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The motivation: Detection of different Ionosphere gradients, which cause different ionospheric delays in aviation applications (GBAS) The objectives: First, estimate the airborne and ground ionospheric delays and second, monitor the ionospheric. Bias between both estimates and compare it to a threshold The contribution: Present a GBAS Ionospheric monitor monitor that allows to estimate the ionospheric differential delay without moving to a whole Dual-Frequency GBAS concept.
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Ionosphere monitoring in GBAS usingdual frequency GNSS measurements
Joan Erencia Guerrero
Supervisors:Thomas Dautermann (DLR)Michael Felux (DLR)Gabriele Giorgi (TUM)
Satellite SubsystemSatellite Subsystem
Ionosphere monitoring in GBAS using DF measurementsINTRODUCTION
GBAS
differential GNSS
approach and landing
Airborne SubsystemAirborne Subsystem
Ground SubsystemGround Subsystem
Aviation Benefits:
Safety, efficiency, capacity and cost
2
Outline
1. Motivation, objectives and contribution
2. Theory and methods
3. Results
4. Conclusions and future work
3
Ionosphere monitoring in GBAS using DF measurementsMOTIVATION
4
Time [s]
Ion
os
ph
eric
del
ay [
m]
Ionosphere ๐ฐ ๐ฎ๐ต๐ซ๐ฐ ๐จ๐ฐ๐น
Nominal Ionosphere No biases
Similar trends(No ionospheric events)
Ionosphere monitoring in GBAS using DF measurementsMOTIVATION
5
Time [s]
Ion
os
ph
eric
del
ay [
m]
๐ฐ ๐ฎ๐ต๐ซ๐ฐ ๐จ๐ฐ๐น
1. Ionospheric spatial gradient
Ionosphere
bias
Initial bias
Ionosphere monitoring in GBAS using DF measurementsMOTIVATION
6
Time [s]
Ion
os
ph
eric
del
ay [
m]
๐ฐ ๐ฎ๐ต๐ซ๐ฐ ๐จ๐ฐ๐น
2. Ionospheric temporal gradient Converging trend during approach(ionospheric gradient stationary or not moving w/airplane)
๐ฐ ๐ฎ๐ต๐ซ๐ฐ ๐จ๐ฐ๐น
Ionosphere monitoring in GBAS using DF measurementsMOTIVATION
7
Time [s]
Ion
os
ph
eric
del
ay [
m]
3. Ionospheric moving gradient Bias constant during approach(ionospheric gradient moving w/airplane speed and direction)
Ionosphere monitoring in GBAS using DF measurementsOBJECTIVES
Estimate
OBJECTIVE 1
8
Monitor
OBJECTIVE 2
Monitor ionospheric differential delay between Airborne and Ground
Time [s]
Ion
osp
her
ic d
elay
[m
]
Time [s]Io
no
sph
eric
Dif
f. d
elay
[m
]
Threshold
Ionosphere monitoring in GBAS using DF measurementsMOTIVATION, OBJECTIVES AND CONTRIBUTION
1. Ionospheric spatial gradient initial bias
2. Ionospheric temporal gradient trend over time
3. Ionospheric gradient moving w/ airplane bias, no trend
1. Estimate GBAS subsystems ionospheric delays (,)
2. Monitor ionospheric differential bias
OBJECTIVES
All ionospheric gradients cannot be detected with single-frequency GNSS.
The proposed ionospheric monitor estimates the ionospheric differential delay without moving to a whole Dual-Frequency GBAS concept.
CONTRIBUTION
MOTIVATION
9
Outline
1. Motivation, objectives and contribution
2. Theory and methods
3. Results
4. Conclusions
10
Ionosphere monitoring in GBAS using DF measurements
Estimate
OBJECTIVE 1
๐ฐ ๐ฎ๐
๐ฐ ๐ฎ๐๐ฐ ๐ฎ๐
๐ฐ ๐จ๐ฐ๐น
1.1. Estimate the ionospheric delay for a receiver
1.2. Estimate the ionospheric delay for each SS
11
Time [s]
Ion
osp
her
ic d
elay
[m
] ๐ฐ ๐จ๐ฐ๐น๐ฐ ๐ฎ๐๐ฐ ๐ฎ๐๐ฐ ๐ฎ๐
Using Pseudorange measurements (C1โP2)
Ionosphere monitoring in GBAS using DF measurements THEORY
Estimate the ionospheric delay for a single receiverGeometry-free ionosphere preserving lin.comb.
OBJECTIVE 1
๐ฉ๐
12
๐๐
Frequency
dependent
1.1. Single rx
๐ฐ ๐๐ณ๐ฐ ๐ +ยฟ +ยฟยฟ
Using Carrier phase measurements (L1โL2)
Ionosphere monitoring in GBAS using DF measurements THEORY
13
Estimate the ionospheric delay for a single receiver Geometry-free ionosphere preserving lin.comb.
