This article presents the design and implementation of a high-precision digital beamforming scatterometer, exploring its key technologies, which include digital beamforming, real-time amplitude and phase correction, and on-orbit real-time signal processing. Leveraging these technologies, the Haiyang-4A (HY-4A) scatterometer can flexibly adjust beam direction electronically, achieving a wide scanning range and efficient observational capabilities without changing the satellite’s flight path. To validate the scatterometer’s performance, we conducted a series of rigorous tests, including microwave anechoic chamber tests, echo simulator joint tests, and airborne flight calibration experiments. The test results demonstrate that the HY-4A digital beamforming scatterometer achieves high accuracy and reliability in measuring sea surface backscatter coefficients, providing robust support for monitoring ocean salinity and surface characteristics.

Ice sheet internal temperature profile plays a key role in the study of ice sheet thermodynamics and ice sheet mass balance. Wideband radiometric remote sensing measurement has been demonstrated to be an effective approach for estimating the ice sheet internal temperature profile. In this study, we make model analysis of the sensitivity of emission observation on different frequency channel to ice sheet internal temperature at different depth, aiming at assessing the value of each channel in deriving ice sheet internal temperature profile. As the emission contribution depth profile can give insight into the emission compositions and emission sensitivity to the ice sheet internal properties at different depth, this study analyses the impact on ice sheet emission contribution depth profile due to the uncertainties of ice sheet temperature profile based on Comprehensive Layer Emission Model (CLEM). The correlation of different frequency channel are further discussed. The analysis results give guidance to construct retrieval approach for better extraction and utilization of the information on ice sheet internal temperature profile providing by the wideband emission observation.

This article is the preliminary results of the in-cloud wind observation of an airborne Doppler scatterometer. This experiment took place on the Qinghai-Tibet Plateau in 2022 and it’s the first time to carry wind observation experiment in this place. During the process procedure, the dual-PRF process was used to extend the max unambiguous velocity, and the VVP method was used to invert the three-dimensional wind. The result provides a 40-second observation of the in-cloud wind, which indicates that the in-cloud wind in the plateau area can be detected through an airborne scatterometer.

The hostile environment and thick sulfuric acid clouds make it difficult to measure the Venusian lower and middle atmosphere. The Venus Volcano Imaging and Climate Explorer (VOICE), which is an orbiting mission, has planned to exploring the thermal structure and composition of the Venusian lower and middle atmosphere by the Microwave Radiometric Sounder (MWRS). This study presents a forward- and inversion- model for the Venusian lower and middle atmosphere at microwave and submillimeter wavelengths, which is developed to simulate the nadir and limb sounding from the MWRS. Important properties of the model with respect to the Venusian atmosphere are its inclusion of molecular thermal movement and collisions induced spectral lines broadening as well as the effects of refraction on the signal propagation in the atmosphere. The model also has potential applications for definition studies for future downward-looking and limb-looking sensors dedicated to Venus exploration.

The Doppler spectrum of a Doppler scatterometer signal is determined by the relative motion between the scatterometer and the ocean surface, including ocean surface motion and platform motion. It is also determined by the modulation from the backscattering coefficient. Estimating the Doppler centroid is an important issue for the application of a spaceborne Doppler scatterometer in ocean surface current retrieval. In this study, we use an echoed signal simulation model to analyze the Doppler spectrum with different incidence angle. Our results show that the satellite velocity and the backscattering coefficient modulation are the main influencing factors that affect the shape of the Doppler spectrum. With the increase of incidence angle, the radial platform velocity increases, and the modulation from the backscattering coefficient decreases. At 52° incidence angle, the Doppler spectrum is closest to the Gaussian distribution, which is suitable for Doppler scatterometer.

Reported radiometric measurements indicate that incoherent and coherent radiative transfer processes characterize the microwave emission features of layered irregular and inhomogeneous medium. In order to develop a forward emission model to be capable of considering the medium and boundary scattering and coherent boundary interaction that may exist in general layered medium, in this article, we present a comprehensive layer emission model (CLEM) based on the scattering operator formulation. We introduce wave-based coherent multiple reflection operators to account for coherent boundary interaction and first integrate them with the intensity-based multiple scattering processes, allowing the comprehensive description of rough boundary scattering, volume scattering, medium/boundary interaction, and coherent boundary interaction in the framework of CLEM. Simulations and analyses for ice- and snow-covered ground cases are conducted based on CLEM to evaluate the coherent boundary interaction and different impacting factors. Validation on CLEM is conducted with emission observations of snow-covered terrain in campaign Nordic Snow Radar Experiment (NoSREx) 2010–2013 during dry snow period and time-series emission observations of frozen soil during freezing and thawing processes. CLEM simulation results show a good agreement with measurements. For NoSREx, root-mean-square errors (RMSEs) at L- to Ka-band are below 5.5 K for both polarizations, which are of different levels of promotion compared with the incoherent model simulations, especially for horizontal polarization at L- and X-band. Application to frozen soil case illustrates the capability of CLEM to explain coherent oscillation feature with impact from incoherent scattering effect.

