Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
PROGRESSES OF DEVELOPMENT OF CFOSAT SCATTEROMETER
Xiaolong Dong, Di ZhuCAS Key Laboratory of Microwave Remote Sensing
National Space Science Center, CASPO Box 8701, Beijing, China
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Outline of the Presentation
• Introduction to the Mission• Specifications of SCAT• Description of SCAT system• Simulation of SCAT system
performances• Progresses• Summary
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
CFOSAT Mission
• CFOSAT: Chinese French Oceanography SATellie
• Launch plan: 2014• Mission Objectives: monitoring the wind and waves at the ocean
surface at the global scale in order to improve:– The wind and wave forecast for marine
meteorology (including severe events)– the ocean dynamics modeling and
prediction,– our knowledge of climate variability– fundamental knowledge on surface
processes linked to wind and waves
• Two payloads:– SWIM (Sea Wave Investigation and
Monitoring by satellite)• A Ku-band real aperture radar for
measurement of directional ocean wave spectra;
– SCAT (SCATterometer)• A Ku-band rotating fan-beam radar
scatterometer for measurement of ocean surface wind vector.
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012 4
Mission-measurement requirements• Joint measurement of ocean surface wind vector
and sea-state parameters from radar – Both wind vector and wave parameters can be measured using active micro-wave
remote sensing (heritage of altimeter, sactterometer and SAR missions, and airborne radar measurements)
– Wind vector => optimal configuration at medium incidence angle (20-50°)– Wave spectra => optimal configuration at low incidence angle (< 15°)
• CFOSAT mission with two payloads– SWIM: wave scatterometer: multi-beam Ku-Band radar at low incidence – SCAT: wind scatteromer: Fan beam Ku-Band radar at medium incidence
4
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Mission-Wind Vector Payload -SCAT• A Ku-band rotating fan-beam radar
scatterometer (Ku-RFSCAT) for sea surface wind vector retrieval by measurement of the sea surface backscattering coefficient.
• Adapted to the platform constraints (small size);
• 2 fan beams (HH & VV) cover incident angles from 26 degree to 46 degree from nadir
• scanned with a rotation speed of around 3.5 rpm.
• For each of the ground resolution cells, more than four looking angles can be obtained to retrieval wind vector information.
5
Rotating fan-beam antenna
Nadir Point
Flight direction
Swathfootprint
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Characteristics of CFOSAT SCAT
• Wide swath by rotating of beam;– Decided by outer edge of incident angle of beam
• More number of azimuth look angles by overlap of beam;– Decided by flying speed, rotating speed and beamwidth
• NRCS/sigma 0 dependent on antenna beam;– Decided by local antenna gain along elevation
• Single antenna for all azimuth directions;– No inter-beam balance required– But azimuth fluctuation may exist due to rotating
mechanism
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Azimuth look angle combinations for surface resolution cells
Track of nadir porints
Surface resolution cell 2
Surface resolution cell 1
Overlap between adjacent scannsfor large number of azimuth view for each pixel. Dual polarization is used to improve retrieval of outer and center part of the swath
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Specifications for SCAT
• Objectives:– Measurement of global surface sigma 0– Retrieval of global ocean surface wind vector
• Data requirements– Swath width: >1000km– Surface resolution: 50km (standard); 25km (goal)– Data quality (at 50km resolution)– s° precision:
• 1.0dB for wind speed 4~6m/s• 0.5dB for wind speed 6~24m/s
– Wind speed: 2m/s or 10% @ 4~25m/s– Wind direction: 20deg @ 360deg for most part of the swath
• Life time: 3yrs
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Specifications of SCAT
Ku-RFSCAT Parameters Antenna Spinning rate :Polarization:PRF/channel:Pulse peak power (Pt):Pulse bandwidth (B):Pulse duration (τp):Swath width:Receive gate length(Tg):Receive gate delay: Inclination:
3.5 rpmVV, HH75 Hz/channel120 W0.5 MHz1.3 ms1000 km2.82 ms3.74 ms 97.5 deg
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Description of SCAT system
• System overview• Choice of system type• Operation mode• System configuration• Key parameters
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
System overview
• Ku-band rotating fan-beam scatterometer– Platform dimension– Technology heritage– Available GMFs
• Long LMF pulse with de-ramp pulse compression– TX: 1.35ms– RX: 2.72 ms
• Digital I-Q receiver with on-board pulse compression processing and resolution cell regrouping
• TX/RX channel except antenna and switch matrix identical primary/backup design to ensure liability
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Choice of system type-Why rotating fan beam?
• Why rotating beam?– Overlap of surface coverage with
SWIM is requirement, nadir gap should be avoided.
