international geoscience and remote sensing symposium vancouver, canada, 24-29 july, 2011
DESCRIPTION
ESTIMATION OF AIR AND SURFACE TEMPERATURE EVOLUTION OF THE EAST ANTARCTIC SHEET BY MEANS OF PASSIVE MICROWAVE REMOTE SENSING M. Brogioni , G. Macelloni , S. Pettinato , F.Montomoli IFAC - Institute of Applied Physics National Research Council Firenze, Italia. - PowerPoint PPT PresentationTRANSCRIPT
ESTIMATION OF AIR AND SURFACE ESTIMATION OF AIR AND SURFACE TEMPERATURE EVOLUTION OF THE EAST TEMPERATURE EVOLUTION OF THE EAST
ANTARCTIC SHEET BY MEANS OF PASSIVE ANTARCTIC SHEET BY MEANS OF PASSIVE MICROWAVE REMOTE SENSING MICROWAVE REMOTE SENSING
M. BrogioniM. Brogioni, G. Macelloni, S. Pettinato, , G. Macelloni, S. Pettinato, F.MontomoliF.Montomoli
IFAC - Institute of Applied PhysicsNational Research Council
Firenze, Italia
International Geoscience and Remote Sensing Symposium Vancouver, Canada, 24-29 July, 2011
1/20
2/20
Introduction
• Antarctica is the coldest and emptiest place on Earth
• Antarctica influence directly the Earth climate due to its extension (14-30 million of km2) and average temperature ~ -50°C As a comparison: Arctic 8 million of km2, Greenland 2 million of km2, Europe 10 million of km2
• It is one of the most important indicators of the climate changes
• Knowledge about Antartica is limited due to the harsh environment
Monagham, WWI Mag. 22.13/20
South Pole
AntarcticaAntarctic Peninsula4% of Antarctica (like California)Glacial retreats are widespreadsand move to South
West Antarctica20% of Antarctica (like Greenland)Stores 6m of global sea levelMarine based (it rests over the sea)It is shrinking overall
East Antarctica76% of Antarctica (larger than USA)Stores 60m of global sea levelApproximatively in balanceMean altitude ~3000m
4/20
Aim of the work
Passive microwave sensors are working since the 80s’ and can image Antarctica several times per day (up to 8 in the Dome C region (75° S)
Antartica is the most undersampled continent due to the cost of the manned exploration and the difficulties related to the impervious environment
The use of remote sensing techniques can help in monitoring the spatial and temporal characteristics of large regions.
Some interesting topics are the spatial and temporal evolution of temperatures, the snow mass balance, the detection of melting zones.
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1/05 7/05 2/06 8/06 3/07 9/07 4/08 11/08
Time
Bri
gh
tnes
s T
emp
erat
ure
(K
)
-80
-70
-60
-50
-40
-30
-20
-10
0
Sn
ow
tem
per
atu
re (
°C)
TBm37V
T50 (C)T 50
37 GHz
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180
185
190
195
200
205
1/05 7/05 2/06 8/06 3/07 9/07 4/08 11/08
Time
Bri
gh
tnes
s te
mp
erat
ure
(K
)
-70
-60
-50
-40
-30
-20
-10
0
Sn
ow
tem
per
atu
re (
°C)
TBm19V
T100 ( C )T 100
19 GHz
MW and Snow temperature data (Dome-C)
The temporal behavior of Tb was closely related to the snow temperature at
different depths
This analysis was conducted on more than 25000 images (at least five images per day)
The mean value of the 3x3 pixel area was extracted from each image in order to reduce noise.
