CYGNSS Microsatellites Will Use GPS Signals To Study Hurricanes

Artist’s concept of one of the eight Cyclone Global Navigation Satellite System satellites deployed in space above a hurricane. Image Credit: NASA

December 13, 2016 – The same GPS technology that helps people navigate cars will soon be used to improve hurricane forecasting. On December 14, NASA will launch a set of eight identical microsatellites that will use this technology to measure wind speeds over Earth’s oceans and enable scientists to better understand and predict hurricanes.

At the heart of the Cyclone Global Navigation Satellite System (CYGNSS) mission is a SGR-ReSI (space GNSS receiver remote sensing instrument) — an observatory payload in the form of a delay Doppler mapping instrument (DDMI) made by Surrey Satellite Technology LLC. 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, Surrey 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. The delivery marked a significant hardware shipment from Surrey’s Englewood, Colorado, manufacturing facility.

CYGNSS SGR-ReSI flight models. Image Credit: Surrey Satellite Technology LLC

The Technology

The SGR-ReSI is an advanced Global Navigation Satellite System (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, and requires less than 10 watts to operate. This makes it perfectly suited for small satellites.

SGR-ReSI receiver module electronics. Image Credit: Surrey Satellite Technology LLC

GNSS Reflectometry

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.

CYGNSS microsatellite observatories in orbit. Image Credit: Southwest Research Institute

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 promise.

Surrey 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.

The Southwest Research Institute (SwRI) in San Antonio built the CYGNSS micro satellites. SwRI will host the mission operations center at its Boulder, Colorado location. Other team members include the University of Michigan Department of Climate and Space Sciences and Engineering and Sierra Nevada Corporation.