Developments in GNSS Reflectometry from the SGR-ReSI on TDS-1

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Jewel Simon
5 years ago
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(SSTL), Brent Abbott SST-US Christine Gommenginger, Giuseppe Foti

1 Changing the economics of space Developments in GNSS Reflectometry from the SGR-ReSI on TDS-1 Martin Unwin Philip Jales, Jason Tye (SSTL), Brent Abbott SST-US Christine Gommenginger, Giuseppe Foti (NOC) 30 th AIAA/USU Conference on Small Satellites August

2 Overview TDS-1 GNSS-R Exploitation Project Surrey Satellite Technology Partnership with National Oceanography Centre Supported by ESA Presentation Overview Background to GNSS Reflectometry TDS-1 Mission and Instrument Overview Data and Products Applications Recent results and future Data access through Thanks to: CEOI, ESA, University Of Surrey, NERC, EPSRC, InnovateUK, UKSA, SEEDA, University Of Bath, PIL, Satellite Applications Catapult, CYGNSS Team (Michigan, SwRI), SSTL R&D, TDS-1 Projects and Ops Teams 2

3 Spaceborne GNSS Reflectometry GNSS Reflectometry Detecting GPS / GNSS signals reflected off the Earth s surfaces Multipath signals should contain geophysical imprint Bistatic radar but no need for radar transmitter Using Earth-reflected GPS signals for ocean sensing first discussed in ESA proposed reflectometry for ocean Altimetry PARIS US & European studies on Scatterometry in late 90s 00s First reflected signal detected 1998 (JPL using SIR-C data) First dedicated in-orbit experiment: UK-DMC (2003) First on-board processing instrument: UK TDS-1 (2014) First GNSS-R Constellation: NASA CYGNSS (2016) 3

over sea, land and ice 20 seconds each, total ~23 minutes data Signals detected from all surface types Ocean

4 UK-DMC Experiment 2003 GPS Reflectometry experiment flown as opportunity on 100kg UK-DMC satellite GPS receiver modified to add + Downward pointing antenna + Data recorder link Sept ~60 collections over sea, land and ice 20 seconds each, total ~23 minutes data Signals detected from all surface types Ocean reflections shown to be related to sea state => surface winds Imager Reflectometry Antenna Delay Doppler Map (DDM) 4

TDS-1 and SGR-ReSI TechDemoSat-1 Mission 160 kg UK Satellite

SGR-ReSI Launched July 2014 SGR-ReSI COTS Based GNSS Receiver

patch Nadir antenna 13 dbi gain, LHCP 30 beamwidth flared spiral Also

5 TDS-1 and SGR-ReSI TechDemoSat-1 Mission 160 kg UK Satellite Demonstration 8 UK payloads Includes SSTL s GNSS-R payload the SGR-ReSI Launched July 2014 SGR-ReSI COTS Based GNSS Receiver Co-processor for Reflectometry Zenith antenna: hemispherical dual patch Nadir antenna 13 dbi gain, LHCP 30 beamwidth flared spiral Also two single freq. zenith patch antennas 5-10 watts, 1.5 kg Nadir Antenna SGR-ReSI Unit Zenith Antenna 55

SGR-ReSI Operating Modes Either 1) Raw sampling mode (L0)

Post process with Software Receiver 2) Delay Doppler Map (DDM)

from 4 reflections collected each second GPS L1 C/A code

6 SGR-ReSI Operating Modes Either 1) Raw sampling mode (L0) Sampled data (like UK-DMC) Typically 2 minutes of data, 1 GByte Post process with Software Receiver 2) Delay Doppler Map (DDM) (L1a) On-board processing Data rate ~200 kbps continuous DDMs from 4 reflections collected each second GPS L1 C/A code signals acquired Potential for GPS L2C and Galileo E

7 Example Raw Data L0 to L1b(SW) Processed through software receiver RD2, Raw Collection #0 Strong signals from 3 PRN channels High res DDM examples: 4 ms coherent integration 500 incoherent looks (2 sec) PRN 25 PRN 2 PRN 12 7

Reformat, add meta-data, calibration information DDMs L1B

8 On-board DDMs Largest volume of data collected is on-board processed DDMs Level 1A Processed on ground into Level 1B Reformat, add meta-data, calibration information DDMs L1B processed into Wind Speed and mean square slope Level 2 Products of operational use 8

9 Viewing L1b in Google Earth Selection by time Summary image of up-to 30 DDMs spaced along the track Data View Show Elevation Data Peak SNR, Noise, Antenna Gain Commercial in Confidence 9

