A routine operational backscattering coefficient regrouping algorithm for a HY-2A scatterometer

The routine operational sigma0 regrouping method is proposed for a HY-2 A scatterometer（HSCAT） that maps time-ordered sigma0 s and related parameters into a subtrack aligned grid of wind vector cells（WVCs）. The regrouping method consists of two critical steps： ground grid generation and sigma0 resampling. The HSCAT uses subtrack swath coordinates, in which the nadir track of the satellite represents the center and the designated positions are specified in terms of a pair of along-track and cross-track coordinates. To calculate the subtrack coordinates for each sigma0, a ＂triangle marking＂ resampling method is developed. Three points, including the point of intersection, the center of a pulse footprint, and the origin of the subtrack coordinate system, form a right triangle; the length of the two right-angled sides is used to represent the cross-track and the along-track coordinates in the subtrack coordinate system. In addition, a nadir point interpolation correction is used to ensure the operation of the regrouping algorithm when the nadir point positional information is missing. To illustrate the ability of the proposed regrouping algorithm, the distribution of the WVC positions and wind vector retrieval results are analyzed, which show that the proposed regrouping algorithm meets the requirements for high-quality sea surface wind field retrieval.

A stochastic discrete model of tissue and its ultrasonic backscattering coefficient

The discrete scatterer model is improved to take into account the random distribution of the size and the acoustic impedance of scatterers. The backscattering coefficient and its dependence on the frequency are calculated and analyzed. An experiment with a liver mimic phantom is conducted to verify the theoretical model.

Atmospheric temperature dependence of the aerosol backscattering coefficient

In extracting vertical profiles of aerosol backscattering coefficient from lidar signals, the effects of atmo- spheric temperature are usually ignored, In this study, these effects are analyzed using a rotational Raman-Mie lidar system, which is capable of simultaneously measuring atmospheric temperature and vertical profiles of aerosols, A method is presented to correct the aerosol backscattering coefficient using atmospheric temperature profiles, obtained from Raman scattering signals. The differences in the extracted aerosol backscattering coefficient with and without considering temperature effects are fur- ther discussed. The backscattering coefficients for scattering off clouds are shown to be more sensitive to temperature than that of aerosols and atmosphere molecules; the aerosol backscattering coefficient is more sensitive to temperature in summer due to higher atmospheric temperatures,

Variations in Optical Scattering and Backscattering by Organic and Inorganic Particulates in Chinese Lakes of Taihu, Chaohu and Dianchi

This study presents an investigation of the scattering and backscattering properties of the particulates in three Chinese inland lakes(the Taihu Lake, the Chaohu Lake and the Dianchi Lake) based on in situ measurements taken at 119 sites. We modeled the particulate scattering spectra using a wavelength-dependent power-law function, finding that the power-law exponents in the Taihu Lake and the Chaohu Lake differ from those in the Dianchi Lake but are similar to the values in the U.S. coastal waters. In contrast to the open ocean, the backscattering properties in the three lakes can not be determined only from chlorophyll-a concentration. The backscattering ratio spectra exhibit a wavelength dependence feature in all three lakes, generally decreasing with the increasing wavelength. Analysis results of the correlations between the backscattering ratio and the individual water quality parameters clearly show that there are distinctive relations among the three lakes, attributed primarily to different compositions of optically active materials in the three lakes. Analysis of the mass-specific scattering and backscattering coefficients shows that the coefficients at wavelength 532 nm in the Taihu Lake and Chaohu Lake are similar, but they are apparently different from those in the Dianchi Lake. Lastly, Model I multiple linear regressions were adopted to partition the mass-specific cross-sections for scattering and backscattering into organic and inorganic cross-sections to further interpret the scattering and backscattering properties. The relative contribution of organic and inorganic particulates to scattering and backscattering is clearly different among the three lakes. The scattering and backscattering properties of the particulates in the three inland lakes vary significantly based on our collected data. The results indicated that the existing semi-analytical water quality retrieval models of the Taihu Lake can not be applied perfectly to the Chaohu Lake and the Dianchi Lake.

