Wenming Lin

Some considerations about the in-orbit calibration of spaceborne rotating fan beam radar scatterometer

Rotating fan-beam scatterometer (RFSCAT) is a new kind of spaceborne scatterometer for ocean surface vector wind (OSVW) measurement. In this paper, some consideration about the calibration of a Ku-band RFSCAT is presented. Both internal calibration and external calibration are described. Preliminary analyses about the internal calibration precision and external calibration accuracy are presented. Based on the method of Long, etal, external calibration method for RFSCAT is proposed. Some simulation results for the external calibration with natural extended targets, such as Amazon forest, are presented.

A Ku-band rotating fan-beam scatterometer: Design and performance simulations

This paper introduces the design and simulation results of a Ku-band rotating fan-beam radar scatterometer for ocean surface wind vector measurement. It will be flown on a small satellite dedicated to provide data for investigation of the ocean wave and ocean surface wind vector interactions, along with another payload for measurement of directional ocean wave spectra by a real-aperture radar with multiple scanned pencil beams. Key issues about the design of a Ku-band rotating fan-beam radar scatterometer, and results of performance simulations are provided as well. The performance of the system is simulated by the absolute and relative specifications. For the absolute specifications, retrieval performances for both wind speed and wind direction are evaluated, with the maximum likelihood method being employed. For the relative specifications, the figures of merit (FOM) is simulated, for comparison with other Ku-band scatterometers and optimization of system parameters. Simulation results of both the σ° precision and wind retrieval accuracies for different wind speed from 4m/s to 24m/s will be provided, which shows that SCAT can satisfy the performance requirements within most part of the swath.

Doppler effect and compensation in a Rotating Fanbeam Spaceborne Scatterometer

Spaceborne Rotating Fanbeam Scatterometer, RFSCAT, has a wider continuous swath that can provide a large number of independent samples of Sigma0 for wind speed and direction retrieving. But the large swath and footprint result in a wideband Doppler frequency shift. For a low earth orbiting satellite, the maxim Doppler bandwidth between forward and backward echoes will be about 500 KHz. Even in a single echo of RFSCAT, the Doppler bandwidth is about 90 KHz, while in a pencil beam scatterometer the Doppler bandwidth is almost a single tone. A method of Doppler frequency compensation both on center frequency of transmitted pulses and signal processing section of the echoes are carried out and evaluated.

Design of the interface of a calibration transponder and an altimeter / scatterometer

A transponder system is developed to fulfill the in-orbit calibration of the HY-2 satellite altimeter (ALT) and scatterometer (SCAT). The interaction of a calibration transponder and radar (altimeter / scatterometer) is rather complicated. After a brief description of the two active payloads on HY-2 satellite, several key issues are investigated in detail, including time arrangement and power budget. There are some innovations in calibration strategy, including the pre-distortion technology in ALT calibration and the Single-Input-Multiple- Output (SIMO) technology in the SCAT calibration.

Pulse Compression with Very Low Sidelobes in a Spaceborne Weather Radar

Pulse compression with very low sidelobes is one of challenges in the design of spaceborne weather radar. To detect the weak echoes of clouds occurring near the strong echoes of sea surface, sidelobe performance below -60 db is needed in the pulse compression system. Based on the traditional ways of pulse compression, double Kaiser Windows are applied here for sidelobe suppression and the Peak Sidelobe Level (PSL) can reach -75 db. To avoid power and SNR loss, the time domain Kaiser Window weighted on transmitter was replaced by the frequency domain window weighted on receiver equally. A real time signal processor and digital predistortion method based on successive overrelaxation (SOR) arithmetic is carried out. It can be used for verifying the arithmetic and modifying the nonlinear and noise character of the system.

Development of a signal processing subsystem for a spaceborne rotating, fan-beam scatterometer

This paper introduces an on-board signal processing subsystem of a spaceborne rotating fan-beam scatterometer in China. The subsystem processes returned signal after downconversion to intermediate frequency. To reduce the data stream downlinked from the satellite, the final data bins are summed into 34 energy slices, each with a range resolution of 10 km. Then a simulation process is adopted to analyze the Doppler effects due to the motion of the spacecraft, and to generate the Doppler compensation table and the bin summation table. This method is also used to analyze the measurement variance Kpc of each detected slice. Finally, the coefficients of the expression of Kpc are presented.

System design and performance simulation of a spaceborne Ku-band rotation fan-beam scatterometer

A spaceborne Ku-band rotation fan-beam scatterometer (RFSCAT) for sea surface wind field measurement is introduced. The system will be operated in Ku-band frequency so that the dimension of its antenna can be shortened enough for a small satellite platform. Then a simulation method is adopted to analyze the performance of this system. The results show that the proposed scatterometer has a good performance in wind retrieval.

Performance simulation of a spaceborne dual-frequency Rotating Fanbeam SCATterometer

In this paper, a conceptual design for a dual-frequency Rotating Fanbeam SCATterometer (RFSCAT) to fly onboard the future satellite (e.g. FY-3) with altitude of 836km is studied. System configurations of the studied C-band Ku-band RFSCAT are introduced respectively. Then an end-to-end simulation process is adopted to analyze the backscatter measurement accuracy, ant to assess the wind retrieval quality of the proposed RFSCAT. For a wind vector cell with spatial resolution of 25 km, the communication noise ranges from 4% to 90% for the Ku-band measurement, and from 3% to 25% for the C-band one, depending on ocean surface wind speed. The simulation results indicate that the proposed system would promote the wind retrieval qualities significantly by combining the C-band Ku-band microwave measurement.

Status and recent progresses of development of the scatterometer of CFOSAT

In this paper, the status and progress of the scatterometer (SCAT) of the Chinese-French Oceanography Satellite (CFOSAT) will be reported. SCAT/CFOSAT will be the first rotating fan-beam scatterometer (RFSCAT) ever flown on a satellite for global ocean vector wind measurement. The mission schedule, some design and development status and simulation results of its performances will be presented. It is shown that the RFSCAT will have some advantages for wind vector retrieval for high wind speed situations.

Simulation and optimization of the performance of space-borne radar ocean wave spectrometer

In this paper, a simulation method is presented to analyze and to optimize the performance of a real aperture radar system for measuring oceanic directional wave spectra, taking into account of data processing parameters. The results show that spaceborne radar ocean wave spectrometer (SB-ROWS) can measure spectra of fully developed waves with significant wave heights (SWH) over approximately 2.0 meter and swell surface under low wind conditions. The minimum detectable wavelength in the study is about 40 m. The wavelength resolution for a wavelength of 200 m is better than 30 m, and the directional resolution after averaging is better than 20o.