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Geoscience and Remote Sensing, IEEE Transactions on

Issue 5 • Date Sep 1988

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Displaying Results 1 - 25 of 25
  • Application of 2-D Hilbert transform in geophysical imaging with potential field data

    Page(s): 502 - 510
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    The relationship between two-dimensional (2-D) Hilbert transforms and three-dimensional (3-D) potential field data (gravity and magnetic) is reviewed and applied to quantitative interpretation of magnetic and gravity anomalies as well as their derivatives. The vertical and horizontal derivatives of potential field anomalies due to multiprism models were used to test the 2-D Hilbert transform algorithms and their application. The gravity and magnetic contour maps of the Sudbury area, Canada, were digitized and Hilbert-transformed to be correlated with satellite digital images and with the previously known geology. The results indicate that the 2-D Hilbert transform technique can, in a robust fashion, be utilized for the extrapolation of geological boundaries through overburdened areas and subsequently provide a mathematical tool for a step-by-step integration of potential field data and geological remote sensing View full abstract»

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  • Relationship between and measurement of differential scattering coefficient (σ0) and bidirectional reflectance distribution function (BRDF)

    Page(s): 660 - 665
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    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 θi cos θr, where θi and θr 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 View full abstract»

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  • A `free' 3-dB cross-polarized SAR data

    Page(s): 700 - 702
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    It is proposed that by merging the complex signals available from both of the cross-polarized receive channels of a time-multiplexed coherent polarimetric radar, an effective doubling of the signal-to-noise ratio in the cross-polarized component can be realized with no increase in transmitter power, as compared to the more conventional method of using only one channel. A spectral analysis of the merged sequence is presented showing advantages unique to this approach with applications in reflectivity measurement and channel phase calibration View full abstract»

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  • Pulse time-delay method for geophysical tomography

    Page(s): 511 - 517
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    Geotomography methods are presented for reconstructions of index-of-refraction distributions for time-delay measurements. Two versions of the algebraic reconstruction technique (ART) are compared to the conjugate residual (CR) method with Lagrange multiplier conditioning. The CR method with Lagrange multiplier conditioning provided the best reconstructions for good anomaly boundary definition under noisy conditions. A ray bending model to account for refraction is also used in the reconstructions. Modifications are made in the algorithm to simplify its use and to improve the convergence stability. Two image filters, the two-group minimum-variance partition-average (MVP2-AVE) one and the selective smoothing (SS) one, are used in succession and some of the limitations of each filter are eliminated. This improves the implementation of the filters and the accuracy of the reconstructions View full abstract»

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  • A knowledge-based system for highway network extraction

    Page(s): 525 - 531
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    A knowledge-based system has been set up to extract highway networks automatically from Landsat thematic mapper (TM) imagery. The system was developed using image processing algorithms and some artificial intelligence techniques. It inputs raw TM data and outputs an interpreted image clearly identifying highway and road networks. The main algorithms in the system are discussed in detail, results are presented, and features of the system are examined. Landsat TM images of study areas in Toronto, Canada, are presented by way of illustration View full abstract»

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  • Spatial considerations in SAR speckle consideration

    Page(s): 666 - 672
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    An approach to the simulation of synthetic-aperture-radar (SAR) image products is described that departs from most of the other simulation algorithms in the method of speckle generation. Speckle is prepared corresponding to the combination of the frequency weightings and look sum strategy of the radar processes desired and then multiplied by the source scene data preconditioned by the desired resolution. The method allows output pixel spacings to be specified independently of more fundamental system parameters. Typical results are presented for SIR-B images View full abstract»

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  • The emissivity of sea foam at 19 and 37 GHz

    Page(s): 541 - 547
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    An airborne experiment was conducted over the Nantucket Shoals determine the emissivity of sea foam at 19 and 37 GHz, for vertical (V) and horizontal (H) polarizations. These frequencies represent those channels of the satellite-borne system Special Sensor Microwave Imager which are used to estimate the sea surface wind speed. Nine whitecaps were identified as providing 100% coverage for at least part of their signatures. The emissivities of these whitecaps were calculated on the basis of the peak brightness temperature recorded at 37 V, 37 H, and 19 V. The mean values of the emissivities at the respective frequencies and polarizations lie within 3% of the values predicted by the model of A. Stogryn (J. Geophys. Res., vol.77, p.658-1666, 1972). The 37-GHz emissivities vary by 25 to 30% of the mean while the 19-GHz values lies within 15% of the mean. The data are consistent with a single-parameter model depending on an effective foam fraction View full abstract»

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  • Modeling of atmospheric effects on the angular distribution of a backscattering peak

