Jin-Young Hong

Polarimetric Backscattering Coefficients of Flooded Rice Fields at L- and C-Bands: Measurements, Modeling, and Data Analysis

The polarimetric backscattering coefficients (vv-, hh-, hv-, and vh-polarizations) of a flooded rice field are measured using L- and C-band ground-based polarimetric scatterometers. These measurements were made during the rice growth cycle, i.e., from the transplanting period to the harvest period (May to October 2006), to understand the feasibility of modeling and estimating rice growth. We also collected ground truth data that include fresh and dry biomasses, plant height, leaf area index, and leaf size. To study the incidence angle effect, the scatterometer data were collected at four different incidence angles, i.e., 30deg , 40deg, 50deg, and 60deg. In this paper, we show that the backscattering coefficients of a rice field can accurately be modeled using the radiative transfer theory. We also demonstrate that a polarimetric scatterometer is an effective tool for estimating rice growth. The hh-polarized backscattering coefficient is more sensitive to rice growth than its vv-polarization counterpart. The polarimetric ratio can be used to estimate rice growth accurately.

Effect of Surface Profile Length on the Backscattering Coefficients of Bare Surfaces

The root mean square (rms) height s and autocorrelation length l are commonly used as the surface roughness input parameters to surface scattering models. Whereas it is well known that the surface roughness parameters of a natural soil surface are underestimated with a short surface profile, it is not clear how much the underestimated surface parameters affect the backscattering coefficients of the surface for various incidence angles and polarizations. In this paper, the backscattering coefficients of simulated and measured surface profiles are computed using the integral equation method and analyzed to answer this question. A 4000lmacr-long rough surface is generated numerically, where lmacr is the true correlation length of the surface, and the backscattering coefficients of the surface are computed and analyzed for various conditions. The rms error of the backscattering coefficient at a medium range of incidence angles is less than 1.5 dB for vv-polarization and 0.5 dB for hh-polarization if the profile length is larger than 5lmacr for a surface with ks=1.0, kl=10.0, and epsiv r=(10.0,2.0). Similar results are obtained from numerous simulations with various roughness conditions and various wavelengths. It is also shown that the rms error of the backscattering coefficients between 5- and 1-m-long measured surface profiles is 1.7 dB for vv-polarization and 0.5 dB for hh-polarization at a medium range of incidence angle (15deglesthetasles70deg), whereas the surface roughness parameters are significantly reduced from 2.4 to 1.5 cm for the rms height s and from 35.1 to 10.0 cm for the autocorrelation length l

Polarimetric measurements of radar backscatters of a wet-land rice field throughout a growth period at L- and C-bands

Backscattering coefficients and phase-difference statistics of a wet-land rice field in Suwon, Korea are measured using a ground-based polarimetric scatterometer at 1.9 and 5.3 GHz throughout a growth year from transplanting period to harvest period (May to October in 2006). The ground truth data including bio-mass, plant height, and leaf-area index (LAI) are also collected for each measurement. The measured backscattering coefficients and phase difference statistics are analyzed based on the growth age for each polarization, frequency, and incidence angle. It is found that the hh-polarized backscattering coefficients have wider sensitivity region than the w-polarized backscattering coefficients with respect to the rice growth age.

Moment method/ Monte Carlo simulation of the microwave backscatter of wet-land rice fields

Polarimetric microwave backscattering coefficients of wet-land rice fields are simulated using a full-wave analysis with the moment method (MM) and Monte Carlo technique. An electric field integral equation (EFIE) for equivalent volume current distributions is formulated with a dyadic Greens function for three-dimensional lossy dielectric bodies above water surface which is approximated with an impedance boundary. The numerical computations are repeated for many (N=50) different 4times4 clusters which are generated numerically with the Monte Carlo method, to get accurate statistics for the backscattering coefficients. It is found that the numerical results agree quite well with backscatter measurements of a rice field.