Combined use of active and passive remote sensing can provide complementary information to simultaneously characterize the internal structure and internal physical properties of ice sheet. Well constraints of layering structure and density variation are the precondition to retrieve ice sheet internal temperature profile using radiometric measurements. This paper makes further improvement to the combined active and passive remote sensing approach presented in our previous preliminary study, mainly in density variation profile characterization, emission modeling, and density variation estimation method. In the combined approach, ice-penetrating radar-echo profile is used to estimate the ice sheet density variation, correcting the input density parameter for ice sheet emission model when interpretating the ice sheet emission observations. Validation of the improved combined approach is conducted with SMOS data and radar profiles collected by CReSIS around several ice core sites in Greenland. Evaluation of availability and advantage of the improved combined approach is performed based on the results.

Ocean surface current system contains multi-scales, including large-scale geostrophic current, basin-wide gyres, and ageostrophic currents, such as Ekman currents, Stokes, tides, etc. Understanding the full ocean surface current system requires measuring the total ocean surface current vector at multi-scales. Today's satellite observations cannot directly measure the total ocean surface current vector with global coverage, even though the large-scale geostrophic current can be derived from spaceborne altimetry based on the geostrophic balance assumption. This study uses the most recent 5-year GDP (Global Drifter Program) drifter data to derive near-surface ocean current velocity. After correcting the wind-induced slippage contribution from drifter observations, GDP drifter-derived ocean current velocity is compared with the existing commonly-used ocean current datasets, i.e., OSCAR (Ocean Surface Currents Analyses Real-time) and AVISO (Archiving Validation and Interpolation of Satellite Oceanographic Data) geostrophic current datasets. There are discrepancies among these three datasets, and the significant discrepancies are evident, especially around the equator regions since the geostrophic assumption is not valid at the equator. Our results indicate that the existing ocean current datasets cannot fully resolve the variability of total ocean surface current. A clear solution is to measure the global total ocean surface current vector, which is highly desirable.

The Doppler shift of microwave radar signal is determined by the relative motion between radar and ocean surface, including contributions from the movement of the radar platform and the wind-wave-induced motion (phase velocity of the resonant Bragg waves and orbital motions of ocean waves that are longer than the Bragg waves) in addition to the ocean surface current. One of the main challenges in ocean surface current retrieval is the accurate estimation of the wind-wave-induced Doppler shift, which needs to be accurately removed from the total Doppler shift to determine the surface current. In this study, we investigate the effects of different wave directional spectra on estimates of the wind-wave-induced Doppler shift using a modulation transfer function (MTF)-based and time-independent Doppler model. Our results show that the wind-wave-induced Doppler shift estimates are highly dependent on the selection of wave spectra and the directional spreading function. This study also confirms the importance of ocean wave spectra parameterization on Doppler estimation of the ocean current. We find that Apel’s spectra model is a more consistent fit to the observations, but the optimal spreading function is wind-speed-dependent.

Microwave emission from layered inhomogeneous medium is affected by both incoherent scattering and coherent interaction within the layer. Reported emission observations of snow-covered surface and ice sheet indicate that effects of layer boundary interference are more prominent at low frequencies. This paper presents a comprehensive layer emission model (CLEM) for layered inhomogeneous medium that fully accounts for incoherent scattering and coherent boundary interactions within the layer. The CLEM model is based on scattering operator (matrix doubling) formulation, which provides the basic framework for integrating rough boundary scattering, volume scattering, and coherent multiple reflections at layer boundaries. Coherent boundary interactions are accounted for through novel integrated wave- and intensity-based layer scattering operators. Initial model validation using published Elbara-II data and SodRad data shows good agreement between CLEM predictions and measured results.

An airborne validation experiment using a pencil-beam Doppler scatterometer was carried out in south of Yangjiang River, Guangdong Province, China. Its purpose is to validate the feasibility of spaceborne Doppler scatterometers and simultaneous observations of ocean wind and currents. This study presents the pencil-beam airborne Doppler scatterometer system, and its data processing algorithm. To investigate the accuracy of measured ocean wind and currents in the airborne campaign, we made a comparison with other datasets. The results show that 1) The speed error of wind is 1.2m/s, and wind direction error is around 13.19°. 2) The current speed error is better than 0.15 m/s, the current speed is better than 15 degree.