    Page(s): 649 - 659
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    Atmospheric radiative transfer calculations with extremely high angular resolution of the radiance distribution are used to analyze the effects of atmospheric multiple scattering and absorption on the angular distribution of a narrow retroreflection peak such as the canopy hot spot, or Heiligenschein. Using a realistic aerosol-loaded atmospheric model, the results demonstrate that the angular width of the model hot spot (for half widths between 1° and 4° and various types of vegetative canopies) is, to within about 10%, invariant to atmospheric perturbations for total optical depths of the atmosphere up to 1.0 at 0.55 μm and up to 0.9 at 0.86 μm. This result is a consequence of the angular filter effect of the surface bidirectional reflectance distribution function and the comparatively broad angular signature of atmospheric backscattering. However, the contrast ratio of the backscattering peak is strongly influenced by atmospheric extinction. As a consequence for satellite remote sensing, the results indicate that the canopy hot spot can be classified as an angular reflectance signature with an angular width that remains invariant to atmospheric scattering and absorption View full abstract»

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  • The Land Analysis System (LAS) for multispectral image processing

    Page(s): 693 - 697
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    The Land Analysis System (LAS) is an interactive software system available in the public domain for the analysis, display, and management of multispectral and other digital image data. LAS provides over 240 applications functions and utilities, a flexible user interface, complete online and hard-copy documentation, extensive image-data file management, reformatting, conversion utilities, and high-level device independent access to image display hardware. The authors summarize the capabilities of the current release of LAS (version 4.0) and discuss plans for future development. Particular emphasis is given to the issue of system portability and the importance of removing and/or isolating hardware and software dependencies View full abstract»

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  • Millimeter-wave polarimetric measurements of artificial and natural targets

    Page(s): 562 - 573
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1252 KB)  

    The millimeter-wave polarimeter (MMP), a scatterometer system uses the HP 8510A vector network analyzer for coherent processing of the received signal, provides the polarization and phase measurement capability needed to measure the complete scattering matrix of a given target. A calibration and measurement technique that was used with the MMP at 35 GHz to measure the scattering matrix for both distributed and point targets is described. The measurement accuracy was analyzed by comparing theoretical and measured values for a set of conducting spheres and finite-length conducting cylinders. As an extension of the analysis to natural targets, the scattering matrix was measured for a series of twigs and various smooth and rough surfaces View full abstract»

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  • Potential uses of the differential propagation phase constant to estimate raindrop and hailstone size distributions

    Page(s): 639 - 648
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    One of the Doppler radars operated by the National Severe Storms Laboratory can measure the difference between propagation phase constants KDp at horizontal and vertical polarization. This study examines the use of this parameter K Dp in addition to the reflectivity factor ZH and the differential reflectivity ZDR, to obtain information about rain and hail. It is shown from theory and experiments that a third parameter of the drop size distribution, obtained from KDP, can be used to support Z DR measurement and/or to point out mixed-phase hydrometeors. Quantitative information on hail size distribution can be obtained for small hailstones when their major axes are nearly vertically aligned, giving rise to negative ZDR and KDP values View full abstract»

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  • Results from the Push Broom Microwave Radiometer flights over the Konza Prairie in 1985

    Page(s): 590 - 596
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    Four flights of the NASA C-130 aircraft carrying the Push Broom Microwave Radiometer (PBMR) over the Konza Prairie Research Natural Area in eastern Kansas were made to observe surface soil moisture variations. The radiometer operates at the 21-cm wavelength and has four beams that sweep out a swath of about 1.2 times the aircraft altitude. The resolution of each beam is 0.3 times the altitude. At the time of the flights the soil conditions ranged from very wet to moist and the microwave emission expressed as brightness temperatures for the burned watersheds ranged from below 200 to about 245 K. The brightness temperatures were correlated (r2=0.5) with surface moisture measurements, and the slope of the regression was in good agreement with prior results over other grasslands. However, for the unburned watersheds the brightness temperatures were around 270 K and roughly independent of the soil moisture conditions. In these unburned watersheds, a buildup of a thatch layer serves as highly emissive layer above the soil, causing high brightness, especially when wet View full abstract»

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  • Calibration of a cross-polarized SAR image using dihedral corner reflectors

    Page(s): 697 - 700
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    An X-band cross-polarized synthetic aperture radar (SAR) image taken from an aircraft has been absolutely calibrated using 45°-inclined dihedral corner reflectors with an aperture dimension of 15 cm×25 cm. The experiment was carried out during an airborne SAR campaign (called the SAR-580 Experiment) conducted by the National Space Development Agency of Japan in 1983. The experimental procedure, the characteristics of the corner reflector, and the results of the experiment are described View full abstract»

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  • Satellite microwave radiometry of forest and surface types in Finland