Frequency
dependent
๐ฉ๐ฝ ๐๐ฝ
OBJECTIVE 1
1.1. Single rx
๐ณ๐ฐ๐ฝ +ยฟ +ยฟยฟ๐ฐ๐ฝ ๐๐ฝ๐ต๐ฝ+ยฟ
Ionosphere monitoring in GBAS using DF measurements THEORY
Code noise
Code bias
14
Ionospheric delay* (*using GIM)
Phase bias
+
Estimate the ionospheric delay for a single receiver Geometry-free ionosphere-preserving lin.comb.
OBJECTIVE 1
1.1. Single rx
๐ฟ๐ฝ๐ณ ๐ฐ๐
๐ฟ๐ ๐ณ๐ฐ ๐
๐ฐ๐๐
(Phase-based approach)(Code-based approach)
1. Reduce code noise 2. Estimate biases
Ionosphere monitoring in GBAS using DF measurements THEORY
15
LPF๐๐๐
๐ฝ๐๐
๐๐๐, ๐๐๐
(๐=๐๐๐๐ )(๐=๐๐๐๐ )(๐=๐๐๐๐ )
๐ณ ๐ฐ ๐=๐
๐โ๐ ๐๐
๐ ๐๐
(๐๐โ ๐๐ )
๐ณ ๐ฐ๐=๐
๐โ๐ ๐๐
๐ ๐๐
(๐๐๐๐โ๐๐๐๐)
ยฟ๐๐๐
ยฟ๐ฝ๐๐
Estimate the ionospheric delay for a single receiver Reduce code noise
OBJECTIVE 1
1.1. Single rx
๐ฟ๐ฝ๐ณ ๐ฐ๐
๐ฟ๐ ๐ณ๐ฐ ๐
๐ฐ๐๐
๐ฟ๐ฝ๐ณ ๐ฐ๐
๐ฟ๐ ๐ณ๐ฐ ๐ , ๐๐๐
๐ฐ๐๐
Ionosphere monitoring in GBAS using DF measurements THEORY
16
Estimate the ionospheric delay for a single receiver Estimate biases
๐ฉ๐๐ฝ
OBJECTIVE 1
Remember the bias to be estimated:
Using the code-phase differential bias
Estimating the biases now will involve:
1. Estimate code biases
2. Estimate differential bias
1.1. Single rx
๐ฉ๐
Ionosphere monitoring in GBAS using DF measurements THEORY
17
Estimate the ionospheric delay for a single receiver Estimate code biases ()
OBJECTIVE 1
Estimate code biases
, are constant over 24h[1]
i. are obtained from IONEX files
ii. are calibrated using GIM
Sv IFB
1.1. Single rx
Rx IFB
Sv IFB๐ฉ๐
Rx IFB
[1] Sardon et al, โEstimation of the transmitter and receiver differential biases and the ionospheric total electron content from global positioning system observationsโ
๐ฟ๐ฝ๐ณ ๐ฐ๐
๐ฟ๐ ๐ณ๐ฐ ๐ , ๐๐๐
๐ฐ๐๐
Estimate the ionospheric delay for a single receiver Estimate phase bias
Ionosphere monitoring in GBAS using DF measurements THEORY
18
OBJECTIVE 1
1.1. Single rx
๐ฉ๐๐ฝ
๐ฉ๐๐ฟ๐ฝ๐ณ ๐ฐ๐
๐ฟ๐ ๐ณ๐ฐ ๐ , ๐๐๐
๐ฐ๐๐
Estimate differential bias
1. Wait smoothing time in order to use the
code-smoothed estimate
2. Compute code-phase differential bias:
3. Indirect estimation of phase bias as:
Estimate the ionospheric delay for a single receiver Summary of the method
Ionosphere monitoring in GBAS using DF measurements THEORY
19
OBJECTIVE 1
1.1. Single rx
๐ฟ๐ฝ๐ณ ๐ฐ๐
๐ฟ๐ ๐ณ๐ฐ ๐
๐ฐ๐๐
๐ฟ๐ฝ๐ณ ๐ฐ๐
๐ฟ๐ ๐ณ๐ฐ ๐
๐ฐ๐๐
Rx IFB
Sv IFB๐ฉ๐
๐ฉ๐๐ฝ
Ionospheric delay estimates
1. Geo-free iono-preserving:
2. Code-noise smoothing (LPF)
3. Code biases
i. with from IONEX, from GIM.
