Measurement of Solar Absolute Brightness Temperature Using a Ground-Based Multichannel Microwave Radiometer

Lianfa Lei,Yingying Ma,Zhenhui Wang,Lei Zhu,Jiang Qin,Rui Chen,Jianping Lu

doi:10.3390/rs13152968

Abstract

Ground-based multichannel microwave radiometers (GMRs) can observe the atmospheric microwave radiation brightness temperature at K-bands and V-bands and provide atmospheric temperature and humidity profiles with a relatively high temporal resolution. Currently, microwave radiometers are operated in many countries to observe the atmospheric temperature and humidity profiles. However, a theoretical analysis showed that a radiometer can be used to observe solar radiation. In this work, we improved the control algorithm and software of the antenna servo control system of the GMR so that it could track and observe the sun and we use this upgraded GMR to observe solar microwave radiation. During the observation, the GMR accurately tracked the sun and responded to the variation in solar radiation. Furthermore, we studied the feasibility for application of the GMR to measure the absolute brightness temperature (TB) of the sun. The results from the solar observation data at 22.235, 26.235, and 30.000 GHz showed that the GMR could accurately measure the TB of the sun. The derived solar TB measurements were 9950 ± 334, 10,351 ± 370, and 9217 ± 375 K at three frequencies. In a comparison with previous studies, we obtained average percentage deviations of 9.1%, 5.3%, and 4.5% at 22.235, 26.235, and 30.0 GHz, respectively. The results demonstrated that the TB of the sun retrieved from the GMR agreed well with the previous results in the literature. In addition, we also found that the GMR responded to the variation in sunspots and a positive relationship existed between the solar TB and the sunspot number. According to these results, it was demonstrated that the solar observation technique can broaden the field usage of GMR.

Highlights

We introduced an experiment and theory that solar radiation can be remotely sensed by using the Ground-based multichannel microwave radiometers (GMRs) and propose a method to measure the antenna pattern and absolute TB of the sun by using the GMR; the results are compared with previously available results
We introduced an application for tracking and observing the sun that utilizes the GMR
Based on the theory of thermal radiation and its transfer in the atmosphere, we provided a convenient method to measure the absolute TB of the sun by using observations from the GMR

Summary

Introduction

The sun is an important source of the energy for the earth and the atmospheric system and the sun continuously emits radio emissions at all wavelengths. The solar brightness temperature (TB) represents a basic property of the solar atmosphere. At millimeter and submillimeter wavelengths, the solar emission primarily originates in the chromosphere, which is an approximate blackbody of 6000 to 20,000 K. Solar emission measurements at multi-frequencies are useful for emissions that arise from different layers of the solar atmosphere [1]. The observations of the thermal radio emission of the sun at millimeter wavelengths are important in evaluations of theoretical atmospheric and surface models [2,3,4]

Methods

Results

Discussion

Conclusion