Wideband radiometric measurements can be used to retrieve the internal temperature of ice sheet [1]. However, emission from ice sheet is affected by many factors including layering structure, density profile and grain size distribution. These factors are not well constrained due to the lack of ice sheet characterization data, and thus severely limit the ability to retrieve ice internal temperature profile using radiometric measurements. This paper presents a combined active and passive remote sensing approach, in which ice-penetrating radar provides information that constraint the ice sheet parameters, to improve estimation of ice internal temperature profile using radiometric measurements. In this study, radar reflectivity measurements are used for estimating ice density variations, which are input parameters for the ice sheet emission model. Model analysis of emission from ice layer with internal temperature and structural profiles, and comparison with SMOS data are conducted to assess the viability of the combined approach.

Ocean surface current is an important variable for ocean dynamics, and it plays a key role in air-sea interactions, with gradients of currents creating much strong air-sea coupling. However, retrieving the magnitude of the surface current is still challenging, with accurate wind-wave induced Doppler shift estimates being the main challenge for separating ocean surface current from the total ocean Doppler shift. This separation requires information on wind vectors, wave spectra and forward models to be able to simulate the radar response to the ocean surface. In this study, we investigate the effects of different wave spectra on estimates of wind-wave induced Doppler shift based on a numerical Doppler model. Simulation results show that, this quantity is dependent on the wave spectra. We support the selection of the Apel spectrum by comparing empirical models at C and Ka-band (CDOP and KaDOP). The study also highlights the important effects of wave spectra selection in future satellite Doppler measurements of ocean surface currents, a variable considered important by the National Acadamies.

Space-borne Doppler scatterometer is a new and promising sensor for wide-swath, high-accuracy, and simultaneous measurements of ocean surface current and wind vector. Doppler shift of ocean surface backscattering is determined by the relative motion between the sensor and ocean surface, it includes contributions from ocean surface current, wind-wave, and satellite motion. Accurate Doppler shift due to ocean surface current is estimated by removing the wind-wave and satellite motion effects. Satellite motion contribution can be accurately estimated from the satellite attitude motion of spacecraft. The main challenge for ocean surface current retrieval is uncertainty/error in the estimation of wind-wave induced Doppler shift. In this study, effects of wind estimation errors on surface current retrieval are evaluated through the Doppler scatterometer system simulations. Simulation results show that (1) surface current retrieval is affected more by estimation error in wind direction than in wind speed; and (2) wind estimation errors have larger effect on retrieval accuracy of ocean surface current direction than that of surface current speed.

The first rotating fan beam scatterometer onboard China-France Oceanography Satellite (CFOSAT) was successfully launched on October 29, 2018. CFOSAT SCATterometer (CSCAT) is dedicated to the monitoring of sea surface wind vectors but also provides valuable data for the applications over land and Polar Regions. This article provides an overview of the relevant procedures of CSCAT data processing, including onboard signal processing and operational ground processing. Then a post-launch analysis is carried out to evaluate the first results of CSCAT L1 and L2 products. It shows that the CSCAT instrument is generally stable in terms of noise measurements and internal calibration, unless there is any important change in the system configuration. Specifically, the CSCAT backscatter (σθ) precision and wind quality are studied using a set of collocated ancillary data. The σθprecision degrades as wind speed decreases, and it is relatively low at high incidence angles (e.g., θ >46°). In particular, backscatter estimation of the horizontally polarized beam should be further improved by correcting the noise subtraction factor. The retrieved CSCAT winds are in good agreement with the European Centre for Medium Range Weather Forecasts (ECMWF) winds, the Advanced Scatterometer (ASCAT) winds, as well as the buoy winds. However, due to unresolved calibration and interbeam consistency problems, the wind quality degrades remarkably for the out-swath and the nadir-region wind vector cells, implying that the σθcalibration should be improved in the future updates.

After the launching of CFOSAT (China-France Oceanography Satellite), calibrations of the SCAT (scatterometer onboard the CFOSAT) are carried out to modify the bias of the observed NRCS (normalized radar cross section). In this paper, some preliminary calibration results of CFOSAT SCAT are presented, including both internal calibration onboard the CFOSAT and external calibration on the ground. First, the onboard calibration signals and noise signals are analyzed to ensure the SCAT works in a steady status. Then, calibrations on NRCS are carried out by using the SCAT data from Amazon rainforest area. Furthermore, Calibrations using transponders will be carried out at Inner-Mongolian. Preliminary calibration results show that the NRCS of CFOSAT SCAT are compliable with the NRCS of NSCAT.

The scatterometer (SCAT) onboard the China-France Oceanography Satellite (CFOSAT) is the first rotating fan-beam scatterometer (RFSCAT) in space for global ocean surface vector wind measurement. After the CFOSAT launched in Oct. 29, 2018, the main performances of the CFOSAT scatterometer (CFOSCAT) are being tested in orbit. In this paper, the preliminary data processing results of CFOSCAT are presented, including the calibration signal analyses, system noise analyses, normalized radar cross section (NRCS) processing results and wind retrieval results. The results show that CFOSCAT works properly in orbit, the main system specifications of scatterometer system satisfies the design. Preliminary results also validates the wind retrieval performance.