6/17
y = 1.1186x - 63.874
R2 = 0.9796
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180
185
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200
205
210
200 210 220 230 240 250
Snow Temperature 10 cm (K)
Tb
v 3
7 (
K)
y = 0.9298x - 14.053
R2 = 0.9035
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198
200
210 215 220 225 230
Snow Temperature 200 cm (K)
Tb
v 1
9 (
K)
37 GHz – 10 cm 19 GHz – 200 cm
Correlation analysis
Examples of correlation between snow temperature and brightness
Frequency T50 T100 T200 T300 T400 T600 T800 T1000
6.9 GHz 0.63 0.72 0.62 0.38 0.13 0.08 0.62 0.54
10 GHz 0.74 0.87 0.78 0.51 0.19 0.07 0.73 0.68
19 GHz 0.83 0.94 0.80 0.50 0.17 0.10 0.80 0.70
37 GHz 0.98 0.90 0.55 0.19 0.01 0.39 0.83 0.43
Determination coefficient (R2) between Tb and Snow Temperature at different depths
7/20
Experimental data
AMSR-E :
More than 45000 images Frequencies used: Ku, Ka V polarizationTime: January 2003- December 2008
AWS snow and air temperature measurements:
Air Snow Accumulation
1 89577 Dome A -80.368 77.374 16/01/2005 30/12/2008 X X X2 89578 Eagle -76.420 77.024 26/01/2005 30/12/2008 X X X3 Panda (N) -73.689 76.967 01/01/2008 31/12/2008 X X X4 89813 GC41 -71.603 111.263 28/10/1984 29/12/2005 X X5 89757 LGB20 -73.833 55.672 17/01/1991 31/08/2004 X X6 89568 LGB 35 -76.043 65.010 20/12/1993 30/06/2008 X X8 89828 Dome C -75.050 123.180 01/01/2005 31/12/2008 X X X9 89734 Dome Fuji -77.310 39.700 01/01/1997 31/12/2008 X10 JASE 2007 -75.890 25.830 01/01/2007 31/12/2008 X11 89544 Mizuho -70.700 44.290 01/10/2000 31/12/2008 X12 Panda (S) -82.320 75.990 01/11/2007 31/12/2008 X13 89744 Relay station -74.020 43.060 01/02/1995 31/10/2005 X14 Giulia -75.536 145.859 10/12/1997 31/12/2008 X15 Irene -71.653 148.656 22/11/2001 31/12/2008 X16 Concordia -75.100 123.300 27/01/2005 31/12/2008 X
LON Since ToIFAC index
WMO index
Station LAT
2008Data available
2004
2005
2006
2007
2003
GREEN - Australian Antarctic Survey BROWN - University of Wisconsin*
PURPLE - Italian National Project for Researches in Antarctica**Dome C data were collected also during the IFAC Domex experiment
AGO 1
AGO 4
Panda S
AGO 3
AGO 5
Dome C
GC 41
Giulia
Irene
Dome AEagle
Panda N
LGB 46LGB 35
LGB 20Dome Fuji
Relay Station
MizuhoJASE 2007
West Antarctica
Pen
insu
la
East Antarctica
No data were available in the period 2003-2008
Only air temperature was available
Air and snow temperature available
No data were available in the period 2003-2008
Only air temperature was available
Air and snow temperature available
AWS sites
Sites of the AWS consideredin this work
8/20
Methodology
9/20
The study was carried out by using linear regressions between ground measurements and satellite data (i.e. Tair and Tb 37GHz, Tsnow 50cm and Tb 19 GHz).
In order to keep the temporal variability of the datasets, Tair, Tsnow and Tb were not temporal averaged. Here we considered up to 8 measurements per day.
Brightness temperature were spatially averaged over a 3x3 pixel area in order to lower the noise. This has a tiny impact since the std dev of the 9 measurements is lower than 1K.
We didn’t use ANN techniques (already considered in previous works) because their performances seems to be comparable to the ones of the regressions for this kind of study.
