Traditionally, Radiative Transfer (RT) formulation has been used to simulate scattering from snow layer with the incorporation of phase matrix of scatterers in the formulation. Typically, spherical scatterers were assumed to represent the ice particles embedded inside the air medium and Mie phase matrix was applied. However, the real scatterers in the actual snow are generally more irregular than the assumed spherical shape. In this paper, a numerical solution based on the Hierarchical Equivalent Source Algorithm (HESA) has been developed to calculate the phase matrix of scatterers of other shapes to be incorporated in the existing RT formulation. Results from the new model shows good agreement with the ground truth measurement data collected from NASA Cold Land Processes Field Experiment (CLPX). The comparison shows that the scatterer shape could have significant contribution on total backscattering when the frequency is high.

Very little work has been carried out to examine the potential of synthetic aperture radar (SAR) imaging data for growth monitoring, disease monitoring, and yield prediction of oil palm plantations. In this paper, we present a scattering model for oil palm based on the radiative transfer equations, solved iteratively up to the second order, to better understand the backscattering behavior of oil palm canopies for SAR image interpretation. The oil palm canopy is modeled as a multilayer background host medium embedded with discrete scatterers of different shapes, with elliptic disks representing the leaves and cylinders representing the fronds and trunks. We consider the effects of coherent scattering through the dense medium phase and amplitude correction theory, as well as the near-field interactions between closely spaced scatterers through the Fresnel phase and amplitude corrections. Ground-truth data are used as input parameters for the model. The model is used to calculate the backscattering coefficients of oil palm canopies at different stages of growth and for different polarizations, frequencies, and incident angles. Comparisons between model calculations and C-band scatterometer measurements of multipolarization backscattering coefficients of 4-year-old oil palm canopies in Bangi, Malaysia show good agreement. Our model also predicts that SAR images at L-band are more sensitive to changes in the structure of the canopies, particularly that of the fronds, so will be the best frequency for oil palm growth monitoring and disease detection.

The design and development of Synthetic Aperture Radar (SAR) is one of the focused research areas in Malaysia since early 2000s. The main objective of this research is to develop an all-weather instrument for earth resource monitoring in Malaysia. The first SAR sensor developed was a C-band (5.3 GHz) SAR mounted on a small unmanned aerial vehicle (UAV) [1]. In 2013, a new SAR sensor operating at S-band (3.125 GHz) frequency has been developed for earth resource monitoring. It is an enhanced version of the former C-band SAR sensor, with 1.5 m spatial resolution and onboard SAR processing capabilities. This paper presents the design and development of the new S-band SAR system and its preliminary test results for remote sensing applications.

The development of microwave remote sensing models for the monitoring of vegetation has received wide attention in recent years. For vegetation in the tropics, it is necessary to consider a dense medium model for the theoretical modelling of the microwave interaction with the vegetation medium. In this paper, a multilayer model based on the radiative transfer theory for a dense vegetation medium is developed where the coherence effects and near field interaction effects of closely spaced leaves and branches are considered by incorporating the Dense Medium Phase and Amplitude Correction Theory (DM-PACT) and Fresnel Phase Corrections. The iterative solutions of the radiative transfer model are computed with input based on ground truth measurements of physical parameters of oil palm plantations in the state of Perak, Malaysia, and compared with the SAR images obtained from RADARSAT2. Preliminary results are analyzed for dominant scattering mechanisms as well as monitoring of growth variation of oil palm trees for further development of operation models for long term monitoring of oil palm plantations.