The simultaneous measurements of ocean surface current and wind have attracted considerable interest. Since they are closely coupled at sea surface, wind errors (speed and direction) have a transfer effect on current retrieval. In this paper we investigate the effects of wind transfer error on current retrieval for a Doppler scattterometer. We analyze current retrieved errors in different cross-track distances, and find the best current retrieval position is at sweet spot (i.e., mid-swath). For a single measurement in a current resolution cell of 10km, if no wind errors in 7m/s wind speed, at sweet spot current retrieved errors are around 0.25m/s and 30°, respectively. However, with wind errors existing, current retrieved errors are 0.33m/s and 41°. For comparisons, the results show that wind errors degrade current retrieval performances. Additionally, we also analyze current retrieved errors in different wind and current conditions, the results show that, wind direction error has a larger effect on current retrieval compared with wind speed error, and current direction error is more susceptible to wind errors. Our results indicate that, a simultaneous and accurate wind measurement is critically needed to accurately mitigate its effect on current retrieval.

The RFSCAT(Rotating Fan-beam SCATterometer) is one of the two payloads of CFOSAT, the China-France Oceanography Satellite. It is a radar scatterometer designed to measure the electromagnetic backscatter from wind roughened ocean surface. The operating frequency of the scatterometer is 13.256GHz (Ku-band) and has a swath about 1,000 kilometers. The CFOSAT scatterometer data level-1 processing is the key step to obtain the high-quality sigma0s, and is the guarantee of obtaining high quality wind fields. In this paper, the CFOSAT scatterometer data pre-processing system and level-1 data processing algorithm and level-1 processor operation procedures is introduced. On the other hand, the in-orbit test preliminary results of the CFOSAT scatterometer data level-1 processor is introduced and analyzed.

The China-France Oceanography Satellite (CFOSAT) to be launched in October 2018 will carry two innovative payloads, i.e., the surface wave investigation and monitoring instrument and the rotating fan-beam scatterometer [CFOSAT scatterometer (CFOSCAT)]. Both instruments, operated in Ku-band microwave frequency, are dedicated to the measurement of sea surface wave spectra and wind vectors, respectively. This paper provides an overview of the system definition and characteristics of the CFOSCAT instrument. A prelaunch analysis is carried out to estimate the scatterometer backscatter and wind quality based on the developed CFOSCAT simulator prototype. The overall simulation includes two parts: first, a forward model is developed to simulate the ocean backscatter signals, accounting for both instrument and geophysical noise. Second, a wind inversion processor is used to retrieve wind vectors from the outputs of the forward model. The benefits and challenges of the novel observing geometries are addressed in terms of the CFOSCAT wind retrieval. The simulations show that the backscatter accuracy and the retrieved wind quality of CFOSCAT are quite promising and meet the CFOSAT mission requirements.

The Ku-band rotating fan-beam scatterometer (RFSCAT) onboard the China-France Oceanography Satellite (CFOSAT) is dedicated to the measurement of sea surface wind vectors. The flight model of RFSCAT has been assembled and tested, and the data processing algorithms have been developed. This paper provides an overview of the design and characteristics of RFSCAT instrument, and then a prelaunch analysis is carried out to estimate the scatterometer backscatter and wind accuracy. The overall study includes two parts: first, a forward model is developed to simulate the ocean backscatter signals under certain wind conditions; second, a wind inversion processor is used to retrieve sea surface wind vectors from the outputs of the forward model. Simulations show that the backscatter accuracy and the retrieved wind quality of RFSCAT are quite promising and meet the scientific requirements of the mission.

The scatterometer (SCAT) onboard China France Oceanography Satellite (CFOSAT) will be the first scanning scatterometer with rotating fan-beams. Wind retrieving methods for existed scatterometers, which are with rotating pencil beams or fixed fan beams, are needed to be modified considering efficiency in information extraction from the numerous observations acquired in this working mode. This was achieved in the research of this paper by applying Principle Component Analysis (PCA) method. Firstly, vectors for applying PCA are composed in two different ways for analysis of the effectiveness of information extraction for the SCAT data and for wind retrieving respectively. Then the description of simulated SCAT data considering observing geometry and SCAT working mode was given. Then experiments of PCA based wind retrieving method was carried out with conclusion that it was effective in information extraction for preparing data sets for wind retrieving. Finally, further research has been discussed.