4. Bias estimate
i. with
Code estimate:
Phase estimate:
Ionosphere monitoring in GBAS using DF measurements
Estimate
OBJECTIVE 1
20
1.1. Estimate the ionospheric delay for a receiver
1.2. Estimate the ionospheric delay for each SS
๐ฐ ๐จ๐ฐ๐น
Time [s]
Ion
osp
her
ic d
elay
[m
] ๐ฐ ๐จ๐ฐ๐น๐ฐ ๐ฎ๐ต๐ซ
๐ฐ ๐ฎ๐ต๐ซ
Ground SubsystemGround Subsystem
BR01 BR02 BR03
Airborne SubsystemAirborne Subsystem
AIRB
Ionosphere monitoring in GBAS using DF measurements THEORY
21
Estimate the ionospheric delay for each SS
Average ground ionospheric delay estimates
OBJECTIVE 1
1.2.
Code-phase approach Phase-based approach
๐ฐ ๐ฎ๐ต๐ซ ,๐=๐๐ต โ
๐=๐
๐
๐ฐ๐ ๐ ,๐๐๐ ( ๐ )๐ฐ ๐ฎ๐ต๐ซ ,๐ฝ= ๐๐ต โ
๐=๐
๐
๐ฐ๐๐ฝ ,๐๐๐ ( ๐ )
๐ฐ ๐จ๐ฐ๐น ,๐ฝ=๐ฐ๐๐ฝ ,๐๐ข๐ซSingle receiver estimateSingle receiver estimate
๐ฐ ๐จ๐ฐ๐น ,๐=๐ฐ๐๐ ,๐๐ข๐ซ
Average over Ground station receiver estimates
Average over Ground station receiver estimates
1.1. Estimate the ionospheric delay for a receiver
1.2. Estimate the ionospheric delay for each SS
Ionosphere monitoring in GBAS using DF measurements
Estimate
OBJECTIVE 1
22
๐ฐ ๐ฎ๐
๐ฐ ๐ฎ๐๐ฐ ๐ฎ๐
๐ฐ ๐จ๐ฐ๐น
Time [s]
Ion
osp
her
ic d
elay
[m
] ๐ฐ ๐จ๐ฐ๐น๐ฐ ๐ฎ๐๐ฐ ๐ฎ๐๐ฐ ๐ฎ๐
๐ฐ ๐ฎ๐ต๐ซ
๐ฐ ๐ฎ๐ต๐ซ
Ionosphere monitoring in GBAS using DF measurements23
Monitor
OBJECTIVE 2
๐ฐ ๐จ๐ฐ๐น
๐ฐ ๐ฎ๐ต๐ซ
2.1. Compute the ionospheric alarm threshold
2.2. Estimate the ionospheric differential delay
Time [s]
Ion
osp
her
ic d
elay
[m
] ๐ป๐๐๐๐๐๐๐๐
Monitor Compute the ionospheric alarm threshold
OBJECTIVE 2
Ionosphere monitoring in GBAS using DF measurements THEORY
24
2.1. Threshold
An ionospheric gradient of
is considered dangerous[2]
Near airport :
Far airport :๐ ๐จ๐ฐ๐นโ๐ฎ๐ต๐ซ
๐ฐ ๐จ๐ฐ๐น
๐ฐ ๐ฎ๐ต๐ซ
[2] โGBAS CAT II/III Development Baseline SARPs,
Ionosphere monitoring in GBAS using DF measurements25
Monitor
OBJECTIVE 2
๐ฐ ๐จ๐ฐ๐น
๐ฐ ๐ฎ๐ต๐ซ
2.1. Compute the ionospheric alarm threshold
2.2. Estimate the ionospheric differential delay
Time [s]
Ion
osp
her
ic d
elay
[m
] ๐ฐ ๐จ๐ฐ๐น๐ฐ ๐ฎ๐ต๐ซ
๐ฐ ๐ซ๐ซ= ๐ฐ ๐จ๐ฐ๐นโ ๐ฐ๐ฎ๐ต๐ซ
๐ฐ ๐ฎ๐ต๐ซ
๐ฐ ๐จ๐ฐ๐น
Ionosphere monitoring in GBAS using DF measurements THEORY
26
Monitor
Estimate the ionospheric differential delay
OBJECTIVE 2
2.2.
