Sensors_**2011**, _11_, 719-742; doi:10.3390/s110100719  
_Sensors_  
**ISSN 1424-8220**  
www.mdpi.com/journal/sensors  
_Article_  
**CAROLS: A New Airborne L-Band Radiometer for Ocean Surface and Land Observations**  
[PERSON] 1,2,*, [PERSON] 2, [PERSON] 3, [PERSON] 2, [PERSON] 2, [PERSON] 2, [PERSON] 1, [PERSON] 2, [PERSON] 3, [PERSON] 4, [PERSON] 4, [PERSON] 5, [PERSON] 5, [PERSON] 6, [PERSON] 7, [PERSON] 8 and [PERSON] 9  
CESBIO (CNRS/IRD/CNES/UPS), 18 avenue [PERSON], 31401 Toulouse Cedex 9, France; E-Mail: [EMAIL_ADDRESS]  
Universite Versailles St-Quentin, UPMC, CNRS/INSU, LATMOS-IPSL (UVSQ/CNRS/UPMC), 11 Boulevard d'Alembert, 78280 Guyancourt, France; E-Mails: [EMAIL_ADDRESS] (M.P.); [EMAIL_ADDRESS] (P.F.);[EMAIL_ADDRESS] (D.H.); [EMAIL_ADDRESS] (M.D.); [EMAIL_ADDRESS] (M.L.-L.)  
LOCEAN, Tour 45-55-5 eme etage, Paris, France; E-Mails: [EMAIL_ADDRESS] (J.B.); [EMAIL_ADDRESS] (G.R.)  
DTU-Space, National Space Institute, DTU, B. 348, DK 2800, Lyngby, Denmark; E-Mails: [EMAIL_ADDRESS] (N.S.); [EMAIL_ADDRESS] (S.S.)  
CNRM/GAME (Meteo-France, CNRS), URA 1357, Toulouse, France; E-Mails: [EMAIL_ADDRESS] (C.A.); [EMAIL_ADDRESS] (J.C.C.)  
INRA, UR1263 EPHYSE, F-33140 Villenave d'Ornon, France; E-Mail: [EMAIL_ADDRESS]  
Facultat de Fisica, Universitat de Valencia, C/[PERSON], 50, Burjassot, 46100 Valencia, Spain; E-Mail: [PERSON]S]  
IEEC/ICE-CSIC, Campus UAB/Fac Ciencies, Torre C-5-parell-2a planta, 08193 Bellaterra, Spain; E-Mail: [EMAIL_ADDRESS]  
National Institute of Marine Research (CLS), Brest, France; E-Mail: [EMAIL_ADDRESS]  
Author to whom correspondence should be addressed; E-Mail: [PERSON]SS].  
_Received: 24 November 2010; in revised form: 4 January 2011 / Accepted: 7 January 2011 / Published: 12 January 2011_  
**Abstract:** The \"Cooperative Airborne Radiometer for Ocean and Land Studies\" (CAROLS) L-Band radiometer was designed and built as a copy of the EMIRAD IIradiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling correlation radiometer. It is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments (C-Band scatterometer--STORM, the GOLD-RTR GPS system, the infrared CIMEL radiometer and a visible wavelength camera). Following initial laboratory qualifications, three airborne campaigns involving 21 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in 2007, 2008 and 2009, in coordination with _in situ_ field campaigns. In order to validate the CAROLS data, various aircraft flight patterns and maneuvers were implemented, including straight horizontal flights, circular flights, wing and nose wags over the ocean. Analysis of the first two campaigns in 2007 and 2008 leads us to improve the CAROLS radiometer regarding isolation between channels and filter bandwidth. After implementation of these improvements, results show that the instrument is conforming to specification and is a useful tool for Soil Moisture and Ocean Salinity (SMOS) satellite validation as well as for specific studies on surface soil moisture or ocean salinity.  
**Keywords:** radiometer; CAROLS; L band; SMOS; ocean salinity; soil moisture