Multi-constellation GNSS measurements of atmospheric refractivity in the marine boundary layer
Abstract
Variations in atmospheric refractivity near the surface affect electromagnetic signal propagation and can have significant impacts" on communications and radar, which is an area of significant interest to ONR. Numerical weather models are employed to forecast conditions which may be problematic for these technologies. For example, the US Navy~s Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) was used to investigate the predictability of marine boundary layer structures and ducting layers generated by strong sea surface temperature gradients.Such refractivity gradients can be measured with Global Navigation Satellite System (GNSS) radio occultation measurements, in particular GNSS radio occultation signals recorded from aircraft, to understand more comprehensively the environment in which the ducting layers form.We developed a GNSS (inclusive of both GPS and Galileo) airborne radio occultation system that retrieves high resolution vertical profiles of the atmosphere in the near track environment of a high-altitude aircraft. The proof-of-concept system was flown in a hurricane research field campaign and the results of data assimilation of the profiles into the Weather and Research Forecasting model showed the impact on the hurricane track and intensity. In the analysis of the data from these flights, we discovered that the conditions associated with boundary layer structure are evident in the spectral analysis of the refractive bending angle data, with high verticalresolution.Since then, we have developed and flown a simplified version of the system in North Pacific winter storms, in particular for the atmospheric rivers reconnaissance flights in 2015, 2018, and 2019. Targeted observations were made from the NOAA G-IV and Air Force C-130 aircraft based on the COAMPS adjoint estimate of sensitive regions to investigate the predictability of precipitation at landfall on the west coast US. The system records profiles in regions to the side of the flight path that are not sampled by dropsondes that are released directly below the aircraft, so the observations are highly complementary for effective use of flight time and coverage of the sensitive region. This simplified system tracks the upper part of the atmosphere, above 3-5 km on average, and has enabled us to make great progress in the retrieval and analysis techniques, to evaluate the impact of observations that sample upper level dynamics of the extratropical cyclones. This proposal seeks to acquire an upgraded and miniaturized version of the full GNSS airborne radio occultation system including the raw RF recorder and software receiver with open-loop tracking to extend the capabilities into the boundary layer. The new version will have the latest in data storage and processing capability and expanded capability for 7 channels available for additional antennas. In this way, the previous 300 lb 5-foot tall instrument rack can be replaced with a 3U rack unit which can be easily installed in a wide variety of aircraft. With a 7-channel system we will be able to record simultaneously occultation signals of the lower atmosphere and boundary layer as well as reflected signals that contain information on sea surface roughness andwinds. Understanding the signal propagation effects not only helps characterize ducting in the boundary layer, it also improves derivation of ARO profile measurements of atmospheric temperature, and moisture, that in turn feed back into better weather forecasting in the marine environment through data ass"imilation.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 20, 2019
- Source ID
- N000141912660
Entities
People
- Jennifer Haase
Organizations
- Office of Naval Research
- United States Navy
- University of California, San Diego