Fast Delivery Inversion: DDM => wind speed Aiming for accuracy < 2 m/s Wind:

10 Level 2 Wind Speed Working with National Oceanography Centre Developing GMFs Geophysical Model Functions E.g. Fast Delivery Inversion: DDM => wind speed Aiming for accuracy < 2 m/s Wind: 30 m/s- 20 m/s- 10 m/s- Validation against ASCAT winds shows agreement Currently to ~ <4 m/s Working towards < 2 m/s 10

11 Ocean L1B Histograms of Peak SNR binned by antenna gain SNR range of ~15 db Most data within 5 db Peak SNR[dB] Land SNR range >25 db Peak SNR[dB] Polar Multiple discrete populations many surface types Reduction in GPS coverage over poles Peak SNR[dB] Antenna Gain [db] 11

12 Projection of DDM onto the surface Spatial ambiguity so not real imaging However provides a useful visualisation of the sensitivity of whole DDM DDM power measurements mapped to surface: This shows how we can exploit the surface overlap of a series of DDMs. Stare processing using the ambiguity-free line for multiple looks 12

the surface type seen in optical imagery Very low reflectance from dense vegetation and

13 Land Applications Early investigations in progress Soil moisture, Biomass, Flood monitoring Australia Specular point SNR plotted over land shows very high correlation to the surface type seen in optical imagery Very low reflectance from dense vegetation and deserts High reflectivity of forest clearings, rivers, fertile / irrigated land Amazon basin 13

Patterns over North Africa Data collected from TDS-1 over 1 year (intermittent) January 2015 - Jan 2016 Strong reflections Salt lakes in

14 Patterns over North Africa Data collected from TDS-1 over 1 year (intermittent) January Jan 2016 Strong reflections Salt lakes in Tunisia and Algeria Some desert areas Weak reflections Vegetation Mountain ranges Other deserts Some temporal variations visible, but sparse data 14

15 Reflections off ice are very strong Use of stare processing to increase resolution Find edges and ridges, few km resolution Can be validated using sea/land boundaries Also potential for altimetry over ice Ice Sensing 15

16 MERRByS Accessibility Users have access to: Sample data sets (L0, L1b and L2) Catalogue of L1b DDMs and L2 wind speed (May 2016) L1B data reprocessed with new Meta-data (V0.5) New Level 2 inversion (FDI v1.11) Data now available up to April 18 th 2015 Further data release planned soon More information available on MERRByS website Including Product Documentation Significant effort to prepare data products & service Please excuse bugs, omissions! Feedback is welcome 16

17 TDS-1 Status TDS-1 still operating 2 days out of 8 ESA study supporting further data exploitation of TDS-1 Plus separate scientific assessment study commencing Issues affecting sea state retrieval next on list As demonstrator satellite, attitude determination is patchy Significant error term in inversions try to improve! Radiometric measurements Understanding noise & instrument gain behaviour in orbit Programmable gain mode, switched loads, direct signals Strategies for better recovery of surface reflection coefficient Different processing strategies, DDM settings Dual frequency measurement experimentation GPS L1 and L2C tracking better orbit determination Reflectometry using dual frequency altimetry Higher resolution Galileo signal tracking demo planned Nominal end of mission Summer 2017 Discussions about mission extension Increased duty cycle of SGR-ReSI operations 17

Future NASA CYGNSS mission Using SGR-ReSI on 8 small sats

21 2016 Other future flights of SGR-ReSI Opportunity missions &

18 Future NASA CYGNSS mission Using SGR-ReSI on 8 small sats Sensing hurricanes using GNSS Reflectometry Launch due November Other future flights of SGR-ReSI Opportunity missions & constellations being targeted How to enable via commercial data service? Upgraded SGR-ReSI Multiconstellation GNSS Same SWaP, greater coverage Potential addition of radio occultation (ORORO) 18

Changing the economics of space Thank You www.merrbys.co.uk Surrey Satellite Technology Ltd.

19 Changing the economics of space Thank You Surrey Satellite Technology Ltd. Tycho House, 20 Stephenson Road, Surrey Research Park, Guildford, Surrey, GU27YE, United Kingdom Tel: +44(0) Fax:+44(0) Web:

Recent GNSS Reflectometry Results from the UK TDS-1 Satellite

CHANGING THE ECONOMICS OF SPACE Recent GNSS Reflectometry Results from the UK TDS-1 Satellite Martin Unwin ICGPSRO2018, Taipei, 18-20 April 2018 SSTL 2018 Ack: SSTL, NOC, ESA, Surrey, CEOI, UKSA, InnovateUK,