This paper summarizes the study of dense medium scattering and its applications towards sea ice research in Ross Island, Antarctica. Based on the Radiative Transfer Theory and earlier work by Tjuatja and Fung, an improvement to the phase matrix to account for the near field effects of electrically dense media was developed, called the Dense Medium Phase and Amplitude Correction Theory (DM PACT). An analysis on the scattering of discrete scatterers in an electrically dense medium was carried out and a backscattering model based on the iterative solution of Radiative Transfer Theory, incorporating both the DMPACT and the IEM model to characterize for rough surface was later developed. With the concern on climate change, the study shifted towards the application of dense medium scattering on sea ice and ice shelf. Using ground truth measurement data collected from Ross Island, Antarctica to compute the backscattering coefficient with the developed forward model, a good matching was obtained between the model predictions and the satellite measurements from RADARSAT. The model was then extended to incorporate multiple layers to take into account the effect of the snow layer on top of the sea ice. A good matching was obtained between the multi-layer model, the Matrix Doubling Method and the CEAREX measurements. From here, the research moved towards the development of inverse models for the purpose of sea ice thickness retrieval due to the parameter's importance in the study of climate change. For active remote sensing, the Radiative Transfer Inverse Scattering Model (RTISM), utilizing the RT-DMPACT forward model and Levenberg-Marquardt Optimization Algorithm was proposed. Initial results with the model showed good matching between measurement data and model predictions. For passive microwave remote sensing, two models were proposed for sea ice thickness retrieval: the training of neural networks using the RT-DMPACT forward model and the use of Genetic Algorithm for sea ice thickness retrieval. Both methods showed promise and the results were encouraging.

The study of scattered fields from nonspherical scatterers is becoming an important subject particularly in the area of theoretical modeling of microwave backscatter from vegetation. The generalized Rayleigh–Gans approximation has been widely used in the calculation of scattered fields from scatterers where at least one of its dimensions is comparably smaller than the wavelength. In such calculations, far-field approximations are used, which are not accurate when the observation points are in the Fresnel and near-field regions of the scatterer. Hence, the effects of Fresnel phase and amplitude corrections for the scattered field of circular disks, needles, and cylinders have been examined and shown to be significant in the calculation of closely spaced scatterers. However, the effects of Fresnel corrections in the scattered fields from general ellipsoids and elliptic disks have not yet been studied. In this paper, the scattered fields from general ellipsoids and elliptic disks are formulated based on the generalized Rayleigh–Gans approximation for cases with and without Fresnel corrections. Theoretical analysis shows that the Fresnel effects are important particularly at larger frequencies and at the null locations in the plots of the backscattering cross section. These effects become more important as the ellipticity of the scatterer increases. Comparisons with measurement data demonstrate that the calculated results with Fresnel corrections provide a better match compared with those without.

The alpha-k (alpha - k) curve is an important tool for real-time myriad filtering problems in channels with time-varying impulsiveness. In this letter, we use the asymptotic variance as the criterion to derive the optimal alpha - k curve. We then suggest a new expression for the optimal curve and compare it to the conjectured expression in earlier works.

Early models for paddy fields consist of a single-layered medium in which coherent effects within clusters of leaves are considered but multiple volume scattering is not. In this paper, the paddy canopy is modeled as a multilayered dense discrete random medium consisting of cylindrical and needle-shaped scatterers. Consideration is given to the coherent and near-field effects of the closely spaced scatterers through the Dense Medium Phase and Amplitude Correction Theory and Fresnel corrections, respectively, in the phase matrix. Then, this dense medium phase matrix is applied in the radiative transfer equations and solved up to the second order to consider double-volume scattering. Ground truth measurements of paddy fields were acquired at Sungai Burung, Selangor, Malaysia, for an entire season from the early vegetative stage of the plants to their reproductive stage. Measured parameters are used in the theoretical model to calculate the backscattering coefficients of paddy fields. Theoretical analysis of the simulation results shows in particular that second-order effects are important for cross-polarized backscatter data and that coherent effects need to be considered at lower frequencies. However, the use of needles to represent paddy leaves tends to underestimate the HH-polarized backscattering coefficients especially at the latter stages of plant growth, i.e., when the leaves are broader. The results are also used for comparisons with the backscattering coefficients obtained from RADARSAT images as well as that of earlier models to test the validity of the dense medium model with promising results.