– Deployment of multiple fan-beam antenna is not allowed due to platform capability.
– Large swath at a relatively low orbit (~500km) requires scanning.
• Why rotating fan beam?– Lower rotating speed to ensure
life time of rotating mechanism;– Multiple incident angles for
better wind direction retrieval;– Large incident angle ranges
(20~46°) for investigation of ocean surface scattering characteristics, by compensating with SWIM (0~10°)
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Other constraints
• Antenna dimension: <1.2m• Available Pulsed Ku-TWTA: <140W• Available TWTA PRF: >150Hz• Data rate: <220kpbs• Rotating speed and mechanism lifetime
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Operation mode
• Normal mode: dual polarization with rotation;• Test/cal mode:
– raw waveform with lower PRF;– Including both rotating mode and fixed pointing
mode;• Single polarization mode
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
System configuration
• Antenna subsystem– Antenna and feeding network;– Scanning mechanism;– Servo controller;
• RF subsystem– Switch matrix;– RF receiver;
• RX/TX electronics subsystem– IF receiver;– Frequency synthesizers;– TX up-converter
• Power amplifier subsystem– TWT and EPC
• Digital subsystem– Signal generator;– System controller;– Signal processor;– Communication controller;
• Secondary power supply subsystem– DC-DC power converter;– TC/TM module
• WG & cable assembly
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
System Diagram
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
System configuration
• Interface with structure subsystem– Antenna and part of the
servo mechanism installed outside the satellite;
– Other equipments installed inside the satelltie
EUMETSAT/ESA Scatterometer Science Conference 2011April 11-13, Darmstadt, Germany
Basic radar parameters
Parameter Specifications
Frequency 13.256GHz
Signal bandwidth 0.5MHz
Internal calibration precision Better than 0.15dBReceiver NF ≤2.0dB
Insertion loss of TX channel ≤1.5dB
Insertion loss of RX channel ≤3.0dB
Transmitting power (peak) 120WPulse width 1.35ms
PRF 2×75=150Hz
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Optimization of radar parameters
• Optimization: trade-off between SNR, measurement
samples of each look and number of looks. maximization of wind vector retrieval
performance– Surface resolution– Signal bandwidth– Rotating speed
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Resolution in azimuth direction& azimuth beam-width
• Fan beamlower gainantenna as long as possible
• Decided by antenna beamwidth• Limited by satellite dimension: ≤1.2m• Beamwidth ~1.1 deg resolution in azimuth
direction: 10.5~14.5km
EUMETSAT/ESA Scatterometer Science Conference 2011April 11-13, Darmstadt, Germany
Design of rotating speed• Trade-off between independent
sigma 0measuremrent samples for single look and number of looks
• Optimization of 3.5rpm
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Resolution in elevation direction& signal bandwidth
• Low SNR due to low antenna gain
• Bandwidth 0.5MHz resolution:380~650m• On-board non-coherent re-
grouping to improve sigma 0 precision
resolution of 5km
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Onboard processing• Reduce data rate to ~220kbps• Downlink data resolution: ~10km(az) × 5km(el)
– (original resolution: 10km(az) × (<1km(el))• Signal+noise processing & noise-only processing
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Internal Calibration Loop
Ports:•P1: BJ-140 to TWTA•P2: BJ-140 to antennas•P3: BJ-140 to RF receiver
Compositions:•C1,C2:directional couplers•K1,K2,K3,K4:ferrite switches•K5,K6:mechanical switches•LPF1/2:EMC filters•D: power monitoring detector•Ns:internal noise source
C1K1
C2 K2
K3 K5
LPF1
D
NsK4
AP31
P32
TWTACirculator
P1
P21P22
LPF2
P31
P32
K6
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Simulations of system performances
• Simulation model• Simulation of sigma 0 precision• Simulation of wind vector retrieval
performance
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Simulation model
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Simulation of s° precision
• Modeling– Radar equation– SNR– s° precision
2 2
3 4A4
where: 120 50.82.263 16.53.5 (insturment loss)
r t
t
GP P dARL
P W dBmcm dB
L dB
s
2 2
3 4A
Pr
14
t
SNR SNR
NGP dA
kBT RL
s
s
2 21 1 1 11 1true
true eff true noise true
PKpP N SNR N SNR
ss s s
( ) 10log 1Kp dB Kp
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
• Statistics:number of looks (left) number of independent samples (right)
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