Code-phase approach Phase-based approach
๐ฐ๐ซ ๐ซ๐=๐ฐ ๐จ๐ฐ๐น ,๐โ ๐ฐ๐ฎ๐ต๐ซ ,๐๐ฐ๐ซ ๐ซ๐ฝ=๐ฐ ๐จ๐ฐ๐น ,๐ฝโ ๐ฐ๐ฎ๐ต๐ซ ,๐ฝ
๐ผ๐บ๐๐ท ,๐=1๐โ
๐=1
3
๐ผ 1๐ ,๐๐๐ ( ๐ )
with:๐ผ๐บ๐๐ท , ฮฆ=
1๐โ
๐=1
3
๐ผ 1ฮฆ,๐๐๐ ( ๐ )
with:
Ionosphere monitoring in GBAS using DF measurements27
Monitor
OBJECTIVE 2
๐ฐ ๐จ๐ฐ๐น
๐ฐ ๐ฎ๐ต๐ซ
2.1. Compute the ionospheric alarm threshold
2.2. Estimate the ionospheric differential delay
Time [s]
Ion
osp
her
ic d
elay
[m
]
๐ป๐๐๐๐๐๐๐๐ ๐ฐ ๐ซ๐ซ= ๐ฐ ๐จ๐ฐ๐นโ ๐ฐ๐ฎ๐ต๐ซ
Outline
1. Motivation, objectives and contribution
2. Theory and methods
3. Results
4. Conclusions and future work
28
Ionosphere monitoring in GBAS using DF measurements RESULTS
GROUND SUBSYSTEM AIRBORNE SUBSYSTEM
Monitor performance
1. Smoothing2. Elevation3. Distance to airport4. Cycle slips5. User dynamics
29
GNSS RX
RWY
Ionosphere monitoring in GBAS using DF measurements RESULTS
30
Code-based Monitor performance using different smoothing constant
๐ฐ๐ซ ๐ซ๐=๐ฐ ๐จ๐ฐ๐น ,๐โ ๐ฐ๐ฎ๐ต๐ซ ,๐
๐ผ๐บ๐๐ท ,๐=1๐โ
๐=1
3
๐ผ 1๐ ,๐๐๐ ( ๐ )
with:
Residual noise:
Caused by code noise
Reduced with larger
smoothing constants
Ionosphere monitoring in GBAS using DF measurements RESULTS
31
Phase-based monitor performance using different smoothing constant
๐ผ๐บ๐๐ท , ฮฆ=1๐โ
๐=1
3
๐ผ 1ฮฆ,๐๐๐ ( ๐ )
with:
Initialization bias error:
Caused by estimate
Reduced with larger
smoothing constants
๐ฐ๐ซ ๐ซ๐ฝ=๐ฐ ๐จ๐ฐ๐น ,๐ฝโ ๐ฐ๐ฎ๐ต๐ซ ,๐ฝ
Ionosphere monitoring in GBAS using DF measurements RESULTS
32
Monitor performance considering the user dynamics
GNSS RX
Ionosphere monitoring in GBAS using DF measurements RESULTS
33
Monitor performance considering the user dynamics
Phase-based approach (red)
Jumps in the estimates.
No line-of-sight during turns for a
satellite with low elevation.Bias in the iono. estimates
Code-based approach (blue)
Large noise/MP in some epochs
Problem in smoothing code-based
estimate due to phase jumps
Bad trend in the filter initialization
Measure Waiting after losing
phase measurements
๐ฟ๐
Outline
1. Motivation, objectives and contribution
2. Theory and methods
3. Results
4. Conclusions and future work
34
Ionosphere monitoring in GBAS using DF measurements
๐ฐ ๐ฎ๐ต๐ซ๐ฐ ๐จ๐ฐ๐น
Monitor ionospheric differential delay
between Airborne and Ground subsystems
Time [s]
Ion
os
ph
eric
del
ay [
m]
Time [s]Io
no
sp
her
ic D
iff.
del
ay [
m]
Threshold
35
Ionosphere monitoring in GBAS using DF measurements CONCLUSIONS
36
If this ionospheric monitor were to be implemented:
1. Frequency-dependent biases monitoring To meet integrity requirements, the esimation of biases should be
monitored
2. Ground Subsystem implementation of the monitorEstimation of ground ionospheric delay and broadcast to service area
3. Airborne Subsystem implementation of the monitor Estimation of airborne ionospheric delay
Alarm threshold computation
Ionospheric differential delay, based on estimates
4. Short-term and long-term ionosphere monitoringStorage of monitor data results during approaches.
Characterization of Iono for a certain airport for certain time series (years)
Ionosphere monitoring in GBAS using DF measurements FUTURE WORK
37
Future work would include:
1. Assessing monitor performance using L1-L5 signals L1 โ L5 bands will be used for Safety-of-Life application
Noise in these signals is uncorrelated
2. Monitor verification using data with iono events
Performance of the monitor with the different ionospheric gradients
Effects of signal scintillation on the monitor
3. Statistical study
It is presented a concept for iono. monitoring using two frequencies
The use of this monitor would require a study to describe ,...
Ionosphere monitoring in GBAS using DF measurements
๐ฐ ๐ฎ๐ต๐ซ๐ฐ ๐จ๐ฐ๐น
Thank you for your attention
Questions?
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