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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSlNG, VOL. 4:1, NO. 5, MAY 2()05 025

T'Ile Emissivity of Foanl-Covered Water Surface at L-Band: Theoretical ModeliI1g and Experilnentai

Results FrOln t11e Frog 2003 Field Experiment Adriano Camps, Senior Membel; IEEE, Mercè Vall-Ilossera, Membel; IEEE, Ramon Villarino, Student Mel/dm; IEEE,

Nicolas Reul, Bertrand Çhapron, Ignasi Corbeil a, Membel; IEEE, Nuria Duffo, Membel; IEEE, Franccsc Torres, Mem.bel; IEEE, Jorge José Miranda, Student MembeJ; IEEE, Roberto Sabia, Studenl Membel; IEEE,

Alessandra Monerris, Studem Membel; IEEE, and Rubén Rodrîguez

f\bstract-Sea SUl-t'ace salinity Cllll be measured by microwave radiometry at L-band (1400-1427 MHz), This frequency is a compromise between sensitivity to the salillity, small atmospheI"ic perturbation, and reasonable pixel resolution, The description of the ocean emission depends on two main factors: 1) the sea water permittivity, which is a function of sali nit y, temperature, and frequency, and 2) the sea surface state, which depends on the wind-induced wave spectrum, swell, and raill-induced roughness spectrum, and by the foam coverage and its emissivity, This study presents a simplified two-layel' emission model for foam-covered watel' and the results of a controlled experiment to measure the t'oam emissivity as a function of salinity, foam thickness, incidence angle, and polarization, Experimental results are presented, and then compared to the two-layel' t'oam emission model with the measured toam parameters used as input model parameters, At 37 psu sait water the foam-induced emissivity inCl'ease is ",0,007 per milIimetel' of l'oam thic!mess (extrapolated to nadir), in­creasing with increasing incidence angles at vertical polarization, and oecreasing with increasing incidence angles at hol'Ïzontal po!arÏzation,

Index 1liJ'/lls-BI"ightness temperature, emission, t'oam, mi­crowave radiometry, salinity, sea,

I. INTRODUCTION

T HE IMPROVEMENT of weather prediction, e.g., for nat­ural catastrophes, recluires the knowledge of soil 1110is­

ture (SM) and sea surface salinity (SSS) on a global scale. The knowledge of the SSS distribution at a global scale with a 1110d­erate revisit time is important to climate predictions, since SSS is a tracer of sea surface currents and an indicator of the differ­ence between evaporation and precipitation (E-P). Water den­sity is determined by temperature and sali nit y, and hence the

Manuscript reccived July 8, 2004; revised October 9, 2004. The ('oam emission modeling study was sponsored by the European Space Agency under Contracl5165/0 I/NLISF. The FROG 2003 campaign was sponsorcd in part by MCyT AE. ESP2001-4524-PE, in part by the Spanish Comisi6n Interministe­rial de Ciencia y Tccnologîa and EU FEDER (CICYT TIC20D2-04451-C02-0 1), and in part by Grant "Distinciô dc Recerca de la Generalitat de Catalunya," resolution: UNI/2120/20D2 on July 19, DOGC 3684, 24/07/20D2.

A Camps, M. Vall-llossera, R. Villarino, 1. Corbeil a, N. Du1To, F. Torres, J. J. Miranda, R. Sabia, A. Moncrris, and R. Rodriguez arc \Vith the Department 0(' Signal Theory and Communications, Universitat Politècnica de Catalunya, E-08034 Barcclona, Spain (e-mail: camps@tsc.upc.es).

N. Reul and B. Chapron are with the IrREMER, Depareillent d'Océanogra­phie Physique et Spatiale, Laboratoire d'Océanographie Spatiale, 29280 Plouzané, France.

Digital abject Identifier 1 D.ll 09!rGRS.2004.839651

thermo-haline circulation can also be monitored by SSS mea­surements. Salinity monitoring is useful to improve the quality of the El Nino Southern Oscillation (ENSO) numerical model predictions, as weil [1], [2].

At present, there are two planned space missions to measure global sea surface salinity maps with 10-30-day revisit time: the Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity mission l'rom the European Space Agency (ES A), and the Aquarius Earth System Science Pathfinder (ESSP) mis­sion from the National Aeronautics anc! Space Administration (NASA), with launch dates in February 2007 and September 2008, respectively.

The SSS retrieval l'rom microwave radiometric measurements is based on the fact that the dielectric constant of seawater is a function of sali nit y and temperature [3]. The sensitivity of brightness temperature (TB) to SSS is maximum at low l11i­crowave üequencies, and the optimum conditions for salinity retrieval are found at L-bancl, where there is a protectec! banc! for passive observations (1400-1427 MHz). However, even at this frequency the sensitivity of TB to SSS is low: 0.5 K pel' psu for a sea surface temperature (SST) of 20 oC, decreasing to 0.25 K pel' psu for an SST of 0 oc. Since other variables influence the TB signal (polarization, incidence angle, sea surface tempera­ture, roughness and foam), unless they are properly accounted for, the SSS determination will be erroneOllS.

During SMOS Phase A two field experill1ents named the Wind and Salinity Experill1ent (WISE) were sponsored by the ESA in the fall of 2000 and 200 l to better understand the wind and sea state effects on the L-band brightness temperatures. They consisted of acquiring long time series of TB l'rom an oil rig in the northern Mediterranean Sea to relate it to the sea surface rollghness (wind speed, significant wave height) and the instantaneous foam coverage [4].

Several effects were not complete!y understood during the WISE field experiments: the emissivity of foam and the impact of rain and oil slicks on the 'lB variations. Under Spanish Na­tional funds, the Foam, Fain, Oil Slicks and OPS Reflectom­etry (FROO) field experiment was carried out at the Institut cie Recerca i Tecnologia Agroalill1entàries CIRTA) facilities at the Ebro River delta.

This work is organized into two well-defined parts. ln the first one, a two-Iayer sea foam emission mode! at L-bancl is

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926 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 4J, NO. 5, MAY 2005

Radlotrleler

Region 0 (air)

o Region 2 (waler) Ew

Fig. 1. Oeomclrical conljguration l'or thermal emission l'rom foam-covered ocean. The foam layer is region 1 and is absorplive and scatlering. Region 2 is air bubbles cmbedded in sea \Valer and is absorplive (l'rom rS]; sec Fig. 3).

presented. In the second one, the FROG 2003 field experiment is described, and the foam emissivity measurements at vertical

and horizontal polarizations are presented in a wide range of

water salinities from 0-37 psu. These measurements are then compared to the model presented in the first part using the

measured foam parameters: bubble radii histograms, bubbles'

water coating thickness, derived bubbles' packing coefficient, foam layer thickness, and the void fraction beneath the foam

layer.

II. SEA FOAhl ;]MISSIVITY MODELINO AT L-BAND

Foam and whitecaps belong ta the class of colloidal systems that include two phases: atmospheric gases and sea water. In

the present worle, the foam layers at the ocean surface are mod­

eled as a medium of clensely paCked sticky spherical air bub­bles, coated with thin seawater coating, following the approach

of Guo et ar. [5]. The dipole approximation model developed by Dombrovskiy ancl Raizer [6] is then usecl to clescribe the effec­

tive permittivity of the system.

A. Brightness Temperature Modeling of the Foam-Waler System

Following Guo et al. [5], it is assumed that foam on the

ocean surface is composed of nearly spherical coatecl bubbles describecl by an outer radius '/', made of an air core with per­

mittivity C(J, sllrrollnded by a shell of sea water with thickiless

band permittivity C\V' The foam-covered ocean is moclelecl by the succession of three media: the air (region 0), a fDiuH

layer defined as a region of effective permittivity cNo: with a layer thickness cl (region 1), and the lInderlying seawater with some air bubbles (region 2) with permittivity Ew (see Fig. 1).