Numerical Analysis of the Ground Penetrating Radar's Return Signal for Mine Detection at Various Frequencies and Soil Conditions

Return signals of a ground penetrating radar(GPR) for mine detection at various frequencies and soil moisture contents are analyzed in this paper. We first compute the dielectric constant, conductivity and attenuation loss based on clay loam which is Korea standard soil. The mine-detection images of GPR at various frequencies are also obtained using the finite-difference time-domain(FDTD) technique. Then, the signal-to-clutter ratio(SCR) and received power of the radar are studied. It is shown that the variable frequency channels are suitable for a GPR to detect landmines at various soil conditions.

Comparison of Time-Domain Imaging Algorithms for Ultra-Wideband Radar with One-Dimensional Synthetic Aperture

Delay-sum back projection(DSBP) algorithm and the time reversal algorithm based on the finite-difference time-domain method are compared. The two algorithms, which operate in the time domain, can process the ultra-wideband (UWB) radar data to generate images that are close to the original location and shape of the target. For the experiment, the UWB radar consists of a network analyzer, a resistive V dipole antenna, a scanner, and a control computer. The radar aperture is synthesized by linearly scanning the antenna. A calibration procedure is applied to the measured data to remove signal distortion and clutter. The two algorithms are applied to the same data on the same platform. It is shown that the DSBP algorithm produces better images but takes longer time to produce the images than the FDTD-TR algorithm.

Retrieval of Soil Moisture and Surface Roughness from Backscatter Measurements of Vegetation Canopy

This paper presents an inversion algorithm for retrieving the volumetric soil moisture content and surface rms height from the measured backscattering coefficients of a vegetation canopy. The polarimetric backscattering coefficients of a tall-grass field are measured using a scatterometer at L-band. The water-cloud scattering model for the vegetation canopy are obtained by data-fitting with the measurements. Then, the soil moisture content and surface roughness of the tall-grass field are retrieved using a genetic algorithm. The retrieved soil moisture content and rms surface height of the tall-grass-covered soil surface are compared with the in-situ measured ground truth data, and good agreements between those values are shown.

Verification of Surface Scattering Models and Inversion Algorithms with the Polarimetric Backscatter Measurements of a Bare Soil Surface

The backscattering coefficients of a bare soil surface were measured using an L-band polarimetric scatterometer, which were used to verify the validities of scattering models and inversion algorithms. The soil moisture contents and surface roughness parameters (the RMS height and correlation length) were also measured from the soil surface. The backscattering coefficients of scattering models with these surface parameters were compared with the measured backscattering coefficients. The soil moisture contents of the soil surface were retrieved from the measured backscattering coefficients, and compared with the measured surface parameters. This paper shows that the scattering models agree with the measurements, and also shows the inversion results.

Numerical Computation of the Backscattering Coefficients of Rice Fields Using the Impedance Boundary Condition, Moment Method and Monte Carlo Method

A numerical algorithm for estimating precise backscattering coefficients of rice fields is proposed and its accuracy is verified in this paper. After a bunch of rice plants above water surface is modeled with a bunch of randomly oriented lossy dielectric bodies above an impedance surface and the equivalent volume currents of the lossy dielectrics are computed using the moment method. Then, the scattered fields of a rice field with many bunches are computed with a Monte Carlo method, and consequently the backscattering coefficient of the rice field is computed for various incidence angles and polarizations. Finally, the backscattering coefficient of a rice field is measured at 1.85 GHz using an R-band scatterometer system, and these experimental data are used to verify the numerical algorithm proposed in this paper. It is found that the numerical computation results agree well with the measurement data.

A Simple Model for Scattering Coefficients of Vegetation Canopies

A new simple microwave backward and forward scattering model for vegetation canopies is developed in this study. This simple model has only ten input parameters for a natural earth surface, which is modeled as a two-layer structure comprising a vegetation layer and a ground layer. The computation results of this model are compared with the experimental measurements, which were obtained by a ground-based scatterometer and the NASA/JPL air-borne synthetic aperture radar (SAR) system. It is found that the scattering model agrees well with the experimental data, even though the model uses only ten input parameters.