progresses of development of cfosat scatterometer

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

[email protected], [email protected]

mailto:[email protected]

mailto:[email protected]


(MiRS, CAS)



Outline of the Presentation

• Introduction to the Mission• Specifications of SCAT• Description of SCAT system• Simulation of SCAT system

performances• Progresses• Summary


(MiRS, CAS)



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.


(MiRS, CAS)


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


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



Description of SCAT system

• System overview• Choice of system type• Operation mode• System configuration• Key parameters


(MiRS, CAS)



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


(MiRS, CAS)



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°)


(MiRS, CAS)



Other constraints

• Antenna dimension: <1.2m• Available Pulsed Ku-TWTA: <140W• Available TWTA PRF: >150Hz• Data rate: <220kpbs• Rotating speed and mechanism lifetime


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



System D

iagram


(MiRS, CAS)



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 0.15dB

Receiver NF ≤2.0dB

Insertion loss of TX channel ≤1.5dB

Insertion loss of RX channel ≤3.0dB

Transmitting power (peak) 120W

Pulse width 1.35ms

PRF 2×75=150Hz


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



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

A

P31

P32

TWTACirculator

P1

P21P22

LPF2

P31

P32

K6


(MiRS, CAS)



Simulations of system performances

• Simulation model• Simulation of 0sigma precision• Simulation of wind vector retrieval

performance


(MiRS, CAS)



Simulation model


(MiRS, CAS)



Simulation of s° precision

• Modeling– Radar equation– SNR– s° precision

2 2

3 4A4

where:

120 50.8

2.263 16.5

3.5 (insturment loss)

r t

t

GP P dA

RL

P W dBm

cm dB

L dB

2 2

3 4A

Pr

1

4t

SNR SNR

N

GP dA

kBT RL

2 21 1 1 1

1 1true

true eff true noise true

PKp

P N SNR N SNR

( ) 10log 1Kp dB Kp


(MiRS, CAS)



• Statistics:number of looks (left) number of independent samples (right)


(MiRS, CAS)



SNR

dist

ributi

on

U=4m/s U=8m/s

U=16m/s U=24m/s


(MiRS, CAS)



Kp d

istrib

ution

(25k

m)

U=4m/s U=8m/s

U=16m/s U=24m/s


(MiRS, CAS)



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


(MiRS, CAS)



Parallel and circular wind field(U~[2,24])


(MiRS, CAS)



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


(MiRS, CAS)



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


(MiRS, CAS)



FOM varying with wind speed


(MiRS, CAS)



Random wind field

• Parallel wind field simulated• Wind speed range: 4~24m/s• Wind direction search interval: 10deg• 25km WVC resolution


(MiRS, CAS)



U=8

m/s

U=4

m/s


(MiRS, CAS)



U=1

2m/s

U=1

6m/s


(MiRS, CAS)



U=2

0m/s

U

=24m

/s


(MiRS, CAS)



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


(MiRS, CAS)



Retrieval performance

U(m/s)

Near nadir(-100~+100)

Far range within footprint(>400km)

Near range within footprint(100~400km)

0

(dB)U

(m/s)phi()

0

(dB)U

(m/s)phi()

0

(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


(MiRS, CAS)



Assessment by FOM


(MiRS, CAS)



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


(MiRS, CAS)



RFC test and SCAT integrated test


(MiRS, CAS)



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.


(MiRS, CAS)



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.


(MiRS, CAS)



Thanks for your attentions!

progresses of development of cfosat scatterometer

Documents

ms wind speed

wind scatteromer

oceanocean surface wind

wind vector payload

antenna beam

ms wind direction

fan beam kuband radar

rotating fanbeam antenna