Measurement and behavior of dual-polarization vegetation opticaldepth and single scattering albedo at 1.4- and 5-GHz microwavefrequencies

A measurement procedure has been developed and tested to determine horizontal and vertical polarization radiative transfer properties, i,e., single scattering albedo (ω) and optical depth (τ), of vegetation under field conditions. The procedure was applied to a wheat crop for a series of biomass densities. The measurements were done using two different radiometers (1.4 and 5 GHz) and for different view angles. The measurements and calculations indicated that the ratios of horizontal and vertical polarization radiative transfer properties (α=Γ_h/Γ_ν, α'=τ_h/τ_ν and β=ωh/ω_ν) are slightly dependent on view angle. However, no significant dependence on biomass density could be discerned     

Electrical conductivity values used with the bidomain model ofcardiac tissue

Electrical conductivities in the bidomain model of cardiac tissue are expressed as functions of four parameters. These expressions allow simulations to be performed using nominal, equal, and reciprocal anisotropy without introducing undesired effects, such as length constant variations. Relative values of the bidomain conductivities are estimated to be: σ_iL=1, σ_iT=0.1, σ_eL=1, and σ_eT=0.4     

Vertical eigenstate method for simulation of induction and MWDresistivity sensors

A method for computing responses of induction or MWD (measurement-while-drilling) resistivity sensors in layered formations with invasion zones is presented. The geometry is assumed to have an axial symmetry resulting in a two-dimensional problem. The solution of the wave equation is expressed by a summation of eigenstates in the vertical direction in each cylindrical region. The eigenmodes in each region are found numerically, and the variation of fields in the horizontal direction is expressed in terms of analytical functions. Computed results are used to simulate logging tool responses in invaded formations. It is found that the apparent resistivity reading is a complicated function of the resistivities of the invaded zone, that of the uninvaded zone, bed thickness, and invasion diameter. Since no simple rule can be used to describe the characteristics of the investigation depth of the tool, the use of a computer simulation software, such as the one developed in this work, would be very useful to a log analyst in log interpretation     

Maximum likelihood DOA estimation and asymptotic Cramer-Rao boundsfor additive unknown colored noise

This paper is devoted to the maximum likelihood estimation of multiple sources in the presence of unknown noise. With the spatial noise covariance modeled as a function of certain unknown parameters, e.g., an autoregressive (AR) model, a direct and systematic way is developed to find the exact maximum likelihood (ML) estimates of all parameters associated with the direction finding problem, including the direction-of-arrival (DOA) angles Θ, the noise parameters α, the signal covariance Φ_s, and the noise power σ². We show that the estimates of the linear part of the parameter set Φ_s and σ² can be separated from the nonlinear parts Θ and α. Thus, the estimates of Φ_s and σ² become explicit functions of Θ and α. This results in a significant reduction in the dimensionality of the nonlinear optimization problem. Asymptotic analysis is performed on the estimates of Θ and α, and compact formulas are obtained for the Cramer-Rao bounds (CRB's). Finally, a Newton-type algorithm is designed to solve the nonlinear optimization problem, and simulations show that the asymptotic CRB agrees well with the results from Monte Carlo trials, even for small numbers of snapshots     

Threshold voltage uniformity and characterization of microwaveperformance for GaAs/AlGaAs high electron-mobility transistors grown onSi substrates

We report on DC and microwave characteristics for high electron-mobility transistors (HEMT's) grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). Threshold voltage (V _th) distribution in a 3-in wafer shows standard deviation of V_th (σV_th) of 36 mV with V_th of -2.41 V for depletion mode HEMT's/Si and σV_th of 31 mV with V_th of 0.01 V for enhancement mode, respectively. The evaluation of V_th in a 1.95×1.9 mm² area shows high uniformity for as-grown HEMT's/Si with σV_th of 9 mV for V_th of -0.10 V, which is comparable to that for HEMT's/GaAs. Comparing the V_th distribution pattern in the area with that for annealed HEMT's/Si, it is indicated that the high uniformity of V_th is obtained irrelevant of a number of the dislocations existing in the GaAs/Si. From microwave characteristic evaluation for HEMT's with a middle-(10~50 Ω·cm) and a high-(2000~6000 Ω·cm) resistivity Si substrate using a new equivalent circuit model, it is demonstrated that HEMT's/Si have the disadvantage for parasitic capacitances and resistances originated not from the substrate resistivity but from a conductive layer at the Si-GaAs interface. The parasitic parameters, especially the capacitances, can be overcome by the reduction of electrode areas for bonding pads and by the insertion of a dielectric layer under the electrode, which bring high cut-off frequency (f_T) and maximum frequency of operation (f_max) of 24 GHz for a gate length of 0.8 (μm). These results indicate that HEMT's/Si are sufficiently applicable for IC's and discrete devices and have a potential to be substituted for HEMT's/GaAs     