    Page(s): 622 - 628
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    10.7-, 18-, and 37-GHz data from the Nimbus-7 Scanning Multichannel Microwave Radiometer (Nimbus-7 SMMR) were used to investigate the microwave response to different surface and forest types. SMMR data for the fall seasons of 1978 through 1981 were compared against a digital surface type map that shows seven different surface types for southern Finland and six for northern Finland. For each land-cover category, the brightness temperature behavior as a function of frequency and polarization was determined. The precision of the results is evaluated, and they are compared to other published results. The discrimination of land-cover categories using the brightness temperature is discussed View full abstract»

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  • A knowledge-based system controlled by an iterative quadtree splitting scheme for segmentation of seismic sections

    Page(s): 518 - 524
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    A knowledge-based system for the segmentation of seismic sections is presented. The system can be functionally divided into a texture feature extraction part and a knowledge-based segmentation part. An important characteristic of the proposed approach is the iterative quadtree splitting (IQS) scheme used to control the segmentation process. The final output of the system is a segmentation of the input section into regions (segments) of common signal character. Test runs of the system on a real seismic section from the Gulf of Mexico show that the introduction of domain expert geologic knowledge can significantly improve the overall segmentation. The IQS control scheme provides two functions essential to most knowledge-based image processing and interpretation systems: (1) the coordination of all parallel-operated processes over the entire section for an overall balanced result; and (2) the incorporation of various types of knowledge into the different levels of decision-making in those processes View full abstract»

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  • Radiative properties of deformed hydrometeors for commonly used passive microwave frequencies

    Page(s): 629 - 638
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    Scattering parameters for ensembles of aspherical ice and liquid hydrometeors were calculated at an incidence angle (ψ) of 50° for frequencies of 10.7, 18.0, 37.0, 50.3, and 85.6 GHz. Hydrometeors are assumed to be oblate ellipsoids with semiminor axes aligned with ψ=0°. The angle ψ 50° is determined by the viewing angle of satellite-borne radiometers. The backscattering extinction coefficients at ψ=0° were also calculated at 18, 37, and 85.6 GHz to provide information for future nadir scanning satellite-borne radars. The hydrometeors are assumed to be characterized by Marshall-Palmer drop-size distributions. The extended boundary condition method is used to calculate the extinction and backscattering coefficients as well as the albedo for single scattering and the asymmetry factor of the phase function. Results are fitted to simple functions of the rainfall rate. Some comparisons illustrate the differences and similarities of these results with those obtained from equal volume spheres View full abstract»

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  • A spaceborne LFM scatterometer for ocean surface wind vector measurement-a time domain approach

    Page(s): 532 - 540
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    The limitations of the currently used continuous-wave-pulse (CW-pulse) spaceborne scatterometers for wind-vector retrieval are reviewed. The disadvantages due to purely time-domain or frequency-domain (Doppler filtering) approaches are described. To overcome the limitations of these methods, a modified scheme is proposed wherein the pulse transmitted is linearly frequency modulated (LFM) and the processing is carried out in the time domain. This method is described and compared with other techniques to highlight the improved results obtainable with this LFM technique View full abstract»

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  • Estimation of X-band scattering properties of tree components

    Page(s): 612 - 616
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    An X-band FM-CW very-fine-range resolution scatterometer was used to acquire backscattering data for individual branches for a number of tree species. Using a model to describe the scattering source function and an experimental procedure for selected removal of plant parts, an estimation was made of η, the volume backscatter coefficient, and κ, the volume extinction coefficient. It is found that: (1) leaves are strong attenuators as well as scatterers; (2) the albedo (the ratio η/κ), at a given angle of incidence, is nearly independent of the tree type; (3) the tree limbs are good attenuators but rather poor scatterers; and (4) te albedo changes as a function of the angle of incidence and for deciduous trees is also a function of the season View full abstract»

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  • Estimation of surface roughness parameters from dual-frequency measurements of radar backscattering coefficients

    Page(s): 574 - 579
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    A simple model was developed for estimating the surface roughness parameters of a bare soil field. The model uses a set of dual-frequency measurements of the field's radar backscattering coefficients, which can be matched to calculated results obtained with assumed values for the surface roughness parameters, as represented by the surface height standard deviation σ and its correlation lengths. Scatter plots of measured and calculated radar backscattering coefficients at the C -band (4.25-GHz) frequency versus those at L-band (1.5 GHz) show that it is feasible to estimate the surface roughness parameters using this technique. The estimated values for σ are in excellent agreement with those of measurements. However, there are discrepancies between the estimated and measured values for the correlation length L. For a very rough field, the geometrical optics model could be more appropriate for modeling the C-band data View full abstract»

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  • Microwave polarization index for monitoring vegetation growth

