Cyclone Global Navigation Satellite System

The Cyclone Global Navigation Satellite System (CYGNSS) is a system being developed by NASA with the aim of improving hurricane forecasting by better understanding the interactions between the sea and the air near the core of a storm. In June 2012 NASA sponsored the project with $152 million with the University of Michigan leading its development. Other participants in CYGNSS' development include the Southwest Research Institute of Texas, Surrey Satellite Technology of Colorado and NASA Ames Research Center. The plan is to build a constellation of eight micro-satellites that can be launched into low Earth orbit. The program plans to launch in three years and then observe two hurricane seasons. NASA plans to carry the satellites in a single launch vehicle. CYGNSS is the second of NASA's Earth Venture-class missions (a part of the NASA Pathfinder program), but the first one that is spaceborne; the previous EV-1 grant was divided among five airborne remote sensing missions. Launch is scheduled for October 2016 for a five-year run.

Background
Forecasting the tracks of tropical cyclones since 1990 has improved by approximately 50%; however, in the same time period there has not been a corresponding improvement in forecasting the intensity of these storms. A better understanding of the inner core of tropical storms could lead to better forecasts; however, current sensors are unable to gather quality data on the inner core due to obscuration from rain bands surrounding it. In order to improve the models used in intensity forecasts, better data is required.

In order to overcome this limitation, CYGNSS will measure the ocean surface wind field using a bi-static scatterometry technique based on GPS signals. Each satellite receives both direct GPS signals and signals reflected from the Earth's surface; the direct signals pinpoint spacecraft position, while the reflected or "scattered" signals provide information about the condition of the sea's surface. Sea surface roughness corresponds to wind speed. Using a constellation of eight small satellites in place of a smaller number of larger satellites enables more frequent observations: the mean revisit time is predicted to be 4 hours.

Instruments
Each CYGNSS satellite carries a Delay Doppler Mapping Instrument (DDMI), consisting of:


 * a Delay Mapping Receiver (DMR)
 * two nadir-pointing antennas
 * one zenith-pointing antenna

The instrument receives GPS signals for the purposes of scatterometry.