Overview of results of Spaceborne Imaging Radar-C, X-Band SyntheticAperture Radar (SIR-C/X-SAR)

The Spaceborne Imaging Radar-C, X-Band Synthetic Aperture Radar (SIR-C/X-SAR) was launched on the Space Shuttle Endeavour for two ten day missions in the spring and fall of 1994. Radar data from these missions are being used to better understand the dynamic global environment. During each mission, radar images of over 300 sites around the Earth were obtained, returning over a terabit of data. SIR-C/X-SAR science investigations were focused on quantifying radar's ability to estimate surface properties of importance to understanding global change; and focused studies in geology, ecology, hydrology and oceanography, as well as radar calibration and electromagnetic theory studies. In addition, the second flight featured an interferometry experiment, where digital elevation maps were obtained by interfering data from the first and second shuttle flight, and from successive days on the second flight. SIR-C/X-SAR data have been used to validate algorithms which produce maps of vegetation type and biomass; snow, soil and vegetation moisture; and the distribution of wetlands, developed with earlier aircraft data     

Estimation of snow water equivalence using SIR-C/X-SAR. II. Inferring snow depth and particle size

For pt.I see ibid., vol.38, no.6, p.2465-74 (2000). The relationship between snow water equivalence (SWE) and SAR backscattering coefficients at C- and X-band (5.5 and 9.6 GHz) can be either positive or negative. Therefore, discovery of the relationship with an empirical approach is unrealistic. Instead, the authors estimate snow depth and particle size using SIR-C/X-SAR imagery from a physically-based first order backscattering model through analyses of the importance of each scattering term and its sensitivity to snow properties. Using numerically simulated backscattering values, the authors develop semi-empirical models for characterizing the snow-ground interaction terms, the relationships between the ground surface backscattering components, and the snowpack extinction properties at C-band and X-band. With these relationships, snow depth and optical equivalent grain size can be estimated from SIR-C/X-SAR measurements. Validation using three SIR-C/X-SAR images shows that the algorithm performs usefully for incidence angles greater than 300, with root mean square errors (RMSEs) of 34 cm and 0.27 mm for estimating snow depth and ice optical equivalent particle radius, respectively.     

Estimation of snow water equivalence using SIR-C/X-SAR. I. Inferring snow density and subsurface properties

Algorithms for estimating dry snow density and the dielectric constant and roughness of the underlying soil or rock use backscattering measurements with VV and HH polarization at L-band frequency (1.25 GHz). Comparison with field measurements of snow density during the first SIR-C/X-SAR overpass shows absolute accuracy of 42 kg m/sup -3/ (13% relative error). For the underlying soil, comparisons with the ground scatterometer measurements showed errors of 4% by volume for soil moisture estimation and 4 mm for the surface root mean square (RMS) height. Values of snow density and the properties of the underlying soil are necessary for the estimation of snow water equivalence.     

Dielectric profiles reconstruction via the quadratic approach in 2-D geometry from multifrequency and multifrequency/multiview data

Deals with the reconstruction of the contrast function of a dielectric cylinder with rectangular cross section starting from the knowledge of the electric scattered far field produced under the incidence of plane waves. We analyze the set of the reconstructable Fourier harmonics of the unknown permittivity contrast function with linear and quadratic approaches. This set depends on the ranges of the wavenumbers /spl beta/, of the angles of incidence /spl theta//sub i/ of the impinging plane waves, and of the observation angles /spl theta//sub o/. We discuss a simple way to describe such a dependence, which allows us to find out that the set of the retrievable harmonics for the quadratic approach contains that for the linear one. Moreover, our investigation points out how increasing the amount of independent data through a multifrequency/multiview measurement scheme allows us to enlarge the set of the retrievable unknown harmonics with respect to a multifrequency/single-view one. Our analysis is confirmed by numerical results. Memory storage requirements and processing time consumption for the quadratic approach are greatly reduced thanks to the massive use of the fast Fourier transform algorithm.     