    Page(s): 617 - 621
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    It is known that microwave emission for soil is partially polarized, whereas the polarization degree of radiation from crops is either very small or equal to zero. The effect of vegetation on the polarized emission from the soil is analyzed by means of a model based on the radiative transfer theory. A comparison between the values predicted by the model and the experimental data obtained at 10 and 36 GHz shows that the model is particularly adequate for corn at 10 GHz, in which case different values of leaf area index can be estimated. At 36 GHz, the polarization degree changes very rapidly as vegetation grows and it is possible to distinguish only bare soil from vegetated soil View full abstract»

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  • Spatial compression of Seasat SAR imagery

    Page(s): 673 - 685
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1824 KB)  

    The results of a study of the techniques for spatial compression of synthetic-aperture-radar (SAR) imagery are summarized. Emphasis is on image-data volume reduction for archive and online storage applications while preserving the image resolution and radiometric fidelity. A quantitative analysis of various techniques, including vector quantization (VQ) and adaptive discrete cosine transform (ADCT), is presented. Various factors such as compression ratio, algorithm complexity, and image quality are considered in determining the optimal algorithm. The compression system requirements are established for electronic access of an online archive system based on the results of a survey of the science community. The various algorithms are presented and their results evaluated considering the effects of speckle noise and the wide dynamic range inherent in SAR imagery View full abstract»

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  • Thermal modeling for the estimation of energy losses from municipal heating networks using infrared thermography

    Page(s): 686 - 692
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    Analysis and simulation results are reported showing that there generally is a strong correlation between the thermal IR (infrared) contrast of a district heating line and its heat losses. A computer model based on the method of finite differences is described by which the temperature field and the heat flux around a buried heating line can be predicted. Algorithms are derived for the estimation of energy losses using thermal IR imagery as input data. The most promising algorithm is based on an integration of the surface temperature profile across the heating line. Under favorable conditions, it seems possible to estimate heat losses with an error (RMS) of 10 to 20% and a sensitivity of 10 to 20 W/m. The main limitations of the technique and the choice of favorable conditions for data acquisition are analyzed and discussed View full abstract»

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  • Significance of agricultural row structure on the microwave emissivity of soils

    Page(s): 580 - 589
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    A series of field experiments was conducted to extend the database available for verifying agricultural-row-effects models of emissivity. Observations were made using a truck-mounted, 21-cm, 1.4-GHz passive microwave radiometer for a range of soil moisture conditions on three bare soil plots: a flat control field, a furrowed field with row height 15 cm and row spacing 75 cm, and a furrowed field with row height 30 cm and row spacing 90 cm. An examination of model predictions for the test conditions indicated that although the composite roughness model tended to overestimate the effect of row structure on emissivity, it reproduced the observations fairly well. Both simulation results and the field measurements indicated that if an error of ±0.03 in estimating emissivity, could be tolerated, then a reliable prediction of equivalent smooth field emissivity can be made for furrowed fields with row-height/row-spacing ratio less than 0.2, which encompasses most dry-land agricultural planting practices View full abstract»

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  • Interferometric synthetic aperture microwave radiometry for the remote sensing of the Earth

    Page(s): 597 - 611
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    Interferometric aperture synthesis is presented as an alternative to real aperture measurements of the Earth's brightness temperature from low Earth orbit. The signal-to-noise performance of a single interferometric measurement is considered, and the noise characteristics of the brightness temperature image produced from the interferometer measurements are discussed. The sampling requirements of the measurements and the resulting effects of the noise in the measurements on the image are described. The specific case of the electronically steered thinned array radiometer (ESTAR) currently under construction is examined. The ESTAR prototype is described in detail sufficient to permit a performance evaluation of its spatial and temperature resolution. Critical aspects of an extension of the ESTAR sensor to a larger spaceborne system are considered. Of particular important are the number and placement of antenna elements in the imaging array View full abstract»

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  • Airborne SAR imagery of ocean surface waves obtained during LEWEX: some initial results

    Page(s): 548 - 561
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    The potential and the difficulties of using airborne synthetic-aperture radar (SAR) to study ocean surface waves are presented. Airborne C-band SAR imagery obtained with the real-time SAR processor on the Canada Centre for Remote Sensing (CCRS) Convair 580 during the Labrador Extreme Waves Experiment (LEWEX) shows waves propagating through the marginal ice zone as well as through open water regions. Examples are chosen to illustrate both coherent and noncoherent scene motion effects. Coherent scene motion effects include velocity bunching. acceleration defocus, and coherence time limitations. Noncoherent scene motion effects include scanning distortion and look misregistration. The slow platform velocity of airborne SAR precludes replication of spaceborne observations, largely due to coherent motion effects View full abstract»

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Aims & Scope

 

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.

 

Full Aims & Scope

Meet Our Editors

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