Abstract
In this paper, we present the design and implementation tests of a water vapor radiometer (WVR) suitable for very long baseline interferometry (VLBI) observation. We describe the calibration method with an analysis of the sources of measurement errors. The experimental results show that the long-term measurement accuracy of the brightness temperature of the water vapor radiometer can reach 0.2 K under arbitrary ambient conditions by absolute calibration, receiver gain error calibration, and antenna feeder system temperature noise error calibration. Furthermore, we present a method for measurements of the calibration error of the oblique path measurement. This results in an oblique path wet delay measurement accuracy of the water vapor radiometer reaching 20 mm (within one month).
Highlights
Studies of spacecraft tracking techniques have shown that the delay in the radiometric signal caused by changes in the refractive index of the troposphere is a major source of error in very long baseline interferometry (VLBI)
We developed a water vapor radiometer for VLBI observations
We describe the details of the design of the water vapor radiometer, the sources of measurement errors, and the correction methods
Summary
Studies of spacecraft tracking techniques have shown that the delay in the radiometric signal caused by changes in the refractive index of the troposphere is a major source of error in very long baseline interferometry (VLBI). The microwave frequency signal used in the measurements and control will cause a refraction delay of approximately 6–7 ns along the zenith direction when penetrating the troposphere, which corresponds to a path length of approximately 2.3 m. Any accurate phase or delay measurements involving signals propagating between space and the ground must include methods to calibrate tropospheric effects. The deep-space VLBI mission requires precise measurements of the radio signal path delay caused by water vapor in the atmosphere. The water vapor radiometer can measure the wet delay in the troposphere in real time and can reduce the wet delay error to less than 1 cm [2]. The receiver is designed to measure multiple channels in one second
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