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Geoscience and Remote Sensing, IEEE Transactions on

Issue 2 • Date Mar 1994

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Displaying Results 1 - 25 of 26
  • Statistical iterative scheme for estimating atmospheric relative humidity profiles

    Page(s): 254 - 260
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    Estimation of atmospheric relative humidity profiles using passive remote sensing techniques is difficult when the temperature profile is not well known, and such retrievals approach singularity when the atmosphere is nearly isothermal. A retrieval method that is more robust near isothermal regions and temperature inversions is described. Its robust character results from an iterative combination of statistical methods based on a priori data, which stabilize the effects of any singularities, and physical methods that reflect the nonlinear character of the equation of radiative transfer and the dependence of measurements on uncertain surface reflectivities and temperature profiles. This method can be used to interpret data from meteorological satellites. It was tested extensively using simulated clear-sky microwave observations from space at 89 GHz, 166 GHz, and three frequencies near the 183-GHz water vapor resonance and the 60-GHz oxygen band, which is sensitive to the atmospheric temperature profile. Humidity profiles from the tropical, midlatitude, and arctic regions were retrieved. Relative humidity profiles retrieved using the statistical iterative method typically had errors between 5 and 10% in the 300-1000 mbar pressure region. These errors were somewhat less in the tropics and greater in the polar regions, and represented significantly better performances than a linear statistical retrieval method View full abstract»

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  • Evaluating the type and state of Alaska taiga forests with imaging radar for use in ecosystem models

    Page(s): 353 - 370
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    Changes in the seasonal CO2 flux of the boreal forests may result from increased atmospheric CO2 concentrations and associated global warming patterns. To monitor this potential change, a combination of information derived from remote sensing data, including forest type and growing season length, and ecophysiological models which predict the CO2 flux and its seasonal amplitude based on meteorological data, are required. The authors address the use of synthetic aperture radar (SAR) to map forest type and monitor canopy and soil freeze/thaw, which define the growing season for conifers, and leaf on/off, which defines the growing season for deciduous species. Aircraft SAR (AIRSAR) data collected in March 1988 during a freeze/thaw event are used to generate species maps and to determine the sensitivity of SAR to canopy freeze/thaw transitions. These data are also used to validate a microwave scattering model which is then used to determine the sensitivity of SAR to leaf on/off transitions and soil freeze/thaw. Finally, a CO2 flux algorithm is presented which utilizes SAR data and an ecophysiological model to estimate CO2 flux. CO 2 flux maps are generated, from which areal estimates of CO 2 flux are derived View full abstract»

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  • Plant water content and temperature of the Amazon forest from satellite microwave radiometry

    Page(s): 397 - 408
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (956 KB)  

    An attempt is made to derive the evolution of the temperature and the water status of the Amazon forest canopy from satellite microwave radiometry. The Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) temperature-corrected tapes data are analyzed for the 6.6, 10.7, 18, and 37 GHz frequencies, at daytime and nighttime, over a zone near Manaus (3°S, 60°W), Brazil. Two periods are investigated: the wet (April-May) and dry (July-August) seasons of 1985. After separating forest- from river-contaminated pixels, atmospheric corrections are performed for water vapor, clouds, and rain, using surface and satellite data. Algorithms are developed to model the microwave thermal emission of vegetation following a continuous approach and a discrete approach. A sensitivity study is performed in order to determine which frequencies are relevant to retrieve land surface parameters. The models are then used along with an optimization procedure so as to carry out the inversion of the canopy structure parameters. The vegetation temperature and water content are retrieved through the continuous model View full abstract»

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  • Ground penetrating radar tomography: algorithms and case studies

    Page(s): 461 - 467
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    Algorithms based on two inversion procedures suggested in a previous study are applied to the problem of imaging and target detection using ground penetrating radar data acquired at two sites. One inversion procedure, referred to as the Fourier transform method, employs the spatial Fourier transform of measured data and requires subsurface inhomogeneities to be relatively deep. The second inversion method does not require the data to be Fourier transformed; however, it does require the additional restriction that inhomogeneities be relatively small. This is referred to as the far-field method. These two inversion relationships are used to reconstruct images of both spatial variations-in refractive index and log likelihood function. It is found that both procedures perform well at a site where only a single isolated inhomogeneity exists. At a second site, where there are two adjacent inhomogeneities, the Fourier transform method proved superior View full abstract»

