Transcript SW service for GNSS

On developing space weather services
for the end users of GNSS
N. Jakowski
German Aerospace Center (DLR),
Institute of Communications and Navigation, Neustrelitz,
Germany
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OUTLINE
Introduction
Space weather impact on GNSS
Monitoring the ionosphere for
establishing a space weather service
Ground based
Space based
Data processing & service provision
Service data use
Conclusions
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Space Weather Environment
GNSS satellite
Space weather impacts the functionality of Global Navigation Satellite Systems (GNSS) by
damaging transmitting satellites and/or degrading the GNSS signals travelling through
the ionized part of the Earth‘s atmosphere (ionosphere/plasmasphere) to the user.
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Plasma Environment Control
¬¬¬¬¬¬
0.5
1.0
1.5 1012m-3
Electron density
ne
Structure and dynamics of the ionosphere/plasmasphere are strongly controled by the
solar radiation and the solar wind and coupled with other geo-spheres such as the
magnetosphere, thermosphere, lower atmosphere, hydro- and lithosphere
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Ionospheric impact on navigation and positioning
Dual frequency measurements
enable estimating the
Total Electron Content (TEC)
TEC   ne ds
GPS/GALILEO
s
ne
TECV
1st order
ionospheric
range error
Is ~ TEC
Reference
station
Motion of gradients
v
Ionospheric
irregularities
Signal strength fluctuations
availability and safety reduced
User Phase errors
Misleading
Corrections
DGPS
Ionospheric gradients
User
Single point user
Ionospheric scintillations
Ionospheric perturbations will also impact GALILEO
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Storm on 29 October 2003 / Polar TEC
Polar TEC on
29 October
2003 derived
from IGS
ground based
measurements
Map resolution
Time: 10 min
Latitude: 2.5 deg
Longitude: 7.5 deg
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Space weather event on 29 October 2003
WAAS service interrupted in US; GPS receiver outages Finland, Netherlands
Military communications impacted (HF/UHF SATCOM)/OTH
Loran C station in Newfoundland had interference.
network performance
Begin
GPS-service
outage
Polar TEC
06 UT
07 UT
09 UT
10 UT
08 UT
11 UT
Tracked
Processed
Solved
UT
Jakowski, N., Stankov, S.M., Klaehn, D., Schlueter, S., Beniguel, Y., Rueffer, J. (2004): Operational
service for monitoring and evaluating the space weather impact on precise positioning. Proc. European
Navigation Conference GNSS-2004, 16-19 May 2004, Rotterdam, The Netherlands
The storm develops at high latitudes
already before noon indicating the
potential of forecasting
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SW problem at user level
Ionosphere impact
Phase ambiguity fixing is not possible
if signal perturbation exceeds the
error bounds
→ No solution at user level achieved
Ionosphere
model
Time to fix / sec
Real
signal
GNSS
perturbation
of precise
positioning
User
Reference
station
Correction from
GNSS service
provider
Reference
station
Local time / hrs
Fixing time at user level to solve phase ambiguities may increase to hours, i.e. practically no high
precision solution achieved within this time, i.e. correction information cannot be provided to users
Measurement must be repeated
→ user refuses to pay
→ economical loss
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Ionospheric scintillations
0,50
30/10/03
PRN 24
0,40
0,30
s4
sigma phi
0,20
0,10
6,94
6,52
6,12
5,72
5,32
4,92
4,52
4,12
3,72
3,32
2,89
0,00
Allsat GmbH reports
about 25% loss of data
due to ionospheric
perturbations in Jemen
Small scale ionospheric
irregularities of plasma
density (turbulences,
bubbles) cause interfering
rays
This leads to a high
variability of GNSS signal
strength
(radio scintillations)
Severe scintillations cause
problems in signal use or
even loss of lock (no signal
availability)
Regions where
scintillations most
frequently occur:
high latitudes
low latitudes
Time (hour)
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Space Weather Impact on Network Monitoring Integrity
on 25 July 2004
Performance of the GPS
Reference network of Allsat
GmbH Hannover degrades
during the ionospheric storm
on 25 July 2004
Different effects in different
network areas over Germany
 Propagation of perturbation from
high to mid-latitudes
SWACI product: TEC rate
NW
MW
SW
1X1 deg grid resolution
16:30 UT
NW
MW
Provision of ionospheric now- and
forecast information to users
 Information to European users via
the Space Weather European
Network (SWENET)
SW
19:00 UT
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Solar flare effect on 28 October 2003 over Europe - TECrel
Strong solar flare on
28 October 2003
at 11:05 UT
Total irradiance of the
sun enhanced within a
few minutes by 267 ppm
TEC data processing
indicates loss of data at
numerous GPS links
The number of usable
GPS links for TEC
processing was reduced
rapidly from more than
30 to only 7
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Latitudinal dependency of the flare induced TEC jump
on 28 October 2003
Strong latitudinal
dependency of
the height of the
TEC jump
observed,
up to 20 TECU or
3.2 m at L1 !