Antarctica remains the continent with least access to humans due to its harsh weather condition and remoteness from human civilization. However, the major heat sink effect and its critical role in balancing world climate have made Antarctica an important continent to monitor and understand constantly. Due to its remoteness and wide area coverage, remote sensing technology is suitable to be utilized for such purposes. As the majority parts of Antarctia are covered by ice and snow, it is necessary to model the ice and snow media for microwave scattering analysis to interpret from the data. In this paper, a theorethical model is developed to model the sea ice and ice shelf areas in Antarctica by treating them as layers of random discrete medium with scatterers embedded in the host medium. The Dense Medium Phase and Amplitude Correction Theory (DMPACT) which takes into account the close spacing effect among the scatterers is applied to the sea and snow medium [1]. The air-snow interface and snow-sea interface are modelled using Integral Equation Method (IEM) with the consideration of surface multiple scattering effect [2]. This scattering problem of an electrically dense medium such as sea ice and ise shelf is solved using the Radiative Transfer Theory. Gound truth measurement trips were conducted in the years of 2002-2004 at Ross Island, Antarctica with logistic assistance of Antarctica New Zealand to measure the physical parameters of the sea ice, ice shelf and sea water, which were then used in theorethical model calculation. RadarSat images of the study sites were also acquired for the comparison with the theorethical results. The results indicate that the matches between the theorethical predictions and the satellite data over the measurement period are promising. In the theorethical analysis, a study of the physical paraneters affecting the backscattering returns and the major scattering mechanisms involveds is carried out and the analysis is presented.

We provide a simple and elegant framework based on morphological transformations to generate multiscale digital elevation models (DEMs) and to extract topologically significant multiscale geophysical networks. These terrain features at multiple scales are collectively useful in deriving scaling laws, which exhibit several significant terrain characteristics. We present results derived from a part of Cameron Highlands DEM.

The statistics of received signal power at the receiver in a cellular direct-sequence code-division multiple-access (DS-CDMA) system with flat Rayleigh fading and fast closed-loop power control mechanism are studied. A simple model for the fast closed-loop power control mechanism is proposed to ease the analysis. The probability density function (pdf) of the received signal power is derived by taking into consideration the updating frequency of power control mechanism, maximum allowable transmitted power, and Doppler frequency of the fading channel. The pdf derived can be used to study the performance of a reverse-link DS-CDMA system with noncoherent M-ary orthogonal modulation. The result shows that when optimum maximum allowable transmitted power is used, system capacity can be substantially increased for typical normalized Doppler frequency in cellular communication.

Transmitter power control is an effective scheme to improve the performance of cellular DS/CDMA systems. In the reverse link, time-multiplexed pilot symbols are used to assist the estimation of received signal power in order to improve the performance of power control. In this paper, two different approaches for received power estimation in power controlled CDMA systems are proposed and compared in terms of bit error rate (BER) by means of analytical and simulation studies. The first power estimator uses a simple sample average and the second power estimator uses a minimum mean square error (MMSE) filter approach. The MMSE approach requires knowledge of the Doppler spread and the signal-to-interference ratio (SIR). Comparison of the performance of the two power estimators is done with respect to deviations in the SIR and Doppler spread as used for the design of the MMSE filter, from their nominal values. Analysis results show that when the MMSE filter approach is used, BER can be further improved as compared to the simple sample average power estimator.

An analytical approach is developed to determine the impact of signal phase distortion due to polarization mode dispersion (PMD) on the bit error rate (BER) performance of optical heterodyne continuous phase FSK (CPFSK) system with delay demodulation receiver. The computed results at a bit rate of 10 Gb/s show that the CPFSK system suffer a significant amount of power penalty due to the effect of PMD. At a modulation index of 0.5, the penalty at a BER of 10/sup -9/ is found to be 1.0 dB, 1.8 dB and 2.8 dB when the differential group delay is 10 ps, 50 ps and 100 ps respectively for fiber length of 100 km. At modulation index of 1, the penalty is approximate 3.75 dB for differential group delay of 10 ps.

