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Geoscience and Remote Sensing, IEEE Transactions on

Issue 1 • Date Jan 1997

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Displaying Results 1 - 20 of 20
  • Rice crop mapping and monitoring using ERS-1 data based on experiment and modeling results

    Page(s): 41 - 56
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    Information on rice growing areas and on rice growth conditions are necessary in rice monitoring programs and in studies on the emission of methane from flooded rice fields. The objective of this paper is to assess the use of ERS-1 SAR data to map rice growing areas and to retrieve rice parameters. The approach includes first a synthesis of experimental results at two different test areas followed by a development of a theoretical model to interpret the observations. The synthesis of experimental data at two test areas, a tropical site with short cycle rice (Semarang, Indonesia) and a temperate site with long cycle rice (Akita, Japan), has shown that flooded rice fields have characteristic increasing temporal radar responses. When the radar backscattering coefficients are expressed as a function of the rice biomass, the effect of cultural practices and climate (long cycle versus short cycle) is reduced. The observations have been interpreted by a theoretical model, which relies on a realistic description of rice plants and which considers the backscattering enhancement and clustering effects of the scatterers. Good agreement has been obtained between experimental data and theoretical results. The strong temporal variation of the radar response of rice fields is due to the wave-vegetation-water interaction, which increases from the transplanting stage to reproductive stage. By simulations using the validated model, the length of the rice cycle or the rice varieties have shown minor effects on the temporal curve. A method for rice fields mapping has been developed, based on the temporal variation of the radar response between two acquisition dates. Inversion of SAR images into plant height and plant biomass has also been performed. The results appear promising for the use of ERS-1 and RADARSAT data for rice monitoring View full abstract»

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  • Development of a neural network based algorithm for rainfall estimation from radar observations

    Page(s): 160 - 171
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    Rainfall estimation based on radar measurements has been an important topic in radar meteorology for more than four decades. This research problem has been addressed using two approaches, namely a) parametric estimates using reflectivity-rainfall relation (Z-R relation) or equations using multiparameter radar measurements such as reflectivity, differential reflectivity, and specific propagation phase, and b) relations obtained by matching probability distribution functions of radar based estimates and ground observations of rainfall. In this paper the authors introduce a neural network based approach to address this problem by taking into account the three-dimensional (3D) structure of precipitation. A three-layer perceptron neural network is developed for rainfall estimation from radar measurements. The neural network is trained using the radar measurements as the input and the ground raingage measurements as the target output. The neural network based estimates are evaluated using data collected during the Convection and Precipitation Electrification (CaPE) experiment conducted over central Florida in 1991. The results of the evaluation show that the neural network can be successfully applied to obtain rainfall estimates on the ground based on radar observations. The rainfall estimates obtained from neural network are shown to be better than those obtained from several existing techniques. The neural network based rainfall estimate offers an alternate approach to the rainfall estimation problem, and it can be implemented easily in operational weather radar systems View full abstract»

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  • Limitations on the possible resolution enhancement of ERS-1 scatterometer images

    Page(s): 196 - 198
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    If methods can be devised for enhancing the spatial resolution of ERS-1 scatterometer images, then this will help to extend the range of land applications for which this data is appropriate. This paper shows that it is not possible to improve the resolution below a limit of ~25 km View full abstract»

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  • Retrieval of optical depth and particle size distribution of tropospheric and stratospheric aerosols by means of Sun photometry