Snow temperature retrieval
10/20
11/17
R2 RMSE Equation R2 RMSE Equation
Ku, Ka 0.96319 1.7875 Tretr = 0.96231 Tmeas - 1.9594 0.9169 2.0812 Tretr = 0.90335 Tmeas - 5.1737X, Ku, Ka 0.96293 1.7924 Tretr = 0.96149 Tmeas - 1.9494 0.91864 2.0429 Tretr = 0.89834 Tmeas - 5.3126
Bands used
Retrieval with 2005 data
T50 T100
R2 RMSE Equation R2 RMSE EquationKu, Ka 0.96454 1.0167 Tretr = 1.059 Tmeas + 2.6165 0.92548 1.341 Tretr = 1.0168* Tmeas - 0.015978
X, Ku, Ka 0.96365 1.0308 Tretr = 1.0601 Tmeas + 2.6734 0.92633 1.3306 Tretr = 1.0152 Tmeas - 0.13871
Bands usedRetrieval with 2008 data
T50 T100
R2 RMSE R2 RMSE
Ku, Ka 0.98194 1.1735 0.97002 1.2076X, Ku, Ka 0.98213 1.1673 0.97184 1.1715
Bands used
Training with 2006 data
T50 T100
R2 RMSE Equation R2 RMSE EquationKu, Ka 0.98076 1.2154 Tretr = 0.98481 Tmeas - 0.98117 0.96849 1.2645 Tretr = 0.98999 Tmeas - 0.70031
X, Ku, Ka 0.96414 1.7666 Tretr = 0.98602 Tmeas - 0.9592 0.92158 2.0572 Tretr = 1.0068 Tmeas + 0.056809
T50 T100Bands usedRetrieval with 2006 data
R2 RMSE Equation R2 RMSE Equation
Ku, Ka 0.97021 0.9454 Tretr = 1.0776 Tmeas + 3.6287 0.93196 1.3355 Tretr = 1.0634 Tmeas + 2.5763X, Ku, Ka 0.97065 0.9424 Tretr = 1.0824 Tmeas + 3.8617 0.93691 1.3198 Tretr = 1.0943 Tmeas + 4.1456
Retrieval with 2008 data
T50 T100Bands used
R2 RMSE R2 RMSEKu, Ka 0.96401 1.7698 0.91807 2.09688
X, Ku, Ka 0.96414 1.7666 0.92158 2.0572
Training with 2005 dataBands used T50 T100
AN
N
Equation RMSE Bias Equation RMSE BiasKa Tretr = 0.9826 Tmeas + 1.1149 1.174 1.1346Ku Tretr = 0.9909 Tmeas + 0.5475 1.62 0.5525
T50 T100Band usedTraining with 2005 data -> Retrieval with 2006 data
Equation RMSE Bias Equation RMSE BiasKa Tretr = 1.0568 Tmeas + 2.3554 1.014 2.229Ku Tretr = 1.0679 Tmeas + 2.9725 1.433 2.7835
T100Band usedTraining with 2005 data -> Retrieval with 2008 data
T50
RE
GR
ES
SIO
NS
Developed for the year 2005
Equation RMSE Bias Equation RMSE BiasKa Tretr = 0.9624 Tmeas - 1.9582 1.79 -2.035Ku Tretr = 0.8631 Tmeas - 7.6921 2.08 -8.931
Band usedTraining with 2006 data -> Retrieval with 2005 data
T50 T100
Equation RMSE Bias Equation RMSE BiasKa Tretr = 1.056 Tmeas + 2.4288 1.0131 2.3Ku Tretr = 1.0111 Tmeas + 0.1812 1.3569 0.179
Band usedTraining with 2006 data -> Retrieval with 2008 data
T50 T100
Developed for the year 2006
Snow temperature retrieval (Dome C)
12/20
Snow temperature retrieval (Dome A, Eagle)
Dome A and Eagle ground data were obtained from Australian AWS
In these sites, AWS measured Tsnow at 0.1, 0.3, 3 and 10 m below the surface
only Tsnow at 1m is estimated in this work.
