery and climate experiment, IGOR sounder on board constellation observing system for meteorology, ionosphere and climate, GRAS on board meteorological operational, which have been recieving a large number of RO data, but their observed signals come only from global positioning system (GPS). These RO data have been wildly used in NWP and climate monitoring, however they cannot meet the requirements for high accuracy and real time atmosphere observation, in this case compatible RO sounder to obtain more RO observations is significant. Global navigation satellite system occultation sounder (GNOS) on board the fengyun3 C (FY3 C) satellite, which is the first Bei Dou system (BDS)/GPS compatible RO sounder in the world, was launched on 23 September 2013. Up to now, lots of RO observations have been obtained. In this study, the components of GNOS are introduced; one-day GNOS RO events and their global distribution are analyzed; compared with the GPS RO observations, the accuracy and consistency of BDS real-time positioning results and BDS RO products are analyzed. The preliminary results show that the BDS can enhance the number of RO events by 33.3%; the average deviation and standard deviation of BDS real time positioning results are 6 m and 7 m, respectively; the BDS/GPS difference standard deviation of refrectivity, temperature, humidity, pressure and ionospheric electron density are lower than 2%, 2 K, 1.5 g/kg, 2%, and 15.6%, respectively. The BDS observations/products are consistent with those of GPS, therefore BDS RO products can bring benefit to numerical wheather prediction and global chlimate change analysis.
We report a rotating-mirror scanning camera system based on a galvanometer and a CCD camera. This system improves the imaging speed by placing a series of paralleled images on the sensor of the camera so that multiple images are acquired during one single exposure; thus, the frame rate of the CCD camera does not limit the temporal resolution of recorded events. The camera is implemented on a custom designed light-sheet microscopy and aims to improve the imaging speed while the high spatial resolution is still retained on the light-sheet microscope.
Global Navigation Satellite System Reflectometry (GNSS-R) was regarded as a promising way to observe atmospheric duct by utilizing low elevation angle ocean surface reflected signals. To invest the Delay maps' feature of low elevation angle reflected signals in the atmospheric duct, a shipborne GNSS-R campaign was conducted in July, 2015 by the scientific investigation ship called Shiyan 3 on the South China Sea. During the campaign, the atmospheric temperature, pressure, and relative humidity which were used to detect atmospheric duct were recorded by GPS radiosondes and meteorological recorder. The GNSS-R payload developed by National Space Science Center (NSSC) and fixed on the rail of Shiyan3 was used to generate Delay maps. Preliminary results showed that atmospheric duct, especially evaporation duct, existed almost all the time in the experimental ocean region. Ocean surface reflected signals with elevation angle less than 10° were received and formed delay maps successfully. Affected by the direct signal and specular reflected signal's strong interference, apparent code correlation peaks appeared on Delay maps' tail. The experimental values of correlation peaks and simulated code autocorrelation were synthetically used to fit the curve of direct signal and specular reflected signal's strong interference utilizing the least square method. After removing the interference, cleaner reflected signals without direct and specular reflection signals were obtained.
Bessel beams have been proved to have the ability to extend the depth of focus in fluorescence microscopy. But the depth discrimination was not investigated thoroughly. Following our previous work2, we investigated focal fields of Bessel-Gauss beams at different scanning angles. We found that the central focusing lines were tilted differently at different scanning angles. This effect manifests the ability of the true perspective view in the fluorescence stereomicroscopy.
In order to understand the space-borne GNSS Reflection (GNSS-R) performance, an end to end simulator named GREEPS (GNSS-R End-to-End Performance Simulator) was developed by National Space Science Center (NSSC), Chinese Academy of Sciences. The simulator consists of four functional modules: Mission analysis module, forward modeling module, observation system modeling module and inversion/retrieval and precision Analysis module. This paper introduces each module's structure and capabilities. The preliminary simulation results are shown, including average and maximum number of simultaneously reflected GNSS satellites for 24 hours, coverage ratio between the ± inclination of LEO for 24 hours, the sensitivity of Delay Doppler Map (DDM) to the wind field, and wind field and ocean altimetry retrieval precision analysis. GREEPS is a powerful and useful simulation software for space-borne GNSS-R mission and payload design, it will speed up the space-borne GNSS-R applications in China.
The purity of output spectrum of high power microwave vacuum electronic devices is very important for the microwave electronic system. The stray outputs with frequency in or near the operating frequency band have been observed in some Multi-Beam Klystron (MBK). The exits of the stray outputs have serious influence on the normal operation of the microwave electronic systems. The variation of stray outputs with different operating frequency observed in an S band MBK was described, and the reasons for generating the stray outputs were analyzed by using 1D klystron code in this paper. The reflecting electrons and secondary electrons caused by the interception of electron beam on gap head of the cavity are responsible for the stray outputs. They will be accelerated by RF electric field on the cavity gap in reverse direction, and return back to previous cavity. The retuning electrons provide the feedback way between successive two cavities, and generate oscillation, which will be amplified by following cavities and form stray outputs. The stray outputs can be reduced or suppressed by decreasing the number of retuning electrons. It can be realized by making small slots on the surface of the gap head. The new MBK with slots on the gap head was made and tested, the power level of the stray outputs are less than -70dBc.
In the interest of improving the temporal resolution for light-sheet microscopy, we designed a fast frame scanning camera system that incorporated a galvanometer scanning mirror into the imaging path of a home-built light-sheet microscope. This system transformed a temporal image sequence to a spatial one so that multiple images could be acquired during one exposure period. The improvement factor of the frame rate was dependent on the number of sub-images that could be tiled on the sensor without overlapping each other and was therefore a trade-off with the image size. As a demonstration, we achieved 960 frames/s (fps) on a CCD camera that was originally capable of recording images at only 30 fps (full frame). This allowed us to observe millisecond or sub-millisecond events with ordinary CCD cameras.
A two port 2.4 to 24 GHz cryogenic Quadruple-Ridged Flared Horn (QRFH) Feed with 10:1 impedance bandwidth is selected for presentation and investigation in this paper. The antenna geometry is formed by using simulation-based optimization which satisfies several stringent design requirements, including impedance bandwidth and radiation characteristics of the proposed antenna. To verify the theoretical performance, a prototype of the optimized QRFH was manufactured and tested. The reflection coefficients of the antenna are below -10 dB and the mutual coupling is better than -25 dB. Meanwhile, the antenna aperture efficiency is above 55% and maximum gain is from 10.5 to 21.1dBi across the desired working frequency band. Both the simulated and measured results exhibit good agreement. To demonstrate the suitability of the proposed design in a practical environment, a prototype Cryogenic system composed of a cryogenic Dewar and a QRFH, has been designed and its performance was measured. The results showed that the physical temperature reached an acceptable level which was less than 45 K. The overall performance of the proposed QRFH feed suggests that it would be applicable to the receivers for the Square Kilometre Array (SKA) reflector antenna, and meets requirements of the SKA advanced instrumentation program (AIP).
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