Leung Tsang

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• Professor at University of Michigan

Firn aquifers play an important role in polar ice sheet hydrology and the associated mass and energy transport processes. Although firn aquifer extent has been mapped using passive microwave satellite observations, models to predict L-band brightness temperature time series have remained elusive. This paper implements a radiative transfer model for...

Full-wave simulations at L-band using the Fast Hybrid Multiple Scattering Theory Method (FHMSTM) have been applied to the Harvard forest in Massachusetts using the Soil Moisture Active Passive Validation Experiment 2022 (SMAPVEX22) dataset. Due to the limitations of commercial fullwave electromagnetic solvers, the FHMSTM is our choice considering i...

A fast method is developed utilizing the multiple scattering theory with broadband Green’s function (MST-BBGF) to calculate band diagrams for vector electromagnetic waves in 3D periodic structures composed of irregularly shaped scatterers. The method uses the T-matrix of irregular-shaped scatterers to formulate eigenvalue problems for the KKR (Korr...

In this article, we analyze the time series data collected by the Sentinel-1 C-band synthetic aperture radar over the Alps mountains in Southern France. Both the co-polarized and cross-polarized radar data are analyzed. We study the combined effects of the volume scattering of snow and the rough soil surface scattering below the snow using physical...

Measurements of radar backscatter are sensitive to snow water equivalent (SWE) across a wide range of frequencies, motivating proposals for satellite missions to measure global distributions of SWE. However, radar backscatter measurements are also sensitive to snow stratigraphy, to microstructure, and to ground surface roughness, complicating SWE r...

Ice shelves are important parts of the cryosphere that influence ice sheet dynamics and mass loss. The internal temperatures of ice shelves are currently known only from a few borehole sites or from glaciological models. Microwave radiometry in the 0.4-2.5 GHz range is capable of receiving thermal emissions from deep within an ice shelf and thereby...

Full wave simulations of the effective permittivity of firn aquifer and wet snow at L Band are reported. The Monte Carlo simulations are carried out for bicontinuous media embedded in a sphere and the scattering cross section and absorption cross section are calculated. By averaging over realizations, the effective permittivity is extracted by comp...

Measurements of radar backscatter are sensitive to snow water equivalent (SWE) across a wide range of frequencies, motivating proposals for satellite missions to measure global distributions of SWE. However, radar backscatter measurements are also sensitive to snow stratigraphy, microstructure and to surface roughness, complicating SWE retrieval. A...

In this paper, we developed the dense media radiative transfer model (DMRT) for random media with densely packed particle clusters. The dense media are computer-generated by applying the bicontinuous random media characterization. The microstructure of the media is controlled by two parameters: mean grain size 〈ζ〉 and aggregation parameter b . Ph...

To calculate scattering of a vegetation field consisting of a large number of plants, an improved fast version of the hybrid method (FHM) combining fast multiple scattering theory (FMST) and a numerical electromagnetic approach has been developed. In the hybrid method, we use a library of T-matrices and the Foldy-Lax (FL) equation to calculate the...

An airborne microwave wide-band radiometer (500–2000 MHz) was operated for the first time in Antarctica to better understand the emission properties of sea ice, outlet glaciers and the interior ice sheet from Terra Nova Bay to Dome C. The different glaciological regimes were revealed to exhibit unique spectral signatures in this portion of the micr...

This paper presents analysis of P-band radio signal propagation through forest based on 3D Numerical Method of Maxwell's equations (NMM3D). The simulation domain of the forested region covers an area of 35.8 by 35.8 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> that includes 112-121 conifer...

In this paper, we use the Analytical Kirchhoff Solution (AKS) and Numerical Kirchhoff Approach (NKA) to study the bistatic scattering field ( γ ) from mountain terrain at P-band frequency. The study area is Grand Mesa, Colorado (U.S.A), and the properties of land surface roughness are extracted from airborne lidar surveys. The bistatic scattering...

Over the past decade, a series of airborne experiments in the Arctic and Antarctica explored microwave emission from sea ice and ice sheets at frequencies from 0.5 to 2 GHz. The experiments were motivated by the fact that lower frequencies penetrate deeper into a frozen surface, thus offering the possibility to measure physical temperatures at grea...

Seasonal snow cover is the largest single component of the cryosphere in areal extent, covering an average of 46×106 km2 of Earth's surface (31 % of the land area) each year, and is thus an important expression and driver of the Earth's climate. In recent years, Northern Hemisphere spring snow cover has been declining at about the same rate (∼ -13...

