Day 4

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Paper title System design and Doppler measurement error analysis of scatterometer onboard OSCOM
  1. Di Zhu National Space Science Center, Chinese Academy of Sciences Speaker
  2. Xiaolong Dong National Space Science Center, Chinese Academy of Sciences
  3. Jingyu Zhang
  4. Yuanjing Miao Key Laboratory of Microwave Remote Sensing, National Space Science Center, Chinese Academy of Sciences
Form of presentation Poster
  • A8. Ocean
    • A8.10 Ocean Doppler: Challenges and Opportunities for Future Missions of Global Ocean Surface Currents
Abstract text Spaceborne doppler scatterometer is a newly developed radar for ocean surface wind and current field remote sensing. Direct measurement of the global ocean surface current is of great scientific interest and application value for understanding multiscale ocean dynamics, air-sea interaction, ocean mass and energy balance, and ocean carbon budget as well as their variabilities under climate change. DOPpler Scatterometer (DOPS) onboard Ocean Surface Current multiscale Observation Mission(OSCOM) is a dual frequency doppler radar can directly measure ocean surface currents with a high horizontal resolution of 5–10 km and a swath larger than 1000km. DOPS is proposed to use a real-aperture radar with a conically scanning system. The designed satellite orbit is a sun-synchronous orbit with an altitude of 600 km and a field angle from 46° - 48°, corresponding to a ground swath larger than 1000 km. The geometry of the Doppler Scatterometer observationis shown in Figure 1. The aperture of the antenna is about 2 meters, so the beam width of DOPS is about 0.3deg in Ka band and 0.8deg in Ku band. Thus,the azimuth resolution is better than 5 km in Ka band and 10km in Ku band respectively at an orbital altitude of 600km.
At system level, an end to end simulation of DOPS is carried out to evaluate the doppler accuracy. The system noise and nonlinear effect, such as the distortion caused by power amplifier are simulated to evaluated the doppler detection errors. Based on these simulations, the transmit power of DOPS is evaluated to ensure the enough echo SNR for doppler detection. For power amplifier simulations, both Rapp nonlinear model (for solid state amplifiers) and Saleh nonlinear model (for solid state amplifiers) are established. For noise simulations, random noise and phase noise are injected to sea surface echoes. As a result, nonlinear distortion of power amplifier will cause about 0.01m/s doppler error at a low saturation status. For a wide band random noise, 10dB SNR will cause about 0.02-0.03m/s doppler error. The doppler measurement errors of incidence angle and observation azimuth are also evaluated. These errors are caused by satellite attitude determinations, where satellite attitude contains the pitch, the yaw, and the roll. As the results of simulation, to achieve the current velocity accuracy better than 0.1m/s, the measurement errors of incidence angle should be smaller than 0.001°, and satellite velocity should be smaller than 0.01 m/s.