Conference Paper

Brightness temperature correction of the sea state effect using GNSS-R data

Dept. Teor. del Senyal i Comunicacions, Univ. Politec. de Catalunya, Barcelona, Spain
DOI: 10.1109/MICRORAD.2010.5559574 Conference: Microwave Radiometry and Remote Sensing of the Environment (MicroRad), 2010 11th Specialist Meeting on
Source: IEEE Xplore


Sea Surface Salinity (SSS) is a very important océanographie parameter that can be measured using L-band microwave radiometry. The measured brightness temperature measured over the ocean is influenced by the sea state that can even mask the salinity signature. Reflectometry using navigation signals (GNSS-R) has been proven to achieve sea state determination and has been proposed to be used to correct the measured brightness temperature for the sea state effect. In this framework, the "Advanced L-BAnd emissiviTy and Reflectivity Observations of the Sea Surface 2009" (ALBATROSS 2009) field experiment was undertaken collecting an extensive dataset of collocated radiometnc and reflectometnc measurements. In this paper the experimental results and mam conclusions of the ALBATROSS 2009 field experiment are presented.

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    ABSTRACT: Global navigation satellite system reflectometry of signals is a promising technique to remotely sense a number of Earth's geophysical parameters, and it has been proposed for ocean monitoring applications such as mesoscale altimetry or sea state monitoring. So far, the following two main approaches have been considered to retrieve a sea state descriptor from measured delay waveforms or delay-Doppler (DD) maps (DDMs): 1) fitting the measurements to a model tuned with the desired parameter or 2) directly linking a property of the measurements with the parameter to be retrieved (e.g., volume of the normalized DDM). However, these approaches provide a single sea state descriptor related to the overall glistening zone where sea state conditions may not be homogeneous. In this letter, the relationship between the physical space and the DD domains is exploited, and a method to retrieve the bistatic scattering coefficient distribution over the observation ocean surface from measured DDMs is proposed. Index Terms—Bistatic scattering coefficient, delay-Doppler map (DDM), global navigation satellite system reflectometry (GNSS-R), sea state.
    No preview · Article · Jul 2011 · IEEE Geoscience and Remote Sensing Letters
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    ABSTRACT: In February-March 2009, an airborne field cam- paign was conducted using the Passive Active L- and S-band (PALS) microwave sensor and the Ku-band Polarimetric Scat- terometer to collect measurements of brightness temperature and near-surface wind speeds. Flights were conducted over a region of expected high-speed winds in the Atlantic Ocean, for the pur- poses of algorithm development for sea surface salinity (SSS) retrievals. Wind speeds encountered during the March 2, 2009, flight ranged from 5 to 25 m/s. The Global Positioning System (GPS) delay mapping receiver from the National Aeronautics and Space Administration (NASA) Langley Research Center was also flown to collect GPS signals reflected from the ocean surface and generate postcorrelation power-versus-delay measurements. These data were used to estimate ocean surface roughness. These estimates were found to be strongly correlated with PALS-mea- sured brightness temperature. Initial results suggest that reflected GPS measurements made using small low-power instruments can be used to correct the roughness effects in radiometer brightness temperature measurements to retrieve accurate SSS.
    No preview · Article · Nov 2011 · IEEE Geoscience and Remote Sensing Letters
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    ABSTRACT: Reflectometry using GNSS signals of opportunity (GNSS-R) has stood as a powerful technique for ocean remote sensing. Particularly, the use of these techniques has been proposed to retrieve sea state information (i.e. sea surface roughness) among other applications. Precise knowledge of the sea state is a key issue to process L-band radiometric measurements for sea surface salinity retrieval. It has been recently shown that GNSS-R data can be directly linked to the brightness temperature variations caused by the sea state effect, without the use of emission/scattering models or sea spectra models. In this study, this approach is applied to CoSMOS 2007 flights data. Firstly, the radiometric and GNSS-R data sets are presented. Secondly, measured brightness temperature is corrected using the collocated GNSS-R data. In particular, the area under the normalized waveforms is used to directly compute the required brightness temperature correction. Thirdly, the salinity retrievals are presented (achieving an error reduction from 2.8 psu for the raw measurements down to 0.51 psu). Finally, the obtained results are compared with the WISE correction approach, based on the wind speed correction, and the conclusions of this work are presented.
    Preview · Article · Dec 2011 · Radio Science
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