In studying the mass balance of polar ice sheets, the fluctuation of the firn density near the surface is a major uncertainty. In this paper, we explore these variations at locations in the Greenland Ice Sheet and at the Dome C location in Antarctica. Borehole in situ measurements, snow radar echoes, microwave brightness temperatures, and modelling...

In this paper, we provide updates on our recent work on the theory of microwave remote sensing for applications in remote sensing of soil moisture and snow water equivalent (SWE). The three topics are the following. (i) For the effects of forests and vegetation, we developed the hybrid method of NMM3D full-wave simulations over the vegetation field...

Backscattering from rough soil surface has important applications to the remote sensing of soil moisture and snow water equivalent (SWE). To extend simulations to Ku-band, we have performed full-wave simulations up to kh = 15 . Results are simulated for various profiles and show that the scattering at C-, X-, and Ku-bands is influenced by both s...

Although ice sheet internal temperature is a first-order control on glacier dynamics, relatively few in situ borehole temperature profiles exist. The ultra-wideband software-defined microwave radiometer (UWBRAD) was designed to estimate internal ice sheet temperature ( $T_{i}$ ) by measuring microwave brightness temperatures ( $T_{b}$ ) from 0.5...

A comparison of three different electromagnetic scattering models for land surface delay-Doppler maps (DDMs) obtained from global navigation satellite system reflectometry (GNSS-R) along a Cyclone Global Navigation Satellite System (CYGNSS) track in the San Luis Valley, Colorado, USA, is presented. The three models are the analytical Kirchhoff solu...

The full-wave simulations of 3D Maxwell equations of forests at L-band are carried out with a two-step hybrid method. The tallest trees considered include one 8-meter tall trunk, 18 primary branches and 108 secondary branches. In the first step, the T-matrix of a single tree in the representation of vector cylindrical waves (VCW) is calculated by u...

In this paper, we apply the BBGF-KKR-MST (Broadband Green's function-KKR-Multiple Scattering Theory) to calculate Band Structures and Band Field Solutions in topological acoustics. A feature of BBGF is that the lattice Green's functions are broadband, and the transformations to cylindrical waves are calculated rapidly for many frequencies for speed...

We apply the broadband Green’s function-KKR-multiple scattering theory (BBGF-KKR-MST) to calculate normalized band-field solutions of magneto-optic crystals. The advantage of the method is that the matrix eigensystem equations are of low order. For the first three bands, a total of three cylindrical waves is sufficient to characterize the eigensyst...

Seasonal snow cover is the largest single component of the cryosphere in areal extent, covering an average of 46 million square km of Earth's surface (31 % of the land area) each year, and is thus an important expression of and driver of the Earth’s climate. In recent years, Northern Hemisphere spring snow cover has been declining at about the same...

In this article, we study wave propagation in vegetation at multiple frequencies using a hybrid method. First, the multiple scattering within a single plant is captured using the high-frequency structure simulator (HFSS) for extracting the T-matrix of the plant in vector cylindrical waves (VCW). Second, the Foldy–Lax equations (FLE) are applied wit...

—In this paper, we derived Analytical Kirchhoff Solutions (AKS) for bistatic scattering near the specular directions at P band and L band for applications in Signals of Opportunity (SoOp). The land surface profiles are divided into three scales: microwave roughness f1, fine scale topography f2, and coarse scale 30-meter DEM f3 . The microwave rough...

This paper implements a newly developed combined active and passive algorithm for the retrieval of snow water equivalent (SWE) by using three-channel active and two-channel passive observations. First, passive microwave observations at 19 and 37 GHz are used to determine the scattering albedo of snow. An a priori scattering albedo is obtained by av...

Microwave radiometry has provided valuable spaceborne observations of Earth's geophysical properties for decades. The recent SMOS, Aquarius, and SMAP satellites have demonstrated the value of measurements at 1400 MHz for observing surface soil moisture, sea surface salinity, sea ice thickness, soil freeze/thaw state, and other geophysical variables...

In this article, we develop a hybrid method for studying wave scatterings and propagation in a vegetation field. The coherent multiple scatterings among the plants and the gaps in the vegetation field are considered through a two-step hybrid method. First, the T-matrix of a single plant is calculated using the Huygens principle and the vector cylin...

Wheat, canola, and pasture are three of the major vegetation types studied during the Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) conducted to support NASA's Soil Moisture Active Passive (SMAP) mission. The utilized model structure is integrated in the SMAP baseline active retrieval algorithm. Forward lookup tables (data-cub...