Seasonal dynamics of C-band backscatter of boreal forests withapplications to biomass and soil moisture estimation

The seasonal changes of the C-band backscattering properties of boreal forests are investigated by applying 1) a semiempirical forest backscattering model and 2) multitemporal ERS-1 SAR data from two test areas in Finland. The semiempirical modeling of forest canopy volume backscattering and extinction properties is based on high-resolution data from the authors' ranging scatterometer HUTSCAT. The response of ERS-1 SAR to forest stem volume (biomass) and other forest characteristics is investigated by employing the National Forest Inventory sample plots, stand-wise forest inventory data and LANDSAT- and SPOT-based digital land use maps. The results show that the correlation between the backscattering coefficient and forest stem volume (biomass) varies from positive to negative depending on canopy and soil moisture. Additionally, the seasonal snow cover and soil freezing/thawing effects cause drastic changes in the radar response. A novel method for the estimation of forest stem volume (biomass) is introduced. This technique is based on the use of: 1) multitemporal ERS-1 SAR data; 2) reference sample plot information; and 3) the semiempirical backscattering model. It is shown that the multitemporal ERS-1 SAR images can be successfully used for estimating the forest stem volume. The effects of soil moisture variations to ERS-1 SAR results have been analyzed using hydrological soil moisture model and in situ data. The results indicate that the semiempirical model can he used for predicting the soil and canopy moisture variations in ERS-1 images     

Unsupervised classification of multifrequency and fullypolarimetric SAR images based on the H/A/Alpha-Wishart classifier

Introduces a new classification scheme for dual frequency polarimetric SAR data sets. A (6×6) polarimetric coherency matrix is defined to simultaneously take into account the full polarimetric information from both images. This matrix is composed of the two coherency matrices and their cross-correlation. A decomposition theorem is applied to both images to obtain 64 initial clusters based on their scattering characteristics. The data sets are then classified by an iterative algorithm based on a complex Wishart density function of the 6×6 matrix. A class number reduction technique is then applied on the 64 resulting clusters to improve the efficiency of the interpretation and representation of each class. An alternative technique is also proposed which introduces the polarimetric cross-correlation information to refine the results of classification to a small number of clusters using the conditional probability of the cross-correlation matrix. These classification schemes are applied to full polarimetric P, L, and C-band SAR images of the Nezer Forest, France, acquired by the NASA/JPL AIRSAR sensor in 1989     

A multifrequency algorithm for the retrieval of soil moisture on alarge scale using microwave data from SMMR and SSM/I satellites

The sensitivity of microwave emission at different frequencies to soil moisture in bare and vegetated soils has been investigated using experimental data. Since the best frequency for the measurement of soil moisture (L-band) is absent in current satellite sensors, it is necessary to seek alternative solutions. An algorithm is proposed for the retrieval of soil moisture based on the sensitivity to moisture of both the brightness temperature and the polarization index at C-band, one that is able to correct for the effect of vegetation by means of the polarization index at X-band. The algorithm has been tested by using experimental data collected with airborne microwave radiometers on agricultural areas and validated by using the data sets of special sensor microwave/imager (SMM/I) and scanning multichannel microwave radiometer (SMMR). These research activities are planned in view of coming new satellites: AQUA (NASA) and ADEOS-II (NASDA), which will be launched by the end of 2001. These will have new generation microwave radiometers (AMSR-E and AMSR) onboard, which show much better characteristics with respect to the previous sensors, in particular an enhanced spatial resolution     

Complexity and nonlinearity in short-term heart period variability: comparison of methods based on local nonlinear prediction