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  • Boundary element modeling of a capacitive probe for in situ soil moisture characterization

    Page(s): 261 - 266
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    There has been a need for accurate numerical modeling of a capacitive probe dedicated to the in situ characterization of soil moisture in measuring the dielectric permittivity of the soil. The objectives of the author's modeling were to understand the quantitative response of the probe, to optimize the shape of the probe, and to enable accurate calibration. In comparison with other numerical methods (such as the finite element method), the boundary element method appears straightforward and economical. The author presents a generalized version of this method in the case of an axisymmetrical geometry within the quasi-static limit. Numerical results are discussed and compared with the approximation of a lumped circuit View full abstract»

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  • Satellite laser altimetry of terrestrial topography: vertical accuracy as a function of surface slope, roughness, and cloud cover

    Page(s): 329 - 339
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    Analysis of the sensitivity of laser ranging errors to surface conditions indicates that predicted single-shot range errors are primarily dependent on surface slope. Range errors are less sensitive to variations in surface roughness or reflectivity. Values of total surface slope and roughness for nine terrestrial landforms, derived from digital elevation data at a 186 m length scale, vary from 2° to 40° and 0.8 to 15 m, respectively, at a 90% frequency of occurrence. This range of surface morphologies yields a variation in single shot laser ranging error from 0.4 to 8 m, assuming system parameters for the proposed Topographic Mapping Laser Altimeter (TMLA) and a nominal 30% surface reflectivity. The total elevation accuracy of data obtained via satellite laser altimetry, although dominated by the range error, is also a function of additional error sources, including orbit ephemeris, atmospheric, and calibration errors. Averaging of multiple laser measurements improves the vertical accuracy of the elevation data by statistical reduction of random errors. During a three-year mission, two to three laser measurements will be acquired, on average, for each 200-m footprint at low to moderate latitudes, accounting for the latitudinal variation of ground track spacing and cloud cover. For high-latitude regions, the narrow spacing of satellite ground tracks in a polar orbit will provide frequent repeat observations yielding, on average, 4 to 25 measurements of each footprint over the Antarctic and Greenland ice sheets. Averaging of these multiple repeat observations at high latitude will yield an improvement in vertical accuracy by a factor of two to five View full abstract»

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  • Polarization signatures of frozen and thawed forests of varying environmental state

    Page(s): 371 - 381
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    During the two different overflights of the Bonanza Creek Experimental Forest (near Fairbanks, Alaska) by the NASA/JPL radar polarimeter in March 1988, the environmental conditions over the region changed significantly with temperatures ranging from unseasonably warm (1 to 9°C) during one day to well below freezing (-8 to -15°C) during the other. The moisture content of the snow and trees changed from a liquid to frozen state causing significant changes in the radiometric and polarimetric responses of the forest to the radar wave. The L-band polarimetric observations are summarized in this paper. Up to a 6 dB change in the backscatter was observed in certain forest stands at L-band. Features extracted from the Stokes matrices of the same stands from the thawed and frozen days suggest the changes in the relative contribution of the different scattering mechanisms to the radar return. Comparison of the polarimetric signatures indicate relatively higher contribution from diffuse scatterers on the thawed day than on the frozen day. The sensitivity of the polarimetric signatures to changing environmental conditions is clearly demonstrated View full abstract»

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  • Simple model for current leakage in insulating liner

    Page(s): 472 - 474
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    It is argued that a hole in a thin dielectric sheet can be represented by a current source and a sink on opposite sides of the sheet. Such a configuration is analyzed using a quasistatic assumption for current injection from one side of the sheet. The results have possible relevance to schemes for the detection of leaks in membrane-lined impoundment ponds for hazardous liquid wastes View full abstract»

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  • Vegetation studies of the Amazon basin using enhanced resolution Seasat scatterometer data