Water Cycle Observation Mission (WCOM) is a mission dedicated to synergetic observations of global water cycle parameters, with emphasis on soil moisture, ocean surface salinity, snow water equivalent and frozen/thaw. WCOM implements its observation requirements by measurement of microwave emission/scattering of both the frequencies sensitive to the key parameters and also the auxiliary frequencies providing necessary atmospheric and surface roughness corrections. In order to satisfy this measurement requirements, WCOM is equipped with payloads with combination of active and passive microwave sounding capabilities of frequency from L-band to W-band. Dual Frequency Polarized Scatterometer (DFPSCAT) is one of the three payloads onboard the satellite of Water Cycle Observation Mission (WCOM). DFPSCAT is an X/Ku band rotating pencil beam scatterometer with 2-5 km resolution and 1000km swath for mapping of snow water equivalent (SWE) and freeze-thaw process. DFPSCAT achieves fine resolution by linear frequency modulation pulse compression along the elevation direction, and by unfocused synthetic aperture processing (a technique where the Doppler effect is exploited to synthesize a longer aperture to achieve an improved resolution), as well as super-resolution reconstruction by oversampling in the direction of the azimuth. Based on the payloads of WCOM mission, especially with X/Ku scatterometer and L/Ku/Ka radiometer active/passive observations, there are obvious advantages in snow water equivalent retrieval. The atmospheric correction of active and passive data should be performed before the retrieval. The estimation of SWE mainly rely on the high resolution X and Ku band scatterometer, and combined active/passive retrieval can provide more reliable SWE product. The retrieval method of SWE from X/Ku scatterometer is described, and combined active/passive retrieval is also briefly described.

Dual-Frequency Polarized Scatterometer (DPS) is a new system utilizing Doppler Beam Sharpening (DBS) technology for resolution enhancement. Respecting the low azimuth resolution over nadir swath, the Backus-Gilbert method is investigated to improve the resolution. According to the precision definition of scatterometer measurement, a Backus-Gilbert method for scatterometer is derived. Using the method, the tradeoff of resolution and precision of resolution-enhanced backscatter (normalized radar cross section, σ0) is established in a quantitative manner. The results show that resolution enhancement is achieved by the price of greatly decreased precision of reconstructed backscatter.

The aim of the paper is to describe a ground-based microwave scatterometer demonstrator dedicated for the functional verification of MICAP (Microwave Imager Combined Active and Passive). MICAP has been selected to be one of the main payloads for future Chinese ocean salinity mission. The MICAP scatterometer is for estimating ocean surface roughness which measurement will enable the removal of the wind effect from the ocean surface brightness temperature measurement being used to retrieval ocean salinity. The primary technical challenge is its end to end system stability, on the order of 0.1dB. A demonstrator was developed to verify functionality and provide support to trouble shooting in the following project phases. The demonstrator's development and integration, as well as the stability calibration are discussed in the paper.

In this paper, we present the experimental results of a DBF (digital beam forming) scatterometer demonstrator performance on the purpose of development and verification of innovative DBF concepts and advanced operational modes for the future space borne MICAP (microwave imager combined active and passive), China's ocean salinity mission. The hardware configuration of the demonstrator is introduced. The ground-based experiments, verifying the DBF function on receiving and transmitting separately are carried out on the open field using the demonstrator. Analysis of the experimental results verifies the validity of the DBF technique on the receiving and transmitting. At last, the problems caused by the unbalance of the amplitude and phase between channels are discussed. The function verification experiment is the very first step towards the future space borne MICAP, and further researches are in progress.

In typhoon conditions, air-sea interactions are fierce, the wind speeds are quite high and usually tangled with complex rains. Under such circumstances, the combined observations of scatterometer and radiometer would be able to provide good information although traditional wind filed retrieving methods for them, i.e. MLE based on GMF (Geographical Modelling Function) for scatterometer and RTM(Radiative Transfer Method) which are originated from low or median wind conditions will not be applicable. In this paper, a neural network was employed to combine the observations of the two sensors onboard HY-2A satellite: radiometer (HRAD) and scatterometer (HSCAT) to achieve wind speed retrieving under typhoon conditions. The network was trained by GRAPS (global/regional assimilation and prediction system) data used as true values of wind speeds in typhoons. The established network was verified by data excluded from training data set. Results show that the wind speeds obtained from the network are better than the products of HY-2A compared to GRAPS data. The research of this paper has provided a clue of retrieving typhoon wind speeds for HY-2A products and for the data processing of coming HY satellite series, though further work on wind direction obtain, data comparison between different kinds of assimilation and perdition systems and the test of this method on other scatterometer and radiometer data are to be done in the near future.