Ice sheet subsurface temperature is important for understanding glacier dynamics, yet existing methods to obtain the temperature of the ice sheet column are limited to in situ sources at present. The ultrawideband software-defined microwave radiometer (UWBRAD) has been developed to investigate the remote sensing of ice sheet internal temperatures...

The Ultra-Wideband Software Defined Microwave Radiometer (UWBRAD) is a wideband radiometer operating from 0.5 to 2 GHz for remote sensing of polar ice sheet temperature profiles. Small-scale (cm to m) fluctuations in firn density in the upper portion of the ice sheet significantly impact observed brightness temperatures. Previously, a fully coheren...

In this paper, we develop a method of simulations of using the broadband Green’s function (BBGF) in the Korringa Kohn Rostoker (KKR) method. The merit of the method is broadband such that once the initial setup is completed, the calculation at every frequency is calculated rapidly. The broadband Green’s function consists of a frequency-independent...

Accurate calculations of electromagnetic scattering and emission from ocean surfaces with large sizes and root-mean-square (RMS) heights are still a challenge for the full-wave numerical methods. The widely used sparse matrix canonical grid (SMCG) method is only efficient for small and moderate roughness surfaces. This is because of the limitation...

A novel method is developed in this paper to characterize the band diagram and band modal fields of gyromagnetic photonic crystals that support topological one-way edge states. The proposed method is based on an integral equation formulation that utilizes the broadband Green’s function (BBGF). The BBGF is a hybrid representation of the periodic lat...

In near-infrared imaging and spectroscopy, high-fidelity modeling of photon transport for dense polydisperse colloidal suspensions is crucial. We developed photon transport models using the radiative transfer equation (RTE) with the dependent scattering theory (DST) at volume fractions up to 20%. The polydispersity and interference effects strongly...

A hybrid spatial-spectral method for rapid and broadband calculation of the vector potential normal modes and dyadic Green's function (GF) inside the cavity of irregular shape is presented. In the broadband method of simulation, the normal modes of the irregular cavity, which are independent of operation frequency, are first computed through a line...

A partially coherent approach for computing the electromagnetic response of a layered medium having random rough interfaces and a random dielectric profile is presented as an alternative to the full-wave solution of the problem. The statistical nature of this problem, in particular, the random dielectric profile, introduces randomness in the phase...

A semi-analytical approach for rapid calculation of the Green’s function inside a cavity of irregular shape over a broad range of frequency is presented. The method is based on the extraction of the Green’s function at an imaginary wave number from itself to obtain a rapidly convergent hybrid spatial–spectral expansion of the Green’s function. The...

Sea surface salinity (SSS) is an important ocean dynamic parameter, which plays a crucial role in the studies of global climate change, global water cycle forecast, marine environment monitoring, etc.[1-3]. Especially in polar region, SSS becomes a sensitive indicator of climate change. However, the accuracies of retrieved SSS using the popular L-b...

We use full wave simulations of rough surfaces to calculate the emissivities of polar ocean between 0.5 GHz to 2 GHz for applications in ocean salinity. High accuracy is required because the emissivity variations between flat and rough surfaces are at the order of magnitude of 10-3. In addition, the changes of emissivity due to salinity change are...

The increased availability of spaceborne radar data projected over the next decade provides a great opportunity for operational soil moisture mapping with high spatial (< 50 m) and temporal (< 3 days) resolution, by combining the data from multiple SAR missions. Accordingly, a multi-frequency soil moisture retrieval framework has been proposed, bei...

In this paper, we develop a hybrid method to calculate the propagation of microwaves in randomly distributed dielectric cylinders. The hybrid method combines off-the-shelf techniques for single object and our developed techniques of Foldy-Lax method that include extracting the T-matrix for single object, vector translation addition theorem and solv...

In this article, we apply the broadband Green's function for fast full-wave simulations of the radiated emissions from the printed circuit boards (PCBs) of irregular shape. Changes were made on the previous version that improve the computational efficiency and accuracies of the solutions. The improvements include imaginary wavenumber extractions fo...

An ultrawideband radiometer was used to measure microwave brightness temperature spectra over Arctic sea ice in the Lincoln Sea near the north coast of Greenland. Spectra over the range of 0.5-2 GHz were compared to thermal infrared images collected during the airborne campaign and also compared to nearly concurrent Sentinel-1 C-band synthetic aper...