Master Thesis Final Presentation: Ionosphere monitoring in GBAS using Dual Frequency GNSS measurements

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 𝑰 𝑮𝑵𝑫𝑰 𝑨𝑰𝑹

Nominal Ionosphere No biases

Similar trends(No ionospheric events)


5

Time [s]

Ion

os

ph

eric

del

ay [

m]

𝑰 𝑮𝑵𝑫𝑰 𝑨𝑰𝑹

1. Ionospheric spatial gradient

Ionosphere

bias

Initial bias


6

Time [s]

Ion

os

ph

eric

del

ay [

m]


2. Ionospheric temporal gradient Converging trend during approach(ionospheric gradient stationary or not moving w/airplane)



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



3. Results

4. Conclusions

10

Ionosphere monitoring in GBAS using DF measurements

Estimate

OBJECTIVE 1

𝑰 𝑮𝟐

𝑰 𝑮𝟑𝑰 𝑮𝟏

𝑰 𝑨𝑰𝑹

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

] 𝑰 𝑨𝑰𝑹𝑰 𝑮𝟏𝑰 𝑮𝟐𝑰 𝑮𝟑

Using Pseudorange measurements (C1–P2)

Ionosphere monitoring in GBAS using DF measurements THEORY

Estimate the ionospheric delay for a single receiverGeometry-free ionosphere preserving lin.comb.

OBJECTIVE 1

𝑩𝝆

12

𝝃𝝆

Frequency

dependent

1.1. Single rx

𝑰 𝝆𝑳𝑰 𝝆 +¿ +¿¿

Using Carrier phase measurements (L1–L2)


13

Estimate the ionospheric delay for a single receiver Geometry-free ionosphere preserving lin.comb.

Frequency

dependent

𝑩𝚽 𝝃𝚽

OBJECTIVE 1

1.1. Single rx

𝑳𝑰𝚽 +¿ +¿¿𝑰𝚽 𝝀𝚽𝑵𝚽+¿


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

𝜿𝚽𝑳 𝑰𝝓

𝜿𝝆 𝑳𝑰 𝝆

𝑰𝒐𝒏

(Phase-based approach)(Code-based approach)

1. Reduce code noise 2. Estimate biases


15

LPF𝝆𝟏𝟐

𝚽𝟏𝟐

𝝆𝟏𝟐, 𝒔𝒎𝒕

(𝝉=𝟔𝟎𝟎𝒔 )(𝝉=𝟑𝟎𝟎𝒔 )(𝝉=𝟏𝟎𝟎𝒔 )

𝑳 𝑰 𝝆=𝟏

𝟏−𝒇 𝟏𝟐

𝒇 𝟐𝟐

(𝝆𝟏− 𝝆𝟐 )

𝑳 𝑰𝝓=𝟏

𝟏−𝒇 𝟏𝟐

𝒇 𝟐𝟐

(𝝀𝟏𝝓𝟏−𝝀𝟐𝝓𝟐)

¿𝝆𝟏𝟐

¿𝚽𝟏𝟐

Estimate the ionospheric delay for a single receiver Reduce code noise

OBJECTIVE 1

1.1. Single rx



𝑰𝒐𝒏


𝜿𝝆 𝑳𝑰 𝝆 , 𝒔𝒎𝒕

𝑰𝒐𝒏


16

Estimate the ionospheric delay for a single receiver Estimate biases

𝑩𝝆𝚽

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

𝑩𝝆


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 IFB𝑩𝝆

Rx IFB

[1] Sardon et al, “Estimation of the transmitter and receiver differential biases and the ionospheric total electron content from global positioning system observations”



𝑰𝒐𝒏

Estimate the ionospheric delay for a single receiver Estimate phase bias


18

OBJECTIVE 1

1.1. Single rx

𝑩𝝆𝚽

𝑩𝝆𝜿𝚽𝑳 𝑰𝝓


𝑰𝒐𝒏

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


19

OBJECTIVE 1

1.1. Single rx



𝑰𝒐𝒏



𝑰𝒐𝒏

Rx IFB

Sv IFB𝑩𝝆

𝑩𝝆𝚽

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:


Estimate

OBJECTIVE 1

20



𝑰 𝑨𝑰𝑹

Time [s]

Ion

osp

her

ic d

elay

[m

] 𝑰 𝑨𝑰𝑹𝑰 𝑮𝑵𝑫

𝑰 𝑮𝑵𝑫

Ground SubsystemGround Subsystem

BR01 BR02 BR03

Airborne SubsystemAirborne Subsystem

AIRB


21

Estimate the ionospheric delay for each SS

Average ground ionospheric delay estimates

OBJECTIVE 1

1.2.

