The role of weather models in mitigation of tropspheric delay for SAR Interferometry.ppt
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Transcript of The role of weather models in mitigation of tropspheric delay for SAR Interferometry.ppt
July 27, 2011 1
The role of numerical weather models (NWM) in mitigation of tropospheric delay for SAR Interferometry
Shizhuo Liu1, Agnes Mika2, Wenyu Gong3, Franz Meyer3, Ramon Hanssen1, Don Morton3 and Peter Webley3
1 Delft institute of Earth Observation and Space Systems (DEOS), the Netherlands2 BMT AGROSS, the Netherlands3 University of Alaska Fairbanks, United States
Department of Earth Observation and Space Systems (DEOS), Aerospace engineering
InSAR WRF
Delay observed by repeat-pass SAR Interferometry
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€
Dp,qt1, t2 = Dp - Dq( )
t1- Dp - Dq( )
t2
• Temporal difference:
• Spatial difference:
€
DpDt = Dp
t1 - Dpt2
€
Dpq = Dp
t - Dqt
p q
t1 t2
observed delay: (spatio-temporal difference)
€
Dpt1
€
Dpt2
€
Dqt1
€
Dqt2
Spatial characteristics of delay in InSAR
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8 ERS1/2 tandem interferograms over Groningen, the Netherlands
a b c d
e f g h
trend: c, e, h
local anomaly: a, g
trend+anomaly: b, d, f Trend + Variation (water vapor)
mm
Delay in mountainous regions
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p
q
Atmospheric-only interferogram Hawaii topography
h
trend + variation+ vertical stratification
mmm
Studies of regions with different climates
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Netherlands
Hawaii
Mexico City
Lake Moore, WA
Forecasting setup
• WRF (ver 3.1): includes non-hydrostatic dynamics;• Spatial domains: 27, 9, 3, 1 km ;• Spin-up time: 12-16 hours ;• Initial-boundary condition: FNL data (100 km, 6
hours);• Land topography data: SRTM (90 m);• Land-use data (MODIS 20-category);• Microphysics: Morrison 2-moment• Vertical levels: 28 (10 under 2km)
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InSAR - WRFInSAR (35-day)
Hawaii (case No.1)
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InSAR WRF InSAR - WRF
€
σinsar =19.4mm
s wrf = 23.8mm
s diff =11.4mm
WRF
Foster JGRL, vol. 33, 2006
mm
Hawaii (case No.2)
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InSAR (35-day) WRF InSAR - WRF
InSAR WRF InSAR - WRF
€
σinsar =16.9mm
s wrf =14.2mm
s diff =10.5mm
Topography of Mexico City
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m
Mexico City (case No.1)
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InSAR (35-day) WRF InSAR-WRF
InSAR WRF InSAR-WRF
€
σinsar = 7.6mm
s wrf = 7.6mm
s diff = 4.6mm
mm
Mexico City (case No.2)
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InSAR (35-day) WRF InSAR - WRF
InSAR WRF InSAR - WRF
€
σinsar =11.7mm
s wrf = 9.5mm
s diff = 5.9mm
Inconsistency (case No.3)
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InSAR (35-day) WRF InSAR - WRF
€
σinsar = 8.0mm
s wrf = 7.4mm
s diff = 9.4mm
Cross-validation with MERIS
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WRFInSAR MERIS
mm
Flat regions
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Netherlands (9 cases)
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InSAR (35-day) WRF InSAR-WRF
€
σinsar = 6.9mm
s wrf = 4.0mm
s diff = 5.4mmNo.1
€
σinsar = 5.3mm
s wrf =1.7mm
s diff = 5.8mmNo.2
€
σinsar = 4.2mm
s wrf = 2.4mm
s diff = 5.5mmNo.3
mm
Netherlands
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€
σinsar = 4.4mm
s wrf = 2.1mm
s diff = 4.7mm
€
σinsar = 5.0mm
s wrf = 2.8mm
s diff = 3.8mm
€
σinsar = 3.7mm
s wrf =1.1mm
s diff = 3.7mm
InSAR (35-day) WRF InSAR-WRF
No.4
No.5
No.6
Netherlands
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€
σinsar = 3.4mm
s wrf = 0.9mm
s diff = 3.4mm
€
σinsar = 3.8mm
s wrf = 2.1mm
s diff = 3.4mm
€
σinsar = 4.0mm
s wrf = 2.0mm
s diff = 3.7mm
InSAR (35-day) WRF InSAR-WRF
No.7
No.8
No.9
Southwest Australia (5 cases)
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InSAR (35-day) WRF InSAR-WRF
€
σinsar =1.9mm
s wrf = 0.8mm