Earth observation satellites play a critical role in providing information for understanding the global water cycle, which dominates the Earth-climate system. However, limitations in observations will restrict our current ability to reduce the uncertainties in the information used to make decisions regarding to water use and management. Under the support of “Strategic Priority Research Program for Space Sciences” of the Chinese Academy of Sciences, a new satellite concept of global Water Cycle Observation Mission (WCOM) is proposed, aiming to provide higher accuracy and consistent measurements of key elements of water cycle from space, including soil moisture, ocean salinity, freeze-thaw, snow water equivalent and etc. The expected more consistent and accurate datasets would be used to refine existing long-time series of satellite measurements, to constrain hydrological model projections and to detect the trends necessary for global change studies. The WCOM is expected to be implemented during the 13thfive-year-plan period (2016–2020).

Water Cycle Observation Mission (WCOM) is a mission dedicated to synergetic observations of global water cycle parameters, with emphasis on soil moisture, ocean surface salinity, snow water equivalent and frozen/thaw. WCOM implements its observation requirements by measurement of microwave emission/scattering of both the frequencies sensitive to the key parameters and also the auxiliary frequencies providing necessary atmospheric and surface roughness corrections. In order to satisfy this measurement requirements, WCOM is equipped with payloads with combination of active and passive microwave sounding capabilities of frequency from L-band to W-band. In addition to the multiple frequency requirement, the requirement for spatial resolutions and swath width leads to large aperture antennas and scanning of antenna beams, the accommodation of the three payloads becomes the major challenge for the design of the WCOM satellite. In order to satisfy the temporal resolution requirement, the design of data downlink and ground segment are also discussed. In this presentation, a preliminary design for WCOM satellite is provided, some technical issues need further investigation are also discussed.

Dual-Frequency Polarized Scatterometer (DFPSCAT) is a new system utilizing Doppler beam sharpening (DBS) technology for azimuthal resolution enhancement. Considering the DBS technology is inapplicable for the middle areas of the swath, a theoretical framework of deconvolution signal processing is proposed to improve resolution. A deconvolution method of the nonlocally centralized sparse representation (NCSR) is adopted to verify its feasibility, and simulation results show that the deconvolution method have obviously better resolution enhancement and higher recovery accuracy than these of the classical scatterometer image reconstruction (SIR) method.

The wind fields retrieved by scatterometers from GMF (Geographical Modelling Function) would be invalidated under rainy conditions, due to scattering and attenuation effects of rain drops. The scatterometer (HSCAT) and the scanning microwave radiometer (RM) onboard HY-2A can give observations over sea surface at the same time. In this paper, firstly, data of HSCAT and RM onboard HY-2A observing rainy ocean surface were selected as experiment data, with corresponding buoy wind fields. Secondly, an artificial neural network was established for wind fields retrieval under rain conditions, which was tested by other data sets.

The Rotating fan-beam scatterometer (RFSCAT) onboard the Chinese-French Oceanography Satellite (CFOSAT) is a novel kind of scatterometer whose performance had been preliminarily verified by airborne campaign. In this paper the whole data processing chain that can achieve wind field derivation from original data set transmitted from the scatterometer had been proposed with definition of corresponding data levels that would be applied for RFSCAT in the CFOSAT mission. The pre-processing part in the processing chain was validated for it was derived from the same system verified by the airborne campaign. While for the post-processing prime algorithms, validity was concluded from processing some of the data gained in that experiment as well. Further researches needed had been explored as well.

The MICAP(microwave imager combined active and passive), which has been selected to be a candidate payload for future Chinese ocean salinity mission, contains an L-band digital beam forming(DBF) scatterometer for the purpose of elimination of ocean surface roughness and wind retrieving. In this paper, data pre-processing flow for this scatterometer to obtain data ready for sea surface salinity and ocean surface wind retrieval was presented after corresponding data level definitions in this flow had been introduced. The processing flow was verified by processing data resulted from a data set simulated in a simple progress. Future work to perfect the pre-processing progress was also discussed.

A 1-D interferometric system at 1.4GHz, 6.9GHz, 18.7 GHz and 23.8GHz combined with a scatterometer at 1.26GHz, called microwave imager combined active/passive (MICAP), has been proposed to retrieve sea surface salinity (SSS) and to reduce geophysical errors due to surface roughness and sea surface temperature (SST). The MICAP will be a candidate payload onboard the Ocean Salinity Satellite of China. The sensitivity of active/passive microwave observations to SSS, SST and wind is analyzed and the stability requirement of the instruments is estimated, with the objective of designing an optimized satellite instrument, dedicated to an “all-weather” estimate of the SSS with high accuracy from space.

The RFSCAT(Rotating Fan-beam SCATterometer) is one of the two payloads of CFOSAT, the China-France Oceanography Satellite. It is a radar scatterometer designed to measure the electromagnetic back-scatter from wind roughened ocean surface. The operating frequency of the scatterometer is 13.256GHz (Ku-band) and has a swath about 1,000 kilometers. In this paper, an end-to-end data simulation system of CFOSAT RFSCAT is developed for processing algorithm validation and performance analysis. Using the simulation system, the slice and WVC geometries are determined and the measurement performance is analyzed. Based on the simulated data, the wind is retrieved and the performance of wind retrieval is estimated. Meanwhile, according to the simulation and wind retrieval of CFOSAT RFSCAT, some considerations of the actual data processing are introduced.