    Page(s): 172 - 182
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    Aerosol optical depth measurements by means of ground-based Sun photometry were made in Bern, Switzerland during two and a half years primarily to provide quantitative corrections for atmospheric effects in remotely sensed data in the visible and near-infrared spectral region. An investigation of the spatial variability of tropospheric aerosol was accomplished in the summer of 1994 in the Swiss Central Plain, a region often covered by a thick aerosol layer. Intercomparisons are made with two Sun photometers operated by the Swiss Meteorological Institute in Payerne (Swiss Central Plain) and Davos (Swiss Alps, 1590 m a.s.l.). By means of an inversion technique, columnar particle size distributions were derived from the aerosol optical depth spectra. Effective radius, columnar surface area, and columnar mass were computed from the inversion results. Most of the spectra measured in Bern exhibit an Angstrom-law dependence. Consequently, the inverted size distributions are very close to power-law distributions. Data collected during a four month calibration campaign in fall 1993 at a high-mountain station in the Swiss Alps (Jungfraujoch, 3580 m) allowed the authors to study optical properties of stratospheric aerosol. The extinction spectra measured have shown to be still strongly influenced by remaining aerosol of the June 1991 volcanic eruptions of Mount Pinatubo. Inverted particle size distributions can be characterized by a broad monodisperse peak with a mode radius around 0.25 μm. Both aerosol optical depths and effective radii had not yet returned to pre-eruption values. Comparison of retrieved aerosol optical depth, columnar surface area and mass, with the values derived from lidar observations performed in Garmisch-Partenkirchen, Southern-Germany, yielded good agreement View full abstract»

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  • Radar backscatter measurement accuracy for a spaceborne pencil-beam wind scatterometer with transmit modulation

    Page(s): 102 - 114
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    Scatterometers are remote sensing radars designed to measure near-surface winds over the ocean. The difficulties of accommodating traditional fan-beam scatterometers on spacecraft has lead to the development of a scanning pencil-beam instrument known as SeaWinds. SeaWinds will be part of the Japanese Advanced Earth Observing Satellite II (ADEOS-II) to be launched in 1999. To analyze the performance of the SeaWinds design, a new expression for the measurement accuracy of a pencil-beam system is required. In this paper the authors derive a general expression for the backscatter measurement accuracy for a pencil-beam scatterometer which includes the effects of transmit signal modulation with simple power detection. Both separate and simultaneous signal+noise and noise-only measurements are considered. The utility of the new expression for scatterometer design tradeoffs is demonstrated using a simplified geometry. A separate paper, ibid., 1997, describes detailed tradeoffs made to develop the SeaWinds design View full abstract»

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  • An entropy based classification scheme for land applications of polarimetric SAR

    Page(s): 68 - 78
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    The authors outline a new scheme for parameterizing polarimetric scattering problems, which has application in the quantitative analysis of polarimetric SAR data. The method relies on an eigenvalue analysis of the coherency matrix and employs a three-level Bernoulli statistical model to generate estimates of the average target scattering matrix parameters from the data. The scattering entropy is a key parameter is determining the randomness in this model and is seen as a fundamental parameter in assessing the importance of polarimetry in remote sensing problems. The authors show application of the method to some important classical random media scattering problems and apply it to POLSAR data from the NASA/JPL AIRSAR data base View full abstract»

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  • The processing of hexagonally sampled signals with standard rectangular techniques: application to 2-D large aperture synthesis interferometric radiometers

    Page(s): 183 - 190
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    In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10-20 km, a radiometric resolution of 1 K and a revisit time of 1-3 days. Compared to total power radiometers aperture synthesis interferometric radiometers are technologically attractive because of their reduced mass and hardware requirements. In this field it should be mentioned the one-dimensional (1D) linear interferometer ESTAR developed by NASA and MIRAS a two-dimensional (2D) Y-shaped interferometer currently under study by European Space Agency (ESA). Interferometer radiometers measure the correlation between pairs of nondirective antennas. Each complex correlation is a sample of the “visibility” function which, in the ideal case, is the spatial Fourier transform of the brightness temperature distribution. Since most receiver phase and amplitude errors can be hardware calibrated, Fourier based iterative inversion methods will be useful when antenna errors are small, their radiation voltage patterns are not too different, and mutual coupling is small. In order to minimize on-board hardware requirements-antennas, receivers and correlators-the choice of the interferometer array shape is of great importance since it determines the (u,v) sampling strategy and the minimum number of visibility samples required for a determined aliasing level. In this sense, Y-shaped and triangular-shaped arrays with equally spaced antennas are optimal. The main contribution of this paper is a technique that allows the authors to process the visibility samples over the hexagonal sampling grids given by Y-shaped and triangular-shaped arrays with standard rectangular FFT routines. Since no interpolation processes are involved, the risk of induced artifacts in the recovered brightness temperature over the wide held of view required in Earth observation missions is minimized and signal to noise ratio (SNR) is preserved View full abstract»