Yeardelay (days) R2 RMSE
(K)p1 p2
2005 -4 0.89312 1.2276 0.7424 233.2
2006 -2 0.89307 1.2846 0.7907 235.7
2007 -3 0.86075 1.2385 0.8059 236.1
ALL -3 0.88568 1.2871 0.777 234.9
Eagle (76.43°S, 77.02°E)
Yeardelay (days)
R2 RMSE p1 p2
2005 2 0.96326 0.67422 0.5738 223.42006 <1 0.96367 0.65563 0.5548 222.52007 2 0.94298 0.76879 0.5785 223.82008 <1 0.94747 0.80977 0.5253 220.8
2009 -2 0.96976 0.598 0.5413 222.2
ALL <1 0.95151 0.76065 0.5515 222.3
Dome A (80.44°S, 77.21°E)
Regressions between Tb 19GHz and Tsnow 1m
R2 0.89R2 0.95
13/20
Dome A (80.44°S, 77.21°E)Eagle (76.43°S, 77.02°E)
We verified that (at least in these sites) it is possible to estimate snow temperature 1m below the surface with an RMSE of about 1.5K,
The error seems to be stable throughout the years
Test of the method was carried out at different latitude and longitude
Results of snow temperature retrieval
14/20
It is worth noticing that:
-The accuracy of the retrieval (i.e. the RMSE) and the determination coefficients (R2) obtained, makes this study useful for estimating the snow sub-superficial temperature when precision of 1K are sufficient,
Snow temperature retrieval
-For climatological issues, the obtained precision could not be adequate (i.e. if the accuracy required is one order of magnitude higher),
-It seems somewhat difficult to lower the RMSE of the relationships since the accuracy of the measuring instruments (i.e. the AMSR-E and SSM/I radiometers) is of the same order (around 1.5K).
15/17
Air temperature retrieval
16/17
Snow temperature variations are primarily driven by air temperature fluctuation which heat (and cool) the snow by convection. This is different from land surfaces whose temperature depends on the solar radiation.
Tair and Tsnow (on which depends the microwave Tb) are quite good correlated,
making possible an attempt to estimate air temperature from
Tb measurements.
Correlation between air and Tb at 37GHz (the highest frequency commonly used in the remote sensing of snow) is not high as with the Tsnow due to the heat latency of snow.
Few remarks
R2 = 0.6488
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-40
-35
-30
-25
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-50 -45 -40 -35 -30 -25 -20
Tsnow 10cm (°C)T
air
2m
(°C
) Data collected at Eagle in 2005
In order to obtain better performances it is useful to consider the temporal changes of snow emissivity
17/17
Snow equivalent emissivity
In order to perform the Air temperature retrieval by means of MW data, we used an equivalent emissivity of snow obtained as
because the snowpack is subject to metamorphic changes due to the weather conditions (mainly air temperature and wind action).
Eagle Dome A
18/17
Eagle Dome A
LGB35
Examples of air temperature retrieval results
Usually the average regression provide the best results!
19/20
Results of the air temperature retrieval
Site Average relationship R2
Years consideredMean
RMSE (°C)2003 2004 2005 2006 2007 2008
Eagle Tb37GHz = 0.5256 Tair + 222.82 0.746 5.65
Dome A Tb37GHz = 0.5486 Tair + 211.75 0.775 8.06
LGB20 Tb37GHz = 0.6180 Tair + 233.64 0.843 5.4
LGB35 Tb37GHz = 0.8280 Tair + 226.40 0.919 3.9
Dome Fuji Tb37GHz = 0.6207 Tair + 216.25 0.744 7.48
Mizuho Tb37GHz = 0.7334 Tair + 203.91 0.62 6.28
Relay station Tb37GHz = 0.5642 Tair + 223.42 0.757 6.43
Giulia Tb37GHz = 0.7059 Tair + 221.93 0.854 5.25
Irene Tb37GHz = 0.4918 Tair + 233.14 0.692 8.71
Despite the quite high R2, the mean RMSE obtained is not very good (betw.4 and 8K)
Possible causes can be:- the heat latency of snow which damped the Tair variations, making the Tb slightly "insensitive" to the Tair variations,
- the quality of the AWS data were not always good due to the enviromental conditions which in some cases affect the normal service of the AWSs
20/20
Future works
The results found outline that it is possible to retrieve the snow and air temperature from microwave data, albeit with a RMSE error of some degrees.
Next steps of this work will be the exploitation of the spatial and temporal trends of the retrieved Snow and Air temperatures over a long time period (since the 80’s) in order to assess the climate variations on the East Plateau. This will be obtained by using passive microwave data, consolidated relationships between Tsnow, Tair and Tb, and assimilation methods (like kriging).
Future possible improvements could be obtained by the joint use of microwave and infrared images, albeit these latter are affected by the weather conditions and, for a certain extent, by the diurnal cycle.
