CYGNSS satellites in vibration testing. Image credit: Southwest Research Institute.
At the heart of the CYGNSS mission is Surrey’s SGR-ReSI
(space GNSS receiver remote sensing instrument)—an observatory payload in the form of a delay Doppler mapping instrument (DDMI).
The mission’s space segment consists of a constellation of eight micro-satellites to be carried to orbit on a single launch vehicle. Each CYGNSS satellite carries a DDMI that collects GPS signals reflected off the ocean surface. These GPS signals penetrate hurricanes and are changed by the roughness of the ocean surface, enabling a new method for measuring wind speeds inside hurricanes.
At the end of last year, we delivered 9 SGR-ReSI flight models and 27 low-noise amplifiers (LNAs) and antennas (including flight spares), to Southwest Research Institute (SwRI) for final integration into the CYGNSS observatories. This delivery marks a significant hardware shipment out of the Surrey Englewood, Colorado, manufacturing facility.
The SGR-ReSI is an advanced GNSS receiver with signal processing and storage capability to enable searching for and mapping of weak reflected GNSS signals. It can be configured to use signals from multiple antennas. Each CYGNSS SGR-ReSI instrument suite consists of a receiver module plus three sets of antennas and low-noise amplifiers: a single low-gain antenna is zenith-oriented and two high-gain antennas are nadir-oriented to cover a large area of the ocean. The CYGNSS receiver module is about the size of a laptop, weighs less than 1.5 kilograms, takes less than 10 watts, and so can be easily accommodated on small satellites.
GPS reflectometry is a low-cost remote sensing technique using space-borne collection of GPS signals reflected off the Earth’s surface with the intent to recover geophysical parameters from the reflected signals. More generically, signals from all Global Navigation Satellite Systems (GNSSs), such as GPS, Glonass, and Galileo, can be used, so the technique is often referred to as GNSS reflectometry. GNSS reflectometry is a form of bistatic radar. Since existing GPS satellite transmitters are utilized, reflectometry only requires a modified GNSS receiver, which can be readily accommodated even on a small satellite.
Unlike higher frequency scatterometry, GNSS reflectometry measures longer wavelengths and is more directly sensitive to ocean swell than wind. The measurement of swell is closely related to wind speed and to significant wave height—parameters of great interest to mariners, the offshore industry, and to scientists for long-term climate modeling. The instrument’s ability to detect sea ice edges and ice concentration also shows much promise.
We developed and successfully demonstrated the SGR-ReSI technology on two prior missions: UK-DMC
and the still-operational TechDemoSat-1
mission. This proven expertise has made the CYGNSS mission possible. A previous blog described the TechDemoSat-1 mission and the SGR-ReSI it carried: SGR-ReSI Instrument Measures Maritime Winds and Waves
Here at Surrey we continually strive for excellence through innovation. Our SGR-ReSI technology is a great example of our innovation, and we are excited to have another opportunity to prove this technology on the CYGNSS mission. We are counting down the days until launch and will eagerly anticipate news related to the data acquisition.
*The CYGNSS team is made up of the University of Michigan Department of Climate and Space Sciences and Engineering, Southwest Research Institute (SwRI), Surrey Satellite Technology, and Sierra Nevada Corporation.