- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada 1
M. Brogioni1, S. Pettinato1, E. Santi1, S. Paloscia1, P. Pampaloni1, E. Palchetti1, J. Shi2,3, C. Xiong1,2,
1Institute of Applied Physics - IFAC-CNR, Firenze, Italy
2Institute for Remote Sensing Applications, Beijing, China 3University of California, Santa Barbara (CA), USA
The Potential of Cosmo-Skymed SAR Images in Mapping Snow Cover and
Snow Water Equivalent
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Outline
Motivations
The ASI Cosmo-Skymed mission and data
Model investigations
Experimental Results
Retrieval of Snow cover and Snow Water Equivalent
2
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Introduction
3
Several experiments have documented the ability of C- band SAR in mapping the extent of wet snow. But the high transmissivity of dry snow cover at this frequency makes difficult to detect it.
The study aims at evaluating the potential of X-band COSMO-Skymed SAR in generating snow cover maps and estimating snow water equivalent
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
The ASI/Cosmo-Skymed mission
4
4 medium-size satellites, equipped with an X-band SAR HH, VV, HV, VH pol
sun-synchronous orbit at ~620km height
Full constellation revisit time : 12 h
- 1 Spotlight mode, for metric resolutions over small images- 2 Stripmap modes, for metric resolutions over tenth of km images; one mode is polarimetric with images acquired in two polarizations- 2 ScanSAR for medium to coarse (100 m) resolution over large swath
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Example of COSMO-Skymed data
CSK 2, Himage, HH, = 26.5°
Temporal variation of backscattering on alpine regions
CSK® © ASI
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Model Investigation: Snow backscattering model
Snow as a single layer of identical scatterers
Flat air-snow interface
Rough snow –soil interfacee2
e0
eS
e0
z=0
z=-d
AIR
SNOW
GROUND
DMRT-QCA(Tsang et al., 2007)
Multiple scattering effects
Mie Scattering
Stickyness
Snow volume scattering
6
Surface scattering AIEM
(Chen et al., 2004)
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada 7
The surface scattering: The AIEM model
)()()()( SSSS qpc
qpkc
qpk
qpo
The normalized scattering coefficient is composed of three terms: Kirchhoff, cross and the complementary one.
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Volume scattering: The DMRT/QCA Model(Tsang et al. 2007)
8
zIPdd
zIPddzIkdz
zIde
,,,;,sin
,,,;,sin,,,,
cos
''''2
0
''2
0
'
''''2
0
''2
0
'
i
i
i
i
s
s
s
s
V
U
I
I
PP
PP
P
P
V
U
I
I
12
12
2
1
4443
3433
22
11
12
12
2
1
00
00
000
000 qfP2
1111
qfP2
2222
qffP *221133 Re
4433 PP
qffP *221134 Im
3443 PP
coscos1
121
1)()()()(
111
max
nNn
Nnn
Mn
Mn
N
nr
XTXTnn
n
KkR
if
coscos1
121
1)()()()(
122
max
nNn
Nnn
Mn
Mn
N
nr
XTXTnn
n
KkR
if
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Model Simulations
(DMRT – QCA model)
9
Data chosen to account for the different type of snow cover on the Alps
Frequency (GHz) 5.3, 9.6, 17.2
Polarization VV, HH, HV
Incidence angle (deg) 20 - 50
Density (Kg/m3) 200 - 500
Grain radius (mm) 0.1 - 1.5
Snow depth (cm) 20 - 300
Soil smooth
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Model SimulationsExtinction and Penetration depth
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Radius
Crystal radius (mm)
Frequency Band
Penetration depth (1/ke) (m)
250 Kg/m3 350 Kg/m3
0.5 C 66.8 81.9 X 9.5 17.5
Ku 1.2 2.5
0.9 C 18.8 39.3 X 2.3 5.31
Ku 0.33 0.67
1.3 C 7.4 17.8 X 0.99 2.16
Ku 0.15 0.29
Density
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Sensitivity of backscattering to grain radius
11
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Model Simulations: Sensitivity to SWECrystal radius: 0.1 mm – Incidence angle: 35°
12
Bac
ksca
tter
ing
(dB
)
5.3 GHz
SWE
Total scattering
Snow contribution
Soil contribution
9.6 GHz
SWE
Density 150-400
SWE
17.2 GHzBac
ksca
tter
ing
(dB
)
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada 17.2 GHz
SWE (mm)
Bac
ksca
tter
ing
(dB
)
13
9.6 GHzBac
ksca
tter
ing
(dB
)
SWE (mm)
Total scattering
Snow contribution
Soil contribution
5.3 GHz
SWE (mm)
Bac
ksca
tter
ing
(dB
) Model Simulations: Sensitivity to SWE
Crystal radius: 0.3 mm – Incidence angle: 35°
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada 14
Total scattering
Snow contribution
Soil contribution
17.2 GHz
SWE (mm)
Bac
ksca
tter
ing
(dB
)
5.3 GHz
SWE (mm)
Bac
ksca
tter
ing
(dB
)
Model Simulations: Sensitivity to SWECrystal radius: 0.5 mm – Incidence angle: 35°
9.6 GHz
SWE (mm)
Bac
ksca
tter
ing
(dB
)
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Model Simulations
Sensitivity to SWE
15
5.3 GHz 9.6 GHz 17.2 GHz
Bac
ksca
tter
ing
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Experimental sensitivity to Snow Depth:Temporal trends
16
Wet snow
D SWE
Depth Hoar
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada 17
Generation of snow cover maps and Retrieval of SWE
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Principle of the algorithm
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DEM + air temperature
Optic
SAR
clear sky snow cover
wet snow
clouds ?
