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Geoscience and Remote Sensing, IEEE Transactions on

Issue 6 • Date Nov 1988

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Displaying Results 1 - 21 of 21
  • Scattering from non-Gaussian randomly rough surfaces-cylindrical case

    Publication Year: 1988 , Page(s): 790 - 798
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    A numerical method is developed to simulate electromagnetic wave scattering from computer-generated two-dimensional randomly rough surfaces. The rough surface generated for scattering simulation is specified only up to the second moment statistics, i.e. the height distribution and the autocorrelation function. The coherent and noncoherent scattering from four different types of random surfaces is examined. The four different types of surfaces are: Gaussian distributed heights and Gaussian correlation, Gaussian distributed height and non-Gaussian correlation, modified exponential distributed height and non-Gaussian correlation, modified exponential distributed height and Gaussian correlation, modified exponential distributed height and non-Gaussian correlation surfaces. It is shown by simulation that the dominating factor in coherent scattering is the surface height density and the autocorrelation can cause a higher order effect View full abstract»

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  • A statistical and geometrical edge detector for SAR images

    Publication Year: 1988 , Page(s): 764 - 773
    Cited by:  Papers (220)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    A constant-false-alarm-rate (CFAR) edge detector based on the ratio between pixel values is described. The probability distribution of the image obtained by applying the edge detector is derived. Hence, the decision threshold can be theoretically determined for a given probability of false alarm as a function of the number of looks of the image under study and the size of the processing neighborhood. For a better and finer detection, the edge detector operates along the four usual directions over windows of increasing sizes. A test performed, for a given direction, on a radar image of an agricultural scene shows good agreement with the theoretical study. The operator is compared with the CFAR edge detectors suitable for radar images View full abstract»

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  • Magnetic dipole excitation of a long conductor in a lossy medium

    Publication Year: 1988 , Page(s): 720 - 725
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    A formulation is presented for the excitation of currents on an infinitely long conductor by electric or magnetic dipoles of arbitrary orientation. The conductor can be either insulated or bare to model ungrounded or grounded conductors. Specific calculations are presented for a vertical magnetic dipole source because this source produces the appropriate horizontal polarization and could be used in a borehole-to-borehole configuration. Numerical results for the induced current and secondary magnetic field indicate that long conductors produce a strong anomaly over a broad frequency range. The secondary magnetic field decays slowly in the direction of the conductor and eventually becomes larger than the dipole source. Results have been presented for frequencies from 20 kHz to 2 MHz, and the entire frequency range appears to be useful View full abstract»

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  • Electromagnetic wave scattering from some vegetation samples

    Publication Year: 1988 , Page(s): 799 - 808
    Cited by:  Papers (73)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    For an incident plane wave, the field inside a thin scatterer (disk and needle) is estimated by the generalized Rayleigh-Gans (GRG) approximation. This leads to a scattering amplitude tensor equal to that obtained via the Rayleigh approximation (dipole term) with a modifying function. For a finite-length cylinder the inner field is estimated by the corresponding field for the same cylinder of infinite length. The effects of different approaches in estimating the field inside the scatterer on the backscattering cross section are illustrated numerically for a circular disk, a needle and a finite-length cylinder as a function of the wave number and the incidence angle. Finally, the modeling predictions are compared with measurements View full abstract»

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  • Fields of horizontal currents located above the Earth

    Publication Year: 1988 , Page(s): 726 - 732
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The plane-wave spectrum technique is used to derive the field of horizontal currents located in a horizontal plane above the Earth. The far field is derived asymptotically, and the near field is computed by a two-dimensional fast Fourier transform. Specific numerical results are presented for a pair of oppositely directed dipoles, and the results have application to detection of buried objects. When the antenna is located at low heights, the field is enhanced in the Earth and decreased in the air View full abstract»

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  • Theory of microinduction measurements

    Publication Year: 1988 , Page(s): 707 - 719
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB)  

    The microinduction sensor consists of miniature transmitter and receiver coils and can be used to make a noncontacting conductivity measurement of inhomogeneous media. Theoretical models for the microinduction sensor are presented that make it possible to better understand the response of the sensor in a wide variety of circumstances. For example, the issue of resolution, depth of investigation, standoff, coil tilt, and effect of Maxwell-Wagner charge accumulation are better understood using the model. A Green's function approach is used to formulate an integral equation whose lowest Born approximation and geometrical factor theory can be used to gain physical intuition and to predict the response of the sensor in certain special cases. To solve more general problems, a full wave of theory for the sensor over a layered medium is introduced that includes all electrodynamic effects View full abstract»

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  • Microwave emission and reflection from the wind-roughened sea surface at 6.7 and 18.6 GHz

    Publication Year: 1988 , Page(s): 860 - 868
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    Microwave radiometric observations were made with specially designed microwave radiometers at 6.7 and 18.6 GHz, and the results were compared with those of other investigators, over the frequency range of 1-40 GHz. Dependences of sea surface emission and reflection on wind speed, frequency, incidence angle, and polarization type are discussed in detail, following discussions of the reflective processes of sky radiation and error estimation in the retrieval of mainlobe-averaged brightness temperature. The wind speed sensitivity of brightness temperature, emissivity, and reflectivity is formulated with respect to frequency and incidence angle in each polarization. The brightness temperature, emissivity and reflectivity at arbitrary wind speed are derived employing this formulation. Based on the results obtained it is suggested that the 10-19-GHz band may be optimal for satellite microwave radiometer observations of sea-surface wind View full abstract»

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  • Surface identification using satellite microwave radiometers