A vegetation medium can generally be modeled as a discrete random medium where scatterers such as disks, needles, and cylinders are used to represent the leaves, branches, and trunks. At low frequency, it is possible that the spacing between the scatterers is comparable or smaller than the wavelength. This medium is considered electrically dense, and the coherence effect from the scatterers indicates that the assumption of independent scattering of the scatterers is no longer valid. In addition, in a dense vegetation medium where the scatterers are close to each other, near field interactions should also be considered. In this paper, the coherence effect from the various correlated scatterers is taken into account by introducing the array phase correction to the phase matrices of the scatterers. For the near field interaction effect, both the Fresnel phase correction and the amplitude correction are considered. The Fresnel phase correction is incorporated by including the higher order terms in the phase of the scattered field from a scatterer, whereas the amplitude correction is obtained from the near field amplitude term of the scattered field. These corrected phase matrices for the disks, needles, and branches are applied in the single layer random discrete medium where the second order iterative radiative transfer solutions are obtained. Theoretical analyses of the effects of these corrections to the backscattering returns for various volume fractions, frequencies, incident angles, orientations, and sizes are carried out. It is found that the array phase correction is important for an electrically dense medium, whereas the amplitude and the Fresnel phase corrections are required when the frequency increases and enters into the Fresnel region. Good agreements are obtained from the comparisons of the theoretical predictions with the multifrequency and multipolarization measurement results of the Japanese cypress and boreal forest.

A dense medium phase matrix developed based on the concept of random lattice perturbation is employed in the radiative transfer theory to calculate the coand cross-polarized backscatter from a layer of randomly distributed spherical scatterers. The position randomness properties are characterized by the variance and correlation function of scatterer positions within the medium. The dense medium phase matrix differs from the conventional one in two major aspects, i.e., there is an amplitude and a phase correction. These corrections account for the effects of close spacing and position correlation between scatterers in a dense discrete random medium. This study shows that phase coherency and close-spacing amplitude modifications are two separate corrections necessary for an electrically dense medium. Results indicate that there is a need to distinguish between spatially and electrically dense medium. The phase correction is found to have a greater impact on cross-polarized than like-polarized backscatter coefficients; the converse is true of the amplitude correction. Backscattering calculations from the theory are compared with measurements from controlled microwave experiments on random media consisting of closely packed spheres, and from field measurements of dry snowpack. Predictions from such a theory agree well with the measured data.

In the derivation of the conventional scattering phase matrix of a discrete random medium, the far-field approximation is usually assumed. In this paper, the phase matrix of a dense discrete random medium is developed by relaxing the far-field approximation and accounting for the effect of volume fraction and randomness properties characterized by the variance and correlation function of scatterer positions within the medium. The final expression for the phase matrix differs from the conventional one in two major aspects: there is an amplitude and a phase correction. The concept used in the derivation is analogous to the antenna array theory. The phase matrix for a collection of scatterers is found to be the Stokes matrix of the single scatterer multiplied by a dense medium phase correction factor. The close spacing amplitude correction appears inside the Stokes matrix. When the scatterers are uncorrelated, the phase correction factor approaches unity. The phase matrix is used to calculate the volume scattering coefficients for a unit volume of spherical scatterers, and the results are compared with calculations from other theories, numerical simulations, and laboratory measurements. Results indicate that there should be a distinction between physically dense medium and electrically dense medium.

The paper reports on the measured dielectric constants of leaves of two tropical crops, namely rubber and oil palm, as a function of moisture content at X-band. Using a microcomputer-based automated system consisting of a Wiltron scalar network analyzer and a slotted waveguide, the measurements are done based on the waveguide thin sheet technique. Theoretical values from the dual-dispersion model by Ulaby and El-Rayes [1987] and from the simple dielectric theory of Fung and Fung [1977] are compared with the experimental data. The model from Ulaby and El-Rayes is found to be able to give good estimates of the dielectric constants for the two types of leaf samples at X-band.>