Drift velocity and ionization coefficient for holes in single-valley semiconductors

An analytical theory has been developed for drift velocity (V_d) and ionization coefficient (_h) of holes in silicon. Based on Boltzmann transport equation, expressions for drift velocity (V_d) and ionization coefficient (_h) are derived. The theoretical approach is based on calculation of the collision operator for ionization probability, approximated by a delta function. It is observed that the values of drift velocity (V_d) and ionization coefficient (_h) are in good agreement with experimental results for ionization length (l_io = 70 Å) and ionization energy (ε_i = 2.5 eV). This confirms the validity of the developed theoretical model for drift velocity and ionization coefficient of holes.     

Relationship between and measurement of differential scatteringcoefficient (σ0) and bidirectional reflectancedistribution function (BRDF)

The microwave and optical scattering formulations are reviewed, a relationship between them at the same wavelength is presented, and the measurement conditions for obtaining range-independent and equipment-independent values are discussed. It is shown that the physical mechanism of scattering of electromagnetic beams from a surface can be quantified by either a differential scattering coefficient (σ⁰) or a bidirectional reflectance distribution function (BRDF). For a diffuse surface, σ⁰=4π BRDF cos &thetas;_i cos &thetas;_r, where &thetas;_i and &thetas;_r are the incident and reflected angles, respectively, from the surface normal. The geometrical constraints inferred in the measurement of coherent electromagnetic wave scattering from relatively small objects are easily satisfied to obtain range- and equipment-independent values, but care in experimental design is required when dealing with large surfaces. More care is also required when dealing with surfaces entailing specular features in addition to diffuse features     

An empirical model for interpreting the relationship betweenbackscattering and arid land surface roughness as seen with the SAR

The nature of the surface in a flat arid zone located in the western Sahara desert was studied and its roughness parameters defined. The main geological units were compared with backscattering data from ERS-1 images. Results showed a close correlation between the backscattering coefficient, σ₀, and the maximum height, h_max, of the rocks making up the arid landscape. The simplified relationship σ₀=4.63.1og h_max-15.29 (with h_max in cm and σ₀ in dB) was established from field measurements, giving an r² of about 88%. This empirical relationship is confirmed by another close relation between σ₀ and the statistical parameter s, the height standard deviation. The advantage of h_max is that it can be extracted for any site, whatever its roughness may be. The spatial distribution of the rock facets and the geometric characteristics of the incidence angle of the radar signal seem to explain the results     

Effect of tree structure on X-band microwave signature ofconifers

Experimental studies are performed on some coniferous trees, Austrian pine, Nordmann spruce, and Norway spruce, to investigate the relation between the tree architecture and radar signal at X-band. For a single tree, the radar cross section (RCS) is measured as a function of the scatterer location at 90° incidence. It is found that the main scatterers are the leafy branches, and the difference between σ_vv and σ_hh is significant at the upper portion of the tree. At the lower portion of the tree σ^o_vv and σ°_hh have almost the same level. For a group of trees the angular trends of σ°_vv and σ°_hh are measured. It is found that the levels of σ°_vv and σ° _hh are of the same order, but their angular trends vary from one tree species to the other, depending on the tree species structure. The experimental results are interpreted with the help of a theoretical model which accounts for the structure of the tree     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

A binary analog to the entropy-power inequality

Let {X_n}, {Y_n} be independent stationary binary random sequences with entropy H( X), H(Y), respectively. Let h(ζ)=-ζlogζ-(1-ζ)log(1-ζ), 0⩽ζ⩽1/2, be the binary entropy function and let σ(X)=h^-1 (H(X)), σ(Y)=h^-1 (H(Y)). Let z_n=X_n⊕Y_n , where ⊕ denotes modulo-2 addition. The following analog of the entropy-power inequality provides a lower bound on H(Z ), the entropy of {Z_n}: σ(Z)⩾σ(X)*σ(Y), where σ(Z)=h^-1 (H(Z)), and α*β=α(1-β)+β(1-α). When {Y _n} are independent identically distributed, this reduces to Mrs. Gerber's Lemma from A.D. Wyner and J. Ziv (1973)     

Laboratory measurements of the 36 GHz backscattering cross sectionfrom water waves

