th1.t04.2_multi-frequency microwave emission of the east antarctic...

MULTI-FREQUENCY MICROWAVE EMISSION OF

THE EAST ANTARCTIC PLATEAU

IGARSS- Vancouver – July 24-29 2011

Marco Brogioni G.Macelloni, S. Pettinato CNR-IFACR. Zasso, A. Crepaz CVA-ARPAVB. Padovan, J. Zaccaria PNRA M. Drinkwater ESA-ESTEC


Outline Objectives and background The Domex experiment Satellite (SMOS- AMSR-E) and ground data The e.m. model Model comparison Conclusions and Perspectives


Objectives Verify the applicability of the East Antarctic plateau

as an extended target for calibrating and monitoring low frequency microwave radiometers using ground based (the Domex-2 experiment) and satellite data (SMOS)

Understanding the multi-frequency microwave emission of the Antarctic plateau by using satellite and ground data in combination to e.m. model


Dome C and the Antarctic Plateau• The site is view on a sub-daily

frequency by polar-orbiting satellites, at a variety of incidence and azimuth angles.

• Homogeneity of snow surface at the 100 km scale.

• Small surface roughness relative to other ice sheets.

• Low snow accumulation rate (around 3.7cm/yr).

• Clear sky, and extremely dry and stable atmosphere.

• Well known topography and environmental condition

Concordia Station (Dome C): 75.125 S, 123.25 E 3270 a.s.l

Dome C

© CSA


The Domex-2 experiment With a view to the launching of the ESA’s SMOS satellite, an experimental

activity called DOMEX, supported by ESA and PNRA, was started at Dome-C, Antarctica in 2005 with a first pilot project (Domex-I, duration one month) and continue with Domex-2.

The main scientific objective is to demonstrate the stability of the site in order to provide L-band microwave data for SMOS calibration.

DOMEX-2 experiment consisted in an L-band and an infrared (8-14 µm) radiometers (RADOMEX) installed at Concordia base on an observation tower at a height of 15 m respect to the ice sheet. Data were collected continuously (24/24 h) over two entire Austral annual cycle, starting from December 2008. Snow measurements (including snow stratigraphy, density, grains size and shape, temperature) and meteorological data, were also collected during the experiment.


The DOMEX Campaign

Concordia base

Air temperatureMean: - 53 degsMax: - 23 degsMin: - 78 degs

TOWER VIEW


Complementary Snow measurements

Winter

Summer

Snow layers:TemperatureHardnessDensityGrains shape and SizeDielectric Constant

Snow deposition:Grains shape and SizeClassification(precipitation, hoar,wind, etc.)


170

180

190

200

210

220

230

240

250

01/12/08 01/01/09 01/02/09 04/03/09 04/04/09 05/05/09 05/06/09 06/07/09 06/08/09 06/09/09 07/10/09

Brig

htne

ss T

empe

ratu

re [K

]

Time

Tv

Th

Domex -2 – 2009 campaign

Power Failure > 10 daysRadomex Temperature < -60°C !!!

No temperature control Low temperature /High fluctuation

Theta = 42° SMOS angle


0

2

4

6

8

10

12

14

16

18

20

170

175

180

185

190

195

200

205

210

215

220

01/12/08 01/01/09 01/02/09 04/03/09 04/04/09 05/05/09

Sky

Brig

htne

ss T

empe

ratu

re [K

]

Snow

Brig

htne

ss T

empe

ratu

re [K

]

Time

Tv

Th

TvTbv = 186.3 K - Dev.st = 0.6 K

Tbv = 209 K - Dev.st = 0.3 K

Temporal Stability – corrected values

6 Months Scale = December 2008 – May 2009


Domex-2 : 2010 campaign

Power FailurePC crash April 10

ProblemSolved –July 2010

11 months data


SMOS comparison - Temporal Trends

some jumps: surface effect (?)

The target response is very stable.

Fluctuation are typical of the SMOS data.

Domex Tb could be used as a

benchmark for improve SMOS

data?


Possible Explaination: wind effect

Lines= High Wind Speed (> 7 m/s)


DOMEX- Angular Trend


SMOS – comparison: Angular Trend

SMOS data provided by CESBIO

dots – SMOSdots – SMOS

lines - DOMEXlines - DOMEX


Multi-frequency Tb data: temporal trends

L C X Ku Ka

175 153.16 152.84 154.70 150.36

- 1.15 1.29 1.65 2.12

L C X Ku Ka

218 200.23 194.93 184.83 169.88

- 0.50 0.57 0.81 1.80

Obs. angle 55 deg

Mean

Std Dev

V pol H pol

almost a Black Body

V pol fluctuates less because of the Brewster angle!


Tb – StdDev vs Frequency (AMSR-E & DOMEX)

0.0

0.5

1.0

1.5

2.0

2.5

1 10 100

Frequency [GHz]

TB

Sd

ev

[K

]

.

LC

X

Ku

Ka

Tbh

Tbv

Tb sdev decreases when frequency decreases

The site is stable at L band


The snowpack is modeled as a stack of n layers with planar boundaries over a half-space medium.

Each layer is characterize by:

temperature Tl,

grain radius rl,

depth dl,

density l,

fractional volume fl,

permittivity eff l.

All the parameters used in the model are derived from Dome C snowpack measurements (EPICA, Drinkwater et al.,2003).

The electromagnetic model

d1

d2

d3

dn-1

dn

d0

i

z

.

.

.

n layers

Half-space


The permittivity of the layers is modeled by using the SFT.

The model is based on the wave approach which accounted for the reflection and transmission between the layers by means of the propagating matrix (Kong,1990).

The vertical and horizontal brightness temperatures are expressed by adding the contributions of the snow layers by means of the fluctuation dissipation theorem (Jin,1984).

The electromagnetic model


Comparison of temporal trends

Model Results

37 GHz

19 GHz

10 GHz

6.8 GHz

1.4 GHz The model is able to estimate the e.m. data with a good accuracy

Some discrepancy are present at Ku- and Ka-band


Penetration depths

Model Results

Pen

etration

De

pth

Frequency (GHz)

Penetration depth (m)

1.4 165

6.8 22

10 12

19 3.5

37 1.5


Conclusions The DOMEX-2 experiment started in November 2008 and ended in

December 2010. The high temporal stability of Tb at V polarization is confirmed in

both 2009 and 2010. Tb at H polarization exhibits a high fluctuation due to the surface and sub-surface effect (as expected).

The angular and temporal trends exhibit a very good agreement with SMOS data

Multi-frequency data emphasize the mechanisms that dominate the emission of the ice sheet

A e.m. was developed and validated using satellite and ground data The e.m. is able to explain the jumps observed in H pol. data

IGARSS- Vancouver – July 24-29 2011 RADOMEX looking in the Antarctic night

Thanks for the attention!

th1.t04.2_multi-frequency microwave emission of the east antarctic...

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