dry snow SWE
snow cover + SWE wet snow
dry/wet snow
clear cloudy
Ref. Image
Threshold ANN
for high SWE values
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Validation of SWE Algorithm with experimental X-band data
19
Date Sensor Sensor mode Polarization08/03/2009 CSK2 STR_HIMAGE HH27/05/2009 CSK2 STR_HIMAGE HH14/07/2009 CSK2 STR_HIMAGE HH22/01/2010 CSK2 STR_HIMAGE HH26/03/2010 CSK2 STR_PINGPONG VV/VH29/03/2010 CSK1 STR_PINGPONG VV/VH02/09/2010 CSK1 STR_PINGPONG VV/VH
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
First verification of SWE Algorithm with exper. data
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22/01/2010 08/03/2009 27/05/2009
SWE (200
Kg/m3)
SWE (300
Kg/m3)SWE NN
SWE (200
Kg/m3)
SWE (300
Kg/m3)SWE NN
SWE (200
Kg/m3)
SWE (300
Kg/m3)SWE NN
Monti Ornella 272 408 270 500 750 masked 194 291 wet snow
Col dei Baldi 268 402 350 574 861 544 90 135 wet snow
Pradazzo 192 288 280 306 459 400 no data no data -
Ravales 280 420 masked 488 732 masked 260 390 masked
Cherz 200 300 290 240 360 270 no data no data -
26/03/2010 29/03/2010
SWE
(200 Kg/m3)SWE
(300 Kg/m3) SWE NNSWE
(200 Kg/m3)SWE
(300 Kg/m3) SWE NN
Monti Ornella 304 456 380 332 498 438
Col dei Baldi 296 444 390 294 441 masked
Cima Pradazzo 204 306 masked 198 297 masked
Ravales 304 456 378 332 498 480
Cherz 270 405 masked 230 345 masked
Single polarization
Dual polarization(co & cross )
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Example of Snow Cover Area
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January 22, 2010 March 29, 2011
SWE
40 Km
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Summary and conclusions
22
The sensitivity of ASI/Cosmo-Skymed X-band SAR to snow cover and SWE has been investigated by using experimental results and model simulations.
An algorithm to generate snow cover maps by combining optical and SAR data has been developed and validated
It has been found that X-band data can contribute to the retrieval of SWE for snow depth higher than about 40-50 cm and relative high crystal size .
More investigations and data validations are needed to demonstrate the full potential of Cosmo-Skymed SAR in snow detection
AknowledgmentThis work has been funded by the Italian Space Agency (ASI) under
the COSMO-Skymed project 1720
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Model simulations
Sensitivity of X band backscattering to snow density
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Snow depth : 1 m - Grain radius : 0.5 mm
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Model investigations : Snow-pack scattering
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Z^
z=0
z=-dN
AIR
SNOW
GROUND
z=-d1
z=-d2
z=-dN-2
z=-dN-1
•Density
•Depth
•Size/shape of crystals
• Liquid water contet
•Height St Dev
• Correlation length
• Autocorrelation function
- Microwave Remote Sensing Group
IGARSS 2011, July 23-29, Vancouver, Canada
Test of SWE Algorithm with simulated data
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10000 input values randomly varied: 5000 for training - 5000 for test
Snow depth =10 - 150 cmDensity = 200-300 kg/m3
Grain radius = 0.1 – 1.0 mmIncidence angle = 20°-70°
Single polarization (RMSE=~ 32 mm)
y = 0.9495x + 11.107R2 = 0.9342
0
100
200
300
400
500
600
0 100 200 300 400 500 600
SWE misurato (mm)
SW
E c
alc
ola
to (
mm
)
Dual polarization (RMSE=~ 25 mm)