    Page(s): 449 - 460
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    The Seasat-A scatterometer (SASS) was designed to measure the near-surface wind field over the ocean by inferring the wind from measurements of the surface radar backscatter. While backscatter measurements were also made over land, they have been primarily used for the calibration of the instrument. This has been due in part to the low resolution of the scatterometer measurements (nominally 50 km). In a separate paper the present authors introduced a new method for generating enhanced resolution radar measurements of the Earth's surface using spaceborne scatterometry. In the present paper, the method is used with SASS data to study vegetation classification over the extended Amazon basin using the resulting medium-scale radar images. The remarkable correlation between the Ku-band radar images and vegetation formations is explored, and the results of several successful experiments to classify the general vegetation classes using the image data are presented. The results demonstrate the utility of medium-scale radar imagery in the study of tropical vegetation and permit utilization of both historic and contemporary scatterometer data for studies of global change. Because the scatterometer provides frequent, wide-area coverage at a variety of incidence angles, it can supplement higher resolution instruments which often have narrow swaths with limited coverage and incidence angle diversity View full abstract»

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  • The influence of polarization on canopy transmission properties at 6.6 GHz and implications for large scale soil moisture monitoring in semi-arid environments

    Page(s): 409 - 415
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    Nimbus/SMMR 6.6 GHz data were used together with an extensive data base of surface moisture to study the influence of polarization on radiative transfer characteristics of savannah vegetation in south-eastern Botswana. Ratios of virtual and horizontal polarization optical depths and ratios of albedos were found to be almost constant throughout a three-year period. This conclusion led to a new approach to eliminate the vegetation components in the remotely sensed brightness temperatures, which is important for soil moisture monitoring from space. Using the same data set, this dual-polarization approach was compared with an earlier described synergistic approach, in which NDVI was used to eliminate the vegetation effects. The root mean square error between ground based soil moisture and satellite estimated surface soil moisture was reduced to 1.2% by volume from 5% by volume using the dual polarization approach View full abstract»

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  • Directional wave spectra by inversion of ERS-1 synthetic aperture radar ocean imagery

    Page(s): 340 - 352
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    An algorithm that extracts the directional ocean wave spectrum from synthetic aperture radar (SAR) ocean image spectra is implemented and applied to spaceborne C-band SAR data obtained from the ERS-1 satellite. The nonlinear iterative algorithm is based on the Hasselmann's forward spectral transform extended to include the range bunching effect. An analytic expression for the wave spectral increment is derived based on the exact gradient of the quasilinear ocean-to-SAR transform. Enhanced wave spectra have been obtained using first-guess wave spectra either from the numerical wave model WINCH operated by the Norwegian Meteorological Institute or synthesized from nondirectional wave data and meteorological conditions. The inverted spectra are compared to in situ directional wave data. It is concluded that the wave imagery from ERS-1 appears to be of excellent quality, and as soon as the backscatter modulation transfer functions are properly understood, satellite SAR data will be an important tool for enhancing and extending conventional wave measurements and results from numerical wave models View full abstract»

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  • Reduction of noise in AVHRR channel 3 data with minimum distortion

    Page(s): 315 - 328
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    The channel 3 data of the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA series of weather satellites (NOAA 6-12) are contaminated by instrumentation noise. The signal to noise ratio (S/N) varies considerably from image to image and the between sensor variation in S/N can be large. The characteristics of the channel noise in the image data are examined using Fourier techniques. A Wiener filtering technique is developed to reduce the noise in the channel 3 image data. The noise and signal power spectra for the Wiener filter are estimated from the channel 3 and channel 4 AVHRR data in a manner which makes the filter adaptive to observed variations in the noise power spectra. Thus, the degree of filtering is dependent upon the level of noise in the original data and the filter is adaptive to variations in noise characteristics. Use of the filtered data to improve image segmentation, labeling in cloud screening algorithms for AVHRR data, and multichannel sea surface temperature (MCSST) estimates is demonstrated. Examples also show that the method can be used with success in land applications. The Wiener filtering model is compared with alternate filtering methods and is shown to be superior in all applications tested View full abstract»

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  • A moment-based approach to registration of images with affine geometric distortion