SNR
dist
ributi
on
U=4m/s U=8m/s
U=16m/s U=24m/s
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Kp d
istrib
ution
(25k
m)
U=4m/s U=8m/s
U=16m/s U=24m/s
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Simulation of wind retrieval
• Only s°data with precision better than 1.0dB will be used for wind retrieval;
• Standard MLE method and NSCAT GMF are used for simulation;• Median filter algorithm for wind direction ambiguity removal
• 2 kinds of wind field simulated– Spatially correlated parallel wind field and circular wind field– Random wind field
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Parallel and circular wind field(U~[2,24])
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Retrieval performance of parallel wind field
U Qe(m/s)-U QRMS(m/s)-U Qe (o)-phi QRMS (o)-phi468
1012141618202224
0.430.450.550.680.830.991.171.381.601.862.13
0.650.660.760.931.131.331.571.832.122.432.75
51.515.910.910.110.210.310.811.312.112.913.4
65.922.316.515.415.615.716.317.018.119.119.8
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Retrieval performance of circular wind field
U Qe(m/s)-U QRMS(m/s)-U Qe (o)-phi QRMS (o)-phi468
1012141618202224
0.440.460.550.690.861.021.221.441.681.932.19
0.680.680.770.951.171.381.621.902.202.512.83
39.115.610.910.210.410.611.111.812.713.514.0
51.922.316.615.716.016.316.917.819.020.020.7
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
FOM varying with wind speed
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Random wind field
• Parallel wind field simulated• Wind speed range: 4~24m/s• Wind direction search interval: 10deg• 25km WVC resolution
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
U=8
m/s
U=4
m/s
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
U=1
2m/s
U=1
6m/s
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
U=2
0m/s
U
=24m
/s
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Wind vector retrieval performance
Input wind speedRMS of wind speed
(m/s)RMS of wind direction
(o)
468
1012141618202224
0.70.70.81.01.21.41.61.92.22.52.8
35.522.316.615.716.016.316.917.819.020.020.7
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Retrieval performance
U(m/s)
Near nadir(-100~+100)
Far range within footprint(>400km)
Near range within footprint(100~400km)
s0
(dB)U
(m/s)phi()
s0
(dB)U
(m/s)phi()
s0
(dB)U
(m/s)phi()
4 0.89-1.79 0.4 44.1 1.43-3.07 1.1 44.7 0.66-2.07 0.4 31.8
8 0.46-0.66 0.9 24.2 0.51-1.01 1.3 26.9 0.44-0.74 0.6 11.0
12 0.41-0.53 1.2 22.7 0.45-0.63 1.8 26.6 0.41-0.54 0.9 10.4
16 0.40-0.49 2.1 22.7 0.44-0.54 2.2 27.6 0.40-0.49 1.3 11.3
20 0.40-0.48 2.9 24.8 0.43-0.50 2.9 30.1 0.40-0.47 1.8 12.8
24 0.39-0.47 3.8 26.3 0.43-0.48 3.6 32.0 0.39-0.46 2.4 14.1
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Assessment by FOM
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Progresses of CFOSAT/SCAT
• 2010.04 PDR of SCAT• 2010.12 Detailed design review• 2011.07 Delivery of electrical models (except
antenna subsystem) and satellite electrical performance test – System specifications, interface compatibility confirmed
• 2011.11 Delivery of mechanical and thermal models• 2011.12 Satellite mechanical test• 2012.02 Satellite thermal test• 2012.05 RF compatibility test• 2012.07 Onboard full operation mode test
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
RFC test and SCAT integrated test
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Summary
• Design and performance of CFOSAT SCAT is presented:– When U<4m/s, SCAT/CFOSAT cannot provide useful wind
retrieval due to its low SNR;– For U=4~8m/s, SCAT/CFOSAT can provide wind retrieval
similar to QSCAT only within swath of 800km;– For U>8m/s, SCAT/CFOSAT can provide better wind retrieval
with its designed swath of 1000km, compared with QSCAT;– For U>16m/s, the advantage of SCAT/CFOSAT become
obvious, due to its more number of looks.• Development of SCAT on time for the scheduled launch
in 2014.
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Further to do…
• New quality control for sigma-0 measurement with more number of looks and lower SNR;
• Development of retrieval making use of increased number of looks;
• Evaluation of rain effect, compared with pencil beam system like QSCAT;
• Calibration for rotating fan beam system:– In-orbit antenna pattern calibration;– In-orbit possible azimuth-dependent antenna gain
variation due to rotary joint.
Key Laboratory of Microwave Remote SensingChinese Academy of Sciences
(MiRS, CAS)
National Space Science CenterChinese Academy of Sciences
IGARSS 2012, Munich, GermanyJuly 22-27, 2012
Thanks for your attentions!