Code-phase approach Phase-based approach

𝑰 𝑮𝑵𝑫 ,𝝆=𝟏𝑵 ∑

𝒋=𝟏

𝟑

𝑰𝟏 𝝆 ,𝒈𝒏𝒅 ( 𝒋 )𝑰 𝑮𝑵𝑫 ,𝚽= 𝟏𝑵 ∑

𝒋=𝟏

𝟑

𝑰𝟏𝚽 ,𝒈𝒏𝒅 ( 𝒋 )

𝑰 𝑨𝑰𝑹 ,𝚽=𝑰𝟏𝚽 ,𝐚𝐢𝐫Single receiver estimateSingle receiver estimate

𝑰 𝑨𝑰𝑹 ,𝝆=𝑰𝟏𝝆 ,𝐚𝐢𝐫

Average over Ground station receiver estimates

Average over Ground station receiver estimates




Estimate

OBJECTIVE 1

22

𝑰 𝑮𝟐

𝑰 𝑮𝟑𝑰 𝑮𝟏

𝑰 𝑨𝑰𝑹

Time [s]

Ion

osp

her

ic d

elay

[m

] 𝑰 𝑨𝑰𝑹𝑰 𝑮𝟏𝑰 𝑮𝟐𝑰 𝑮𝟑

𝑰 𝑮𝑵𝑫

𝑰 𝑮𝑵𝑫

Ionosphere monitoring in GBAS using DF measurements23

Monitor

OBJECTIVE 2

𝑰 𝑨𝑰𝑹

𝑰 𝑮𝑵𝑫

2.1. Compute the ionospheric alarm threshold

2.2. Estimate the ionospheric differential delay

Time [s]

Ion

osp

her

ic d

elay

[m

] 𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅

Monitor Compute the ionospheric alarm threshold

OBJECTIVE 2


24

2.1. Threshold

An ionospheric gradient of

is considered dangerous[2]

Near airport :

Far airport :𝒅𝑨𝑰𝑹−𝑮𝑵𝑫

𝑰 𝑨𝑰𝑹

𝑰 𝑮𝑵𝑫

[2] “GBAS CAT II/III Development Baseline SARPs,


Monitor

OBJECTIVE 2

𝑰 𝑨𝑰𝑹

𝑰 𝑮𝑵𝑫



Time [s]

Ion

osp

her

ic d

elay

[m

] 𝑰 𝑨𝑰𝑹𝑰 𝑮𝑵𝑫

𝑰 𝑫𝑫= 𝑰 𝑨𝑰𝑹− 𝑰𝑮𝑵𝑫

𝑰 𝑮𝑵𝑫

𝑰 𝑨𝑰𝑹


26

Monitor

Estimate the ionospheric differential delay

OBJECTIVE 2

2.2.

Code-phase approach Phase-based approach

𝑰𝑫 𝑫𝝆=𝑰 𝑨𝑰𝑹 ,𝝆− 𝑰𝑮𝑵𝑫 ,𝝆𝑰𝑫 𝑫𝚽=𝑰 𝑨𝑰𝑹 ,𝚽− 𝑰𝑮𝑵𝑫 ,𝚽

𝐼𝐺𝑁𝐷 ,𝜌=1𝑁∑

𝑗=1

3

𝐼 1𝜌 ,𝑔𝑛𝑑 ( 𝑗 )

with:𝐼𝐺𝑁𝐷 , Φ=

1𝑁∑

𝑗=1

3

𝐼 1Φ,𝑔𝑛𝑑 ( 𝑗 )

with:


Monitor

OBJECTIVE 2

𝑰 𝑨𝑰𝑹

𝑰 𝑮𝑵𝑫



Time [s]

Ion

osp

her

ic d

elay

[m

]

𝑻𝒉𝒓𝒆𝒔𝒉𝒐𝒍𝒅𝑰 𝑫𝑫= 𝑰 𝑨𝑰𝑹− 𝑰𝑮𝑵𝑫

Outline



3. Results


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


30

Code-based Monitor performance using different smoothing constant

𝑰𝑫 𝑫𝝆=𝑰 𝑨𝑰𝑹 ,𝝆− 𝑰𝑮𝑵𝑫 ,𝝆

𝐼𝐺𝑁𝐷 ,𝜌=1𝑁∑

𝑗=1

3

𝐼 1𝜌 ,𝑔𝑛𝑑 ( 𝑗 )

with:

Residual noise:

Caused by code noise

Reduced with larger

smoothing constants


31

Phase-based monitor performance using different smoothing constant

𝐼𝐺𝑁𝐷 , Φ=1𝑁∑

𝑗=1

3

𝐼 1Φ,𝑔𝑛𝑑 ( 𝑗 )

with:

Initialization bias error:

Caused by estimate

Reduced with larger

smoothing constants

𝑰𝑫 𝑫𝚽=𝑰 𝑨𝑰𝑹 ,𝚽− 𝑰𝑮𝑵𝑫 ,𝚽


32

Monitor performance considering the user dynamics

GNSS RX


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

𝜿𝝉

Outline



3. Results


34



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 – 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 ,...



Thank you for your attention

Questions?

Technology

Master Thesis Final Presentation: Ionosphere monitoring in GBAS using Dual Frequency GNSS measurements