New GNSS weather datasets available from TechDemoSat-1

GNSS-R Data collections. The measured reflection tracks are shown in yellow over the Globe. A sequence of Delay Doppler Maps from one track is shown below — the spread of each is related to the sea surface roughness and surface wind speed.

New weather datasets, which could prove highly valuable for weather forecasting and for longer term climate monitoring, have just been made available from the Space GNSS Receiver-Remote Sensing Instrument (SGR-ReSI) instrument on board TechDemoSat-1, a small technology demonstration satellite launched by Surrey Satellite Technology Ltd (SSTL) in 2014.

With support from the European Space Agency, SSTL and the National Oceanography Centre (NOC) are continuing to work on the data received from TechDemoSat-1 and have been steadily improving the calibration of the measurements and researching new techniques and applications.

New data, including delay Doppler maps and wind speed analysis over oceans, has been released on the MERRYBS website (Measurement of Earth Reflected Radio-navigation Signals By Satellite).

Looking to the future, the NASA CYGNSS mission due to launch later this year will fly eight satellites carrying SSTL’s SGR-ReSI instrument to measure the winds within cyclones, hurricanes and typhoons.

The SGR-ReSI instrument was developed by SSTL and is able to calculate TechDemoSat-1’s position and speed in much the same way as does a car-based SatNav, by measuring ranges and triangulating its position from high-altitude GNSS satellites orbiting 20,000 km above the satellite itself. The SGR-ReSI also carries a high-gain nadir (downward-pointing) antenna to utilize GNSS reflectometry, a technique where the GNSS signals scattered off the Earth’s surface are collected and measured.

A calm ocean will give a clean reflection, while a rough, wind-driven ocean will spread the signal out. SSTL’s partner, the National Oceanography Centre in Southampton, has developed an algorithm that calculates from the signals the ocean roughness and in turn estimates the wind speed at the surface of the ocean.

To validate the algorithm, NOC has compared the wind speed measurements from the SGR-ReSI against radar measurements from EUMETSAT’s MetOp satellite. These wind speed measurements are valuable for weather forecasting, and could also prove to be of significant benefit to the scientific community for climate monitoring.

The GNSS reflections off ice are much stronger than reflections off the ocean, and it has been possible to demonstrate from the results a new method for measuring the changing location of ice edges over time, and the potential for a new method of measuring ice height and thickness.

GPS reflections are not only collected by the SGR-ReSI over the ocean, but over land, where measurements to date show strong variations that could contain valuable geophysical information about the land surface. For instance, healthy vegetation will absorb more of the signal while damp soil can cause stronger reflections. Soil moisture is considered an essential parameter for climate monitoring, and is not currently measured with sufficient coverage over the globe.

TechDemoSat-1 was in part funded by Innovate UK and is jointly operated by SSTL in Guildford and by the Satellite Applications Catapult in Harwell.

SSTL received funding to support the development of the SGR-ReSI and ground processing from the UK CEOI, SEEDA, Innovate UK and the European Space Agency.

The below videos show processing and application of the SGR-ReSI data.

https://youtu.be/RmjbM5bc1pE

Video 1: This video shows in about 20 times real-time speed the motion of the TechDemoSat-1 satellite over an orbit, indicated by a white cross on the world map. The specular reflections targeted by the SGR-ReSI are shown by yellow spots, and the measurement tracks are shown in yellow.

The four Delay Doppler Map channels from measurement tracks are shown in yellow. The four Delay Doppler Map channels from the SGR-ReSI are shown at the top right.

The spreading horseshoe shape is caused by reflections being received away from the specular point, and a rougher ocean causes more spreading. When reflections are received from over land and over ice, there is much less spreading.

The red band on the map indicates the collection of “raw” unprocessed data, which takes a few minutes to transfer before the processed Delay Doppler Maps resume.

https://youtu.be/hztM4mo8_bo

Video 2: This video shows reflections over the Northwest Passage, with and without ice.