The backscattering cross section per unit area σ₀ of a roughened water surface at 36 GHz is needed in the development of new remote sensing instrumentation that will operate at this frequency. One instrument, the multimode airborne radar altimeter (MARA), will illuminate the surface at incidence angles ranging from nadir to 12° off-nadir. Laboratory tests were performed at the Wallops Wind-Wave Tank Facility to determine the variability of σ₀ at these angles and as a function of windspeed. The measurement procedures used in a 6-in.-diam aluminum sphere as the calibration source. The results are compared with earlier measurements at this frequency. Little variability with windspeed was found in the cross-section values for 12° off-nadir, while the cross section decreased with windspeed at nadir. The nadir cross section exceeded the off-nadir result by about 7 dB at a windspeed of 10 m/s (at a 10-m effective height above sea level)     

QuikSCAT geophysical model function for tropical cyclones andapplication to Hurricane Floyd

The QuikSCAT radar measurements of several tropical cyclones in 1999 have been studied to develop the geophysical model function (GMF) of Ku-band radar σ₀ values (normalized radar cross section) for extreme high wind conditions. To account for the effects of precipitation, the authors analyze the co-located rain rates from the Special Sensor Microwave/Imager (SSM/I) and propose the rain rate as a parameter of the GMF. The analysis indicates the deficiency of the NSCAT2 GMF developed for the NASA scatterometer, which overestimates the ocean σ₀ for tropical cyclones and ignores the influence of rain. It is suggested that the QuikSCAT σ₀ is sensitive to the wind speed of up to about 40-50 m s^-1. The authors introduce modifications to the NSCAT2 GMF and apply the modified GMF to the QuikSCAT observations of Hurricane Floyd. The QuikSCAT wind estimates for Hurricane Floyd in 1999 was improved with the maximum wind speed reaching above 60 m s^-1. The authors perform an error analysis by comparing the QuikSCAT winds with the analyses fields from the National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD). The reasonable agreement between the improved QuikSCAT winds and the HRD analyses supports the applications of scatterometer wind retrievals for hurricanes     

95-GHz scattering by terrain at near-grazing incidence

This study, consisting of three complimentary topics, examines the millimeter-wave backscattering behavior of terrain at incidence angles extending between 70 and 90°, corresponding to grazing angles of 20° to 0°. The first topic addresses the character of the statistical variability of the radar backscattering cross section per unit area σ_A. Based on an evaluation of an extensive data set acquired at 95 GHz, it was determined that the Rayleigh fading model (which predicts that σ_A is exponentially distributed) provides an excellent fit to the measured data for various types of terrain covers, including bare surfaces, grasses, trees, dry snow, and wet snow. The second topic relates to the angular variability and dynamic range of the backscattering coefficient σ⁰, particularly near grazing incidence. We provide a summary of data reported to date for each of several types of terrain covers. The last topic focuses on bare surfaces. A semi-empirical model for σ⁰ is presented for vertical (VV), horizontal (HH), and cross (HV) polarizations. The model parameters include the incidence angle &thetas;, the surface relative dielectric constant ϵ, and the surface roughness ks, where k=2π/λ and s is the surface root mean square (RMS) height     

Error-erasure decoding of binary cyclic codes, up to a particularinstance of the Hartmann-Tzeng bound

It is shown that error-erasure decoding for a cyclic code allows the correction of a combination of t errors and r erasures when 2t+r<σ₀; the parameter σ₀ denotes a particular instance of the Hartmann-Tzeng bound. This procedure is an improvement on the error-erasure decoding algorithm developed by G.D. Forney (1965), which works when 2t+r<σ, where σ denotes the BCH-bound of the code     

Spectral gain hole-burning at 1.53 μm in erbium-doped fiberamplifiers

Spectral gain hole-burning at λ₀=1.53 μm was observed in an erbium-doped fiber amplifier at temperatures between 4.2 and 77 K. The hole width was found to broaden with temperature for T ⩾20 K according to a T^1.73 law. From the data, the room-temperature homogeneous linewidth associated with the 1.531-μm transition in the ⁴I_13/2-⁴I_15/2 laser system was determined to be Δλ_h=11.5 nm for aluminosilicate fibers     

Theoretical study of deep-trap-assisted anomalous currents inworst-bit cells of dynamic random-access memories (DRAM's)

High-level leakage (anomalous) currents in worst-bit cells of dynamic random-access memory (DRAM) devices, i.e., in the tail region of the cumulative probability of the data retention time distribution, are analyzed by utilizing device simulation. Deep-traps are assumed to be located near the metallurgical junction, and the anomalous current is evaluated as a function of the number of traps as well as a function of energy level (E_t) and capture cross-section (σ). Calculated leakage currents are compared with measured data. It is found that: (1) acceptor-type deep-traps located in an n-region, as well as donor-type deep-traps in a p-region, can generate the high-level current flowing through pn junctions; (2) heavy-metal contamination of the order of 10³ atoms/cell can generate the high-level current when E _t is situated near the center in the energy gap and σ is around 10^-15 cm²; and (3) current induced by point defects is two to six orders of magnitude lower than that induced by the heavy-metal contamination. Several sets of material constants are examined for obtaining the best fit between the calculated current and measured data. This examination theoretically predicts Zn and Au atoms (of the order of 10³ per unit cell) as the origins of the anomalous current in worst-bit cells     