Boundaries between each region are assumed l1at. The brightness tempe rature of the foam-water system at inci­

dence angle Oi and polarization li = h (horizontal) or v (vertical) is then equal ta

(1)

where T, is the Foam layer physical temperature, the coefficient RJ) is the rel1ection coeftlcient of the foam layer medium with the effective dielectric constant C N" and is given by

(2)

where I[i is an attenuation factor that depends on the foam layer thickness d, the electromagneticwavelength /\0, and the effec­

tive permittivity CNe,

(3)

In (2), R~l are the Fresnel rellection coefficients between the air (region 0) ancl the l'oam (region 1)

COS(Bi) - JENn - Si112 Bi

cos(O;) + JENn - sin2 Oi

cNn COS(Oi) - V ENa: - sin2 Oi

ENa COS(Oi) + VENrx - Sill2

(1.;

(4a)

(4b)

and RJ,2 are the Fresnel rellection coeftlcients between fa<lll1

(region 1) and water (region 2)

VCNet - sin2 (Oi) - Jc,," - Sill2 fJ·i

(Sa)

VEND: - sin2 (0'i) + Jc,," - sin2 Bi

EwVCNet - sin2 (0.;) - cNaVcw - sin2 Bi Rt,2(Bi ) = . (Sb)

EwVENe, - sin2 (0;) + ENa JE", - sin2 fJ·i

Region 2 consists of air bubbles embedded in the ocean bacle­ground and is assumed to be absorptive. To solve (1 )-(5), one needs to define an effective permittivity for region 1, namely CNe" and for region 2, namely Ew.

B. Effective Pennittivity ofSea Foam Formations at L-Band

The main parameter of the previous multilayer emissivity model for fmun is tbe effective permittivity EN" of the foam layer considerec1. To c1etlne tbis parameter, the well-known Lorenz-Lorentz and van cle Hulst equations can be usec1 and modifiecl for the polyclispersed system of bubbles. The tlrst formula takes into account dipole interaction of bubbles in a close-packed dispersecl system (the quasi-static approxima­tion). The van clé Hulst equations describe the contribution of the multipole moment of bubbles into the effective permittivity of the system. Spectral calculations by Chemy ancl Raizer [7] show that the fi.rst resonant electromagnetic elTects by van de Hulst's mechanism occur for bubbles' radius (], ::::: /\0/'1. At L-band (/\0 = 21 cm); this corresponds ta bubble diameters on the orCIer of 10 cm. Such very large bubbles are extremely rare at the sea surface and therefore, the multipole mechanism may be neglected at L-band for which only the clipole term

Il

p te li y p

\\

a c

" a tl

P tl

tl ti

1 c

(l05

"nt ith

er ,,­y !

\ ')

Il l, il

1\

! :,1

• p! LJ! '.j

J

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CAMPS /'/ (II.: EMISSIVITY OF FOAM-COVERED WATER SURFACE AT L-BAND

may be considered. In the present work, we use the dipole ap­proximation mode! developecl by Dombrovskiy and Raizer 161 to describe the cffective permillivity of the system. Il involves the use of a modification of the Lorenz-Lorentz equation and yields the following simple formula for the complex effective pennitlivity ENnof a foam layer [6], ITI:

where

1 -1- ~7r N . o{r)

l -17rN. n{r) (6)

(7)

and N is the volumetric concentration of the bubbles, n:('r) is the complex polarizability of a single bubble with external radius 'l', N. is the so-called packing coefficient or stickiness parallleter, and Jl J CI') is the normalized probability distribution function of the bubbles' size. In natural media such as foam, the densely paclœd particles can have adhesive forces that make them adhere to form aggregates. This e[fect is accounted for in the model by the stickiness parallleter h;, which is inversely proportional to the strength of the attractive forces between bubbles [8].

According to Dombrovskiy and Raizer [6], the complex po­larizability depends on the external radius of the bubbles 'l', the complex permittivity of the shell medium (salt water) Ew, and the bubbles' filling factor q = 1- 6/1' following

Since the bubble size distribution depends on the vertical po­sition within the foam layer, the effective pennittivity depends on the vertical position as weil: ENu = ENo:(;;). In the sim­plest case, the foam-water system may be modeled as a succes­sion of elementary foam layers, each of them having a homoge­neous effective dielectric constant. However, the exact depen­dence of such fUl1ction with vertical position, which de pends on the vertical distribution of the bubbles' size, is very poorly known. It is very like!y that the vertical distribution of the bub­bles' size p.rCr, ;;) is a function of the intensity and sc ale of the underlying breaking event. Moreover it will certainly strongly evolve during a transient breaking evenl. Nevertheless, in order to keep a tractable number of parameters in the presel1t model, we choose to consider a uniform vertical distribution of bubbles' sizes ]lfC",;;) = JJfCr) within the foam layer.

The foam void fraction (i.e., the ratio of the volume of air to the total volume of the foam) depends on the distribution of the bubbles' filling factor q. Therefore, the distribution of bubbles radii p./'Cr) together with the distribution of coating thicknesses f (6) determine the foam layer void fraction. In the present sim­plified model, we fixed the value of the shell thickness b, but the outer bubble radius T is a ranclom variable. According to Dombrovskiy [9], this approximation reflects an experimentally establishec! fact for an emulsion layer of foam (young foam), but it requires verification for a foam with honeycomb structure

927

Fig. 2. Location or the WISE ancl FROO lielcl expcriments.

(aged [oam). Numerous observations of oecanic bubble size dis­tributions are reported in the literature based on acoustic, photo­graphic, optical, anc! holographic methods [1 1]. Currently, it is not clear how to parameterize the ocean surface bubble size dis­tribution. Following Bordonskiy et al. [12] and Dombrovskskiy and Raizer [6], we used a'T distribution for the size distribution function of the bubbles

(9)

where A and B are parameters of the distribution with '/'1' = .11/ B being the !11ost probable radius.

Finally, to ca\culate Ew, a simple physical model based on in­duced c!ipoles is used. Let Es", denote the permittivity of the sea­water (see [13] for Es", at L-band), anc! fn the fractional volume occupied by the air bubbles. Then, the effective permiltivity Ew is given by the Maxwell-Garnett mixing formula [5]

where

1 -1- 2f"y Ew = Esw l j' '1 - nY

1. - Esw Y=

1. -1- 2Esw

(l0)

(lI)

Note that the effective permittivity Ew here c!oes not include scatlering extinction, which is small due to the fact that the sea­water is heavily absorptive. According to our simplillec! emis­sivity !11odel for [mlln, the brightness temperature induced by a sea foam layer is a function of

TB = function(O.,, ./',p,T,,, 'l'Ill b, li;, d, fn, SSS, SST) (12)

where (Ji is the rac\iometer incidence angle, f the electromag­netic frequency, p is the polarization, T" is the foam physical temperature, TT' is the most probable radius, 6 is the bubbles' water coating thickness, li; is the bubbles' packing coefficient (same as stickiness parameter), cl is the l'oam layer thickness, fa is the void fraction beneath the l'oam layer, and finally, SSS

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928 HiEE TRANSACTIONS ON GEOSCIENCE AND IŒMOTE SENSING, VOL. 43, NO. 5, MAY 200S

(a)

(b)

Fig. 3. (a) Pool filled with \Vater during a foam emissivity measurement incidence angle scan. (b) Detail of the air diffusers used to gencrate foam.

and SST are the sea surface salinity and temperature, respec­tive!y, Ali these parameters are either known (Oi, j', li) or mea­surecl (TH, '/'J!' li, cl, fa., SST, SSS), except the packing coeff1cient (h:) that will be derived by minimizing the rms error between the FROO 2003 measurements and lhc lheoretical mode! (see Scction III-B).

