Improved Spatial Resolution of Active and Passive Microwave Sensors’ Observations with High Efficiency Deployable Antennas

Space based environmental observations are essential for the entire planet. To meet the expanding needs and diversity of such data and to be able to provide around the clock awareness of the environment, NESDIS is mandated to enhance and expand NOAA’s Earth Observing assets. More importantly, new Earth Observing technologies and measurement spectra must be developed to improve awareness of the changes and challenges of extreme weather events, climate change, large scale wildfires, water resources crises, and to deliver adequate, actionable weather intelligence to businesses.

Space based microwave sensors offer unique insights into climate dynamics and the water and energy cycle. A warming climate speeds up the water cycle that is one of the drivers behind disruptive weather events, such as flooding, droughts, stronger hurricanes, heat waves among others.

The observation and measurement of precipitation (rainfall and snowfall) on a global scale is one of the most crucial variables for our understanding of the Earth system that is impacting societies across many levels. Precipitation provides a direct link between the local cycle of energy and water. However, observations of precipitation are challenging. To provide observations for a wide range of precipitation events, from heavy rain, tropical cyclones, to light precipitation and snow, a wide range of microwave frequencies need to be used. Active sensors, such as Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) (13.6 GHz), Dual frequency Precipitation Radar (DPR) of The Global Precipitation Measurement (GPM) (13.6 and 35.5 GHz), and CPR (94 GHz) operate between 13 and 95 GHz. Passive microwave imagers and sounders contribute to precipitation retrieval significantly. Extending their frequency coverage can improve precipitation retrieval, as shown by (Bauer, Moreau and Di Michele 2005), (Di Michele and Bauer 2006), and others.

To improve global precipitation mapping, improved spatial, spectral, and temporal resolution of observations are required, (Kidd, et al. 2021). The authors state, “Since the spatial variability of precipitation is on the order for a few kilometers, resolving this variability at 1 km or less would be ideal...” Improved spatial resolution has to be accompanied with a corresponding improvement in temporal resolution, the revisit time has to be shorter. For example, with a 15 km spatial resolution, achieving a correlation coefficient better than 80% between precipitation observed in situ and space based passive microwave sensor retrieval would require sampling at 1.5 hours. That requires at least 8 sensors on orbit. For such spatial resolution at 7 GHz, the antenna aperture for a conically scanning passive microwave sensor would be ~7 m.

Offset parabolic deployable antennas can enable the economical deployment of such passive or active sensors. The advantage of a parabolic reflector is that it can support a wide range of operational frequencies, e.g., from 6 to 120 GHz. In addition, the offset parabolic reflector is considered electrically the most efficient antenna solution.

Compact deployable reflectors are the solution that enables a new generation of the microwave observing systems with improved spatial resolution, while keeping the sensors costs affordable and enabling shorter sensor revisit times. The talk will describe the available state of the art of deployable antenna technology and the solutions it provides as well as describing the improved range of capabilities that this technology affords to remote sensing systems.

References

Bauer, P., E. Moreau, and S. Di Michele. 2005. "Hydrometeor Retrieval Accuracy Using Microwave Window and Sounding Channel Observations." Journal of Applied Meteorology 1016-1032.

Di Michele, S., and P. Bauer. 2006. "Passive microwave radiometer channel selection based on cloud and precipitation information content." Quarterly Journal of the Royal Meteorological Society 132 (617): 1299-1323.

Kidd, C., G. Huffman, V. Maggioni, P. Chambon, and R. Oki. 2021. "The Global Satellite Precipitation Constellation. Current Status and Future Requirements." Bulletin of the American Meteorological Society. doi:10.1175/BAMS-D-20-0299.1.