design of kompsat-6 polarimetric calibration system
TRANSCRIPT
Design of Kompsat-6 Polarimetric Calibration System
Dochul Yang*, Horyung Jeong, Dong Kim, Donghan Lee
S AR Im age , 백두산 Opt ica l Im age , 백두산
• K6 Mission & Characteristics
• K6 Calibration System
• K6 Multi-Polarimetric Calibration Subsystem
• K6 Calibration Equipment Development
K-6 Mission & Characteristics
K6 Mission
Objectives: Expedite provision of the space-borne SAR standard images with sub-meter resolution required for the national demand in GIS (Geographical Information Systems), Ocean & Land management, Disaster monitoring, and ENvironment monitoring
Mission Application: “GOLDEN”
• GIS : Acquisition of independent high resolution images
• Ocean & Land Management : Survey of natural resources
• Disaster & ENvironment Monitoring : Surveillance of large scale disasters and its countermeasure
Expected Launch Date: September, 2020
Life Time: 5 years
K6 Characteristics
SAR Payload
• Space-borne Synthetic Aperture Radar
• X-band radar with an active phased array antenna
• Implemented by four SAR modes
High Resolution A/B Modes : Sliding Spot
Standard Mode : Stripmap
Wide Swath Mode : TOPS
• Electrical steering capability in both azimuth and elevation planes
• Coherent Dual Polarization (HH+HV, VV+VH)
• Quad Polarization & ATI/GMTI as Experimental Modes
Imaging Operation Performance
Observation Mode
• High Resolution-A Mode (Spotlight) : 0.5 m resolution / 5 km swath
• High Resolution-B Mode (Spotlight) : 1 m resolution / 10 km swath
• Standard Mode (Stripmap) : 3 m resolution / 30 km swath
• Wide Swath Mode (TOPS) : 20 m resolution / 100 km swath
Incidence Angle Range
• 20 ~ 55 deg (nominal)
• 55 ~ 60 deg (extended)
Imaging Time
• Continuously 150 sec per orbit
Target Revisit Time
• 53 hours on average
K-6 Calibration System
K6 Cal. System Overview (1/2)
Functions
• Range & Azimuth Antenna Pointing Offset Measurement
• Geometric Range & Azimuth Offset Measurement using Point Target
• Product Coverage Location Error Measurement
• Antenna Pattern Verification
• Absolute Radiometric Calibration Factor Evaluation
• Polarimetric Effects (Channel Imbalance & Cross-Talk) Compensation
• Long-Term & Daily Calibration Image Scheduling
Subsystems
• PCS: Pointing Calibration Subsystem
• GCS: Geometric Calibration Subsystem
• RCS: Radiometric Calibration Subsystem
• MCS: Multi-polarimetric Calibration Subsystem
• CSS: Calibration Scheduling Subsystem
K6 Cal. System Overview (2/2)
Architecture
MCE IRPE CSS
Image Collection
Plan
RCS MCS GCS PCS
Level Product
IRPE
Ground CAL Target ( Amazon , AT, and CR .)
K 6 CE
Download SAR Science
Data (Image + Ancillary) Upload
CMD
Level
Product
Image Collection
Request
ATT & CMD
Time Offset
APLUT
AZCUT [TBD]
CALCO
Channel
Imbalance &
Cross-talk Azimuth & Range
Time Offset
Channel
Imbalance &
Cross-talk
APLUT
AZCUT [TBD]
CALCO
K-6 Multi-Polarimetric Calibration Subsystem
(MCS)
MCS Overview (1/4)
Function
• Compensate polarimetric distortions of SAR antenna
Measure cross-talk & channel imbalance of SAR antenna using images of Amazon rain forest, K6 Active Transponder (AT), and Corner Reflectors (CR)
Provide estimated polarimetric distortion information to K6 SAR Processor
Verify the estimated polarimetric distortion using AT or CR images
Methodologies
• Quad Pol. Calibration
Use three K6 AT (baseline)
Use Amazon rain forest and AT or CR (backup)
• Dual Pol. Calibration
Use three K6 AT and compensate receiving antenna distortions
• Verification Method
Use ATs and/or CR => Scattering Matrix 1 11 1
and 1 00 1
MCS Overview (2/4)
Procedure (1)
• Quad Pol. & three AT method
1) Calculate the peak points around three AT
imaged with quad pol.
