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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.)
0 50 100 150 200 250 300 350 400
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305V Pol.
Sim
ulat
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DOY(Jan.2004-Dec.2004)
AMSR/E Observation Simulation
0 50 100 150 200 250 300 350 400215
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Sim
ulat
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DOY(Jan.2004-Dec.2004)
AMSR/E Observation Simulation
260 265 270 275 280 285 290 295 300 305260
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300V Pol.
Sim
ulat
ion(
K)
AMSR/E Observation(K)
Tb(K)
220 225 230 235 240 245 250 255
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H Pol.
Sim
ulat
ion(
K)
AMSR/E Observation(K)
Tb(K)
SEE:(stdev. of errors)
V:0.94K
H:1.56K
All obs.
Quick Response to SpaceborneRadiometer Behavior
Comparison of observation and simulation after calibration of AMSR-E 10GHz 2006
220
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1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 121 129 137 145 153 161 169 177 185 193 201 209 217 225 233
DOY
Brightness temperature Something Wrong Here!
Further Investigation Needed for L band Emission Understanding
AMSR-E observation and simulation + bias
Observation and simulated Tb
260
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0 20 40 60 80 100 120 140 160 180 200
Day of Year
Tb(V pol.)
obs.
sim.
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0 20 40 60 80 100 120 140 160 180 200
Observation
Simulation
AMSR-E observation and simulation
260 270 280 290 300
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Sim
ulat
ion
AMSRE Observation
2006 whole year V pol. 6.9GHz
220 230 240 250220
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ion
AMSRE Observation
2006 whole year H pol. 6.9GHz
260 270 280 290 300 310
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AMSRE Observation
2006 whole year V pol. 19GHz
220 230 240 250 260
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AMSRE Observation
2006 whole year H pol. 19GHz
V. Pol. H. Pol.
19GHz
6.9GHz
V. Pol. H. Pol.
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
0
0.05
0.1
0.15
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0.25
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0.35
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200
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-0.05
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1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 281 291 301 311
Weighted Soil Water Content(GSM %)
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0.2
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1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 281 291 301 311
Volume Soil Water Content VSM% (bulk density=1.6)
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]
-70.00
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
10.00
20.00
30.00
Y1
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
1380 1390 1400 1410 1420 1430 1440 1450-80
-70
-60
-50
-40
-30
-20
-10
0
BW3db =20.98MHz
fc =1413.07MHz
-23.66dBm-27.16dBm
Protected Band: 1400~1427MHz
BW60db =35.63MHz
noise floor of the spectrum analyzer
Receiver Normalized Amplitude-Frequency Response
Frequency (MHz)
Gai
n (
dB
m)
1400 1405 1410 1415 1420 1425 14303
4
5
6
7
8
Receiver Noise Figure
Frequency (MHz)
9
NF
(d
B)
Receiver Tests (2):System Linearity (P-V
relationship)P_in (f=1.4135GHz)DTU
V_out
0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.0180
2
4
6
8
10
12
Correlation Coefficient:0.99999
Vout (V)=679.6978 * Pin(mw)-1.2836
Power Input Range: -25.8~-17.8 dBm
Input Power (mw)
Ou
tpu
t Vo
ltag
e (V
)
Detector Linearity Test
0 0.5 1 1.5 2 2.5 3 3.5 4
x 10-10
3
4
5
6
7
8
9
10
11
Correlation Coefficient:0.99999
Power Input Range: -110 ~ -94 dBm
Input Power (mw)
System Linearity Test
Ou
tpu
t Vo
ltag
e (V
)
Receiver Tests (3): System Stability
0 20 40 60 80 100 120 140 1600
1
2
3
4
5
6
7
8
9
10
Time (min)
Det
ecto
r O
utp
ut (
V)
17oC
-20oC0 50 100 150 200 250
0
1
2
3
4
5
6
7
8
9
10
Time (min)
Det
ecto
r O
utp
ut (
V)
45oC
15oC
Mean: 6.9109 V
STD: 0.0390 V
~ 1.8K variance
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
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