    Page(s): 382 - 387
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    A new method is described for automatic control point selection and matching. First, reference and sensed images are segmented and closed-boundary regions are extracted. Each region is represented by a set of affine-invariant moment-based features. Correspondence between the regions is then established by a two-stage matching algorithm that works both in the feature space and in the image space. Centers of gravity of corresponding regions are used as control points. A practical use of the proposed method is demonstrated by registration of SPOT and Landsat TM images. It is shown that the authors' method can produce subpixel registration accuracy View full abstract»

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  • Discrete scatter model for microwave radar and radiometer response to corn: comparison of theory and data

    Page(s): 416 - 426
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    As part of the Multisensor Aircraft Campaign, MACHYDRO, two microwave sensors, NASA's Airborne Synthetic Aperture Radar (AIRSAR) and Pushbroom Microwave Radiometer (PBMR) collected data over the same corn fields during the summer of 1990. During these flights, measurements were made on the ground of soil moisture and plant parameters. In this paper the measured canopy and soil parameters are used in a discrete scatter model to predict the response of both sensors (radar and radiometer). A distorted Born approximation is used to compute the scattering coefficient for the corn canopy. The backscatter coefficient gives the radar response and the radiometer response is obtained by integrating the bistatic coefficient over all scattering angles above ground. The objective of this analysis is to test the model and, in particular, to determine how well a single set of plant parameters and single model can yield agreement with both the radar and radiometer measurements. The model values are in reasonably good agreement with the measurements at horizontal polarization and reflect observed changes in soil moisture View full abstract»

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  • Lossless compression of multispectral image data

    Page(s): 282 - 289
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    While spatial correlations are adequately exploited by standard lossless image compression techniques, little success has been attained in exploiting spectral correlations when dealing with multispectral image data. The authors present some new lossless image compression techniques that capture spectral correlations as well as spatial correlation in a simple and elegant manner. The schemes are based on the notion of a prediction tree, which defines a noncausal prediction model for an image. The authors present a backward adaptive technique and a forward adaptive technique. They then give a computationally efficient way of approximating the backward adaptive technique. The approximation gives good results and is extremely easy to compute. Simulation results show that for high spectral resolution images, significant savings can be made by using spectral correlations in addition to spatial correlations. Furthermore, the increase in complexity incurred in order to make these gains is minimal View full abstract»

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  • Improvements in the split-window technique for land surface temperature determination

    Page(s): 243 - 253
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    Land surface temperature (LST) retrievals obtained from NOAA Advanced Very High Resolution Radiometer (AVHRR) are of considerable importance for climatic research. However, the accurate evaluation of LST from space has been severely limited because of the difficulty in separating atmospheric from surface effects as the surface cannot be modeled as a black-body radiator. With this goal in mind, a novel extension of the split-window technique is presented in which the atmospheric contribution to the radiance measured by the satellite is investigated by the ratioing of covariance and variance of the brightness temperatures measured in channels 4 and 5 of AVHRR/2. Furthermore, the contribution of emissivity is evaluated from coefficients that depend on the spectral emissivities in both thermal channels. Using a wide range of simulations from an atmospheric radiative transfer model it is shown that the proposed algorithm provides an estimate of LST, to within 0.4 K if the spectral surface emissivity is known, which is better than that given by the currently used split-window algorithms for LST determination. Also the limitations on algorithm accuracy are discussed considering different values of noise equivalent temperature. Finally the authors present the preliminary results obtained using the proposed method from AVHRR data over a semi-arid region-of Northwestern Victoria in Australia provided by CSIRO, and a mountainous region of Northeast of France acquired in the frame of Regio Klimat Projekt View full abstract»

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  • Seismic data filtering using a Gabor representation

    Page(s): 467 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    Gabor representations are signal expansions using sets of functions that are localized and concentrated in time and frequency. This characteristic makes them suitable candidates for filtering data where the desired signal or noise is nonstationary or time-dependent. It is shown that Gabor representations formulated with frame theory can be used for time-dependent noise removal. Furthermore, their ability to filter noise in the presence of a nonstationary signal enables them to outperform singular value decomposition eigenimage filtering techniques in the removal of incoherent noise in common midpoint data with a moderate fold View full abstract»

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  • Dielectric permittivity and scattering measurements of Greenland firn at 26.5-40 GHz