The CME
associated with this
flare is larger than
the Sun itself
causing strong
perturbations after
reaching the Earth
on 29/30 October
2003
Jakowski N., B. Fichtelmann, and A. Jungstand,
Solar activity control of ionospheric and
thermospheric processes, J. Atmos. Terr. Phys., 53,
1125-1130, 1991
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Correction of nonlinear refraction effects in
precise positioning applications
True Range

Plasmasphere
R
L
measurement
  (n  1)ds
 sB
TX
S
phase delay
ray path
error
Ionosphere
bending error
2nd order error
magnetoionic
Linear error ~TEC


RX
s2   y1 cos   r  y sin   2r2 cos    TEC
2
1
2
1
2
B
User
TEC map
O
Ionospheric data
service can
provide input
data for higher
order corrections
for precise
positioning
applications
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Ground and space based monitoring by GNSS
Monitoring of the Ionosphere by:
- GNSS Ground stations
1
CHAMP
1
2
3
DLR: over a full solar cycle
since 1995
Europe
North pole area
South pole area
- LEO Satellites carrying GNSS
receivers onboard
DLR: CHAMP
(GRACE, TerraSAR-X)
Radio occultation
Topside reconstruction
2
3
- Non-GNSS based techniques
e.g. : vertical sounding network
(DIAS), in situ measurements on
spacecrafts
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10 se
(LI
NK
Occulting GPS Neutral atmosphere
se
c
(L
IN
K
GPS Sat.
4)
Earth
20 msec
data
(
LIN
K
Neutral atmosphere
Ground
receiver
1)
2)
Ionosphere
da
ta
10 sec da
ta
Occulting LEO
K
IN
(L
Ground
receiver1-
GPS Sat.
ta
da
1-s
ec
da
ta
4)
GPS Sat.
10 sec
data
3)
GPS sounding of the Ionosphere
onboard CHAMP
10
(L
IN
K
c
se
m
10 sec da
ta
g LEO
GPS Sat.
a
at
d
c
se
20
ta
a
cd
e
s
1)
2)
Ionosphere
GPS Sat.
LIN
K
K
LIN
da
ta
20 msec
data
(
a(
0
1se
c
10
a
at
d
c
se
10 sec da
ta
Occulting LEO
GPS Sat.
