Development, deployment and initial measurements of an alternative riometer

Riometry is a technique used for remote sensing of the lower ionosphere. The riometer monitors ionospheric absorption of signals from natural galactic radio sources (cosmic noise). Typically, decreases in the intensity of cosmic noise (absorption) are observed when increases in the collision frequency at ionospheric D-region heights occur, driven by increases in electron density at those heights.

We have developed, deployed and are current evaluating an alternative riometer (Relative Ionospheric Opacity Meter) operating in the 24 - 48 MHz frequency range. The system uses a Software Defined Radio (SDR) digital receiver and a Long Wavelength Array (LWA) antenna. A prototype of the riometer was installed on the campus of the Pontifical Catholic University of Peru (PUCP) in Santa Maria, Lima, Peru (12.40° S, 76.76° W) for tests. In the near future, the site will also receive one of the LWA radio-telescopes that will expand the observational capabilities of Jicamarca Radio Observatory.

Here we describe the system, deployment and examples of observations. In particular, we present results of an absorption event detected on 28 March 2025 at 1520 UTC. Results show that the system detected the absorption coinciding with the peak of an X1.1-class solar flare and illustrates the ability of the system this type of event. Absorption was estimated by comparing the measured noise power to the expected levels on a quiet day, defined as the Quiet Day Curve (QDC). Additionally, to reduce the impact of external interference, each frequency bin in the spectrum is treated as an independent time series for signal processing. On the day of the event, we estimated an absorption of 4 dB at 30 MHz and 2 dB at 38.2 MHz.

Analyses of measurements and improvements of the system will continue as part of an ongoing effort by UTD’s Upper Atmosphere Remote Sensing (UARS) Lab towards the creation of alternative instrumentation and opportunities for education and training relevant to geospace science and engineering.