Spaceborne Detections of Reflected SBAS Satellite Signals
This presentation is the property of its rightful owner.
Sponsored Links
1 / 20

Jason Tye, Prof Craig Underwood Surrey Space Centre, University of Surrey, UK PowerPoint PPT Presentation


  • 197 Views
  • Uploaded on
  • Presentation posted in: General

Spaceborne Detections of Reflected SBAS Satellite Signals. Jason Tye, Prof Craig Underwood Surrey Space Centre, University of Surrey, UK Dr Martin Unwin, Dr Philip Jales Surrey Satellite Technology LTD, UK SPACE REFLECTO Brest, France, 5 th November 2013. Contents. Background

Download Presentation

Jason Tye, Prof Craig Underwood Surrey Space Centre, University of Surrey, UK

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Jason tye prof craig underwood surrey space centre university of surrey uk

Spaceborne Detections of Reflected SBAS Satellite Signals

Jason Tye, Prof Craig Underwood

Surrey Space Centre, University of Surrey, UK

Dr Martin Unwin, Dr Philip Jales

Surrey Satellite Technology LTD, UK

SPACE REFLECTO

Brest, France, 5th November 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Contents

  • Background

  • Coverage Simulations

  • The Software Receiver

  • Results of SBAS search

  • Discussion of Direct Signal Crossover

2

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Background

  • Spaceborne GNSS-R in its infancy

  • SSTL’s influence:

    • UK-DMC, TDS-1, CYGNSS

    • In orbit demonstration of GNSS-R

  • Remote sensing targets

  • Number of signals of

    opportunity growing

  • Introduction to PhD

Image courtesy of SSTL

3

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

About SBAS

  • Satellite Based Augmentation Service primarily for integrity of service data and corrections for aircraft using GPS services

  • Geostationary ~ 35,800km altitude

  • Broadcast similar C/A PRN codes to GPS

  • Encoded NAV data at 500bps

    • ~30 message types @ 1Hz

4

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Coverage Simulation

  • UK-DMC orbit and antenna pattern over 1 day

  • Maximum 4 SPs

  • SBAS (B), GPS (R)

  • Appears to have a 'generous' bias with respect to antenna gain

    • Should be consistent across both satellite systems

  • 0.67dB average SP gain

  • +24.5% Global cells covered

5

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Coverage Simulation

  • Clear advantage seen for GPS+SBAS especially focusing around the 4 specular point threshold

6

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

The Software Receiver

  • Adapted to process SBAS signals

    • Changes to data structures and processing methods, particularly navigation

  • Re-processing of UK-DMC data with help of the WaveSentry catalogue

7

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Results

  • Multiple examples of SBAS reflections obtained from ‘challenging’ geometries and different constellations

  • DDMs are incoherently accumulated for 7s at 1ms coherent integration steps

  • Sacrifice surface resolution for correlation power for detection

    • No science is to be done immediately

8

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Results

  • First identified SBAS reflection

  • Two MSAS satellites in one collection

  • Coincident with successful targeting of a GIOVE-A reflection (Jales)

T NMEA 50

TxSBAS

T NMEA 42

SPSBAS

Papua New Guinea

SP NMEA 42

SP NMEA 50

Rx

Map Images: Google Earth

9

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Results

Delay (Chips)

(B) Doppler (Hz)

(A) Doppler (Hz)

  • (A) MT-SAT 2 (MSAS) with NMEA ID 50

  • (B) MT-SAT 1R (MSAS) with NMEA ID 42

10

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Results

Delay (Chips)

Doppler (Hz)

TxSBAS

  • ESA Artemis (EGNOS) on 18/02/2009

SPSBAS

11

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Results

Delay (Chips)

(A) Doppler (Hz)

(B) Doppler (Hz)

(C) Doppler (Hz)

  • Reflections of Inmarsat 3 f3 (WAAS) taken in 2004

  • (A) and (B) share almost identical geometries taken on different days

  • (C) is the most 'extreme' of reflections and shows a bias in Doppler typical of being on the antenna fringes

12

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Detection Conclusions

  • Developed and demonstrated SBAS processing capability of the software receiver

  • We have tracked and decoded navigation data from direct SBAS signals in the UK-DMC data and reflection DDMs have been plotted

  • Provided proof of concept for use of SBAS satellites as reflectometry sources

  • Work must be done to establish fully the data quality retrieved for science purposes in context of a link budget as typically SBAS signal strength is a few dB less than GPS at source

13

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Direct Signal Overlay

  • GPS Code repeats every 1 ms => 298 km wrap-around

    Direct Signal Overlay is geometric effect based on the difference between reflected and direct paths as a multiple of code length

  • MOD[|TxS|+|SRx|-|TxRx|, 298(km)]

Tx

Rx

S

14

CYGNSS TIM


Jason tye prof craig underwood surrey space centre university of surrey uk

Direct Signal Overlay

  • Sensitivity to orbital height -

    UK-DMC Zenith reflection path difference: 680+680km = 4 fold ambiguity

  • Ambiguities as multiples of code length “unwrap” from a zenith reflection to the Earth limb where the direct and reflected signal paths are equal

Earth limb

15

CYGNSS TIM


Jason tye prof craig underwood surrey space centre university of surrey uk

Direct Signal Overlay

  • 30 chip wide window of bad data during ambiguity unwinding

  • Simple analysis using spherical Earth approximation

16

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Direct Signal Overlay

GPS PRN 15 from R102, 1s

SBAS PRN 134 from R7, 200ms

  • Direct signal travels through the DDM over the collection period due to vRx

  • Direct signal more prominent over short incoherent integration periods

  • Effect was noted in GPS-R DDMs from UK-DMC also

17

CYGNSS TIM


Jason tye prof craig underwood surrey space centre university of surrey uk

Direct Signal Overlay

Delay (Chips)

  • Direct signal offset from predicted reflection at

    139.86 - 141.19 µs – Verified

  • -20 chip signal is a land reflection

    • Would expect negative delay as land is above Geoid

Doppler (Hz)

18

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Direct Signal Overlay Conclusions

  • The direct signal is picked up in the UK-DMC nadir antenna

    • Direct signal may regularly overlay reflected signals in DDM

  • Appearance of direct signal could potentially affect DDM inversion – depending on method

  • Direct and Reflected signals have different dynamics in DDM

    • Direct signal attenuated if longer integration times used

  • An automated geometry check could flag potential risks to data quality owing to direct signal overlay

  • One could envisage that channel allocation might take this effect into account if quantified appropriately

19

SBAS Reflectometry, SPACE REFLECTO 2013


Jason tye prof craig underwood surrey space centre university of surrey uk

Thank You for Listening!

20

SBAS Reflectometry, SPACE REFLECTO 2013


  • Login