TIl, SEA FOAM EMISSIVITY MEASUREMENTS AT L-BAND

A, FROC 2003 Field Experilllellf Description

Thc FROO 2003 cxpcrimenl was sponsorccl by lhe Spanish Oovernmcnt 10 detcrmine thc emission of these factors. The controlled cxpcrimcnt was performcd at the facililics of thc 1n­stilllt de Rccerca cn Tècniqucs Agropecllitries CIRTA) at Poble Nou dcl Dclla, in lhc Ebro Rivcr mouth (Fig. 2).

The L-banc1 Automatic Rac1iometer (LAURA) radiomeler [4] was mountcd on onc sidc of a 3 m x 7 m pool fillcd with a mix­ture of sea watcr and frcsh water l'rom the Ebro River. The river watcr was mixcd with the sea waler 10 adjusl lhc salinily ovcr thc range l'rom 0-37 psu [Fig. 3(a)], A melallic net was mounted around the pool, and at the edges the net was inclinecl45° to re­Hect lhe sky radiation, avoicling contamination of the measure­ments l'rom ground racliation collecled through thc scconclary

c)

e) fl

1) h)

Fig. 4. Suite of instruments dcployed to acquire ancillary data. (a) Six sub­surface temperature sensors. (b) Metal bars of the instantaneous surface level sensor. (c) and (d) Array of 16 gold electrodes of the air fraction measurement systcm. (e) Periscope \Vith vidco camera to acquire vertical l'oam profiles. (1') lnfrarecl radio!1leter to measure surface cmission with l'OHm. (g) Video camera to clcrive surface foam coveragc [as in (h)[.

lobes of the antenna, and cnlarging the raclio-eleclric horizon. The measurcmcnl slralcgy consistee! of performing incidence angle scans l'rom 25° to 55 0

, in 5° sleps, and measuring lhe sur­facc's emissivity wilh the foam gencrators off, on, ancl finally off again at each incidence angle, Ali measllremenls were pcr­formccl ancr Sllnset to avoid sllnconlamination, andlhe pool was orientecl to the north which minimizecl the Oalaclic backgrouncl noise, Foam was createcl by a network of 104 air c1iffusers placecl at the bottolTl of the pool, and conncclecl to an acljustable air pump with a maximum air flow of 500 m3 /h [Fig. 3(b)].

A series of instrumenls was cleployecllo acquire ancillary clala

to be usecl as inputs to theoretical moclcls as follows:

• six temperature scnsors locatecl below the water surface [Fig, 4(a)];

two metallic bars usecl in a condllctivity-basecl inslanla­neous surhlce level scnsor [Fig. 4(b)J;

c

)05

))

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CAMPS 1'1 (//.: EMISSIVITY OF FOAM-COVEIŒD WATER SURFACE 1\1' L-BAND 929

c)

f)

i)

Fig. 5. Foam vertical profiles at di l'l'ercnt salinities (seale in ccntimetcrs). (a) () psu, (b) 5 psu, (c) 10 psu, (d) 15 psu, (e) 20 psu, (f) 25 psu,(g) 30 psu, (h) 37 psu, and (i) horizontal view of natural sea surface bubbles (photograpl) l'rom Gran Canaria island, SSS33.8 psu, rel'erence size = 0.50 Euro com).

• array of 16 golc1 eleclrodes [Fig. 4(c)] of a conductivily­basec1 subsurface voie! fraction profîler [Fig. 4(d)];

• uttrale video camera wilh a large angular lens mounlec1 on a periscope to acquire foam vertical profiles [Fig. 4(e)];

• CIMEL CE 312 four-bane! lhermal-inl'rarecl rae!iomeler: 8-13, 11.5-/2.5, 10.5-11.5, ane! 8.2-9.2 l/,Ill [Fig. 4(0], l'rom the Universitat de València;

• Sony SSC-DC393 video camera and zoom [Fig. 4(g)] 10 match the field of view to the radiometer' s anlenna beam [Fig. 4(h)], usecl to derive the water surface's l'oam coverage;

• porlable meteorological station usee! to measure air tem­peralure, pressure and relative humiclity, and wincl speee! ane! direction.

B. Radiometrie Measure/llents

Foam-Free Measurements: The fîrsl measuremenls con­sisted of measuring lhe emissivily of the flal waler surface at clifferent salinily levels

,Wat.el'( /' 0 SSS SST) = 1 - rF'l',,-,ncl (0 E.( /' SSS SST)). cp .,' ,~ p , , , , , . (13)

Down-welling radiation ane! finite beamwic\lh effecls were correclec\. As expected, the brighlness temperalures (or alterna­tively emissivilies) decrease with increasing salinily levels, in agreement with the lheory using lhe Klein-Swift dieleclric con­stant model [9].1

IThe goodness of the agrcement bctween the moclelcd Tu ancl the measured 1'/1 is ~().12 K. Salinity retrievals using measurcd Tu cxhibit a 0.26 psu bias for the SSS l'rom 0-37 psu, and SST l'rom 14 oC to 20 oc.

j Il L-J. ___________ ~

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.......... _ .. ___ ._. ___ ~ ___________________ ........... _ ... ""·I..i",W",tfWttOlli' __ W_hN1iit L.b·'~'""i;;ÎiliO_"

(no IEEE TI(ANSACTlONS ON GEOSCIENCE AND REMOTE SENSINCi, VOl. .• U, NO. 5, MAY 2(H15

a) SSS: a psu. mean fp: a0211m, medlan f p: 78911m,

c)

Fig. 6. Delail of foam and bubbles verlical profiles. (a) Fresh \Vatel' and (b) 15 psu. Corresponding bubble radius histograms. (c) Fresh waler: mean radius = 80211.111, median radius = 789/1.111 and (d) 15 psu (mean radius = 437 Ilm, median radius = 423 J1m).

Foam Mcasurclllcnfs: As explained in Section II, in addition to the foam surface coverage needed to estimate the foam emis­sivity from the measurements, modeling foam emission requires the knowledge of: 1) the fmuu layer thickness; 2) the bllbbles' radii distribution; 3) the bubbles' water coating thickness; 4) the stickiness parameter; and 5) the air fraction beneath the [oam layer, as follows.

• The foam layer thickness was measurecl by the vicleo camera mountecl on the periscope. For the same air f10w rate the foam thickness is very small for Fresh water (Iower surface tension) and increases with increasing salinity (higher surface tension). Fig. 5 presents ni ne vertical profîles corresponcling to nine clifferent salinities l'rom 0-37 psu. Alltomatecl image processing was llsecl to cletermine the mean thickness of each photogram in a systemalic manner.

• The estimation of the bubbles' radii clistribution requirecl the recognition of isolated bubbles, ancl fîncling the equiv­aIent spherical bubble. Fresh water bubbles are lar'ger, ancl their shape is less spherical than salt y water bllbbles. The measurecl mean raclii are: ~0.80 mm for fresh water bubbles [Fig. 6(a) ancl 6(c)], ~0.63 mm at 5 psu, ancl nearly constant ancl approximately equal to ~0.44 mm above 10 psu [Fig. 6(b) ancl6(d)J.

In orcier to check the gooclness of the artifîcially gener­atecl fmul1 as comparecl to natural foam encountered over the sea aner a wave splash, 80 photographs of the sea surface (SSS ~ 33.8 psu) were acquirecl in the coasts of the Gran Canaria islancl al'ter wave breaking. A top view is shown Fig. 7(a), with its corresponcling histogram [Fig. 7(b)]. This is representative of the whole volume, since the foam containecl only one layer of bubbles.2 The most noticeable fealures of the histogram are that the av­erage radius is ~0.60 mm, as compared to ~0.40 mm for the artificially generated bubbles (Fig. 6), and that the histogram is less symmetric around the mean value, with a much longer tail, which corresponds to Im'ger bubbles formed l'rom combinations of smaller ones. The best fît by a gamma function bubble radii pelf' is also shown in Fig. 7(c), showing that the mcasurccl histogram is more peaky and narrower them the gamma pdf.

