Development of RFI Mitigation Strategy to Enhance Protection of Global Navigation Satellite System (GNSS) Radio Occultation (RO) Measurements for Earth Observation

Measurements utilizing Global Navigation Satellite System (GNSS) Radio Occultation continue to gain acceptance in the weather forecasting community and their value has been demonstrated in several experiments and publications. Due to the perceived high return on investment, additional RO missions utilizing GPS and international radio-navigation signals are planned. From an Earth observation and remote sensing point of view, the GNSS-RO technique utilizes relatively weak signals that can easily incur interference from other radio systems due to unique aspects of the measurement geometry as well as the spectrum regulatory structure. First, space-based operation of GNSS receivers may incur interfering signals originating from a much larger distance, as defined by the line-of-sight to the receiver, compared with traditional operation of the receivers in terrestrial or airborne applications. Further, interference criteria for GNSS measurements defined by the radio-navigation service must consider the aggregate effect of all interfering signals. Secondly, the current regulatory structure protects receptions of GNSS signals within the Radio-navigation service in contrast to the Earth Exploration Service (EESS) under which Earth observing systems are recognized from a regulatory perspective. This paper will address the initial steps that have been taken in order for Earth observing applications of GNSS signals to be recognized within the spectrum regulatory structure as well as examine the current Radio Frequency Interference (RFI) criteria with respect to protection of GNSS-RO measurements for EESS in contrast to RFI criteria based solely on Radio-navigation applications.