Ka波段天测与测地VLBI观测的利弊分析

Analysis of the Advantages and Disadvantages of Astrometric and Geodetic VLBI Observation at Ka-band

分析了天测与测地甚长基线干涉测量(very long baseline interferometry,VLBI)观测频率设置的必要性,重点分析了Ka波段观测的利弊。相比于X波段,Ka波段观测的优点包括河外源更致密、核移效应更小,更有利于提高射电天球参考架的实现精度以及与天体物理学全球天体测量干涉仪(global astrometric interferometer for astrophysics,Gaia)计划准惯性光学参考架的连接精度。在深空探测方面的优点表现为遥测数据率高,VLBI跟踪测量精度高,更有利于减小大气电离层和太阳等离子体对测量时延的不利影响。缺点包括河外源相对较弱,天线反射面精度和指向精度要求较高,大气吸收和辐射效应的影响更大等,但是这些因素所造成的系统灵敏度的降低有望通过高数据率采样而得到补偿。结合我国VLBI技术现状提出了发展建议。

The development and necessity of the frequency settings in astrometric and geodetic Very Long Baseline Interferometry（VLBI）observations are analyzed,especially on the advantages and disadvantages of observations at Ka-band.Compared to X-band,the advantages at Ka-band include more compact extragalactic sources,relatively smaller core shift effect,as well as efficiency to improve the precision in the realization of radio celestial reference frame and in the linkage to the quasi-inertia optical frame of Gaia project.Advantages in terms of deep space exploration are high in telemetry data rate,high in VLBI tracking precision,and helpful to mitigate the detrimental effects of ionosphere and solar plasma on the observed time delay.Disadvantages include relatively weak extragalactic sources,high precision requirement of reflector and antenna pointing,and susceptible to atmospheric absorption and emission effects.But the loss in system sensitivity due to these factors could be mostly compensated by the rapid development in high data rate sampling and recording technology.Finally in accordance with the current status of VLBI technique in China some specific recommendations for further development are recommended for criticism by readers.