Simulation of positron backscattering and implantation profiles using Geant4 code

For the proper interpretation of the experimental data produced in slow positron beam technique, the positron implantation properties are studied carefully using the latest Geant4 code. The simulated backscattering coefficients, the implantation profiles, and the median implantation depths for mono-energetic positrons with energy range from 1 keV to 50 keV normally incident on different crystals are reported. Compared with the previous experimental results, our simulation backscattering coefficients are in reasonable agreement, and we think that the accuracy may be related to the structures of the host materials in the Geant4 code. Based on the reasonable simulated backscattering coefficients, the adjustable parameters of the implantation profiles which are dependent on materials and implantation energies are obtained. The most important point is that we calculate the positron backscattering coefficients and median implantation depths in amorphous polymers for the first time and our simulations are in fairly good agreement with the previous experimental results.

An analysis of the radar backscatter from oil-covered sea surfaces using moment method and Monte-Carlo simulation: preliminary results

An analysis of the radar backscattering from the ocean surface covered by oil spill is presented using a mi- crowave scattering model and Monte-Carlo simulation. In the analysis, a one-dimensional rough sea sur- face is numerically generated with an ocean waveheight spectrum for a given wind velocity. A two-layered medium is then generated by adding a thin oil layer on the simulated rough sea surface. The electric fields backscattered from the sea surface with two-layered medium are computed with the method of moments （MoM）, and the backscattering coefficients are statistically obtained with N independent samples for each oil-spilled surface using the Monte-Carlo technique for various conditions of surface roughness, oil-layer thickness, frequency, polarization and incidence angle. The numerical simulation results are compared with theoretical models for clean sea surfaces and SAR images of an off-spilled sea surface caused by the Hebei （Hebei province, China） Spirit oil tanker in 2007. Further, conditions for better oil spill extraction are sought by the numerical simulation on the effects of wind speed and oil-layer thickness at different inci- dence angles on the backscattering coefficients.

Coastal wind field retrieval from polarimetric synthetic aperture radar

Coastal winds are strongly influenced by topology and discontinuity between land and sea surfaces. Wind assessment from remote sensing in such a complex area remains a challenge. Space-borne scatterometer does not provide any information about the coastal wind field, as the coarse spatial resolution hampers the radar backscattering. Synthetic aperture radar （SAR） with a high spatial resolution and all-weather observation abilities has become one of the most important tools for ocean wind retrieval, especially in the coastal area. Conventional methods of wind field retrieval from SAR, however, require wind direction as initial information, such as the wind direction from numerical weather prediction models （NWP）, which may not match the time of SAR image acquiring. Fortunately, the polarimetric observations of SAR enable independent wind retrieval from SAR images alone. In order to accurately measure coastal wind fields, this paper proposes a new method of using co-polarization backscattering coefficients from polarimetric SAR observations up to polarimetric correlation backscattering coefficients, which are acquired from the conjugate product of co-polarization backscatter and cross-polarization backscatter. Co-polarization backscattering coefficients and polarimetric correlation backscattering coefficients are obtained form Radarsat-2 single-look complex （SLC） data.The maximum likelihood estimation is used to gain the initial results followed by the coarse spatial filtering and fine spatial filtering. Wind direction accuracy of the final inversion results is 10.67 with a wind speed accuracy of 0.32 m/s. Unlike previous methods, the methods described in this article utilize the SAR data itself to obtain the wind vectors and do not need external wind directional information. High spatial resolution and high accuracy are the most important features of the method described herein since the use of full polarimetric observations contains more information about the space measured.This article is a useful addition to the work of independent SAR wind retrieval. The experimental results herein show that it is feasible to employ the co-polarimetric backscattering coefficients and the polarimetric correlation backscattering coefficients for coastal wind field retrieval.