Theoretical analysis of word-level switching activity in thepresence of glitching and correlation

This paper presents a novel analytical approach to compute the switching activity in digital circuits at the word level in the presence of glitching and correlation. The proposed approach makes use of signal statistics such as mean, variance, and autocorrelation. It is shown that the switching activity α_f at the output node f of any arbitrary circuit in the presence of glitching and correlation is computed as α_f=Σ_i=1^S-1α(f _i,i+1)=Σ_i=1^{S- 1}p(f_i+1)(1-p(f_i))(1-ρ(f_i,i+1 )) (1) where ρ(f_i,i+1)=ρ(f_i,i+1)=(E[f_i(Sn)f _i+1(Sn)]- p(f_i)p(f_i+1))/(√(p(f _i)-p(f_i)²)(p(f_i+1)- p(f_i+1²))) (2). S number of time slots in a cycle; ρ(f_i,+1) time-slot autocorrelation coefficient; E[x]=expected value of x; p_x=probability of the signal x being “one”. The switching activity analysis of a signal at the word level is computed by summing the activities of all the individual bits constituting the signal. It is also shown that if the correlation coefficient of the higher order bits of a normally distributed signal x is ρ(x_c), then the bit P₀ where the correlation begins and the correlation coefficient is related hy ρ(x_c)=erfc{(2(P₀-1)-1)/(√2σ_x )} where erfc(x)=complementary error function; σ_x=variance of x. The proposed approach can estimate the switching activity in less than a second which is orders of magnitude faster than simulation-based approaches. Simulation results show that the errors using the proposed approach are about 6.1% on an average and that the approach is well suited even for highly correlated speech and music signals     

Dependence of the normalized radar cross section of water waves onBragg wavelength-wind speed sensitivity

Measurements of the normalized radar cross section (σ°) made by the YSCAT ultrawideband scatterometer during an extended deployment on the Canada Centre for Inland Waters (CCIW) Research Tower located at Lake Ontario are analyzed and compared with anemometer wind measurements to study the sensitivity of σ° to the wind speed as a function of the Bragg wavelength. This paper concentrates on upwind and downwind azimuth angles in the wind speed range of 4.5-12 m/s. While YSCAT collected measurements of σ° at a variety of frequencies and incidence angles, this paper focuses on frequencies of 2.0, 3.05, 5.30, 10.02, and 14.0 GHz and incidence angles within the Bragg regime, 30-50°. Adopting a power law model to describe the relationship between σ° and wind speed, both wind speed exponents and upwind/downwind (u/d) ratios of σ° are found using least squares linear regression. The analysis of the wind speed exponents and u/d ratios show that shorter Bragg wavelengths (Λ<4 cm) are the most sensitive to wind speed and direction. Additionally, vertical polarization (V-pol) σ° is shown to be more sensitive to wind speed than horizontal polarization (H-pol) σ, while the H-pol u/d ratio is larger than the V-pol u/d ratio     

Efficient upconversion by a frequency factor between two and threeusing an optical parametric oscillator

We present the theory of a scheme for frequency up-conversion from pump frequency ω_p to a desired frequency ω_d between 2ω_p and 3ω_p. The proposed device consists of three nonlinear crystals in series inside a cavity resonating light at a signal frequency ωs. Sum-frequency generation (SFG) in the first crystal produces the desired radiation, ω_s+ω_p=ω_d. Second-harmonic generation (SHG) in the second crystal doubles the frequency of the residual pump, 2ω_p=ω_h, while the signal passes through unaffected. Optical parametric oscillation (OPO) in the third crystal generates the signal and idler frequencies, ω_h=ω_s+ω. A plane-wave analysis predicts a quantum efficiency close to 30% over an extended range of pump intensity. Iteration of the plane-wave solutions over many passes yields dynamics very similar to that recently calculated for the SFG-OPO device. As in that device, a small detuning of the SFG interaction enlarges the dynamic range yielding stable operation. Highest efficiency occurs when ω_i is at the low-frequency end of the OPO crystal transmission window. As an example, we consider a device using a noncritically phase-matched KTP SFG crystal, a quartz crystal polarization rotator, an angle-tuned KTP SHG crystal, and a noncritically phase-matched LiNbO₃ OPO crystal. This device is designed to convert λ_p=1.064 μm to λ_d=0.455 μm. We calculate a power conversion efficiency as great as 73%