21/20
22/17
23/17
Outline
Why to study Antarctica for the climate changes
Experimental data description
Retrieval of snow temperatures
Future actions
24/20
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Dep
th (
m)
Layer Contribution (%)
CXKuKaP
ene
tra
tion
dep
th (
1/e
)
Model Analysis:Contribution of Layers (0-100 m)
Multilayer model based on the Strong Fluctuation TheoryInput: experimental data from Epica and Domex campaigns
25/17
Retrieval of snow temperature : 1 – 10 meters
T10
0T200 T300 T400 T500 T600 T800 T1000
ΔT [°C] 25 17.03 10.30 6.74 4.31 3.39 1.60 0.99
R2 0.95 0.89 0.90 0.89 0.94 0.97 0.90 0.88
SE [°C] 1.9 1.21 0.74 0.54 0.26 0.17 0.12 0.08
SE/ΔT [%] 7.6 7.1 7.2 8 6 5 7.5 8.1
ΔT = Maximum – Minimum Temperature, R2 = Correlation coefficient , SE = Standard Error of Estimate, Err = Mean Percentage Error
Very good correlation !
26/17
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-80 -70 -60 -50 -40 -30 -20
Tmeasured (°C)
Tre
trie
ve
d (
°C)
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-60
-50
-40
-30
-20
-80 -70 -60 -50 -40 -30 -20
Tmeasured (°C)
Tre
trie
ve
d (
°C)
Retrieval of snow temperature : 1 m
100 cm
y = 0.9909x + 0.5475R2 = 0.9531
100 cm
Trained 2005Retrieved 2008
y = 1.0679x + 2.9725R2 = 0.9688
Trained 2005Retrieved 2006
27/17
Previous study: retrieval of Tsnow 0-2 meters
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-80 -70 -60 -50 -40 -30 -20
Tsnow Measured [°C]
Tsn
ow R
etrie
ved
[°C
]
50 cm
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-50
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-80 -70 -60 -50 -40 -30 -20
Tsnow Measured [°C]
Tsn
ow R
etrie
ved
[°C
]
100 cm
Data measured for the year 2006 compared with the retrieved one. Relationship between Tb and Tsnow for the year 2005 were used for the retrieval
R2=0.98, SE=1.5 °C R2=0.95, SE= 1.9 °C
28/17
The electromagnetic model
The Brightness Temperature Tb was computed according to the
wave approach which accounts for reflection and transmission
between the layers by means of the propagating matrix
(Kong,1990).
The V and H components of Tb were obtained by adding the
contributions of the snow layers by means of the fluctuation
dissipation theorem (Jin,1984).
The obtained value of Tb was the results of the average of 50
realizations each one corresponding to a profile of (z)
29/17
Model input parameters:
Density (z) was modeled as:
(z) = m + f(z) ;
m = measured mean value; f = fluctuating part
<f(z1) f(z2)> = p2 exp (- z1 – z2/lz) (Gaussian)
The correlation length was obtained from a semi-empirical
relationship derived from ice core data permittivity was
computed from the strong fluctuation theory as a function of
correlation length and density
Snow Temperature and Grain Sizes were obtained from
measurements
30/17
The snow measurements
31/17
0 10 20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
Dep
th (
m)
Layer Contribution (%)
LCXKuKa
Model Analysis : Contribution of Layers (0-100 m)
Pe
netr
atio
n d
epth
(1
/e)
32/17
1
)(
)(*
*
*
*
nWn
Ws
xWxdw
dGi
i
jijij
i
The Getis local statistic of the i-th pixel
j
iji dwW )(*sum of the weight in the window
x and s are the mean and the standard deviation of the entire image
xj value of the j-th image pixel
)(dwij weight of the pixel : 1 if the pixel belong to the window, 0 elsewhere
i
j
Spatial and temporal analysis (I)
33/17
Spatial and temporal analysis
Analysis performed on 2 orbits (22 and 23 images) in 2008
0
0.5
1
1.5
2
2.5
3
Std
Dev
(K
)
6.8 GHz
4
5
6
7
8
9
10
11
12
13
Std
Dev
(K
)
37 GHz
34/17
0
0.5
1
1.5
2
2.5
3
Std
Dev
(K
)
6.8 GHz
4
5
6
7
8
9
10
11
12
13
Std
Dev
(K
)
37 GHz
Spatial and temporal analysis (II)
Maps
Isolines
