Active‐passive synergy for interpreting ocean L‐band emissivity: Results from the CAROLS airborne campaigns

Abstract

The impact of the ocean surface roughness on the ocean L-band emissivity is investigated using simultaneous airborne measurements from an L-band radiometer (CAROLS) and from a C-band scatterometer (STORM) acquired in the Gulf of Biscay (off-the French Atlantic coasts) in November 2010. Two synergetic approaches are used to investigate the impact of surface roughness on the L-band brightness temperature (Tb). First, wind derived from the scatterometer measurements is used to analyze the roughness contribution to Tb as a function of wind and compare it with the one simulated by SMOS and Aquarius roughness models. Then residuals from this mean relationship are analyzed in terms of mean square slope derived from the STORM instrument. We show improvement of new radiometric roughness models derived from SMOS and Aquarius satellite measurements in comparison with prelaunch models. Influence of wind azimuth on Tb could not be evidenced from our data set. However, we point out the importance of taking into account large roughness scales (>20 cm) in addition to small roughness scale (5 cm) rapidly affected by wind to interpret radiometric measurements far from nadir. This was made possible thanks to simultaneous estimates of large and small roughness scales using STORM at small (7)(8)(9)(10)(11)(12)(13)(14)(15)(16) ) and large (30 ) incidence angles.

Satellite observed salinity distributions at high latitudes in the Northern Hemisphere: A comparison of four products

“…Aquarius makes use of its active measurements from its collocated radar scatterometer to improve the surface roughness correction, which is an asset that neither SMOS nor SMAP have (SMAP's radar failed three months into the mission in July 2015). Remote sensing theory and airborne experiments have demonstrated the importance of the radar in providing complementary information about the wind and surface roughness for L-band remote sensing [Yueh et al, 2001[Yueh et al, , 2010Martin et al, 2014] and uncertainty on Aquarius SSS retrievals is significantly reduced with the inclusion of radar observations [see Meissner et al, 2014, Table 3].…”

Roughness and foam signature on SMOS-MIRAS brightness temperatures: A semi-theoretical approach

“…The effect is dominant at high WS due to strong wave breaking that generates more foam over the ocean surface. To derive e w , many in-situ and airborne efforts using various instruments and observation techniques have been performed, e.g., the experiment made from a tower (Hollinger, 1971), the Wind and Salinity Experiments (WISE) Etcheto et al, 2004), the airborne Passive-Active L-band Sensor (PALS) campaign (Yueh, Dinardo, Fore, & Li, 2010) and the Combined Airborne Radio instruments for Ocean and Land Studies (CAROLS) campaign (Martin et al, 2012;Martin, Boutin, Hauser, & Dinnat, 2014). Recently, new empirical roughness models were proposed using space-borne measurements such as those from the Soil Moisture and Ocean Salinity (SMOS) mission (Guimbard et al, 2012;Reul & Tenerelli, personal communication, 2012) and the Aquarius mission (Yueh et al, 2013;Yueh et al, 2014;Meissner, Wentz, & Ricciardulli, 2014).…”

Assessment and Improvement of Sea Surface Microwave Emission Models for Salinity Retrieval in the East China Sea

“…The extraterrestrial radiation is about 2.725 K caused by the cosmic microwave background radiation related to the Big Bang nucleosynthesis and continuum radiation [36]. Although the impact of galactic radiation (hydrogen emission and continuum radiation) could be strong when these radiation sources are limited to the specular reflection into the main antenna beam, these contaminated observations could easily be discarded because reflectivity of the sea surface is large (in the order of 0.7) and the galactic signal scattered from the sea surface is near specular reflection [10,17,37]. Thus, the steady and continuous downward radiation could be due to the cosmic background radiation plus the emission from the atmosphere.…”

“…Besides the atmospheric effects, the increasing of sea surface emissivity due to the sea surface roughness and foam effects is the main source of error, which could significantly hamper the accuracy of SSS retrieval [11]. Over the past decades, the correction for sea surface roughness effects were studied based on the in-situ and airborne measurements; for example, the experiments made from a tower [12], wind and salinity experiments (WISE) [13,14], airborne Passive-Active L-band Sensor (PALS) campaign [15] and Combined Airborne Radio instruments for Ocean and Land Studies (CAROLS) campaigns [16,17]. Many rough surface emission models have also been developed based on the theoretical and empirical methods.…”