Analysis of GNSS radio occultation data from satellite ZH-01

The electromagnetic satellite Zhangheng 01(ZH-01) was successfully launched on February 2, 2018. The GNSS Radio Occultation(GRO) receiver on board the satellite is able to observe the occultation events of GPS and BeiDou navigation satellites. We analyzed the data acquired during the in-orbit testing period. We concludes that the GRO ionosphere inversion results are reasonable,the trend is correct, the satellite can observe about 600 ionosphere occultation events each day. The global coverage of more than 30000 consecutive GRO events in more than two months were analyzed and compared with COSMIC observations: both the GRO and COSMIC occultation can realize global coverage: the Nm F2 and Hm F2 global distributions are similar and change obviously with latitude. We used three digisondes at different latitudes to analyze and compare the spatio-temporally consistent GRO data: the RMSE of GRO Nm F2 relative to digisonde is better than 9.41%, the correlation coefficient is better than 0.8682: the relative RMSE of Hm F2 is better than 7.80% and the correlation coefficient is better than 0.7066.

Geometric Calibration and Image Quality Assessment of High Resolution Dual-Camera Satellite

The evaluation of geometric calibration accuracy of high resolution satellite images has been increasingly recognized in recent years.In order to evaluate geometric accuracy for dual-camera satellite images based on the ground control points(GCP),a rigorous geometric imaging model,which was based on the collinear equation of the probe directional angle and the optimized tri-axial attitude determination(TRIAD)algorithm,is presented.Two reliable test fields in Tianjin and Jinan(China)were utilized for geometric accuracy validation of Pakistan Remote Sensing Satellite-1.The experimental results demonstrate a certain deviation of the on-orbit calibration result from the initial design values of the calibration parameters.Therefore,on-orbit geometric calibration is necessary for optical satellite imagery.Within this research,the geometrical performances including positioning accuracy without/with GCP and band registration of the dual-camera satellite were analyzed in detail,and the results of geometric image quality are assessed and discussed.As a result,it is feasible and necessary to establish such a geometric calibration model to evaluate the geometric quality of dual-camera satellite.

Multi-band microwave photonic satellite repeater scheme employing intensity Mach-Zehnder modulators

To solve the satellite repeater＇s flexible and wideband frequency conversion problem, we propose a novel microwave photonic repeater system, which can convert the upload signal＇s carrier to six different frequencies. The scheme employs one 20 GHz bandwidth dual-drive Mach-Zehnder modulator （MZM） and two 10 GHz bandwidth MZMs. The basic principle of this scheme is filtering out two optical sidebands after the optical carrier suppression （OCS） modulation and combining two sidebands modulated by the input radio frequency （RF） signal. This structure can realize simultaneous multi-band frequency conversion with only one frequency-fixed microwave source and prevent generating harmful interference sidebands by using two corresponding optical filters after optical modulation. In the simulation, one C-band signal of 6 GHz carrier can be successfully converted to 12 GHz （Ku-band）, 28 GHz, 34 GHz, 40 GHz, 46 GHz （Ka-band） and 52 GHz （V-band）, which can be an attractive method to realize multi-band microwave photonic satellite repeater. Alternatively, the scheme can be configured to generate multi-band local oscillators （LOs） for widely satellite onboard clock distribution when the input RF signal is replaced by the internal clock source.