# Earth-to-Earth Microwave Rain Attenuation Measurements: A Survey On the Recent Literature
## 1 Introduction
For data validation, a disdrometer (DSDm) Rd 69 was used next to the receiver as well as a tipping-gauge at a distance of 2 km north of the path. Data from tropical rainfall measuring mission (TRMM) satellite radar was also used, although these were not sufficient. [PERSON] and [PERSON] used signal attenuation measurements at 25 and 38 GHz, and measured rainfall rate and DSD [10]. The transceiver system was placed 20 m above the ground, and the used antennas were of horn type. The antennas were covered with a dielectric material to keep water out of the antennas. Along the 2.3 km link, there were six tipping buckets four optical rain gauge and DSDm. On the receiver side, there was a data system based on a PC with a built-in hard disk (HD) and a digital signal processor (DSP) on board. The power data were recorded continuously in real-time. The tipping buckets network validated the measurements with an accuracy of 0.254 mm. The data from the rain gauges were sampled every 3 s and stored together with the microwave data using the RS-485 bus. Most of the work in the last fifteen years has focused on measurements from cellular backhaul networks due to the already existing but rapidly developing structures at frequencies between 10 to 38 GHz. The idea of measuring rainfall through commercial microwave links dates back to 2005 and to the work of [PERSON], where the basic requirements were determined so that the process of estimating rainfall through the attenuation of the signal to be accurate [11]. Due to their work, measurements were presented from a dual-frequency link, in the Bolton area of England, with working frequencies of 13.9 and 22.9 GHz and path link 14 km. The future possibility was formulated towards using the links for online calibrations of radar as well as for real-time flood warning. [PERSON] et al. in their groundbreaking work introduced the idea of using cellular links for environmental monitoring [12]. Preliminary measurements took place in Tel Aviv and Haifa in Israel on 19 and 20 January 2005. The time resolution for microwave data was 15 min. Validation of the measurements was accomplished with weather radar and through rain gauges with integration times of 30 min in Tel Aviv and 10 min in Haifa. The measurements showed a possible contribution to the already existing techniques to have more accurate results. One of the first essential research works presenting rainfall measurement through cellular communication networks was published in 2007 by [PERSON] et al. (2007). Data were collected over two months from October to November 2003 in the Netherlands and from two cellular microwave links. Rainfall intensities estimated from microwave links were compared to the rainfall intensities acquired with the use of a rain gauge and two C band weather radars. The two communication links with path lengths 7.75 km and 6.72 km were nearly parallel. The operating frequency was 38.5 GHz, while the receiver was common to both links. The power resolution was of 1 dB, while the received power was measured once or twice every fifteen minutes at random intervals. Due to rainfall, signal attenuation was measured for a frequency of 27 GHz over a path-link of 4890 m ([PERSON] et al., 2007). The experiment took place in the summer of 1999 from 28 May to 23 July in the central Netherlands. The experimental setup antennas had a diameter of 0.6 m and were mounted at 46 m and 19 m, respectively, above the ground. The received signal was sampled with a rate of approximately 18 Hz. Along the link, seven rain gauges with 0.2 mm resolution were used to estimate the path-average fall intensity. The results have shown that it is essential to limit as much as possible the errors on the transmitter and receiver. The possibility is that the protected antenna could eliminate wet-antenna effects. Furthermore, wet antenna correction functions to the link data show that the instrument was well-suited for the measurement of path-averaged rainfall.