Integrating Remote Sensing and Proximal Sensors for the Detection of Soil Moisture and Salinity Variability in Coastal Areas

Soil moisture and salinity are two crucial coastal saline soil variables, which influence the soil quality and agricultural productivity in the reclaimed coastal region. Accurately characterizing the spatial variability of these soil parameters is critical for the rational development and utilization of tideland resources. In the present study, the spatial variability of soil moisture and salinity in the reclaimed area of Hangzhou gulf, Shangyu City, Zhejiang Province, China, was detected using the data acquired from radar image and the proximal sensor EM38. Soil moisture closely correlates radar scattering coefficient, and a simplified inversion model was built based on a backscattering coefficient extracted from multi-polarization data of ALOS/PALSAR and in situ soil moisture measured by a time domain reflectometer to detect soil moisture variations. The result indicated a higher accuracy of soil moisture inversion by the HH polarization mode than those by the HV mode. Soil salinity is reflected by soil apparent electrical conductivity （ECa）. Further, ECa can be rapidly detected by EM38 equipment in situ linked with GPS for characterizing the spatial variability of soil salinity. Based on the strong spatial variability and interactions of soil moisture and salinity, a cokriging interpolation method with auxiliary variable of backscattering coefficient was adopted to map the spatial variability of ECa. When compared with a map of ECa interpolated by the ordinary kriging method, detail was revealed and the accuracy was increased by 15.3%. The results conclude that the integrating active remote sensing and proximal sensors EM38 are effective and acceptable approaches for rapidly and accurately detecting soil moisture and salinity variability in coastal areas, especially in the subtropical coastal zones of China with frequent heavy cloud cover.

Sensitivity of X-Band (σ0, γ) and Optical (NDVI) Satellite Data to Corn Biophysical Parameters

The objective of this work was to evaluate the sensitivity of three different satellite signals (interferometric coherence (γ), backscattering coefficient (σ0) and NDVI) to corn biophysical parameters (leaf area index, height, biomass and water content) throughout its entire vegetation cycle. All of the satellite and in situ data were collected during the Multi-spectral Crop Monitoring (MCM’10) experiment conducted in 2010 by the CESBIO Laboratory over eight different agricultural sites located in southwestern France. The results demonstrated that the NDVI is well adapted for leaf area index monitoring, whereas γ27.3° is much more suited to the estimation of the three other Biophysical Parameters throughout the entire crop cycle, with a coefficient of determination ranging from 0.83 to 0.99, using non-linear relationships. Moreover, contrary to the use of the NDVI or backscattering coefficients, the use of coherence exhibited a low sensitivity to the changes in vegetation and soil moisture occurring during senescence, offering interesting perspectives in the domain of applied remote sensing

The observations on Polar Stratospheric Clouds at Zhongshan Station，Antarctica

lidar system (694 nm) was used to measure the stratospheric aerosol layer at Zhongshan Station (69°22'S, 76°22'E ) in 1993. A total of 53 sets of lidar data presented in this paper were obtained over a period of 224 days between March 27 and November 5, 1993. The average vertical profiles of stratospheric aerosol backscattering ratio and the integrated backscatter coefficient over the 12 km～30 km altitude range were reversed from the return signal of lidar. The results of observations show that the stratospheric aerosol content more noticeably enhanced in 1993 than that in 1990 due to Mt. Pinatubo eruption in Philippines in June of 1991. Polar Stratospheric Clouds (PSCs) were observed from late May until early August. The vertical profiles of stratospheric aerosol backscattering ratio at Antarctica in 1993 show a clear double-layer structure. One layer is at an altitude of about 12 km,the other is at an altitude of about 25 km. The upper layer is varied with season.

On temporal-spatial distribution of backscatter coefficients over China determined by TOPEX/Poseidon mission

This paper deals with the backscatter coefficients known as sigma0 at Ku band and C band based on the GDR-M (Merged Geophysical Data Record) of TOPEX/Poseidon (T/P) through Jan.1993 to Dec.2004 over land surface of China.After smoothing and interpolating the backscatter coefficients for both bands, we achieve the 5′×5′ grid data and the time series of backscatter coefficients in 12 years.The spatial distribution of sigma0 over typical areas (wetland, desert, mountainous area, agriculture base, etc.) of Chinese territory is analyzed and discussed.The fast Fourier transformation (FFT) is used to detect the cycles of seasonal variations of sigma0 time series and gives that the annual period is the major cycle.Meanwhile a semiannual period is also found in some places.We use the least squares method on both periods and find that the amplitude of annual period is obviously greater than that of semi-annual period.The relationship among the anomalousness of time series, variations of environment and climate change, and the serious natural calamity (flood, drought) is also discussed.Data of topography slope extracted from SRTM are used to do correlation analysis with the backscatter coefficients in parts of China to quantify the impact of slope on backscatter coefficients in Ku and C bands, and the results show that they all have a negative correlation but the magnitudes are different in different places with different coverages.Such as the area of Liaoning and Jilin has the maximum correlation -0.56, the Taklimakan Desert has the minimum correlation -0.11, and the other places commonly have correlations in (-0.3, -0.5).