• Bubbles' coating thickness measurecl from zooms of the vertical profiles (e.g., Figs. 6 and 7) are in the 10-20-/l,m range. However, this is not a critical parameter, since the foeun emissivity, as preclictecl by the theoreticalmodel ex­plain in Section Il, shows little variation with il.

20lher experimenls [1 (rI have shown lhe agreemenl belween lhe bubble sizc hislogram of arlificially gencralecl sca foam anclnalural sea l'Dam.

L

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CAMPS cl 1//.: EMISSIVITY OF FOAM·COVEIŒD \V1\ITil< SURFACE 1\1' L·BAND l):J1

781 pm, ffi"dlun r 695 Ilm,

b) 600 1000 1500 2000 Radius ulm]

:lA 10" Gamma functloo fil a'" 2.9 b=211.9

1.6 î r

f

pd/Ir). --!--.r'·I.e ï ; 'I.G b··J'lJ;l)

1.4

1,2 \1

il ,-\

0.8 " \, ,~ \\

0.6 :1' '\ \ ,1 ,\\

0.;\ 1 \. ' 1 \.'.

0.2 i .",~~~

a) °0 ~-~'\:.~> . .;:,,-,,,,:?,,,,.,,.~~~,.~ __ , ... ~J.,;;o...

c) 1000 2000 '" d ifflil11m l .1iOOO 6000 iSOOiJ

Fig. 7. (a) Top view of nalural sea f'oam (Gran Canari a Island, scale: 50 euro cenl coin). (b) Bubble radius hislogram (mcan radius = 781 Ilm, mosl probable radius = G9G Il.m. (c) Corresponding bubble radius hislogram (higher pcak f'unclion), and bcst fil by a gamma f'unclion (Jower peak).

TABLE 1 ESTIMAI'ED PACKINO COEFFICIENT l" MINIMIZINO THE RMS ERROR BETIVEEN

THE FROG 2003 MEASUREMENTS AND THE THEORETICAL MODEl

SSS Optillluill K (H-pol) Oplillluill K (V-pol) Average K

of H· and V-pol 5 0.14 0.03 0.08 10 0.'10 0.04 0.07 15 0.'13 0.11 0.'12 20 0.13 0.12 0.12 25 0.17 0.15 0.16 30 0.17 0.15 0.16 34 0.21 0.17 0.19

• The bubbles' packing coefflcient or stickiness parame ter plays a very important role in the foam emission. How­ever, since no direct means has been found to measure it, the approach followecl has been its determination by min­imizing the l'ms error between the moclel ancl the mea­surements. Table 1 shows the clifferent values of h~ founcl for clifferent salinities ancl polarizations. Above 10 psu the values at both polarizations are very close, as expectecl, but for low salinities they are significantly clifferent, which is not unclerstoocl, although it may be attributecl to the more flattenecl shape that the large bubbles have at low salini­ties, as comparecl to high salinities. ln the thircl co[umn the

optimum Il. values are chosen to minimize the overall l'ms error at both polarizations.

• The void fraction beneath the faLun layer is also a critical parameter. Ils cletermination From video imagery is subject to large uncertainties clue to the clepth of the fielcl of view (~I cm). To avoicl this problem, the relative conductivity between foam ancl the air-water mixture below ancl water was measurecl. Curtayne's equatian [14]

(14)

relates the ratio of the foam ancl water conductivities to the liquicl fraction (fit, The void fraction beneath the foam layer fu can then be c\eterminecl as

(lS)

Fig. 8 shows two lime series of the evolution of fa. for each of the 16 golcl electrocles. Fig. 9 shows the corresponc\ing av­erage ancl stanclarcl cleviations of fu. of each electrocle. From these plots, c\erivecl l'rom measurements acC]uired with the same air f1ow, it can be appreciatecl that far fresh water .la is ~ [S% to

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t '

932 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 4:1, NO. 5, MAY 2(JO)

Temporal sequence (ail the electrodas) SSS: 0 psu 100

~

c 23 c: 50 0

'" .... w êiî $ .!. ë(

a) 20 40 60 80 100

Samples [sec]

Temporal sequence (ail the electrodes) SSS: 37 psu

Pig.8. Air-waler content (C) lime sequence lor every electrodc. (a) SSS o psu (15 electrodes, the top elcctrocle \Vas air) and b) SSS = .37 psu (16 electrodes).

20% beneath the [oam layer, increasing sharply just below the water surface, while for salt y water, fit is l11uch lower, ~S%,

and the foam layer is thicker,

Fig. 10 shows a typical fmlll1 emissivity l11easurement corre­sponding to a salinity of 33.21 psu. Radiometers' raw clata (m V) are shown at H- (lower plot) and V- (upper plot) polariza'tions, ancl inciclence angle (l'rom 25° to 55°, lower panel) as a func­lion of the time [Fig, lO(a)], The L-band surface emissivity is plotted at H- (lower plots) ancl V - (upper plots) polarizations of the foam-free surface (clottecl line) ancl with 1'0 a 111 (solicl line). The foam coverage as a funelion of the incidence angle is shown in green in Fig, IO(b). The average foam coverage for aIl inci­

dence angles is 86.4%.

The foam emissivity can be clerivecl Ü'OI11 (16)

Total(o) = F, eFOalll(O) -1- [1 - FJ . e Wat.el·(O) eh}v ... li ,v "'h,v (16)

E o SSS: 5 psu °nllO

00 16

0

r--I.....-J-" 11 r 6

10 1( 1

50 100

1'1'

8,

'là 1 50 100

E 0 SSS: 10 psu °111/10 SSS: 15 psu flfi 10

00 16 . ~

':c o 10 50 ---1.J00

16·

11 '

6· 1

J '/0 50 '100

E o SSS: 25 psu °fal1O

16 . -- --" .. _. --~.

50 100

E o SSS: 37 psu 0fal10

00 16

r

~I

'1

1'11

·1 ,1

1l."----~_----'. o 0 50 100

~1

1

6

50 100 Alr·Waler ratio (%] Air·Water ratio 1%)

Fig. 9. Air-water l'l'action U,,) mean value ancl standard deviation 01' instantaneous values (uf" divided by 10) l'or every clcctrode at SSS = 0 tn 37 psu. Each parallel gold clectrode (3 mm x 4 mm, total 16 e1eclrodes) is separatecl by 2 mm l'rom the adjacent c1cctroclc (vertical scale equals 8 cm). Element number 16 is locatccl ab ove the surface, ancl hence the air-water ratio is 100%.

where F is the foam fraction coverage (in the sea it is cleter­mined by the wind, the air-sea instability, the feteh, the salinity etc., [15]) From which the variation with respect to the nat sur­j~lce can be derivecl

e To 1.11 1 (0) _ ('Water(o) A., (0)= .,Foalll(f1)_ ,Wl1ter(fl)= 'Ii,v 'il,v Deh,\' {7 Cil,v {7 Lh,v {7 li' .

( 17)

Fig, 1 1 (a)-(h) shows the intercomparison of the FROG ll1ea­surell1ents of e WaLer (dotted line) and eFOillIl (solid lines with

circIes) scaled to 100% coverage (16), and the theoretical values computed using the model describecl in Section II with the ll1easurecl foam parameters as inputs (solicl lines with tri­angles), The values of the stickiness parameter usecl are the

Tous droits de propriété intellectuelle réservés. Reproduction, représentation ct dil1lision interdites. Loi du 01/07/92.