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  • The potential of multifrequency polarimetric SAR in assessing agricultural and arboreous biomass

    Page(s): 5 - 17
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    Polarimetric radar data collected by AIRSAR and SIR-C over agricultural fields, forests, and olive groves of the Italian Montespertoli site are analyzed. The objective is to investigate the radar capability in discriminating among various vegetation species and its sensitivity to agricultural and arboreous biomass. Results indicate that a combined use of P(0.45 GHz) and L- (1.2 GHz) bands allows one to discriminate between agricultural fields and other targets, while a combined use of L- and C- (5.3 GHz) bands allows the authors to discriminate within agricultural areas. To monitor biomass, P-band gives the best results for forests and olive groves, L-band appears to be good for crops with low plant density (m-2), while for crops with high plant density, both L- and C-bands are useful. The availability of crosspolarized data is important for both classification and biomass retrieval View full abstract»

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

    Page(s): 86 - 92
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    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, hmax, of the rocks making up the arid landscape. The simplified relationship σ0=4.63.1og hmax-15.29 (with hmax 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 hmax 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 View full abstract»

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  • Millimeter wave radar scattering from model ice crystal distributions

    Page(s): 140 - 146
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    Dual-polarization radar observables of cloud ice crystals are simulated at 94 and 220 GHz frequencies. Three crystal shapes are considered: hexagonal columns, hexagonal plates, and stellar crystals. A gamma model size distribution and a three dimensional (3D) canting distribution are used. The radar observables are displayed as a function of radar elevation angle. The linear depolarization ratios LDRh and LDRv, the circular depolarization ratio CDR, and the magnitude of the copolarized cross correlation coefficient ρhv are found to be useful for differentiating columns from plates and stellar crystals. These radar observables have different trends as a function of elevation angle for the model columns and planar crystals (plates and stellar crystals). Furthermore, at vertical incidence they exhibit significantly different values for the two crystal types View full abstract»

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  • Detecting step edges in noisy SAR images: a new linear operator

    Page(s): 191 - 196
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    The author presents a new linear edge detector that is very well suited to process noisy images. Performances of the new operator have been evaluated using Canny's criteria together with experimental comparison results on a noisy SAR image View full abstract»

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  • Tradeoffs in the design of a spaceborne scanning pencil beam scatterometer: application to SeaWinds

    Page(s): 115 - 126
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    SeaWinds is a spaceborne wind scatterometer to be flown on the second Japanese Advanced Earth Observing Satellite (ADEOS-II) in 1999. An important international element of NASA's Earth Observing System (EOS), SeaWinds is an advanced follow-on to the NASA scatterometer (NSCAT) on the first ADEOS platform. Unlike previous operational spaceborne scatterometer systems. SeaWinds employs a scanning “pencil-beam” antenna rather than a “fan-beam” antenna, making the instrument more compact and yielding greater ocean coverage. The goals of this paper are twofold. First, the overall SeaWinds functional design and backscatter measurement approach are described, and the relative advantages of the pencil-beam technique are outlined. Second, the unique aspects of measurement accuracy optimization and signal processing for the SeaWinds instrument are discussed. Applying the results of a separate companion paper, ibid., 1997, a technique to significantly improve measurement accuracy by modulating the transmit pulse is described. Trade-offs to optimize the transmit modulation bandwidth are presented View full abstract»

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  • Understanding the relationships between radar response patterns and the bio- and geophysical parameters of urban areas

