Monitoring GNSS transmit power with small radio telescopes

Abstract

The small radio telescopes SALSA (“Such A Lovely Small Antenna”) refers to the system consisting of two (2.3m) radio telescopes located at the Onsala Space Observatory and built with the aim of introducing students to the world of radio astronomy. In this project, SALSA has been extended with the possibility of tracking satellites that are part of the Global Navigation Satellite Systems (GNSS). This new feature of SALSA allows to carry out observations in an automatic fashion and store all the necessary information for subsequent data analysis. The latter stage aims at deriving important satellite-based parameters, namely the transmit power of GNSS satellites as well as their antenna gain patterns. Good knowledge of transmit power of GNSS satellites is required for an enhanced GNSS orbit modelling and GNSS orbit determination. In addtion, satellite antenna gain patterns are vital for the callibration of data from GNSS reflectometry (GNSS-R). The following report describes the technical specifications, system calibration procedure and measurement performance of SALSA with emphasis on the hardware modifications and software tools required to upgrade an uncalibrated system designed for astronomical observations at 1.4 GHz to a system that can be utilized for satellite observations at frequencies between 1 and 2 GHz. This project can form a foundation of a new routine service, regularly monitoring GNSS signals and providing users with the aforementioned satellite-based products.