CAMPS c/ (/1.: EMISSIVITY OF FOAM·COYERED \VATER SURFACE AT L·BAND

-200

a)

30-Apr-2003, SSS: 33.21 psu, SST: '18.7 oC --~. ~. ~~._':'",:~-- '

- H10am - Vroom

Hfonm.free

V,oam.rree j'

933

30-Apr-2003,100'''H = 0.397, 100'''v c 0.258, SSS: 33.21 psu, SST: 18.7 oc 1 W~:: __ ':::"':":':'---·:_"-~~?~'~~~:_"':'-'- !o'!.',n .•

, - H foarn 0.9 - V foam

••••• Hfoam.tree 0.8 V

••••• foam·free

0.7 A Hspccular .. ! .

~O.6 __ :,_~~~~:~ • ____ ~ :;cn:O.5 ___ ~_:.L .. ~: . ... ~~. . ;

..;. .............. ·0 .!!l 0.4 . ..; .. ;;; .. ~ .• Q.." ............. , .. , E ••••••••••••••• (i)-........... .

LU O. • •• " ......... ;~; ............. ~ ..... : ..... ~~ •• l. .............. l ............... ~ ~2 ,"

0.1

b) ~5 30 35 40 Incidence Angle [0]

45 50

Fio 10 Foam cmissivity mcasurcment at 33.21 psu. (Lower curves) H-polarization and (upper curves) Y-polarization, with (solid line) foam and (dotted line) wi~ilOU; foam. (a) Radiometers' raw data (millivolls) versus (lower plot) incidence angle and (h) surface's emissivity and (Iight gray plot) foam coverage as a function of incidence angle. The variation of the surface's foal11 coverage versus incidence angle is due ta the variallon of the 100U11 patterns gcncrated by the array of diffusers in the 3 m x 7 m pool [see Fig. 4(h)J.

optimum ones found at each sali nit y, which in general in­creases with SSS as the bubbles are more densely packed, as shown in Table I. The l'ms error between the measured data and the theoretical foam emissivity model is calculated and shown in each figure ((J' "'h,,,) and varies l'rom 0.008 to 0.017 at H-polarization, and l'rom 0.011 to 0.033 at Y'polarization. In general the agreement is much better at H-polarization th an at Y'polarization. At Y -polarization, the measured values show a larger variation with incidence angle than the model predic­tions, which requires further analysis and refinement of the mode!. At H-polarization the agreement is excellent, except at low salinities, where there is a bias between the measured and preclictecl emissivites at ail incidence angles.

As shown by Guo et al. [5, Figs. 6~8], the presence of foam in­creases the brightness temperature (emissivity) almost linearly with foam thickness until it saturates.3 Finally, Fig. 12 shows the measured 6eh,,,(f)) values normalizecl to the foam thickness as a function of the salinity at H- and Y -polarizations. The oscil­lations in Figs. 12(a) and 12(b) at low salinity leve1s are due to the small values of the foam thickness, which are clifficult to measure [e.g., Fig. s(a)]. Fig. 12(c) and (d) shows the smoothecl values.

As founcl during the WISE measurements [16], ·at L-band the foam emissivity increase is Im'ger at Y -pohu'ization than at H-polarization, and it increases with inciclence angle at Y -polar­ization, while it clecreases at H-pohu·ization. In order to get the same foum brightness temperature increase as in WISE [161, the effective foam thickness (assumed to be the same for ail foam patches regardless of the type of foam) should be approximately 8 mm.

3Brightness tcmperature saturation depends 011 bubble sizc and frequcncy. At 37 GHz ittakes place l'or l'oamthickness around 4-8 cm, and at 19 GHz around 16-22 cm [5, Fig. 6]. No numerical simulations have been reported at L-band, but thc saturation thickness must be much larger. lndeed, in the FROG 2003 Illcasurements, the cmissivity increasc is very modcst, which suggcsts that the thickness or the generated t'oam is far away l'rom the saturation thickncss.

IV. CONCLUSION

The presence of foam increases the emitted brightness temperature, since it acts as a transition layer that aclapts the wave impedance of the two media: water ancl air. The increase depends on the fraction of the sea surface coverecl by foam F(U10 ), which is usually parameterizedin tenllS of the wincl speed, but it clepends on other factors, such as lile air~sea

temperature difference, the sea surface temperature, the fetch, etc. [15]

,Total(o) - F(U ). oFoitm ,1. [1 - F(U )]. eSea el' - 10 "p' 10 '1'

- Sca + F(U ). [e Foam _ eSea] - el' 10 '1' P

- Sca.L F(U ). "e Foa7n - ep " Hl w. '1' . (18)

The FROG 2003 experiment has provicled the first reportecl L-band emissivity measurements of artificially generated foam on a salt sea water surface over a wide range of incidence an­gles and salinities at both polarizations. The ancillary clata ac­quired (foam thickness, air~water fraction, bubble size distri­bution and water coat thickness) have been usecl as inputs of a simple two-Iayer theoretical mocle!. The intercomparison of model outputs with the measured emissivities has allowed the retrieval of the packing coeHicient, which is approximately h; = 0.112 for ail salinities, and,,; = 0.19 at888 = :34 psu. At Y-pol the model and the measurements tend to disagree at higher salin­ities, and at H-pol at lower salinities. From 6~34 psu, the agree­ment is very good. In addition, the contribution of errors in the estimation of the foam emissivity to the error of the sea sur­face emission are altenuated by a factor equal to the sea surface foam coverage (~ 1 % at 15 mis). The results obtained in FROG 2003, and the t'oam emissivity and coverage clerived from WISE 2001 measurements, indicate that an effective foam thickness of ~8 mm may be appropriate to moclel in a simple way the foam contribution to sea surface emission.

934

Tous droits de propriété intellectuelle réservés. Reproduction, représentation ct ditllIsiofl interdites. Loi du Ol/07/92.

a)

c)

e)

g)

IEEE TRANSACTIONS ON GEOSCIENCE AND IŒMOTE SENSING, VOL. 43, NO, 5, MAY 2(0)

06·Apr·2003, "'u" 0,016, ",w" 0,013, SSS: 1.14 psu, SST: 14·C

1 -.... HfonIlHrlc~:surcd Fonm purametero:

0.9 -'i'- V Io"n",' ... o". thlokllo • ., 6,11 mm 0.8 -... H,o.am.mod(!ol t~: 17.05%

-1â- Vtoam .. model :i: 10 Ilnl

0.7 ..... Hfo.1)m,'r~e 'fi: 802.35 1-1 ln

:> ... ~. V'O.:JAl.ffOO t.: : 0.175 :;0,6 ~~

l;'0,5 _~~:: ........ .. i:!: ~twr{*-e;j( .. ~{~~tt •••• ••• ~., •• ~ ..... , :~O ., ........... .. .ll0:3 .............................................................. ..

0.2

0.1

30 35 40 45 50 Incidence Angle [')

21-Apr·2003, ""II" 0.009, ",w" 0.011, SSS: 10.49 psu, SST: 20.6 oc

1 -'f'- H'~m,me')5ured Foam parametars:

0.9 -w- V ro.sm.fM:lsuted thlcknoslS; 10.99 mm

0.8 ..... H,o,am-model 'Jo: 22.27% -ID- V ro.;trn-modtl .-; ; 10 Iim

0.7 ...... Hto.nm."Clo 'p: 440.35 1Irn

...... V'o.itm.fre-o ... : 0,oa5 ........................ ~~-"'"

:fO,5 ~ ................................ . ·2!O ................ .

.ll0:3 .............................................................. ..