    Page(s): 93 - 101
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    This paper reviews the current understanding of the relationships between radar response patterns and the bio- and geophysical parameters of urban areas. Specifically, it examines the effects of radar system, ground target, and environmental factors on the intensity and pattern of radar returns from urban features. System parameters considered include radar signal wavelength, polarization, incident angle, and look direction. Ground target factors are the dielectric properties and surface roughness of urban features. The environmental variables examined entail terrain relief, street and structure configuration, soil and vegetation types, and the composition, fragmentation, and variation of urban infrastructure elements. The effects of radar data processing techniques on the detectability of settlements and the accuracy of urban land use/land cover mapping are also described View full abstract»

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  • The effect of inhomogeneous roughness on radar backscattering from slightly deformed sea ice

    Page(s): 147 - 159
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    This paper focuses on the spatially varying backscattering signature of an area of refrozen brash ice observed by a ship based scatterometer. The measurements were carried out as part of the Baltic Experiment for ERS-1 in 1994. The scatterometer was operated at 5.4 GHz at different incidence angles and polarizations. By analysing the scatterometer data over azimuth scans, it was found that the backscattering variabilities are not only due to fading but also contain a textural component. Surface height profiles were measured using a laser. The observed ice surface roughness was nonstationary over the measurement area. The ice surface can be approximated by adjacent patches of stationary roughness with patch dimensions of about 4.5 m. From the roughness spectra of different stationary patches, two roughness classes can be distinguished. The implications of estimating the roughness parameters from relatively short profile lengths is discussed and the effect on theoretical predictions of the backscattering coefficient is investigated. The texture variance is evaluated theoretically on the basis of the simulated backscattering coefficients of the two observed roughness classes and is found to compare with the scatterometer data View full abstract»

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  • A posteriori least squares orthogonal subspace projection approach to desired signature extraction and detection

    Page(s): 127 - 139
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    One of the primary goals of imaging spectrometry in Earth remote sensing applications is to determine identities and abundances of surface materials. In a recent study, an orthogonal subspace projection (OSP) was proposed for image classification. However, it was developed for an a priori linear spectral mixture model which did not take advantage of a posteriori knowledge of observations. In this paper, an a posterior least squares orthogonal subspace projection (LSOSP) derived from OSP is presented on the basis of an a posteriori model so that the abundances of signatures can be estimated through observations rather than assumed to be known as in the a priori model. In order to evaluate the OSP and LSOSP approaches, a Neyman-Pearson detection theory is developed where a receiver operating characteristic (ROC) curve is used for performance analysis. In particular, a locally optimal Neyman-Pearson's detector is also designed for the case where the global abundance is very small with energy close to zero a case to which both LSOSP and OSP cannot be applied. It is shown through computer simulations that the presented LSOSP approach significantly improves the performance of OSP View full abstract»

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  • Retrieval of vegetation parameters with SAR interferometry

    Page(s): 18 - 24
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    The potential of SAR interferometric techniques for the retrieval of vegetation parameters was investigated using ERS-1 data over agricultural and forested test sites. In a first experiment an interferometrically derived forest map was generated. The classification was based on the interferometric correlation and the backscatter intensities. The result was geocoded, using the interferometrically derived height map generated from the same ERS SAR data pair, and validated with a conventional digital forest map. Forest mapping accuracies of around 90% and better were achieved. In a second experiment, multitemporal data over an agricultural site were used to investigate the potential of repeat-pass interferometry to monitor farming activity, crop development, and soil moisture variations. The interferometric correlation was used as an indicator of dense vegetation and geometric change. It was possible, for example, to identify harvesting by the high correlation of the post-harvest bare or stubble field. Decreasing interferometric correlation was observed as a consequence of crop growth View full abstract»

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  • A robust statistical-based estimator for soil moisture retrieval from radar measurements

