Statistical analysis of instantaneous frequency scaling factor as derived from optical disdrometer measurements at K/Q bands

Abstract

The rain rate data and statistics of a location are often used in conjunction with models to predict rain attenuation. However, the true attenuation is a function not only of rain rate, but also of the drop size distribution (DSD). Generally, models utilize an average drop size distribution (Laws and Parsons or Marshall and Palmer [1]). However, individual rain events may deviate from these models significantly if their DSD is not well approximated by the average. Therefore, characterizing the relationship between the DSD and attenuation is valuable in improving modeled predictions of rain attenuation statistics. The DSD may also be used to derive the instantaneous frequency scaling factor and thus validate frequency scaling models Since June of 2014, NASA Glenn Research Center (GRC) and the Politecnico di Milano (POLIMI) have jointly conducted a propagation study in Milan, Italy utilizing the 20 and 40 GHz beacon signals of the Alphasat TDP#5 Aldo Paraboni payload. The Ka- and Q-band beacon receivers provide a direct measurement of the signal attenuation while concurrent weather instrumentation provides measurements of the atmospheric conditions at the receiver. Among these instruments is a Thies Clima Laser Precipitation Monitor (optical disdrometer) which yields droplet size distributions (DSD); this DSD information can be used to derive a scaling factor that scales the measured 20 GHz data to expected 40 GHz attenuation. Given the capability to both predict and directly observe 40 GHz attenuation, this site is uniquely situated to assess and characterize such predictions. Previous work using this data has examined the relationship between the measured drop-size distribution and the measured attenuation of the link [2]. The focus of this paper now turns to a deeper analysis of the scaling factor, including the prediction error as a function of attenuation level, correlation between the scaling factor and the rain rate, and the temporal variability of the drop size distribution both within a given rain event and across different varieties of rain events

Rainfall Estimation from Tropospheric Attenuation Affecting Satellite Links

“…A relevant part of the data used during this work is collected within the measurement campaign of the Alphasat Aldo Paraboni propagation experiment [12], whose main goal is to better investigate the propagation impairments that affect Ka/Q/V band satellite channels. In 2014, NASA Glenn Research Center (GRC) joined the experimental campaign by installing the equipment to receive the beacon signals transmitted by the Aldo Paraboni Payload (also known as Technology Development Payload 5-TDP 5) [13] aboard the Alphasat geosynchronous Earth orbit satellite at Politecnico di Milano. The payload is equipped with two beacons that transmit coherent, continuous-wave signals at 19.701 and 39.402 GHz, respectively.…”

“…Recently, increasing attention has been paid to the exploitation of satellite downlink signals for the estimation of rainfall, as most of the commercial satellite communication systems currently operate in the Ku band (12)(13)(14)(15)(16)(17)(18) and the K band (18)(19)(20)(21)(22)(23)(24)(25)(26): in fact, in such a frequency range, rain significantly impairs the propagation of electromagnetic waves [5,6]. Some approaches have been developed for estimating the intensity of precipitation on a large scale from space-borne signals, with a spatiotemporal resolution between that of rain gauges and of weather radars.…”

Scaling of Rain Attenuation Models: A Survey

“…The main challenge in frequency scaling is the nonuniform rain rate distribution and the nonuniformity of the DSD of the rain along its path. The distribution of the frequency scaling factors in the K and Q bands was examined with the rain rate, and the DSD measurement results in [14]. However, it was not easy to compare these two results due to the unavailability of the rain rate distribution and the DSD of the rain information along the entire path.…”

“…Instant frequency scaling is an attenuation of the reference frequency scaling to anticipate the attenuation in each unit period at the desired frequency [6]. Scaling of statistic frequencies allows link budgets to be determined for new systems with a fixed attenuation margin [14]. Traditional device design requires a margin to resolve the anticipated fading within a link budget.…”

NASA's alphasat propagation terminals: Milan, Italy, and Edinburgh, Scotland

“…In addition to the Ka‐band and Q‐band beacon receivers, a suite of collocated weather instrumentation includes an RM Young weather station providing measurements of temperature, pressure, humidity, wind speed, wind direction, rain accumulation by means of a tipping bucket, as well as a Thies Clima laser disdrometer, which yields droplet size and velocity distributions. Previous work has taken advantage of these additional measurements to investigate frequency scaling from 20 to 40 GHz using the drop size distribution (DSD), as well as the impact of the scattering model on the specific attenuation as derived from the DSD . Additionally, a Radiometer Physics Gmbh (RPG) water vapor radiometer was installed in November 2016, providing radiometric measurements that will be used to validate the digital radiometric measurement recently added to the receivers.…”