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 Kpc 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.
Highlights
Ocean surface wind and current are tightly coupled surface environment parameters
We present a Ku-Ka dual-frequency Doppler Scatterometer (DopScat) for wide-swath and high-accuracy simultaneous measurements of ocean surface wind and current
Considering that the Ka-band DopScat has a better performance in both effective wide-swath and high-accuracy, the ocean surface Doppler frequency and moving velocity measurement are mainly implemented by the Ka-band
Summary
Ocean surface wind and current are tightly coupled surface environment parameters. Surface wind drives current, but in turn, it is modulated by current because the forcing wind stress is pertinent to the current’s moving reference frame [1]. The measurements of oceanic quantities and atmosphere-ocean interaction processes play a key role in weather and ocean state forecasting, as well as in oceanography and climate research For these reasons, it is desirable to be able to obtain simultaneous synoptic measurements of ocean surface current and wind on a global scale. The Doppler Scatterometer (DopScat) is a new type of marine remote sensing radar that maintains the ocean vector wind capability and extends to Doppler shift estimation capability with sufficient accuracy for surface current estimation, by measuring the interferometric phase differences between pulses. We present a Ku-Ka dual-frequency DopScat for wide-swath and high-accuracy simultaneous measurements of ocean surface wind and current. Considering that the Ka-band DopScat has a better performance in both effective wide-swath and high-accuracy, the ocean surface Doppler frequency and moving velocity measurement are mainly implemented by the Ka-band.
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