The scatterometer onboard the China-France Oceanography Satellite (CFOSAT) will be the first rotating fan-beam scatterometer (RFSCAT) ever flown in space for global ocean vector wind measurement. The status and progress of the scatterometer will be presented, including the mission schedule, payload design and development, validation experiments. The internal calibration strategy, Doppler compensation method and onboard signal processing arithmetic are also reported.

Dual Frequency Polarized Scatterometer (DFPSCAT) is one of the three payloads onboard the satellite of Water Cycle Observation Mission (WCOM). DFPSCAT is an X/Ku band rotating pencil beam scatterometer with 2-5 km resolution and 1000km swath for mapping of snow water equivalent (SWE) and freeze-thaw process [1]. DFPSCAT achieves fine resolution by linear frequency modulation pulse compression along the elevation direction, and by unfocused synthetic aperture processing (a technique where the Doppler effect is exploited to synthesize a longer aperture to achieve an improved resolution), as well as super-resolution reconstruction by oversampling in the direction of the azimuth.

Ocean surface current is a very important parameter of ocean dynamic environment, which has been connected to global climate change, marine environment forecasting, marine navigation, engineering security and so on. Doppler scatterometer is a new type of scatterometer that can be used to measure ocean surface current as well as the ocean wind vector in space. The Doppler Scatterometer is based on a real aperture radar, which can achieve a very wide swath. It can provide the ocean surface current and wind vector information in a certain resolution and achieve global coverage quickly, which is very important for the marine environment forecasting and climate changes research.

Dual-Frequency Polarized Scatterometer (DFPSCAT) is a pencil-beam rotating scatterometer which is used to measure snow water equivalence (SWE). Respecting the low azimuth resolution of its forward-looking region, an adaptive regularization deconvolution super-resolution method, based on the scatterometer echo signal model, is proposed. Compared with the classical SIR and MAP algorithms, the proposed method can better reconstruct the original signal, and has less noise amplification. The algorithm processing accuracy with different Kpcis also studied, and the results show that when the value of Kpcis less than 0.1, nearly the entire restored data can satisfy the requirement of 0.5dB accuracy.

Sea surface salinity (SSS) plays an important role in global water cycle. In recent years, satellite based remote sensing has proven to be a promising approach for global SSS observation. A new payload concept, named MICAP (microwave imager combined active and passive), has been introduced in this paper. MICAP is a suit of active/passive instrument package, which includes L/C/K band one-dimensional MIR (microwave interferometric radiometer) and L-band DBF (digital beamforming) scatterometer, sharing a parabolic cylinder reflector. MICAP has been selected to be a candidate payload for future Chinese ocean salinity mission. In this paper, the MICAP instrument concept, specification and preliminary system design will be introduced.

In order to satisfy a high resolution for the measurement of snow water equivalent, we use the system of using the dual frequency(X-band 9.6GHz and Ku-band 17GHz ) and full polarization. This paper discusses the various system options(scanning pencil-beam, high PRF, high SNR) and tradeoffs considered for improving the azimuth resolution of scatterometer are required.

The RFSCAT(Rotating Fan-beam SCATterometer) is one of the two payloads of CFOSAT, the China-France Oceanography Satellite. It is a radar scatterometer designed to measure the electromagnetic back-scatter from wind roughened ocean surface. The operating frequency of the scatterometer is 13.256GHz (Ku-band) and has a swath about 1,000 kilometers. In this paper, based on the characteristics of echo signal of RFSCAT, the on-board processing of RFSCAT signal is introduced. A Doppler pre-compensation LUT and A slice division LUT are developed, and the signal processing algorithms are validated and the wind retrieval performances of RFSCAT are analyzed based on the well-developed data simulation system of CFOSAT RFSCAT.

In order to measure the ocean surface current vector in a direct way, an interferometric method using pencil-beam scatterometer is proposed and the parameters of the traditional scatterometer are modified. What's more, the measurement principle and correlation model are introduced in this paper. The simulation results show that the Std of ocean surface current speed in both along-track and cross-track direction can be smaller than 10cm/s when the wind speed is larger than 4m/s. And the effective swath is greater than 445km when the wind speed is larger than 7m/s. The Kpcof the modified scatterometer is better than that of the tradition scatterometer.

