A document describes a scanning Doppler radar system to be placed in a geostationary orbit for monitoring the three-dimensional structures of hurricanes, cyclones, and severe storms in general. The system would operate at a frequency of 35 GHz. It would include a large deployable spherical antenna reflector, instead of conventional paraboloidal reflectors, that would allow the reflector to remain stationary while moving the antenna feed(s), and thus, create a set of scanning antenna beams without degradation of performance. The radar would have separate transmitting and receiving antenna feeds moving in spiral scans over an angular excursion of 4° from the boresight axis to providing one radar image per hour of a circular surface area of 5,300-km diameter. The system would utilize a real-time pulse-compression technique to obtain 300-m vertical resolution without sacrificing detection sensitivity and without need for a high-peak-power transmitter. An onboard data-processing subsystem would generate three-dimensional rainfall reflectivity and Doppler observations with 13-km horizontal resolution and line-of-sight Doppler velocity at a precision of 0.3 m/s.
This work was done by Eastwood Im, Stephen Durden, John Huang, Michael Lou, Eric Smith, and Yahya Rahmat-Samii of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-40423
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Radar for Monitoring Hurricanes From Geostationary Orbit
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Overview
The document presents a technical overview of a novel radar system designed for monitoring hurricanes and severe storms from a geostationary orbit, referred to as NEXRAD in Space (NIS). Traditional Geostationary Operational Environmental Satellites (GOES) are limited to cloud top measurements and lack the ability to penetrate clouds to directly measure rainfall. In contrast, the NIS employs a 35 GHz Doppler radar, which allows for three-dimensional measurements of precipitation, significantly enhancing the understanding of hurricane structures and dynamics.
The NIS is designed to operate at an altitude of 36,000 km, utilizing a deployable 30-meter spherical antenna reflector with two antenna feeds for signal transmission and echo reception. This configuration enables a spiral scanning technique that covers a circular area of approximately 5300 km on the Earth's surface, allowing for continuous and smooth transitions between radar footprints. The system is capable of producing rainfall rate measurements with a horizontal resolution of 13 km and a vertical resolution of 300 m, along with line-of-sight Doppler velocity measurements at a precision of 0.3 m/s.
The radar operates at a pulse transmission rate of 3.5 KHz, allowing for a vertical observation window of 25 km. A complete disk scan of the targeted area is achieved within 60 minutes, with each spiral taking varying amounts of time to complete. The design incorporates advanced antenna technologies, aiming for high gain and low sidelobe levels to improve measurement accuracy.
The document emphasizes the importance of this radar system for improving numerical weather prediction models, which can enhance the accuracy of weather forecasting and nowcasting. By providing frequent and detailed observations of hurricanes, the NIS aims to fill the gaps left by existing satellite systems and ground-based radars, particularly during the early stages of hurricane development over the ocean.
Overall, the NIS represents a significant advancement in remote sensing technology, with the potential to revolutionize hurricane monitoring and contribute to better preparedness and response strategies for severe weather events. The development of this radar system is part of NASA's Earth Science Technology Program, reflecting ongoing efforts to leverage innovative technologies for improved environmental monitoring.
