Quantifying Weather Effects on Ka-band Communication Links: A Parker Solar Probe Study

A Ka-band communication channel provides a high capacity link critical for deep space science data downlink. However, data transmissions over Ka-band are highly susceptible to weather conditions (such as wind, clouds, water vapor, etc.), In this work, we conduct a comprehensive statistical analysis based on the first year of Parker Solar Probe measurements to quantify weather effects on a Ka-band science data downlink. To this end, we compare the results of link models using Deep Space Network (DSN) aggregate annual and monthly statistics, and annual International Telecommunication Union (ITU) standards. Our results show a general agreement between monthly DSN and ITU models with a superior performance over annual DSN statistics. The Ka-band link models can match the observed carrier power to approximately 1 dB. However, the link models in general underestimate the symbol signal to noise ratio (SSNR). Furthermore, using ITU standards, we examined the use of local weather parameters such as mean air temperature, humidity, and barometric pressure to model atmospheric gaseous attenuation. We find an excellent agreement between the measured and modeled system noise temperature (SNT) based on atmospheric attenuation due to gas for clear days. For cloudy days, one needs to account for cloud contribution to atmospheric attenuation using total columnar content of liquid water. In terms of mission operations, the results of our statistical analyses provide the first steps toward ingesting short-term weather predictions into the link models which will allow for an increased data rates during tracks with favorable weather forecasts, and will ultimately enhance the overall data return of science data with little increase in the percentage of dropped frames.