Potential Synergetic Use of GNSS-R Signals to Improve the Sea-State Correction in the Sea Surface Salinity Estimation: Application to the SMOS Mission

Abstract

Abstract-It is accepted that the best way to monitor sea surface salinity (SSS) on a global basis is by means of L-band radiometry. However, the measured sea surface brightness temperature (T B ) depends not only on the SSS but also on the sea surface temperature (SST) and, more importantly, on the sea state, which is usually parameterized in terms of the 10-m-height wind speed (U 10 ) or the significant wave height. It has been recently proposed that the mean-square slope (mss) derived from global navigation satellite system (GNSS) signals reflected by the sea surface could be a potentially appropriate sea-state descriptor and could be used to make the necessary sea state T B corrections to improve the SSS estimates. This paper presents a preliminary error analysis of the use of reflected GNSS signals for the sea roughness correction and was performed to support the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission; the orbit and parameters for the SMOS instrument were assumed. The accuracy requirement for the retrieved SSS is 0.1 practical salinity units after monthly averaging over 2• × 2 • boxes. In this paper, potential improvements in salinity estimation are hampered mainly by the coarse sampling and by the requirements of the retrieval algorithm, particularly the need for a semiempirical model that relates T B and mss.Index Terms-Auxiliary data, global navigation satellite system-reflections (GNSS-R) signals, mean-square slope (mss), microwave radiometry, sea salinity retrieval.

Towards an ocean salinity error budget estimation within the SMOS mission

“…The effectiveness of this auxiliary data set was primarily limited by the limited number of GNSS specular reflection points in each overpass that does not allow an efficient spatiotemporal averaging [6].…”

“…The limited performance of this substitution can be related to the uncertain knowledge of the relationship between mss and wind speed, and to the coarse sampling of the test zone, both conditions suitable of improvements in the next future [6].…”

SNR Degradation in GNSS-R Measurements Under the Effects of Radio-Frequency Interference

“…One of these applications is GNSS-Reflectometry (GNSS-R), a promising technique in the field of remote sensing, that was first proposed in 1988 for scatterometry applications [6]. Later in 1993, GNSS-R was first suggested for mesoscale ocean altimetry [7], and since then, this technique has been used in the retrieval of many geophysical parameters such as measuring sea surface state [8], sea surface salinity [9], soil moisture [10], and ocean altimetry [11] among others.…”

Calibration of the GNSS signal amplitudes in the Interference Pattern Technique for altimetry

“…Several applications have been studied, including the characterization of sea surface roughness [2], salinity [3] and temperature [4]; soil moisture estimation [5] and snow depth retrieval [6]. These applications are especially useful for coastal or wet area monitoring, or for avalanche prediction.…”