Permafrost environment monitoring on the Qinghai-Tibet Plateau using time series ASAR images

The permafrost in Qinghai-Tibet Plateau(QTP)has long been the focus of many researchers.In this study,we first use the method that integrates synthetic aperture radar(SAR)intensity and phase information to monitor permafrost environment in the Beiluhe Region,using time series advanced SAR images.The backscattering coefficients(σ^(0))and deformation were extracted for the main features,and the influences of meteorological conditions to them were also quantified.The results show that both the change inσ^(0)and surface deformation are closely related to the active layer,and the deformation is also affected by the permafrost table.First,over meadow and sparse vegetation regions,σ^(0)rose about 6.9 and 4 dB from the freezing to thawing period,respectively,which can be mainly attributed to the thaw of the active layer and increased precipitation.Second,seasonal deformation,derived from the freeze-thaw cycle of the active layer,was characteristic of frost heave and thaw settlement and exhibited a negative correlation with air temperature.Its magnitude was larger than 1 cm in a seasonal cycle.Last,significant secular settlement was observed,with rates ranging from-16 to 2 mm/a,and it was primarily due to the thaw of the permafrost table caused by climate warming.

Best analytical approximation of slow electrons and positrons elastic scattering cross-section: A comparative study

The purpose of this work is to determine the best analytical approximation of the differential cross-sections,used in Monte Carlo simulation,to study the electron and positron slowing down in solid targets in the energy range up to 10 keV.For this,our comparative study has been carried out on the angular distribution of the scattering angle,the elastic total and the first transport cross-sections which are the essential quantities used generally in both the electron and the positron transport studies by using either stochastic or deterministic methods.Indeed,the obtained results using the relativistic partial wave expansion method and the backscattering coefficient(BSC)experimental data are used as criteria to evaluate the used model.

Simulation and retrieval for spaceborne aerosol and cloud high spectral resolution lidar of China

Clouds and aerosols can significantly affect global climate change and the atmospheric environment,and observing them three-dimensionally with high spatial and temporal resolutions is a long-standing issue.Spaceborne lidars are effective instruments for the vertical detection of clouds and aerosols globally.Numerous Mie scattering lidars were successfully launched and widely used,such as the Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP)and Geoscience Laser Altimeter System.However,the retrieval of Mie scattering lidar data is an ill-posed problem that introduces a large uncertainty.The spaceborne Aerosol and Cloud High Spectral Resolution Lidar(ACHSRL)of China is currently under development and scheduled for launch in the near future.The ACHSRL attracted extensive attention,because it can separate Mie and Rayleigh scattering signals and avoid ill-posed retrieval.In this study,we conducted ACHSRL signal simulation and retrieval to explore the potential of the ACHSRL.First,we proposed a simplified scheme for retrieving optical parameters,which reduced the number of equations and intermediate variables of the traditional method and avoided false extrema in the backscatter coefficient retrieval.Additionally,the experiments showed that the backscatter coefficient retrieval was overestimated owing to the influence of the Poisson noise but can be corrected.Second,we examined the feasibility of the strategy of“first retrieving the lidar ratio then retrieving the extinction coefficient”to improve the extinction coefficient retrieval.We found that the retrieval error in the simulated cases can be reduced to less than 1%of the original retrieval error.Furthermore,we discussed the influence of the uncertainty of the iodine filter transmittance on the retrieval of the optical parameters and found that the average relative error was less than 1‰.Finally,we conducted simulation and retrieval based on the atmospheric parameters measured by the CALIOP.Results showed that the relative error in the backscatter and extinction coefficients at night was 12%and 28%for test cases,respectively,which was superior to that in the backscatter and extinction coefficients of the corresponding CALIOP product(i.e.,75%and 82%).This research is significant and useful for the development and application of satellite lidars in the future.