0,2

0.1

~~5------~30~----~3~5~----~4~O------~45~----~50' Incidence Angle [")

28-Apr·2003, n"u" 0.009. n,IV' 0,024, S5S: 23,24 psu, 55r: 20 oC

1 ........ H'oam-m~a;unld Foam paramoters:

0.9 -19- V'o>!TI.mmore<l lhlcknc .. : 16,31 mm

0.8 ..... H,o...lm.mOdel '.11: ~2.21% -8- Vf04m.modcl f,: 10 !Im

0.7 •••• HfCl,3m.rtec rp: A43.4S flm

> .ou V'o.1m.frco .t: : 0.125 ",0,6 .. ' ~

;; ~'P"""-' . ;;0,5 ___ =-;;;..--- .•.. ' io. . ...... ';;:::!t. -, ........... $ ............ ~ ...... .. 0.3 ..................................... : ...................... ~ 0,2

0,1

30 35 40 45 50 Incidence Angle l')

30·Apr·2003, 0,11" 0,017, ".IV" 0,012,555: 33,21 psu, 55T: 18,7 oC

1 ~ Hfoam.mll';l$I.rrfi'd Foam paramotors:

0,9 -'l!'- V'o.m-m ... orcd 'hICkno .. : 10,65mm 0.8 ......- Hfoam.mod~1 '.1: ~,59%

-~ V'O.1m.model 1-: 10 'lm 0.7 ..... Hr~m-freo 'p: GM.1111m

>' u"V'o.lm.hvo ... :0.160 iO.6 _ .. _ ....... -.~_._--- ~,~="'> .. ""tiW

f!'~=,,~""""'--~;:O.5 _----=-:~- . ,.."."

j::3:::::::::::::::::::::::: .......... ~ 0.2

0,1

30 35 40 45 50 Inclde"c. Angle r)

b)

d)

f)

h)

2G·Apr.2003, n.,fI' 0,011, ",w" 0.011, SSS: 6,18 psu, S5T: 19 oC

1

~ H'o~m.nlO.a,ur~d 0.9 -.I/f- Vto.a-m.nlt-aJUtlKl

0.8 -ft- H,oam.model """@- V toam.model

0,7

Foam paramotors:

thlèkne-u: 10.41 tnm ',,: n.63 1A-.

b: 10 Ilnl

H,oittn.rtu " ... V fo..ml.free

r'l: 833,131101

~ : 0,060 :;; e:0,6

f:r=::=·~::::~.:::;c~'~' .. .. .. ~ ........... ....... . 0.2

~1 .

~ W • ft ~ ~ Incidence Angle [0)

25·Apr·2003, ""HU 0.010, n,,y" 0.016, S5S: 16,29 psu, 55T: 16.4 oC

1 -... H,oam-mfJUUrOd

0,9 ...... - V'""", __ •• or<l<l

0.8 ..... H,o.am-model -.. V toam,model

0.7 .. u. Hfo.tm,fleil •••• Vfrutm,ftee

Foam parumeters: IhlCknou: 13,0" mm ':.: 10.oit'/Î,

li: 10pm rp: .437,46 Jtm

~: 0.115

,.. ~O,6

~::J3~ .. :··~ .. ~ .. ~ .. = .. ~ .. : .. ~ .. : .. : .. : ... ~ .. ~ .. -.. -.. -.. -.. ~ .. -.. -.. -.. -.. -.. ~ .. ~ .. -.. -.. -... -.~ ... 0.2

0.1

30 35 40 ~ 50 Incldenco Angle [')

24-Apr·2003, n,IH. 0.008, n,IV· 0.032, 5SS: 25,5 psu, S5T: 18.8 'C

1 ...... H'Oolm-fMtlSUrnd

0.9 -'1p- Vtoam.moluurnd Foam paramotors:

thfeknc!l'; 1J,76 mm ',1: 9.21% 0.8 -e- Hfoam-model

-$- VrO/lm.mOdcl .': 10 'lm 0.7 ..... Hf~m.trec rp: 536,75 ~m

S ...... V~?-~~~ l;:0.160.~ t O

•6 ~

!0.5t:===~~ ............ .. ·~O ••••• _ ....... ~ ........ - ...... ~ ....... . .ll ..... ..

0.3 .............................................................. ..

0.2

0.1

30 35 40 45 50 Incidence Angle [0)

23~Apr .. 2003, ",'H= 0.011, ",WC 0.033, SSS: 37.33 psu, 55T; 15.6 <le 1

-v- H,o.llm.fM.uufcd Foam parameters: 0.9 ~! ... Vfoam-rnC;tSUrCd thlcJmes5: 12.73 mm

0.8 .... H'oam-modol f,.: 4,14% -1)}- V foam-modo-I ,'1 : 10 Jlm

0.7 H.' H'Mm."e-e 'p: 457.96 Iim

~0.6 ~ ... v,oam:"..., ,: 0,190-------i~ ~0,5.!... __ -~~ ..• ' :~O, ~ .......................... , w

0,3 ............................................................. '"

0.2

0.1

30 35 40 45 50 Incidence Angle [')

Fig. II. Emissivities at (lower three plots in each panel) H·poJarization and (upper three plots in each panel) V-polarizfltion for dil'ferent salinities in the 1-37-psu range, Dashee! lines ine!icate fOflm-free conditions. (Sol id Jine with circles) FROO measureinents. (Solid line marked \Vith triangles) Theoretical model \Vith measurcd paramcters: [oam thickness, bubbles radii, air-water fraction, /j == 10 1r.n1, ane! optimum packing coefficicnt derived by filling the cmission modelto the measurements,

1

l, i ~ d ri

li ,~ l';

\'t l,

200S

Tous droits de propriété intellectuelle réservés. Reproduction, représentation ct dimlsiol1 interdites.

CAMPS 1'1 al.: EMISSIVITY OF FOAM-COVrmEIl \VATER SUI(I'i\CE AT L-BAND

0.012

50

a) sss [psu) Incidence Angle [0)

Filtered lleH = OH (!OIIm) - eH (1",,".lr .. ) [l/mm]

0,012

30 50 20

10

c) sss [psu) Incidence Angle [0)

b)

d)

0.012

0,008

0,004

o 40

0,012

0,004

0 40

935

'"

50

10 35 30

sss [psu] o 25 Incidence Angle [']

Filtered llev = ev (Io.m) - ev (IOIIm./r .. ) [l/mm]

30 50

20 40 10 35

30 sss [psu] 0 25

Incidence Angle [']

Fig. 12. Foam emissivity increase per foam thickness unit inmi\limeters, at 100% coverage, at H- and Y-polarizations as a function of SSS and Il;. (a) Measured data points (H-polarization). (b) Measured data points (Y-polarization). (c) Panel (a) low-pass filtered. (d) Panel (b) low-pass filtered. Osci\lations in (a) and (b) are due ta errors in the foam thickness measurement, which is very sma\l l'or low salinities.

ACKNOWLEDGMENT

Special th an les are given to the Institut de Recerca de Tèc­niques AgropeCjuàries (IRTA)-Poble Nou ciel Delta personnel for their help cluring the experiment at their facilities ancl to J. Fant, C. Gabarro, ancl A. Julià (Institut cie Ciències ciel Mar CMIMA/CSIC-Barcelana) for analyzing the water samples. The authars wish ta aclenawleclge twa ananymaus reviewers for their comments ta improve the clarity af the text.

REFERENCES

Il] G. S. E. Lagerloer. (2000, Jan.) Report of the Third Workshop, Salinity Sea Iee Working Group, Field Programs and Algorithms: Sate\lites and Science, San Antonio, Texas, USA. [Online]. Availablc: hllp:llwww.esr.org/ssiwg3/SSIWG_3.html

[21 .1. Johanncsscn el al., "Scientilic reqllirements and impact or space obser­vations orocean salinity l'or modeling and climate stlldies," ESA, NOOl'd­wiik, The Netherlands, Final Report, ESA Contract 14273/00/NLlDC, 2002.

13] C. T. Swift and R. E. Mclntosh, "Considerations l'or microwave remote sensing of ocean-surrace salinity," IEEE nal/s. Geosci. Eleclrol/., vol. GE-21, no. 4, pp. 480-491, Oct. 1983.