2) Estimate antenna polarimetric distortions
(cross-talk and channel imbalance together)
using the ratios between peak points of
different ATs with different scattering matrix
3) Eliminate antenna polarimetric distortions from
point target (AT or CR) images
4) Verify the antenna distortion estimates by
measuring co-pol and cross-pol responses of
AT and/or CR
Extraction of Peak Points from 3AT Quad
Pol. Images
Estimating of Antenna Polarimetric Distortions (X-talk, CI)
Elimination of Antenna Distortions
from Point Target images (AT or CR)
Verification of Antenna Distortions
using AT or CR Cross-talk: 𝛿1 , 𝛿2, 𝛿3, 𝛿4
Channel Imbalance: 𝑓1, 𝑓2
𝑀𝐻𝐻 𝑀𝐻𝑉
𝑀𝑉𝐻 𝑀𝑉𝑉= 𝐴𝑒𝑗𝜑 1 𝛿2
𝛿1 𝑓1
𝑆𝐻𝐻 𝑆𝐻𝑉
𝑆𝑉𝐻 𝑆𝑉𝑉
1 𝛿3
𝛿4 𝑓2
MCS Overview (3/4)
Procedure (2)
• Quad Pol. & DT method
1) Generate covariance matrix of Amazon rain
forest quad pol. images
2) Estimate (u, v, z, w) components in X-talk
matrix using the generated covariance matrix
3) Estimate (α) component in X-talk matrix using
the noise ratio between HV and VH channel
calculated from calm water on image
4) Eliminate X-talk contribution from point targets
(AT or CR) image
5) Estimate Channel Imbalance using the point
targets image
6) Verify the co-pol and cross-pol responses after
eliminating antenna distortions using AT or CR
Covariance Matrix Generation
X-talk Matrix (u, v, z, w ) Estimation
X-talk Matrix (α) Estimation using
Noise Info.
Eliminate X-talk from P.T. Image
Channel Imbalance Estimation
Verification using AT or CR
2 0 0
( ) 0 01
0 0 11
HH
HH
HV
HV
VH
VV
VV
M v w vwk
u vK k
z w
uz u
SM
S
Sz
M
M
X-talk Matrix
MCS Overview (4/4)
Procedure (3)
• Dual Pol. & three AT method
1) Calculate the peak points around three AT
imaged with dual pol.
2) Estimate antenna polarimetric distortions
(cross-talk and receiving channel imbalance
together) using the ratios between peak points
of different ATs with different scattering matrix
3) Eliminate receiving antenna polarimetric
distortions from point target (AT or CR) images
(transmission cross-talk cannot be eliminated)
4) Verify the cross-pol responses using AT or CR
Extraction of Peak Points from 3AT Dual
Pol. Images
Estimation of Antenna Polarimetric
Distortions (X-talk, receiving CI)
Elimination of Receiving Antenna Distortions
from Point Target images (AT or CR)
Verification of cross-pol responses using
AT or CR
Reception Distortion Transmission Distortion
𝑀𝐻𝐻
𝑀𝑉𝐻= 𝐴𝑒𝑗𝜑 1 𝛿2
𝛿1 𝑓𝑆𝐻𝐻 𝑆𝐻𝑉
𝑆𝑉𝐻 𝑆𝑉𝑉
1𝛿3
MCS Simulation: Quad Pol. & 3 AT Method (1)
Schematic Plot
Polarimetric Distortion & Noise Simulation • Cross-talk Range
Amplitude: −30𝑑𝐵 < 𝛿 < −10𝑑𝐵
Phase: 𝟎° < ∠𝜹 < 𝟗𝟎°
• Channel imbalance Range
Amplitude: 0.9 < 𝑓 < 1.1
Phase: −𝟓° < ∠𝒇 < 𝟓°
Azimuth [m]
Range [m]
Satellite
Active Transponder (AT)
Corner reflector (CR)
Calibration Target
Verification Target
AT
AT
• Noise Range
SNR: 𝟔𝟎 𝒅𝑩
MCS Simulation: Quad Pol. & 3 AT Method (2)
Result
• Co-pol & Cross-pol response of CR after compensating estimated distortions
• 5 Simulation results: CI amplitude
After
Calibration
CI amplitude
Less than ±𝟎. 𝟎𝟒𝟕as in criteria
CI amplitude
MCS Simulation: Quad Pol. & 3 AT Method (3)
Result
• 5 Simulation results: CI phase
• 5 Simulation results: CT amplitude
After
Calibration
CI Phase
Less than 𝟓° as in criteria
CI Phase
After
Calibration
CT Amplitude
Less than 𝟑𝟎 dB as in criteria