Temporal Std Dev
Spatial Getis statistic
2 orbits (22 and 23 images) in 2008
35/17
6.8 GHz
Spatial and temporal analysis (II)
Maps
Isolines
Temporal Std Dev
Spatial Getis statistic
0
0.5
1
1.5
2
2.5
3
Std
Dev
(K
)
Dome C
36/17-80
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-80 -70 -60 -50 -40 -30 -20
Tmeasured (°C)
Tre
trie
ve
d (
°C)
50 cm
2005 2006
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-60
-50
-40
-30
-20
-80 -70 -60 -50 -40 -30 -20
Tmeasured (°C)
Tre
trie
ve
d (
°C)
100 cm
2005 2006
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-70
-65
-60
-55
-50
-45
-40
-35
-30
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sn
ow
Tem
per
atu
re (
°C)
T50 retrieved T50 T100 retrieved T100
2005 2006
Based on the previous study, we performed a regression analysis in order to retrieve the snow temperature
Algorithm developed by using data collected in 2005
snow temperature retrieved for the year 2006
y = 0.9686x + 233.59
R2 = 0.9631160
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210
-70 -60 -50 -40 -30 -20
Snow Temperature @ -50cm (°C)B
rig
htn
es
s T
em
pe
ratu
re @
37
GH
z (K
)
2005
y = 0.474x + 216.69
R2 = 0.9096160
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170
175
180
185
190
195
200
205
210
-70 -60 -50 -40 -30 -20
Snow Temperature @ -100cm (°C)
Bri
gh
tne
ss
Te
mp
era
ture
@ 1
9 G
Hz
(K)
2005
Snow temperature retrieval
RMSE=1.16K RMSE=1.64K
37/17
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-80 -70 -60 -50 -40 -30 -20
Tmeasured (°C)
Tre
trie
ved
(°C
)
50 cm
2005 2008
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-70
-60
-50
-40
-30
-20
-80 -70 -60 -50 -40 -30 -20
Tmeasured (°C)
Tre
trie
ve
d (
°C)
100 cm
2005 2008
-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sn
ow
Tem
per
atu
re (
°C)
T50 retrieved T50 T100 retrieved T100
2005 2008
The algorithm was tested also with the Tsnow data of year 2008
Similar analysis were performed by developing algorithms for the years 2006, then validating them with data collected in different years.
Then, the retrieval was performed also by using ANN in a feed-forward multi-layer perceptron scheme (MLP) with some hidden layers of neurons between the input and output.
Snow temperature retrieval
RMSE=1.01K RMSE=1. 43K
38/17
-80
-70
-60
-50
-40
-30
-20
1997 1998 1999 2000 2001 2002 2003 2004 2005
Sn
ow
an
d A
ir T
emp
erat
ure
(°C
)
Tair T50 regression T100 ANN
Although it is not possible to verify the retrieved snow temperature values, these considerations indicate that the Tsnow estimation do not present appreciable problems
There is always a delay between the Tair and Tsnow temperature.
The range of T100 values is lower than the T50 one, which is in turn lower than the air temperature swing.
It is also worth noticing that the maximum in the Tair (which happened in 2002) corresponds to the maximum of the estimated Tsnow.
Retrieval of Tsnow for the past yearsSebbene nn ci siano dati per verifica
39/17
Analysis of temperature trends
The trend in the air temperature shows an increase of 1.3°C in the period 1997-2008
A first analysis seems to confirm that the temperature of the first layers increases
y = 6E-05x + 188.05
y = 0.0008x + 149.66160
165
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180
185
190
195
200
205
1997 1998 1999 2000 2000 2001 2002 2003 2004 2005 2006 2007 2008
Time (year)
Bri
gh
tnes
s T
emp
erat
ure
(K
)
TBm19V
TBm37V
Can the emissivity constantly increase?
Why Tb are constantly increasing?
y = 0.0003x - 62.157-90
-80
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-60
-50
-40
-30
-20
-10
0
1997 1998 1999 2001 2002 2003 2005 2006 2007
Time (year)
Air
te
mp
era
ture
(°C
)