[4] A. Camps, .1. Font, M. Yall-llossera, C. Gabarrô, 1. Corbella, N. Duffo, F. Torres, S. Blanch, A. Aguasca, R. Yillarino, L. Enrique, .1. Miranda, J. Arenas, A. Julià, .1. Etcheto, Y. Caselles, A. Weill, J. Boutin, S. Con­tardo, R. Niclôs, R. Rivas, S. C. Reising, P. Wursteisen, M, Berger, and M. Martin-Niera, "The WISE 2000 and 2001 campaigns in support or the SMOS mission: Sea surface L-band brightness temperature obser­vations and their application ta multiangular salinity retrieval," IEEE Tral/s. Geosci. Remole Sel/s., vol. 42, no. 4, pp. 804-824, Apr. 2004.

[5] J. Guo, L. 'l'sang, W. Asher, K.-I-!. Ding, and C.-T. Chen, "Applications of dense media radiative transfer theory for passive microwave remote sensing of foam covered ocean," IEEE nal/s. Geosci. Remole Sel/s" vol. 39, no. 5, pp. 1019-1027, May 2001.

[61 L. A. Dombrovskiy and Y. Y. Raizer, "Microwave model of a two-phase medium at the ocean surface," Izvesliya, AI/l/os. Oceanic Phys., vol. 28, no. 8, pp. 650-656, 1992.

l7] y. Cheilly and Y. Y. Raizer, Passive MicrOlvave Re/l/ole Sel/sil/g (~r

Oceal/s. New York: Wiley, 1998. [8] L. M, Zurk, L. Tsang, K. H. Ding, and D. P. Winebrenner, "Monte

Carlo simulations of the extinction rate or densely packed spheres with clustered and nonclustered geometries," .1. 01'1. Soc. A/l/el:, vol. 12, pp. 1772-1781, Aug. 1995.

19] L. A. Dombrovskiy, "Ca\clllation of the thermal radiation emission of roam on the sea surfaccw," !zvesliya, AlI/lOS. Oceal/ic Phys., vol. 15, no. 3, pp. 193-198, 1979.

[10] R. D. Peltzer and O. M. Grimn, "Stability and decay propertics or l'oam in seawater,", NRL Memo. Rep. 5949, Apl'. 24,1987.

r Il.1 J, Wu, "Variation of whitecap covcrage witll wind stress and water tem­perature," J. Pllys. Oceal/ogl:, vol. 18, pp. 1448-1453, 1988.

r

Tous droits de propriété intellectuelle réservés. Reproduction, représentation ct dil1l1s1ol1 intcrditcs. Loi du 01/07/92.

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOT!'. SENSING. VOL. 43. NO. 5. MAY 20D5

112] G. S. Bordonskiy, 1. B. Vasil'kova, N. N. V. V. M. Vesclov. y. A. Mil­itskiy. V. G. Mirovskiy, V. N. Nkitin, V. Y. Raizer, Y. B. Khapin. Y. A. Sharkov. and V. S. Etkin, "Speclral characleristics of the emissivity of foam formations," Izve.Hiya, AllI/os. Oeeal/ie PI/ys., vol. 14, no. 6, pp. '164-'169, 1978.

113 J L. A. Klein and C. T. Swift, "An improved modcl for the diclectric con­stant of sea water at microwave frequcncics," IEEE J. Occl/I/ie EI/g., vol. OE-2, no. l, pp. 104-111, 1977.

1141 D. Wcaire and S. Hlltzlcr, ?'lie l'hysics o/,F(){//II.1'. Oxford: Clarendon. 1999.

r 15] E. C. Monahan and IVI. Lu, "ACollstically relevant bllbble assemblages and their dependcnce on metcreological paramctcrs," IEEE J. Oceal/ie EI/g., vol. 15, pp. 340-349, Oct. 1990.

r 16] R. villarino, A. Camps, M. Vali-liossera, 1. Miranda, and .1. Arenas, "Sea foam and sea state cfTects on the instantaneous brightncss temper­atures at L-band," in Proc. 1.1'1 Resulls Worksl/Ofl 01/ WISEILOSACIEII­roS7i\RSS Ca/llflaigl/s, Nov 4-6, 2002, pp. 95-103.

Adriano Camps (S'91-A'97-M'00-SM'02) was born in Barcelona, Spain, in 1969. He received the Telecommunications Engineering degree and the Ph.D. clegree in telecommunications engineering in 1992 and 1996, respectively, both l'rom the Poly­technic University of Catalonia (UPC), Barcelona, Spain.

From 1991 to 1992, he was with the ENS cles Télécommunications de Bretagne, Bretagne, France, \Vith an Erasmus Fellowship. In 1993, he joined the Electromagnetics and Photonics Engineering

group, at the Department of Signal TheOI"y and Communications, UPC, as an Assistant Professor, and since 1997 as an Associate Professor. In 1999, he was on sabbatical leave at the Microwave Remote Sensing Laboratory, University of Massachusetts, Amherst. His research interests are mierowave remote sensing, with special emphasis in microwave racliometry by aperture synthesis techniques. He has performed numerous studies within the frame of European Space Agency SMOS Earth Explorer Mission. He is an Associate Editor of Radio Sciel/ce.

Dr. Camps reccived the second national award of university studies in 1993, the INDRA award of the Spanish Association of Telecommunication Engineering to the best Ph.D. in 1997, the extraordinary Ph.D. award at the Universitat Politècnica de Catalunya in 1999, the First Duran Farell Award and the Ciudad de Barcelona Award, in 2000 and 2001, respectively, both for Technology Transfer, in 2002. the Research Distinction of the Generalitat de Catalunya for contributions to microwave passive remote sensing, in 2003, the Premi Nacional de Telecomunicacions (Gencralitat de Catalunya) with the members of the Electromagnetics and Photonics Engineering group, ancl in 2004 a EURYI (European Young Investigator) Award. Also, as a member of the Microwave Radiometry Group at UPC, he received in 2000, 200 l, ancl 2004 the Ist Duran Farell and the Ciudad dc Barcclona Awards for Technology Trans­feer, and the Salvà i Campillo Award of the Telecommunications (Engineering College of Catalonia) to the mast innovative research project. He \Vas Chair of Cal '01. He is editor of the IEEE Geosciel/ce al/d Relllole Sel/sil/g News/el/el' and President-Founder of the IEEE Gcosciencc and Remote Sensing Society Spain Chapter.

Mcrcè vall-llossera (M'99) rcccived the Senior Telecommunication Engineer and the Doctor Telecommunication Engineering dcgrecs in 1990 and 1994, respectively, both l'rom the Polytechnic University of Catalonia (UPC), Barcclona, Spain.

She has been lecturing and doing rescarch at the Departlllcnt of Signal Theory and COllllllunications, UPC from 1990 until 1997 as an Assistant Prof'cssor and l'roll! 1997 until present as an i\ssoeiatc Pro­J'essor. She spent a sabbatical year in Montreal with the seholarship of the "Programme Québécois de

Bourses cl' cxcellence" (1996-1997): "Stages de Formation postdoctorale au Québec pour jcunes diplômés étrangers." Hel' researeh interests include numer­ical methods in clectromagnctism, microwavc radiomelry, antcnna analysis. ancl design. Current!y, her rcseareh is mainly rclated to the study of numcrical methods applied ta the sea surface emissivity and their characterization at L-band and the MIRAS/SMOS project.

Dr. Vali-liossera, along with the ather members of the racliometry group at UPC, was awardecl the "9th Edition of the Salvà i Campillo Award" in 2004, the "Primel' Premio Duran Farell de Investigaciôn Tecnol6gica" in 2002, and the "Primer Premio Ciutat cie Barcelona d'lnvestigaciô Tecnolàgica" in 2001.

Ramon Villarino (S'04) recciveclthe Ingeniero and Ph.D. degrees in telecommunications from the Poly­technic University of Catalonia (UPC), Barcelon<l Spain, in 2000 and 2004, respectivcly.