MCS Simulation: Quad Pol. & DT Method (1)
Schematic Plot
Polarimetric Distortion & Noise Simulation • Cross-talk Range
Amplitude: −30𝑑𝐵 < 𝛿 < −10𝑑𝐵
Phase: 𝟎° < ∠𝜹 < 𝟗𝟎°
• Channel imbalance Range
Amplitude: 0.9 < 𝑓 < 1.1
Phase: −𝟓° < ∠𝒇 < 𝟓°
• Noise Range
SNR: 𝟔𝟎 𝒅𝑩
Noise Ratio between HV and VH channels
𝜎𝑉𝐻/𝜎𝐻𝑉: 1.5
Azimuth [m]
Range [m]
Satellite
Distributed target (DT)
Active Transponder (AT)
AT
Corner reflector (CR)
Calibration Target
Verification Target
MCS Simulation: Quad Pol. & DT Method (2)
Distributed Target
• Azimuth symmetric is satisfied
• Covariance matrix
HH (dB) HV (dB)
VH (dB) VV (dB)
Average: 62.592 dB Average: 55.0425 dB
Average: 55.0424 dB Average: 62.3786 dB
1 0.0121 0.0082 0.5847
0.0121 0.1737 0.1651 0.0091
0.0082 0.1651 0.1751 0.0091
0.5847 0.0091 0.0091 0.9668
MCS Simulation: Quad Pol. & DT Method (3)
Result
• Co-pol & Cross-pol response of CR after compensating estimated distortions
Items Criterias Results
Polarimetry
HH/VV amplitude ratio ≤ 𝟏 ± 𝟎. 𝟎𝟒𝟕 𝟎. 𝟗𝟖𝟑𝟖 ± 𝟎. 𝟎𝟒𝟑𝟑
HH/VV phase difference [deg.] ≤ 𝟓° −𝟎. 𝟐𝟑𝟕𝟓° ± 𝟐. 𝟑𝟓𝟕𝟓°
Cross talk [dB] ≤ −𝟑𝟎 𝐝𝐁 −𝟒𝟎. 𝟓𝟗𝟔𝟕 ± 𝟓. 𝟗𝟏𝟗𝟒 𝐝𝐁
MCS Simulation: Quad Pol. & DT Method (4)
Result
• 100 times Monte-Carlo simulation results: co-pol response of CR
• 100 times Monte-Carlo simulation results: cross-pol response of CR
HH/VV amplitude 0.9838 ±0.0433
HH/VV Phase −0.2375° ± 2.3575°
Cross-Talk -40.5967 ±5.9194 dB
MCS Simulation: Dual Pol. & 3 AT Method (1)
Schematic Plot
Polarimetric Distortion & Noise Simulation • Cross-talk Range
Amplitude: −30𝑑𝐵 < 𝛿1, 𝛿2 < −10𝑑𝐵
Phase: 𝟎° < ∠𝛿1, 𝛿2 < 𝟗𝟎°
Transmission X-talk 𝛿3 ≈ 0
• Channel imbalance Range
Amplitude: 0.9 < 𝑓 < 1.1
Phase: −𝟓° < ∠𝒇 < 𝟓°
Azimuth [m]
Range [m]
Satellite
Active Transponder (AT)
Corner reflector (CR)
Calibration Target
Verification Target
AT
AT
• Noise Range
SNR: 𝟔𝟎 𝒅𝑩
MCS Simulation: Dual Pol. & 3 AT Method (2)
Result
• 5 Simulation results: Cross-talk
After
Calibration
Less than 𝟑𝟎 dB as in criteria
CT Amplitude CT Amplitude
K-6 Calibration Equipment Development
Active Transponder Development (1/2)
Active Transponder Development Strategy
• Comply the requirement assigned by system for radiometric calibration
• Develop H/W considering enhanced payload parameters (compared to K5)
• Develop functions to support radiometric and multi-polarimetric calibration activity
• Consider “experiences and lessons” learned from K5 active transponder operation during development
Functions to support radiometric calibration
• Transfer stable power to satellite continuously during imaging operation
Operates as point target having stable RCS on ground
• Receive and record satellite TX signal versus time accurately
Supports azimuth antenna verification performed by RCS
Functions to support multi-polarimetric calibration
• All polarization (HH+HV+VH+VV) signal transferring
• Precise scattering property of AT are measured
Active Transponder Development (2/2)
Performance Requirements
• RCS Value: 60 dBsm
• RCS Accuracy: 0.2 dB (RF system), 0.4 dB (all AT system)
• Full Polarimetric support
• Recording of azimuth antenna
• Portable (by 2 persons)
• Weather protection, operating temperature (-20 ~50 °C)
Prototype Design of Kompsat-6 AT
Corner Reflector (Mongolia)
KOMPSAT-5 CR (Reuse)
• Number of CR: ST (20), HR (32)
ST (45dBm2)
HR (35dBm2)
200km
THANKS FOR YOUR ATTENTIONS
KOMPSAT-6