New Observations From the SWIM Radar On-Board CFOSAT: Instrument Validation and Ocean Wave Measurement Assessment

Abstract

This paper describes first results obtained from the SWIM (Surface Waves Investigation and Monitoring) instrument carried by CFOSAT (China France Oceanography Satellite), which was launched on October 29 th , 2018. SWIM is a Ku-Band radar with a near-nadir scanning beam geometry. It was designed to measure the spectral properties of surface ocean waves. First, the good behavior of the instrument is illustrated. It is then shown that the nadir products (significant wave height, normalized radar cross-section and wind speed) exhibit an accuracy similar to standard altimeter missions, thanks to a new retracking algorithm, which compensates a lower sampling rate compared to standard altimetry missions. The off-nadir beam observations are analyzed in details. The normalized radar cross-section varies with incidence and wind speed as expected from previous studies presented in the literature. We illustrate that, in order to retrieve the wave spectra from the radar backscattering fluctuations, it is crucial to apply a speckle correction derived from the observations. Directional spectra of ocean waves and their mean parameters are then compared to wave model data at the global scale and to in situ data from a selection of case studies. The good efficiency of SWIM to provide the spectral properties of ocean waves in the wavelength range [70m-500m] is illustrated. The main limitations are discussed, and the perspectives to improve data quality are presented. 1

New Directional Wave Satellite Observations: Towards Improved Wave Forecasts and Climate Description in Southern Ocean

“…Except for waves propagating close to the along‐track direction, two‐dimensional wave spectra can be accurately recovered over the wavelengths range of 70–500 m (see Hauser et al., 2020). In this study, we used SWIM wave spectra derived from the most recent processing version V5.0 which has been shown to significantly reduce the noise impact on the detection of wave partitions (see Hauser et al., 2020); furthermore, we focus on the directional wave spectra from the beam 10°, demonstrated to perform the best. SWIM also provides Significant Wave Height (SWH) along its track from nadir measurements (every ∼7 km), just like the classical altimeter measurement (referred to as SWIM‐nadir).…”

Validation and Calibration of Nadir SWH Products From CFOSAT and HY‐2B With Satellites and In Situ Observations

“…But a new algorithm is used (Hauser et al., 2019). It is designed that the SWH can be used to calibrate the directional sea wave spectra retrieved from the other five rotating beams (Hauser et al., 2020; Liu et al., 2020).…”

Indian Ocean Crossing Swells: New Insights from “Fireworks” Perspective Using Envisat Advanced Synthetic Aperture Radar

“…Although the Envisat mission ended in 2012, C-band SARs that are equipped with wave mode continue providing swell spectra nowadays, such as European Copernicus missions Sentinel-1A/B [19] and Chinese Gaofen-3 [30]. In addition, Chinese-French joint mission CFOSAT launched in 2018, which is also capable of providing 2D ocean wave spectra globally [31]. With the accumulation of more data in near future, it is encouraging to enlarge the temporal series of remotely sensed swell spectra archive and merging multisensor data, therefore improving the significance of our results.…”