GPS Satellite
Earth
Radio Signal
CHAMP Orbit
CHAMP
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SWACI products – Space based measurements (CHAMP)
Ionospheric Radio occultation (IRO)
Assimilation of GPS measurements into a model
Automatic retrieval of vertical
Operational reconstruction of the
electron density profiles
electron density in the plane of the
(up to 150 profiles per day)
CHAMP revolution (15-16 3D maps/day)
Jakowski, N. Wehrenpfennig, A., Heise, S., Reigber, C. and Lühr, H., GPS
Radio Occultation Measurements of the Ionosphere on CHAMP: Early Results,
Geophysical Research Letters, 29, No. 10, 10.1029/2001GL014364, 2002b
Heise, S., Jakowski, N., Wehrenpfennig, A., Reigber, C., Lühr, H., Sounding of the Topside
Ionosphere/Plasmasphere Based on GPS Measurements from CHAMP: Initial Results,
Geophysical Research Letters, 29, No. 14, 10.1029/2002GL014738, 2002
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Local / regional / global monitoring of the ionosphere
Reconstruction of regional AND global ionosphere needed for getting
reliable information, data assimilation methods
Global TEC map on 01/01/99 at 13:00 UT
Regional
transition region
Local
LBAS
Global TEC
Merging of local/regional
information with global
data sets needed for future
services
(external / internal)
Global data sets provide
optimal boundary
conditions for local
/regional reconstructions
Local/regional
reconstructions enable
highest accuracy
Global TEC map source: IGS, CODE, Bern
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DLR- infrastructure for SWACI- service development
http://w3swaci.dlr.de
SWACI is supported by the state
government of MecklenburgVorpommern
Follow-up project of the former ESA
supported SDA SWIPPA
GNSS data
LEO
Non-GNSS
data
GFZ
IAP
SEC
EVNet
COSMIC-Empfänger
NTrip: Javad /
RTCM-RTK Data
IGS
Ascos
SAPOS
SWACI
EUREF
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SWACI - web portal (http://w3swaci.dlr.de)
Different types of
users
Consortium
partners
Commercial
Non-Commercial
Public
Ground based
data update:
5 minutes
Space based
data update
according to the
data dumps from
CHAMP
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Space Weather service - GNSS user groups
machine control
Standard
service
Precise
Positioning
accuracy in m range
accuracy in (sub) cm range
Ionospheric
model, NRT
tourism
Space
Weather
Service
Accurate TEC, NRT,
forecasts
Ionospheric threats,
NRT, forecasts
Science
Highest accuracy of
physical parameters
requested
Accurate
reconstruction,
post processing
Safety of
Life
Highest priority: system
mut operate within
system specification
MOPS: 99.99999 %
aviation
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Detection / monitoring of ionospheric threats
Definition of a proper
perturbation index on
international level
(e.g. COST 296 task
group has been
established)
Continuous computation
of regional perturbation
indices
Provision of the index
(indices) to users in near
real time streaming mode
The perturbation índex
must be easy to handle
for users and well suited
for forecasting
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Short Term Prediction of perturbations in the
Regional / Local Ionosphere
7 November 2004
High latitude latitudinal
gradient index is well
correlated with the
performance of GPS
reference networks
Systematic investigation
of relationships with
other space weather
parameters required
Development of a
prediction model
Transformation of
predicted ionospheric
parameters into user
terms
60°N
Perturbation
index
40°N
North-Germany
Network Monitoring
Integrity
Source: Allsat GmbH
Delayed
degradation of
the ascos
network
Potential for
prediction
Geomagnetic Index Dst
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Probability of ionospheric perturbations
(geomagnetically based)
Strong coupling
between
geomagnetic and
ionospheric storms
Geomagnetic indices
are choosen as a
preliminary indicator
Future: Ionospheric
perturbation index
should give a more
accurate information
for GNSS users
Degree of
perturbation
Kp
Number of events
from 1994-2004
Meteorological
phenomena
moderate
6
507
wind
severe
7
183
storm
very strong
8
41
thunderstorm
extreme
9
4
tornado
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Conclusions
Reliable now- and forecast services based on real-time ionosphere
monitoring / modeling and related space weather observations
(regional and global) are needed in the future, i.e. also for GALILEO.
Precise Positioning
SW services help to avoid useless efforts, e.g. repeating measurements,
mid-term forecasts (24 ahead helpful for planning work)
SW services helps to achieve high accuracy with less dense reference
networks (WARTK)
Accurate single point positioning possible by reducing the total error budget
(among them ionospheric errors)
Safety of Life (SoL) applications
SW service focuses on detection of integrity threats (moving ionization
fronts, bubbles)
SW services require reliable short term forecasts of threats
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