This paper evaluates the paradigm that proposes to quantify short-term complexity and detect nonlinear dynamics by exploiting local nonlinear prediction. Local nonlinear prediction methods are classified according to how they judge similarity among patterns of L samples (i.e., according to different definitions of the cells utilized to discretize the phase space) and examined in connection with different types of surrogate data: 1) phase-randomized or Fourier transform based, FT; 2) amplitude-adjusted FT, AAFT; 3) iteratively-refined AAFT, IAAFT, preserving distribution IAAFT-1; 4) IAAFT preserving power spectrum, IAAFT-2. The methods were applied on ad-hoc simulations and on a large database of short heart period variability series (approximately 300 cardiac beats) recorded in healthy young subjects during experimental conditions inducing a sympathetic activation (head-up tilt, infusion of nitroprusside, or handgrip), a parasympathetic activation (low dose administration of atropine or infusion of phenylephrine), a complete parasympathetic blockade (high dose administration of atropine), or during controlled respiration at different breathing rates. As to complexity analysis we found that: 1) although complexity indexes derived from different methods were different in terms of absolute values, changes due to experimental conditions were consistently detected; 2) complexity was significantly decreased by all the experimental conditions provoking a sympathetic activation and by controlled respiration at slow breathing rates. As to detection of nonlinearities we found that: 1) IAAFT-1 and IAAFT-2 surrogates performed similarly in all protocols; 2) FT and IAAFT surrogates detected about the same percentage of nonlinear dynamics in all protocols; 3) AAFT surrogates were inappropriate with all the methods and should be dismissed in future applications; 4) methods based on overlapping cells with variable size were characterized by a larger rate of false detections of nonlinear dynamics; 5) short-term heart period variability at rest was mostly linear; 6) controlled respiration at slow breathing rates increased nonlinear components, while the separate activation of the two branches of the autonomic nervous system (i.e., sympathetic or parasympathetic) was ineffective at this regard.     

Measurements and simulation of multipath interference for 1.7-Gb/slightwave transmission systems using single- and multifrequency lasers

Power penalties due to multipath interference (MPI) have been measured for 1.7-Gb/s lightwave systems that use single-frequency (SF) or multifrequency (MF) lasers. Systems that use SF lasers potentially exhibit worse degradation than those using MF lasers. Bit-error-rate (BER) floors occur only under the worse-case conditions of poor receiver margin and large multiple reflections. The use of optical isolation to reduce laser feedback is ineffective in reducing multipath interference, and in many cases may worsen the penalty. It is shown that for a typical transmission system, these degradations are reduced if optical interconnection reflections are maintained below -20.5 dB. The experimental study is in good agreement with theoretical predictions using an analytic expression of the MPI noise power spectral density and with computer simulations using multimode laser rate equations     

On the reconstruction of height functions and terrain maps from dense range data

This paper describes a method for combining multiple, dense range images to create surface reconstructions of height functions. Height functions are a special class of three-dimensional (3-D) surfaces, where one 3-D coordinate is a function of the other two. They are relevant for application domains such as terrain modeling or two-and-half dimensional surface reconstruction. Dense range maps are produced by either a range measuring device combined with a scanning mechanism or a triangulation scheme, such as active or passive stereo. The proposed method follows from a statistical formulation that characterizes the optimal surface estimate as the one that maximizes the posterior probability conditional on the input data and prior information about the application domain. Because the domain of the reconstruction is a two-dimensional (2-D) scalar function, the optimal surface can be expressed as an image, and the variational form of that optimization produces a 2-D partial differential equation (PDE). The PDE consists of two parts: a first-order data term and a second-order smoothing term. Thus optimal surface reconstruction is formulated as the solution to a second-order, nonlinear, PDE on an image, which is related to the family of PDE-based image processing algorithms in the literature. This paper presents the theory for reconstruction and some particular aspects of the numerical implementation. It also analyzes results on both synthetic and real data sets, which show a 75%-95% reduction of the RMS sensor error.     

Elimination of signal distortion and crosstalk from carrier densitychanges in the shared semiconductor amplifier of multifrequency signalsources

The signals from multifrequency sources that utilize a shared semiconductor optical amplifier often exhibit distortion and crosstalk due to carrier density changes in the shared amplifier. We propose a technique that eliminates the signal distortion and crosstalk by keeping the carrier density in the shared amplifier constant via feedforward of the electrical drive signals. We demonstrate the technique using a waveguide grating router multifrequency laser     

Comparisons between measured and theoretical results forC- and Ku-bands backscatter from naturally occurringinternal wave current patterns

Predicted and measured values of radar backscatter and of internal wave surface currents are compared using data obtained during the SCATTMOD internal wave experiment. Radar backscatter and surface truth measurements were obtained during six days in August 1985 and cover nine sets of tide-generated internal waves in the Georgia Strait, Canada. The radar portion of this data consists of approximately 75 sets each of C- and Ku-band fanbeam airborne scatterometer signals, each processed to 25 incidence angles and an along-track resolution of either 12.5 or 6.25 m. Aircraft navigation data were also recorded, simultaneous surface measurements, including wave slope, wave height, current, wind, and ship position, were obtained from the CFAV Endeavour. Current meter were located both fore and aft to allow internal wave-phase velocity estimates to be computed     

