Assessment of instrument STability and Retrieval Algorithms for SMOS data (ASTRA) S.Paloscia IFAC-CNR MRSG - Microwave Remote Sensing Group

Florence (Italy)

Microwave Remote Sensing Group I - DOMEX-2 : long time stability of L-band emission at Dome-C Antarctica

Giovanni Macelloni, Marco Brogioni, Simonetta Paloscia, Simone Pettinato (CNR-IFAC)

Mark Drinkwater (ESA/ESTEC) Andrea Crepaz (CVA-ARPAV) Objectives

Verify the use of the East Antarctic plateau as an extended target for calibrating and monitoring the performances of SMOS:

‰ Evaluation of the long-time stability of L-band microwave emission by using ground data collected at Concordia station in 2008-2009 (Domex-2) and comparison with the results obtained during Domex-1 (2004-2005)

‰ Evaluation of spatial stability of microwave emission by using active and passive satellite data Dome C: Location

©CSA • 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 Dome C 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 Concordia Station (Dome C): 75.125 S, 123.25 E environmental condition 3270 a.s.l Expected L-band stability

50 45 Amsre-2005 Ka 40 SMMR-SSM/I 35 30 25 20 Ku 15 10 X Tbv Annual Variation (K) C 5 L 0 1 10 100 Frequency (GHz) z Extrapolation to L-band indicates average seasonal amplitude << 1 K z C-band suggests that DC Tbs are sufficiently stable to identify drifts in SMOS calibration – But experiments needed to verify annual L-band stability SMOS coverage at Dome-C

Typically 2-7 overlapping passes/day

Azimuth variation Incidence variation Dome C − 75S − 125E 1200 Dome C − 75S − 125E 700

1000 • numerous 600 800 500

overpasses per day 400 N 600 N

300

400 • distributed in 200

200 incidence, azimuth 100

0 0 0 50 100 150 200 250 300 350 0 5 10 15 20 25 30 35 40 45 Azymuth (deg) Incidence (deg) DOMEX-2 Preparation

z L-band radiometer : – New antenna Æ Potter Horn – New thermal system : z 1 year experiment in extreme environmental conditions Temp = -80°C / -15°C z thermal stability z Minimize sun effect (during summer) z Radiometer Tests and Calibration The Instrument

IR radiometer

cm 180

z RaDomeX - Radiometer z Frequency : 1413 MHz z Bandwidth: 27 MHz z Sensitivity = 0.2 K (Ti =2 sec) z Polarization: H and V Actuator z Antenna: Potter Antenna 70 cm z HPBW: 20°

L- Band – Potter Antenna The Instrument

Antenna : Potter horn

IR -radiom

180 cm

OMT

Radiometer 70 cm

PC Thermal Tests

THERMAL CHAMBER • -25 /-65 °C • Diurnal Cycle • IR Lamps – solar effect • ESA TEC – model and design Thermal test results : OMT

12° External Temperature Variation = Negligible Internal Temperature Variation Radiometer Calibration

Lake and Sky Measurements Anechoic Chamber Radiometer Calibration

350 350 Tv y = 1.3003x - 74.383 300 300 ) ) R2 = 0.9989 K K ( ( 250 250 b b 200 200 cal T cal T i i t t 150 150 e e r r 100 100 eo eo h h y = 1.2794x - 75.192 T T 50 2 50 R = 0.9994 Th 0 0 0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350 Measured Tb (K) Measured Tb (K) Domex-2 Experiment

‰ An experimental campaign (DOMEX-2) with ground based radiometers started at Concordia Base in Austral Summer 2008 to check the stability of L band emission at yearly scale, within the framework of the ESA-SMOS calibration and validation activities

‰ Snow measurements (including ice core) were carried out during the summer campaign in order to characterize physical snow properties of the first 10 meters. These data will be used as inputs to a multi- layer electromagnetic model able to simulate Tb The DOMEX Campaign

TOWER VIEW Air temperature Mean: - 53 degs Max: - 23 degs Min: - 78 degs Concordia base Tower Installation

RADOMEX support

RADOMEX Tower Installation

15 m DOMEX-2 Schedule z Start : 29 November 2008 z End: November 2009 (TBC) z Data Transfer : Tower Æ Base Æ Italy (1 day) LAN e-mail z Measurements cycle:

140

s) 120 eg

d 100 e ( l

g 80

n Sky (calib.) 60 90° –130° ce A

n 40

e ICE – SHEET d 20 SMOS Fixed Angle ci 90° – 30° 42° n I 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Time (min.) Complementary Snow measurements

Summer Snow deposition: Grains shape and Size Classification (precipitation, hoar, wind, etc.)

Winter

Snow layers: •Temperature • Hardness •Density • Grains shape and Size • Dielectric Constant Domex-2 – Preliminary results

250 140 Tv

) Tv 120 200 s) e (K r Th Th 100 eg atu e (d er 150 80 l p g m e 60

100 ce an n e ess T d n Theta 40 t ci

h Theta n

g 50 I i r 20 B SNOW SKY SNOW (Fix. Ang.) 0 0 0 50 100 150 200 Time (sec.) Not calibrated data Domex-2 – Preliminary results Instrument Temperature Monitoring

35 RF components )

. 30 25 degs

e ( 20 ur

at 15 Cables and connectors 10 mper e

T 5 0 0 300 600 900 1200 1500 Time (min.) DAILY Fluctuations < 1.5 °C – as expected by ESA-TEC model DOMEX-2 Temporal Stability

250 January / March Comparison )

K 200 l (

150 ical Po t

r 100 e

V January = blue - 50 b March = pink T

0 1070 1120 1170 Time (min.)

Not calibrated & not temperature corrected TB differences < 1 K DOMEX-2 Status and Summary z The instrument has been developed and successfully tested in Italy z The instrument has been installed at Concordia base z Experiment started at the end of November and is now in progress z Thermal stability of the instrument is confirmed (as predicted by the ESA-TEC model) z First results are promising z Absolute calibration will be considered in the next months (temperature correction and deconvolution effect) z Satellite data analysis (spatial variability) is in progress