I-Ie has participated in the development and con­struction of an L-bancl radiometer and in the tlVa WISE field experiments sponsorecl by ESA cluring 2000-2002, in tbe FROG 2003 fielcl experiment to cletermine the emissivity offaam at L-band, and in the MOUSE 2004 experiment carried out at JRC-Ispra to determine the emissivity of clif'ferent types of soils.

Nicolas Reul reccived the B.S. dcgree in marine sci­ences engineering l'rom Toulon University, La Garde Cedex, France, and the Ph.D. clegree in physics (fluid mechanies) l'rom the University Aix-Marseille Il, Marseille, France, in 1993 and 1998, respcctively.

From 1999 to 200 l, he was a Postdoctoral Re­sc archer at the Applied Marine Physics Department, team of Pral'. M. Donelan, Rasensticl Schaol of Ma- . rine and Atmospheric Science, University of Miami. Since 200 l, he has been a Permanent Rsearcher at the Département Océanographie Spatiale, Institut

Francais de Recherche et cI'Exploitation cie la Mer, responsible for the activities conccllling the future SMOS satellite mission. The focus of his research pro­gram is to improve understanding of the physical processes at air-sea interülCC and passive/active remote sensing of the ocean surface. I-Ie has cxperiencc in applied mathematics, physical oceanography, clectromagnetic wave theOl'Y, and its application to ocean remote sensing. He is presenlly a member of the ESA/SMOS Science Advisory Group.

Tous droits de propriété intellectuelle réservés. Reproduction, représentation cl diflllsion interdites. Loi du 0 l/07/92.

CAMPS fi {/I.: EMISSIVITY OF FOMvl-COVERED WATER SURI'ACE AT I.-\JAND

Bertrand Chapron received the B.Eng. degree l'rom Institut National Polytechnique de Grenoble, Grenoble, France, and the Ph.D. clegrec in physics (fluid mcchanics) l'rom the University or Aix-Mar­seille II, Marseille, France, in 1984 ancl 1988, respeetively.

He spent three l'cars as a Pastcloctoral Research Associate at the NASA Goddard Space Flight Centcr, Wall,,!,s Flight Facility. He has cxpcricncc in applicd mathcmatics, physical occanography, elcctromagnetic wave theO/'y, and its application

to ocean remote sensing. He is currcntly a Rcsearch Scientist and is Heacl or the Spatial Oceanography group at the Institut Francais de Recherche ct d'Exploitation de la Mer, Responsible or the Centre ERS Archivage ct Traite­ment. He is a Collaborator or Principal [nvestigator in seve rai ESA (ENYISAT, Global Navigation Satellite System), NASA, and CNES (TOpEX/pOSElDON, JASON) prajeets. He is Coresponsible (with H. Johnsen, NORUT) or the ENYISAT ASAR-wave mocle algorithms and scientific preparation l'or the ENYISAT wind and wave proclucts.

Ignasi COl'bella (M'99) received the Teleeommu­nic~llions Engineering and Dr.Eng. clegrees, both l'rom Universitat Politècnica de Catalunya (UPC), Barcelona, Spain, in 1977 and 1983, respectively.

[n 1976, he joined the School of Telecommunica­tion Engineering in UPC as a Research Assistant in the Microwave Laboratory, where he worked on pas­sive microwave integrated circuit design ancl char­acterization. During 1979, he worked at Thomson­CSF, Paris, France, on I11icrowave oscillators design. In 1982, he became an Assistant Professor at urc,

an Assaciate ProfessaI' in 1986, and a Full ProfessaI' in 1993. He is currently teaching microwaves at the undergraduate level in urc and has designed ancl taught graduate courses on nonlinear microwave circuits. During the school year 1998-1999, he worked at NOAA/Environmental Technology Laboratory, Boulder, CO, as a Guest Researcher, developing methods for radiometer cali­bration and data analysis. His research work in the Department of Signal Them'y and Communications, UPC includes microwave airborne and satellite radiom­etry and micrawave system design.

Nuria Duffo (S'91-!V['99) received the Telecom­munication Engineer degree from the Polytechnic University of Catalonia (UPC), Barcelona, Spain, and the Doctor in Telecommunication Engineering l'rom UPC, in 1990 and 1996, respectively.

Since 1997, she has been an Associate Professor at Upc. Hel' current research interests are numerical methods in electromagnetics, microwave radiometry, antcnna anal l'sis, and design.

Francesc TOlTCS (M'96) received the Ingeniero and Doctor Ingeniera degrees in telccommunication engineering l'rom the Polytechnic University of Catalonia (UPC), Barcelona, Spain, in. 1988 and 1992, respectively.

In 1988-1989, he was a Research Assistant in the RF System Division, European Space Agency, No­ordwijk, The Netherlands, devoted ta microwave de­vice testing and characterization. ln 1989, he joined the Antenna-lvIicrowave-Raciar group, ure, where he is currently an Associate Professor. His main re­

search interests are focused on the design andtesting of microwave systems and subsystems. He is currently engaged in research on interferametric radiometers devoted to earth observation.

937

Jorge José Miranda (S'04) was !Jorn in Las Palmas de Gran Canaria, Canary Islands, Spain, in 1973. Hc received the Telecollllllunication Technical Engineering degree l'rom Las Palmas de Gl1\n Canari a University (ULpGC), Spain, and the Se­nior Telecomlllunication Engineering degree rrom the rolytechnic Univcrsity or Catalonia (UPC), Barcclona, Spain, in 1996 and 200 l, respectively. He is currcntly pursuing the Ph.!). dcgrcc in te1CCOIll­lI1unication engineering l'rolll Ul'c. His ph.D. thcsis is rocused on the sea surrace emissivity at L-band.

It includes the devclopment of new Illodcls for clctermining the sea surrace l'Oughness and the comparison and improvelllent or existing emissivity modcls.

From 1996 to 1999, he was \Vith thc Remote Scnsing and RaclaI' Laboratory (EUITT-ULPGC), where collaborated in satellite image proccssing. [n 1999, he joined the Signal Theory and ComIl1unieations Department, UPC. Since 2002, he has been an Assistant Proressor at the UPC.

Roberto Sabia (S'l)3) \Vas born in Naples, ltaly, on Novcmber 13. 1975. He gracluated (cum laude) in marine environ mental sciences (five-year course study), curriculum in oceanography, rrom the Uni­versità degli Studi di Napoli "Parthenope," Naplcs, in 2002. He is is cUITently pursuing a ph.D. degrec in signal theory and communications at the Universitat Politécnica de Catalunya (UPC), Barcelona, Spain.

ln 2002, he was recipient of a grant l'rom the Microwave Remote Sensing Laboratory . Univcrsità dcgli Studi di Napoli "Parthenope," on sea surface

scaltering models. In 2003, he joined the Departmcnt of Signal Them'y and Communications, UPC. In 2003, he participated in FROG 2003 and REFLEX 2003 measurements campaigns. He is actua]]y worldng on a research con­tract within the ESA's SlvIOS project. His main research interests deal \Vith mÎcrowave radiometry and sea surface salinity retrieval.

Alcssandra Moncrris (S'03) was born in Va­lencia, Spain, in 1977. She received the degree in telecommunication engineering rrom the Unil'ersitat politècnica de Yalència (UPY), Yalencia, Spain, in 2001. She she is cUITently pursuing the ph.D. degree at the Universitat politècnica de Catalunya (UPC), Barcelona, Spain.

She was with the Group or Microwave Applica­tions l'rom UPY developing numerical methods for the electromagnctic anal l'sis or waveguide-based devices. In 2002, she joined the Department or

Signal Theory and Communications, upc. Hel' main research interests deal with surface soil moisture retrieval algorithms l'rom brightness temperaturc Ineasurements.

Rubén RodrîgllCZ, photograph and biography not available at the time or publication.