Operational Monitoring of Weather Radar Receiving Chain Using the Sun

Abstract

A method for operational monitoring of a weather radar receiving chain, including the antenna gain and the receiver, is presented. The ''online'' method is entirely based on the analysis of sun signals in the polar volume data produced during operational scanning of weather radars. The method is an extension of that for determining the weather radar antenna pointing at low elevations using sun signals, and it is suited for routine application.The solar flux from the online method agrees very well with that obtained from ''offline'' sun tracking experiments at two weather radar sites. Furthermore, the retrieved sun flux is compared with data from the Dominion Radio Astrophysical Observatory (DRAO) in Canada. Small biases in the sun flux data from the Dutch and Finnish radars (between 20.93 and 10.47 dB) are found. The low standard deviations of these sun flux data against those from DRAO (0.14-0.20 dB) demonstrate the stability of the weather radar receiving chains and of the sun-based online monitoring.Results from a daily analysis of the sun signals in online radar data can be used for monitoring the alignment of the radar antenna and the stability of the radar receiver system. By comparison with the observations from a sun flux monitoring station, even the calibration of the receiving chain can be checked. The method presented in this paper has great potential for routine monitoring of weather radars in national and international networks.

Analytical formulas for refraction of radiowaves from exoatmospheric sources

“…Huuskonen and Holleman [2007] introduced the detection of solar signals by weather radars and the use for determining the antenna pointing. The method was extended to monitoring of the receiving chain and the differential reflectivity [Holleman et al, 2010a[Holleman et al, , 2010b. Weather radars collect reflectivity data as a function of antenna azimuth and elevation, and from these so-called polar volume data, the rainfall products are derived.…”

“…For instance, radio signals from the Sun are used for monitoring of the antenna alignment and the receiving chain of weather radars [Huuskonen and Holleman, 2007;Holleman et al, 2010aHolleman et al, , 2010b. As weather radars scan close to the horizon, the intercepted radio signals originate from a rising or setting Sun and thus atmospheric refraction is an issue.…”

An integrated approach to monitoring the calibration stability of operational dual-polarization radars

“…The calibration of radar systems using the Sun as a radio source was first proposed by Whiton et al (1976) and developed in several works by Tapping (2001a), Holleman and Beekhuis (2004), Huuskonen and Holleman (2007), Holleman et al (2010a), Huuskonen et al (2014), Gabella et al (2014) and Altube et al (2015). The Sun is used for monitoring the receiver calibration, the alignment of the radar antenna and checking the antenna gain (Rinehart, 2004).…”

“…The Sun is used for monitoring the receiver calibration, the alignment of the radar antenna and checking the antenna gain (Rinehart, 2004). According to Huuskonen and Holleman (2007) and Holleman et al (2010a), the antenna elevation and effective receiver system gain could be determined within 0.05 • and 0.2 dB, respectively. The peculiarities of the Sun as a natural microwave source are -0.57 • apparent angular diameter;…”

“…The method proposed by Holleman et al (2010a) does not require stopping the operational radar scans (in contrast, the Sun tracking task requires stopping the normal radar operations) because it seeks the solar rays intercepted during the operational scanning. The Sun position is computed theoretically at the radar location, and then it is converted into azimuth and range bins.…”