s diff =1.9mm
€
σinsar = 3.2mm
s wrf =1.9mm
s diff = 4.0mm
€
σinsar =1.8mm
s wrf = 0.9mm
s diff =1.9mm
No.1
No.2
No.3
Southwest Australia
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InSAR (35-day) WRF InSAR-WRF
€
σinsar = 5.4mm
s wrf = 3.6mm
s diff = 6.2mm
€
σinsar = 5.7mm
s wrf = 4.4mm
s diff = 7.8mm
No.4
No.5
Variograms of delay
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Netherlands Australia
Distance [km]
InSAR
WRF
Results review
• In mountainous regions, topography dependent delay is well predicted by WRF in most cases. In these cases, 40% to 50% delay reduction can be achieved. However, its reliability is not 100% (80%)
• In flat regions, delay prediction by WRF is unrealistic and hardly bring significant delay reduction
• Moreover, the spatio-temporal delay variation predicted by WRF is underestimated at all spatial scales
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Model tuning
• Initial boundary conditions: FNL -> ECMWF (50 km) ;
• Longer spin-up time: 12 hours -> 24 hours ;
• Vertical levels: 28 -> 40 (30 below ABL) ;
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ECMWF versus FNL
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Mexico City (case No.3) same model settings
Netherlands (case No.2)
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InSAR ECMWF(WRF) InSAR-ECMWF
FNL(WRF) InSAR-FNL
Netherlands (case No.9)
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InSAR ECMWF(WRF) InSAR-ECMWF
FNL(WRF) InSAR-FNL
Longer spin-up time and more vertical levels
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Hawaii Mexico City
Netherlands Australia
InSAR
WRF tuned
WRF original
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• NWM (numerical weather models) work for topography-dependent delay when topography variation is significant (> 2000 km)
- max 50% RMS reduction with ; - a reliability of 80% (improvement for 4 out of 5) ;• NWM fail for lateral variation of water vapor at small scales (< 50 km) - always underestimation ; - max 30% reduction ; - a poor reliability (improvement for 2 out of 14)
The low reliability of NWM for flat regions excludes it from operational tools for delay mitigation in SAR Interferometry. For mountainous
regions, delay correction could go wrong as well, users should be careful and critical
Conclusions
Thank you !
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Is the weather model generally bad for delay prediction ?
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MERIS WRFAbsolute delay:
Mean delay
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Recommendations
• To improve the reliability of NWM it is necessary to include more meteorological observations with high spatial density
• Hindcasting using observations after satellite acquisitions would be also useful to constrain NWM aiming to increase its reliability
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Tropospheric delay experienced by MW
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hydrostatic (gas components) wet (water vapor) cloud droplets
€
Dpt1 = Nhydro
t1ò ds + Nwett1ò ds + Ndroplet
t1ò ds
absolute delay due to troposphere:
hydrostatic: long wavelength spatial gradient(pressure, temperature), i.e., trend
wet/cloud: significant spatial variation, i.e., local variation
Numerical forecasting for delay mitigation
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Earth’s surface
NWMprediction
dh
z(h)
(T, e, P)
P: total air pressuree: water vapour pressureT: air temperature
x
y
wetchydrostati NN
T
ek
T
ek
T
PkN
23'21 ++=
Constants (Davis et al., 1985)
Refractivity
€
Dp,qt1 ,t2 is obtained by taking temporal
and spatial difference in sequence
Hawaii (case No.3)
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InSAR (35-day) WRF InSAR - WRF
InSAR WRF InSAR - WRF
€
σinsar =11.5mm
s wrf =10.2mm
s diff =14.9mm
Hawaii (case No.4)
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InSAR (35-day) WRF InSAR-WRF
InSAR WRF InSAR-WRF
€
σinsar =12.0mm
s wrf = 6.8mm
s diff =13.3mm