SMOS Vicarious Calibration using Takelimgan Sand

DesertWeiguo ZHANG, Ji WU, Heguang

LIU, Hao LIU, Chuandong XU, Dihui LI, Jingshan JIANG

Contents

• Review of the project• Background information about the site• Microwave radiometry characteristics of

the site and its simulation• preparation, consideration and design for

commissioning phase experiment• L band instrument (by Dr. Hao Liu)

Purpose and requirement

• The project aims to provide the scientific community a reliable site to evaluate status of SMOS-like mission and its L1 level data product.

• It requires the site be uniform, of large areas (compatible with the sensor’s spatial resolution), stable, if changes then need to be predictable.

Review of the project• Based on

1. proposal in response to SMOS AO-1 2. discussion on SMOS 1st SVRT meeting (11.2005 )and 6th SMOS workshop (5. 2006)3. agreement between CSSAR and ESA

Review of the project• Action

1. 2007/7-8, the 1st Takla-makan experiment2. Yann’s visit 2007/11 -> an aggressive plan proposed3. Chinese SMOS workshop 2008/3 -> Big bosses together4. Dragon-2 programme 2008/4 -> cooperation extended

Background information about the site

Large area: the 2nd largest desert in the world. Across 12 degrees of longitudes, 4 degrees of latitudes

Extremely arid: annual precipitation 25~45mm, concentrated on May-Aug. most of the precipitation are tiny rain (0.0~2.0mm). annualevaporation 2100~3400mm,

Single land type: 85% is covered with sand dunes. Other places are mixed with sand and shrubs, mainly distributed on brim of the desert.

Surface View

Dem extracted from ALOS PRISM data (Dragon2 TPM )Vertically exaggreted

AMSR/E observation and simulation(2004.Jan.-Nov.)

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Quick Response to SpaceborneRadiometer Behavior

Comparison of observation and simulation after calibration of AMSR-E 10GHz 2006

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Brightness temperature Something Wrong Here!

Further Investigation Needed for L band Emission Understanding

AMSR-E observation and simulation + bias

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Key issues

• Is current simulation methods enough or not suit for L band?• How to evaluate roughness effects?• Primary reference for absolute brightness temperature

accuracy

• What is the water content status 0~3 meters below surface?• Can dielectric constant be measured accurately enough under such a water content

status? • Is it possible to know the soil temperature profile distribution over there?Field experiment and in house measurements

For SMOS stability monitoring and further interpretation Ground Level

Ground based L band radiometer observation For SMOS accuracy reference

Ground Level Instrument

• To what extent does topography influence microwave radiation?• How to aggregate ground measurements to spaceborne

observations?• Fill instrument gap, an absolute standard reference for SMOSairborne L band radiometer observation

For SMOS precision and accuracy monitoring

Airborne Level Instrument

The first Takelimgan field experiment

Soil moisture profile distribution

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Commissioning phase campaign

Commissioning phase campaign

50Km

50Km

50Km

Three sets of Soil temperature profile sensors at every points.(100 sets in all, 10 for backup)Equipped before radiometer Operation. Data should be Recorded by automatic recorder. Wire based data recorder is preferred.

Soil moisture profile beyond 2 mShould be investigated.

Truck mounted radiometer needsto continuously observe sand duneswith different observation angle,

azimuth angle and position at every points for two days.

All 90 points may take 2 months tocomplete. Then tower observation.

After that, soil temperature profile data should be collected from the data recorder once a week until commissioning phase finished.

It may cost 3million RMB$.

The scale may not be exact.

Commissioning phase experimentTower based radiometer can be

used at a fixed place, last for a long time.

Sampling tools

Sampling tools

Summary• Our purpose is to use this site to evaluate status of

spaceborne L band radiometers since it is uniform, stable and predictable.

• Brightness temperature of this site is not a constant, but changing according to some law we have not completely understood. We can use three levels of experiment to find it.

• We have prepared something, but much more works still need to do.

Thank you for this part!

L-band Radiometer for TaklamaganDesert Experiment

• Dual-pol system• Internal calibration: load/noise

• Potter horn antenna• Direct detection

diode receiver

LNA

Dual-pol Antenna

Ref Load

Noise Diode

BPF AMP

H-pol Receiver

Switch

Thermal Control

Isolator Pre Filter

H

VV-pol Receiver

VH

VV

Digital Control

Attenuator

DetectorModule

AMP

Prospect System Parameters:• Central Freq：1.4135 GHz• 3db Bandwidth：19 MHz• HPBW: ～15o

• NeDT: < 0.6 K• Radiometric Accuracy：<

2K

Antenna designCritical Requirements:• 3db beamwidth < 15 degree• High main beam efficiency• High cross-polarization isolation• V/H beam symmetry

Selected Antenna type: Potter Horn• Easy construction• Good performance

Computed Specifications:• 3db beamwidth: 13.2

degree• Beam efficiency: 95%

(2.5*HPBW)• Cross-pol pattern isolation: >35dB

• VSWR: <1.2• Aperture Diameter: 1.2m• Length: 2.77m+0.5m

-80.00 -60.00 -40.00 -20.00 0.00 20.00 40.00 60.00 80.00Theta [deg]

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Ansoft Corporation HFSSDesign1XY Plot 1

m1

m2 m3

m4m5 m6

Curve Info

dB(GainX)Setup1 : LastAdaptivePhi='0deg'

dB(GainX)Setup1 : LastAdaptivePhi='90deg'

dB(GainY)Setup1 : LastAdaptivePhi='0deg'

dB(GainY)Setup1 : LastAdaptivePhi='90deg'

Name X Y

m1 0.4000 -26.0561

m2 -6.6000 -14.8466

m3 6.6000 -15.8045

m4 0.0000 23.5697

m5 -6.6000 20.4986

m6 6.6000 20.5107

Receiver designCritical Requirements:• Gain: ~80dB• RFI Suppression (High Out-band

Rejection)• High Stability• Internal Calibration

Receiver Design• Direct detection receiver• Two cavity band-pass filters,

including a pre-filter before LNA• Two ref sources: 50ohm load/noise

diode

Receiver Tests (1):Frequency Response & Noise

Figure

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fc =1413.07MHz

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Protected Band: 1400~1427MHz

BW60db =35.63MHz

noise floor of the spectrum analyzer

Receiver Normalized Amplitude-Frequency Response

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Receiver Noise Figure

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Receiver Tests (2):System Linearity (P-V

relationship)P_in (f=1.4135GHz)DTU

V_out

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Correlation Coefficient:0.99999

Vout (V)=679.6978 * Pin(mw)-1.2836

Power Input Range: -25.8~-17.8 dBm

Input Power (mw)

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Correlation Coefficient:0.99999

Power Input Range: -110 ~ -94 dBm

Input Power (mw)

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Receiver Tests (3): System Stability

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Mean: 6.9109 V

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Receiver/Detector50 ohm load V_out (0~10V)

High/Low Temperature Chamber

Summary

What we have done:• Antenna design• Receiver development & test

What we will do next:• Antenna development & test• Receiver improvement• Thermo control system

development• Structure design & rotation

mechanism