    Page(s): 57 - 67
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    The authors examine the use of a robust statistical inversion approach to the estimation of soil moisture and roughness statistics from backscatter measurements. Two sets of basis functions are examined; the first is a set of basis functions from multinomial combinations of the inputs (termed the MBF) while the second is a set of basis functions generated by a multilayer perceptron referred to as MLPBF. The authors discuss potential sources of training patterns upon which to base these estimators, including empirical forward models and more rigorous theoretical scattering models such as the IEM. These estimators are applied to a set of measured POLARSCAT data from Oh et al. [1992]. Comparisons are made with other inversion methods including neural networks View full abstract»

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  • Retrieval of forest stem volume using VHF SAR

    Page(s): 36 - 40
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    The ability to retrieve forest stem volume using CARABAS (coherent all radio band sensing) SAR images (28-60 MHz) has been investigated. The test site is a deciduous mixed forest on the island of Oland in southern Sweden. The images have been radiometrically calibrated using an array of horizontal dipoles. The images exhibit a clear discrimination between the forest and open fields. The results show that the dynamic range of the backscattering coefficient among the forest stands is higher than what has been found with conventional SAR using microwave frequencies. The backscatter increases with increasing radar frequency. This work shows an advantage compared to higher frequencies for stem volume estimation in dense forests View full abstract»

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  • C-band repeat-pass interferometric SAR observations of the forest

    Page(s): 25 - 35
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    Properties of ERS-1 C-band repeat pass interferometric SAR information for a forested area are studied. The intensity information is rather limited but, including coherence and effective interferometric SAR (INSAR) height, more information about the forest parameters can be obtained via satellite. Such information is also important for correction of INSAR derived topographic maps. Coherence properties have been used to identify forested/nonforested areas and the interferometric effective height of the forest determined by comparison to a DEM of the area. The authors have developed a model to relate basic forest properties to INSAR observations. These show that the coherence and interferometric effective height of a forested area change between image pairs. The model demonstrates how these properties are related to the temporal decorrelation and the scattering from the vegetation canopy and the ground surface. Gaps in the vegetation are found to be important in the characterization of boreal forests View full abstract»

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  • SAR applications in human settlement detection, population estimation and urban land use pattern analysis: a status report

    Page(s): 79 - 85
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    Over 70 percent of the population of the world's developed countries live in urbanized areas. In developing countries migration to urban areas is continuing at an increasing rate. Detection and analysis of settlement patterns, estimating population, and monitoring population migration in a timely manner are requisite to accurately assess the impact of human activities on the environment. Monitoring urban land use change patterns is among the most critical information needs for future economic development planning, natural resource allocation, and environmental and ecosystem management. Previous research has demonstrated the potential of imaging radar systems in analyzing urban, population, and settlement phenomena. However, the variability and complexity within and between urban land use morphologies present a convoluted environment for analysis. Studies of vegetation, soils, geology, hydrology, and ice and snow have all received more attention and been the subject of considerably more widespread and in-depth radar research. Nevertheless, imaging radars offer some distinct advantages and opportunities for urban-based research. With the arrival of operational space imaging SAR systems, a review of the current status of applications of radar remote sensing in urban studies should be useful for focusing the authors' attention on this important area of radar research and identification of specific problems for in-depth analysis. This paper traces the history of imaging radar research for urban, settlement, and population analysis. It presents a status report on the applications of SAR in settlement detection, population estimation, assessment of the impact of human activities on the physical environment, mapping and analyzing urban land use patterns, and interpretation of socioeconomic characteristics. The demonstrated capabilities and limitations of past and current imaging radar systems with reference to these applications are described. Potential avenues of future research are addressed View full abstract»

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IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING (TGRS) is a monthly publication that focuses on the theory, concepts, and techniques of science and engineering as applied to sensing the land, oceans, atmosphere, and space; and the processing, interpretation, and dissemination of this information.

 

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Editor-in-Chief
Antonio J. Plaza
University of Extremadura