    Page(s): 290 - 295
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    Three blocks of snow approximately 33 cm on each side were harvested from the Greenland ice sheet at depths ranging from 0.3 to 2.7 m below the surface and brought back to the lab. A step frequency radar operated from 26.5 to 40.0 GHz was used to measure the wave velocity through the snow in three orthogonal directions. From these measurements, the relative permittivity was calculated; it varied with density from 1.69 to 1.91 and agreed well with other measurements on terrestrial snow. It was also found that the permittivity of the two deeper firn blocks was anisotropic by 4-7%. This anisotropy is explained by the elongation of the snow grains in the vertical direction. Extinction losses of about 5 dB/m were estimated by measuring the change in amplitude of signals propagating through the blocks. Although the estimated losses were highly variable, a minimum penetration depth of 87 cm into the firn was computed View full abstract»

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  • Mapping biomass of a northern forest using multifrequency SAR data

    Page(s): 388 - 396
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    The results of mapping standing biomass for a northern forest in Maine, using NASA/JPL AIRSAR polarimetric radar data, is presented. By examining the dependence of backscattering on standing biomass using backscatter modeling and aircraft data, it was determined, in agreement with other recent reports, that the cross-polarized (HV) data from longer wavelengths (L, P-band) were the best radar channels for mapping total above-ground forest biomass. The radar signal appeared to lose sensitivity to changes in biomass for dry biomass levels beyond about 15 kg/m2 (150 Mton/Ha). The ratio of HV backscattering from two bands, a longer wavelength P (wavelength=68 cm) or L band (24 cm) to a shorter wavelength C band (6 cm), enhanced the correlation of the image signature to standing biomass (r2=0.83 for P/C and r2 =0.79 for L/C) and showed increased sensitivity to dry biomass beyond 15 kg/m2 View full abstract»

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  • A field-portable thermal infrared grating spectrometer (THIRSPEC)

    Page(s): 307 - 314
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    A thermal infrared grating spectrometer was developed for field studies in the Earth sciences. The design is based on a reflection grating and a 60-element HgCdTe detector array. The useful spectral range of the instrument covers 7.9-11.3 μm with a Nyquist limited resolution of 0.16 μm. The instrument averages over a 12° field of view and compares the exitance of the target to that of an internal black body at ambient temperature. The noise equivalent temperature is approximately 0.06°K over the useful spectral range. Background radiance reflected from the surface of the target can seriously impede the determination of emissivity. This effect is removed from the spectra of geological samples by the use of reference samples View full abstract»

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  • Solving the inverse problem for soil moisture and temperature profiles by sequential assimilation of multifrequency remotely sensed observations

    Page(s): 438 - 448
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    An algorithm is developed to solve the inverse problem for the retrieval of the soil moisture and temperature profiles based on remotely sensed observations of multispectral irradiance. A model of coherent wave radiative transfer and a model of coupled heat and moisture diffusion in porous media are combined in order to estimate the liquid volumetric water content and temperature profiles in a soil column using low-frequency passive microwave and infrared emitted radiation observations and without the use of empirical relations. The central purpose of this mainly theoretical paper is to pose the inverse problem and present the physics-based algorithm as the solution. The algorithm is tested on a basic synthetic example in order to ascertain that the retrieval is feasible. Additional work in the future is necessary and planned in order to test the algorithm with field observations, extend it to include vegetation, and refine it for detail in the specification of heterogeneity in soil types and boundary conditions View full abstract»

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  • Airborne active and passive microwave observations of Super Typhoon Flo

    Page(s): 231 - 242
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    Airborne microwave measurements of precipitation associated with Super Typhoon Flo in the western North Pacific were conducted during September 16-18, 1990. The sensor package aboard the NASA DC-8 aircraft included a dual-frequency precipitation radar at 10 GHz and 34 GHz and a host of radiometers operating at 10 GHz, 18 GHz, 19 GHz, 34 GHz, and 92 GHz, as well as three frequencies near the strong water vapor absorption line of 183.3 GHz. The measurements were made during a few passes over the storm center, and active and passive microwave signatures of the rainbands were detected with a fine spatial resolution. The relationship between the measured brightness temperature and radar-estimated rain rate is examined at the frequencies between 10-92 GHz. At both 34 and 92 GHz this relationship is analyzed with the 10 GHz radar reflectivity factor measured at altitudes above the freezing layer as a further constraint. The results show that frozen hydrometeors strongly scatter radiation at these frequencies, especially at 92 GHz. It was shown from a close examination of both active and passive microwave signatures that a significant scattering of radiation at frequencies 118 GHz occurred in the inner eyewall at altitudes of 3-8 km. This scattering of microwave radiation by hydrometeors in both liquid and frozen forms is discussed under the authors' current understanding of the scattering mechanism View full abstract»

