## 1 Introduction
Computer tomography (CT) and inverse distance weighting (IDW) interpolation have also been applied to rainfall field reconstruction based on the microwave link network, and the results also verify the feasibility of the scheme [26; 27]. However, further research results show that it is difficult for CT and IDW to reconstruct the rainfall field with high precision and high spatial resolution for the real distributed microwave links, which is affected by the link sparsity and irregular structure distribution. Similar to HMLs, the inclined earth-space links (ESLs) between earth communication satellites and ground receiving antennas will also produce significant attenuation due to rainfall in the process of atmospheric propagation. Therefore, the method of using ESLs to retrieve rainfall has also been proposed and deeply studied recently [13; 27; 28]. Since 2010, a large number of experiments have begun to verify the use of a single earth-space link (ESL) to measure rainfall. [PERSON] et al. [13] and [PERSON] et al. [27] studied the feasibility of using the attenuation of ESLs signals in Ku and Ka bands to measure rainfall, respectively. After that, many advanced techniques have been proposed to solve the key factors that affect rainfall retrieval by ESL, such as the identification of the rainy periods, reference baseline and rainfall height [28; 29; 30]. On the basis of considering the influence of microwave attenuation characteristics of the melting layer on ESL propagation, [PERSON] et al. [28; 31] improved the rain attenuation calculation model and proposed an ESL rainfall retrieval method based on machine-learning technique. In addition, the performance of the single ESL to retrieve different grades of rainfall and different types of rainfall has been verified by long-term empirical data [32]. In addition to the research on retrieving rainfall by a single ESL, [PERSON] et al. [33] and [PERSON] et al. [34] studied the feasibility of ESLs network retrieval of large-scale rainfall field through simulation experiments. Compared with other detection instruments, the cost of ESL equipment is lower, and the installation is more convenient. It mainly consists of a small television antenna and a receiver at the user terminal [35; 36]. Moreover, there are a large number of broadcast users all over the world. Therefore, the use of widely distributed ESLs to obtain rainfall information in mountainous areas, islands and plateaus that lack professional rainfall detection instruments is of great potential. On the other hand, with the rapid development and application of satellite communication, a large number of communication satellites will be launched for networking in the near future, such as Starlink, Oneweb and Kuiper constellations [37]. This will make a large number of ESLs closely cover all regions of the world and then providing conditions for using ESLs network to retrieve large-scale and high-precision rainfall fields. Previous studies have always focused on ESL and HML separately. However, the use of these two new detection techniques to retrieve rainfall has the same essential physical mechanism, which is the phenomenon of microwave attenuation caused by rainfall. The realization of joint detection of the two technologies is of great significance to make full use of space-based and ground-based microwave signal resources and supplement traditional detection methods. Moreover, joint detection is more likely to obtain a large-scale rainfall field with higher accuracy and higher resolution. In this paper, we carry out the research of using the joint network of ESLs and HMLs to retrieve rainfall field with high precision and high resolution. Firstly, the simulation experiment of joint network of ESLs and HMLs is carried out based on the atmospheric propagation model of ESL and HML, and a rainfall detection network for retrieving rainfall field is built, which is composed of multiple ESLs and HMLs.