For the operational spaceborne scatterometers, there is no effective way to eliminate the influence of the rain. Echoes contaminated by the rain are discarded directly. In this paper, a special designed spaceborne scatterometer and its decoupling methods of echoes from sea surface and rain are introduced. The main steps of decoupling methods are as follows. First, the scatterometer system parameters are slightly adjusted to acquire both the rain and sea surface echoes simultaneously. Next, the data of the scatterometer are copied and processed separately, one copy for rain retrieving and the other copy for sea surface backscatter retrieving. Finally, the rain attenuations are compensate to modify the bottom rain rate and the sea surface backscatter energy.

Polarimetric backscatter measurements has potential benefits to improve wind retrieval performance [1]. It simultaneously measures co-polarized backscatter coefficient (σhh, σvv) and the correlation coefficient of the co- and cross-polarized component (σvhhh, σhvvv) of radar returns. A pre-processing design of spaceborne polarimetric scatterometer will be introduce in this paper considering to improve the resolution by range filtering [2]. A corresponding formulation for assessing the variance of the measurements due to fading and the thermal noise is presented considering the factors affecting the measurement accuracy.

Airborne experiments were carried out to validate the spaceborne scatterometer. Airborne scatterometer use all the instruments of the spaceborne scatterometer to validate the system design and reliability, except the power amplifier and the antenna. The software of the scatterometer is redesigned due to the observation geometry of airborne platform. The wind retrieval results are compared with the HY-2A scatterometer and the real time wind vector measured on the ship at the center of testing region.

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. The considerations about the calibration of RFSCAT is also presented in this presentation.

The scatterometer can be significantly affected by rain, especially those operated on Ku-band. The effects are related to many parameters, such as rain rate and frequency. In this paper, a model which takes all the parameters into accounted is presented. The effects of all the parameters played on sea surface back scattering with precipitation are analyzed using this model. The analyzed results indicate that rain volume fraction and frequency are key factors, while influence of raindrop size polarization is less obvious.

Spaceborne wind scatterometers has been proved to be an efficient instrument for measurements of ocean surface winds. There have been some experiments show that the polarimetric scatterometer can significantly improve the measurement accuracy compared to the traditional co-polarized scatterometers [1]. In this paper, a Ku-band rotation pen-beam polarimetric scatterometer system simulation model is established and compared with co-polarized mode, further demonstrates that polarimetric scatterometer has better wind retrieval quality. Then discuss the factors affecting the performance of the polarimetric scatterometer.

The scatterometer of HY-2 satellite is a rotating pencil-beam radar. It has a one-meter dish reflector antenna with two beams, the outer beam is VV-polarized and the inner beam is HH-polarized. This paper provides the in-orbit processing and calibration results of HY-2 scatterometer. After analyzing the acquired data for natural targets from the Amazon Rainforest and the Sahara Desert, the in-orbit calibration algorithms are verified and the results are also presented.

Rotating fan-beam scatterometer (RFSCAT) is a new type of satellite scatterometer that was proposed about one decade ago.However, just as other rotating scatterometers, relatively larger wind retrieval errors occur in the nadir and outer regions than in the middle regions of the swath. In order to address this problem, a modified wind vector retrieval algorithm for RFSCAT is presented in this paper. The new algorithm is featured with adaptively extending the range of wind direction for each wind vector cell position across the whole swath according to the distribution histogram of the retrieved wind direction bias. Simulation experiments demonstrated that the new established algorithm can effectively improve the wind direction retrieval accuracy in the nadir and outer regions of the RFSCAT swath.

An airborne multi-pencil beam rotating scatterometer is introduced in this paper. Multi-pencil beam scatterometer can obtain echoes of sea surface and precipitation simultaneously. When the radar system parameters and retrieving arithmetic are carefully designed, sea surface wind vector, three Domain wind vector above the sea and the vertical structure of the precipitation can be refined from the multi-angle echoes. In this paper, the key technologies, such as precipitation and sea surface decoupling arithmetic and pulse compression with low side lobe arithmetic are applied to obtain the wind vector and precipitation structure.

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, et al, external calibration method for RFSCAT is proposed. Some simulation results for the external calibration with natural extended targets, such as Amazon forest, are presented.

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.

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- and 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- and Ku-band microwave measurement.

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.

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 Kpcof each detected slice. Finally, the coefficients of the expression of Kpcare presented.

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.

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 -60db 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 -75db. 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.

Pulse compression techniques are very attractive in the development of new-generation spaceborne meteorological radars, because it has the advantages to reduce the transmit power requirements and improve the measurement precision by increasing incoherent average samples. Compared with TRMM, which employed a pulsed-CW signal, it is very important to analyze the effect of surface clutter from ranging sidelobes of the returned signal after pulse compression. In this paper, the effect of surface clutter with different antenna sidelobe levels and different ranging sidelobe levels are analyzed in details. Based on the analysis of surface clutter, the requirements for antenna sidelobe level and pulse compression range sidelobe level are proposed.