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  • Modeling radar scatter from distributed targets using a coupled scatterer approach

    Page(s): 296 - 306
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    Radar remote sensing deals with the extraction of object information from electromagnetic wave parameters. To fully exploit the potential of acquiring quantitative information requires a detailed description of the interaction between microwaves and objects. For practical reasons a simplified approach is preferred where the radar return of a distributed target is modeled as a sum of scatterer echoes. In this paper a point scatterer model is given to simulate scattering of radar waves by distributed targets. The scatterers may have different heights in synthesizing rough surfaces. The principle of conservation of energy is used to account for electromagnetic coupling between the scatterers in function of target sampling density. The predicted coupling between two scatterers is experimentally verified by indoor radar cross section measurements. The model is verified through comparison with numerically solving the electric field integral equation for linear scatterer arrays. Results are given in the form of bistatic scatter diagrams to provide insight in the full scattering behavior View full abstract»

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  • Evaluation of compositing algorithms for AVHRR data over land

    Page(s): 427 - 437
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    The objective of this study was to evaluate alternative methods for producing both Normalized Difference Vegetation Index (NDVI) and single-channel composite images of land surfaces from the Advanced Very High Resolution Radiometer (AVHRR). As a goal, it was specified that the composite image should approximate as much as possible a single-date image with a constant, near-nadir geometry. The comparative performance of three single-step [maximum NDVI (MaN), maximum apparent temperature (MaT), maximum difference of channels 2 minus 1 (MaD)] and two two-step [maximum NDVI followed by maximum temperature (MaNMaT) or by minimum scan angle (MaNMiSc)] criteria in creating composite images was evaluated for three land cover types, namely, cropland, coniferous forest, and deciduous forest within a boreal ecosystem. The assessment was carried out using 18 images obtained with various acquisition geometries in mid-summer over a 1000×1000 km area in Manitoba, Canada. In addition, MaT performance was compared with that of MaN for all Canada during two compositing periods. It was found that among the five criteria tested, MaT and MaNMiSc were the most effective one- and two-step criteria, respectively. MaN preferentially selected off-nadir pixels from the forescatter region, the degree varying with land cover type; the overall NDVI values were higher than for MaT. MaD showed a very strong preference for high backscatter region pixels, regardless of land cover type. Depending on cover type, the NDVI values resulting from Mao were higher or lower than those from a nadir image. Based on ranking of the five techniques using statistics of the differences between composite and reference images, it was found that MaT and MaNMiSc performed similarly, and better than the remaining criteria. Results of the tests show that although statistically reasonable approximations of the reference image could be produced by one or more methods, none of the criteria could consistently yield composites closely resembling the nadir image on a pixel basis, even for a reasonably long compositing period. Therefore, pixel-specific applications of the composites relying on individual channels will likely have to be based on data corrected for bidirectional effects. The results suggest that such corrections are also required for NDVI and, by analogy, for other AVHRR channel combinations View full abstract»

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  • Efficient maximum likelihood classification for imaging spectrometer data sets

    Page(s): 274 - 281
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    A simplified maximum likelihood classification technique for handling remotely sensed image data is proposed which reduces, significantly, the processing time associated with traditional maximum likelihood classification when applied to imaging spectrometer data, and copes with the training of geographically small classes. Several wavelength subgroups are formed from the complete set of spectral bands in the data, based on properties of the global correlation among the bands. Discriminant values are computed for each subgroup separately and the sum of discriminants is used for pixel labeling. Several subgrouping methods are investigated and the results show that a compromise among classification accuracy, processing time, and available training pixels can be achieved by using appropriate subgroup sizes 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