Perspective of a Ku-Ka Dual-Frequency Scatterometer for Simultaneous Wide-Swath Ocean Surface Wind and Current Measurement

Abstract

Ocean surface wind and current are essential ocean dynamic environment and climate variables, and simultaneous observations at high resolution have attracted considerable interest. The study on surface wind and current will improve our knowledge of energy transfer between the atmosphere and the ocean, as well as the advection of heat, nutrients, and pollutants in the ocean. Since ocean surface wind and current are tightly coupled, we discuss the wind speed and direction errors effects on current, and find that current velocity is sensitive to wind speed and direction errors. Thus, it is necessary to obtain simultaneous wind field information to mitigate the effects of the wind on current retrieval. In this study, we present a Ka-Ku dual-frequency pencil-beam Doppler Scatterometer (DopScat), keeping the Ku-band for wind measurement and the Ka-band for current measurement. We establish an end-to-end simulation model to analyze the performance of the dual-frequency DopScat, and discuss the effects of satellite attitude and velocity determinations on current retrieval. The system parameters were optimized based on the simulation model. The simulation results show that the K pc of the Ku-band DopScat is better than that of the traditional fan-beam and pencil-beam scatterometer, which is beneficial to improve wind measurement accuracy. In the Ka-band DopScat, the standard deviations (Stds) of current velocity in both along-track and cross-track directions could be smaller than 0.05 m/s, when the wind speed is larger than 5 m/s. When the wind speed is 7 m/s, the current field effective swath is 660 km, accounting for 63% of the DopScat swath, with an accuracy of 0.05 m/s. Our results indicate that the use of a Ku-Ka dual-frequency DopScat could be a feasible method for wide-swath and high-accuracy simultaneous measurements of ocean surface wind and current.

On the Optimal Design of Doppler Scatterometers

“…Subsequently, Bao et al [4] examined a point design for a Ku-band surface winds and currents that used a two-frequency approach to mitigate range ambiguities (although they did not examine in detail the impact of correlation on forming pulse-pairs using non-overlapping bandwidths). The design was updated to a dual-frequency Ku/Ka-band instrument in [5]. Bourassa et al presented a Ka-band design for a potential Winds and Currents (WaCM) mission [6], but this design was constrained to use a single PRF because of EM compatibility with another instrument.…”

“…The optimal sampling techniques proposed here can be incorporated into any of the point designs described in the introduction [4][5][6][7], as long as the hardware can support it. The following two major improvements can be expected in the performance:…”

Maximum a Posteriori Based Ocean Surface Current Inversion for Doppler Scatterometer

“…A survey on "User demand index of ocean current" [18] shows that most marine services require the current speed and direction accuracies to be higher than 0.1 m/s and 20 • . To further improve the ocean current inversion accuracy, Dong et al designed a Ku-Ka dual-band DopScat model [19] and achieved a current speed accuracy of 0.05 m/s. However, the complexity of the estimation method is high.…”

Wind Wave Effects on the Doppler Spectrum of the Ka-Band Spaceborne Doppler Measurement

“…For the wind and current information, the measurement at a medium incidence angle is more accurate [26,27]. The OSCOM mission proposed the measurement at a medium incidence angle to directly evaluate the influence of winds on the current fields [28]. The Ocean Dynamics and Sea Exchanges with the Atmosphere (ODYSEA) wind and current mission concept has estimated the current measurement errors varying with wind speeds and look geometry [29].…”