Rigorous modeling of ultrawideband VHF scattering from tree trunksover flat and. sloped terrain

Three electromagnetic models are employed for the investigation of ultrawideband VHF scattering from tree trunks situated over flat and sloped terrain. Two of the models are numerical, each employing a frequency-domain integral-equation formulation solved via the method of moments (MoM). A body-of-revolution (BoR) Mote formulation is applied for a tree trunk on a flat terrain, implying that the BoR axis is perpendicular to the layers of an arbitrary layered-earth model. For the case of sloped terrain, the BoR model is inapplicable, and therefore the MoM solution is performed via general triangular-patch basis functions. Both MoM models are very accurate but are computationally expensive. Consequently, the authors also consider a third model, employing approximations based on the closed-form solution for scattering from an infinite dielectric cylinder in free space. The third model is highly efficient computationally and, despite the significant approximations, often yields accurate results relative to data computed via the reference MoM solutions. Data from the three models are considered, and several examples of application to remote sensing are addressed     

Design and short-term stability of single-frequency CO2lasers

This paper describes a family of sealed-off, single-frequency, TEM00q-mode CO2lasers with output powers up to 15 watts. Short-term frequency stability[1],[2] measurements of the beat note of two free-running lasers in typical laboratory setups are discussed thereafter. The preliminary measurements indicate a short-term stability of about 5 parts in 10¹²for an observation time of 0.05 seconds, and about 5 parts in 10¹³, disregarding the discrete spectral lines resulting from 60-Hz modulation by power supply ripple. One or two orders-of-magnitude improvement is predicted, leading to the possibility of measuring the linewidth limit imposed by quantum noise.     

Radiative transfer modeling of cross-polarized backscatter from a pine forest using the discrete ordinate and eigenvalue method

Radiative transfer models have been widely used to interpret the radar backscatter from forested areas. Most of these models are based on an iterative solution of the radiative transfer equation, usually solved up to first or second order, thus taking into account single and double scattering. Although this method leads to results agreeing well with copolarized backscatter measurements, it produces less accurate estimates for horizontal-vertical (HV) polarization. This paper presents a radiative transfer backscatter model that accounts for multiple scattering by using the discrete ordinate and eigenvalue method applied to a layered medium. Using parameters derived from an architectural tree model, calculations at C- and L-band are compared with HV data acquired for a maritime pine forest in the southwest of France during the Spaceborne Imaging Radar-C missions. Good agreement is found at C-band for all values of forest biomass, and reasonable agreement at L-band for high biomass, when the soil backscatter plays a minor role. For low biomass, the L-band modeling is inadequate because of difficulties in estimating the soil backscatter. Comparison with calculations from a first-order radiative transfer model shows that multiple scattering is significant, especially at C-band.     

复杂地形下光伏电站间距、倾角和方位角的研究

本项目研究如何在复杂地形上合理的布置光伏组件。为今后山地、丘陵等复杂地形条件下的光伏发电站的设计提供更加准确的设计依据,更进一步提高了复杂地形条件下的光伏发电站发电量计算的准确度。     

Seasonal and Regional Variations of Active/Passive Microwave Signatures of Sea Ice

Ku-band (13.3 GHz) scatterometer and K-band (19.4 GHz) radiometer data acquired by the CCRS CV-580 aircraft over the period from 1979 to 1982 in Canadian and Danish (Greenland) coastal waters have been analyzed to determine the seasonal and regional variations of microwave sea-ice signatures. A clustering analysis of the like and cross-polarized scattering cross sections, ?HHo and ?HVo, and the H polarized emissivity ?H, has been used to identify distinct microwave sea-ice signatures for each ice type and to trace the evolution of these signatures with region and season. Ice-type signatures in the high Arctic under cold conditions are quite stable, and major ice classes are readily identified from microwave measurements. Under warmer conditions the signatures change with the structure, moisture content of the snow pack, and with the free water in the surface layers of the underlying ice. An attempt is made to create a consistent picture of the microwave signature transformation by grouping the data into " seaice seasons" (snow and ice surface transformation stages). The separation between microwave ice-class signatures reaches a minimum at the peak of the summer melt.