    Publication Year: 1988 , Page(s): 850 - 859
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    The use of satellite microwave radiometers for identifying natural surfaces is analyzed. A retrieval technique is developed by considering the related mixed-pixel problem where two or more surfaces are contained within the viewing area. At a given frequency &ogr;, the emissivity measurement ε(&ogr;) depends on the fractional amounts f n and a priori emissivities εn(&ogr;) where ε(&ogr;)=Σεn(&ogr;)fn. In applications involving surface identification the fractional amounts act as discriminants to identify the most likely surface among the a priori candidates. In principle, the fractional amounts can be obtained using multispectral measurements of emissivity. However, due to the limited spectral characteristics of emissivity the maximum number of distinguishable surfaces is reduced to three. The fractional amounts are derived using dual-frequency emissivity measurements and the effects of errors in measurement and a priori values are analyzed View full abstract»

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  • Advanced subsurface radar system for imaging buried pipes

    Publication Year: 1988 , Page(s): 733 - 740
    Cited by:  Papers (7)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (708 KB)  

    A subsurface radar system for imaging buried pipes was developed. The system is capable of reconstructing clear pipe images under unfavorable conditions, such as large attenuation rate of the radio waves propagating in soil. The output power of a pulse generator, the amplifier gain, and average number are controlled by moving the observation depth to improve the detection capability. Fast image processing methods are also used. A 6.5-cm-diameter steel pipe, buried at a depth of 2.5 m, was clearly reconstructed as a color image averaged attenuation rate of 12.6 dB/m in the soil. A plastic pipe (6.5 cm in diameter), buried at a depth of 1 m, was also imaged by the system View full abstract»

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  • The design of an onboard digital Doppler processor for a spaceborne scatterometer

    Publication Year: 1988 , Page(s): 869 - 878
    Cited by:  Papers (11)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB)  

    A digital Doppler processor, which will permit the Doppler center frequency of the measurement cell bandwidths to be adjusted to compensate for the effects of the Earth's rotation, will be used in the next NASA spaceborne scatterometer known as NSCAT. The authors describe the design and genesis of the NSCAT digital Doppler processor and discuss the performance tradeoff issues that were evaluated during the design phase. In this FFT (fast Fourier transform)-based technique, computation of the adjustment to the cell center frequencies will be done onboard using an approximate expression for the Doppler shift of the cell center versus orbit time. This technique also permits modification of the parameters used to locate the radar-backscatter-coefficient measurements cells by ground command in response to orbit changes View full abstract»

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  • On the application of averaging median filters in remote sensing

    Publication Year: 1988 , Page(s): 832 - 838
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    The application of averaging median filters to remote sensing has been investigated, and the results are presented with some discussion and recommendations. Averaging median filters can be considered as a subclass of the standard median filters. For image processing purposes, a two-dimensional window is first filtered by a number of average filters, and the final result of the averaging filters is equal to the median of the central pixel value and the averaging filter results. Applications of this averaging median filter to Landsat images are presented, and the results show that the fine details are preserved while attenuating the impulsing noise View full abstract»

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  • Measurements of the aureole phase function during heavy rain

    Publication Year: 1988 , Page(s): 879 - 881
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    The results of ground-based forward-scattering UV radiation measurements during heavy rain are reported. A distinctive diffraction pattern was observed with secondary peaks at 1.2° and 1.9°. It is suggested that millimeter-sized raindrops break up and generate 10-μm particle spray. It is concluded that a rain model must include the spray effect to predict correctly the propagation of thermal IR radiation near the ground View full abstract»

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  • Radar polarimetry: analysis tools and applications

    Publication Year: 1988 , Page(s): 774 - 789
    Cited by:  Papers (94)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2780 KB)  

    The authors have developed several techniques to analyze polarimetric radar data from the NASA/JPL airborne SAR for Earth science applications. The techniques determine the heterogeneity of scatterers with subregions, optimize the return power from these areas, and identify probable scattering mechanisms for each pixel in a radar image. These techniques are applied to the discrimination and characterization of geologic surfaces and vegetation cover, and it is found that their utility varies depending on the terrain type. It is concluded that there are several classes of problems amenable to single-frequency polarimetric data analysis, including characterization of surface roughness and vegetation structure, and estimation of vegetation density. Polarimetric radar remote sensing can thus be a useful tool for monitoring a set of Earth science parameters View full abstract»

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  • A digital calibration method for synthetic aperture radar systems

    Publication Year: 1988 , Page(s): 753 - 763
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1028 KB)  

    A basic method to calibrate imagery from synthetic aperture radar (SAR) systems is presented. SAR images are calibrated by monitoring all the terms of the radar equation. This procedure includes the use of both external (calibrated reference reflectors) and internal (system-generated calibration signals) sources to monitor the total SAR system transfer function. To illustrate the implementation of the procedure, two calibrated SAR images (X-band, 3.2-cm wavelength) are presented, along with the radar cross-section measurements of specific scenes within each image. The sources of error within the SAR image calibration procedure are identified View full abstract»

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  • Combining Laplacian images of different spatial frequencies (scales): implications for remote sensing image analysis

    Publication Year: 1988 , Page(s): 826 - 831
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    The author proposes a solution to the longstanding problem of how to combine the different scales of analysis in multifrequency image analysis. The premise for combining different scales of analysis is that the absolute value of the result of the difference of two Gaussian filters (DOG) will be at a maximum at different parts of an object for the DOGS passing the spatial frequencies composing those parts. Combining images derived from a DOGS passing a range of frequencies (called Laplacian images or the Laplacian pyramid) is performed by taking the maximum absolute value among the values in the Laplacian image being combined (for each pixel) to form what is called a multifrequency Laplacian image. The rationale for the development of a multifrequency Laplacian pyramid and its implications for multifrequency image analysis and remote-sensing image classification are discussed View full abstract»

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  • Non-Gaussian surface generation

    Publication Year: 1988 , Page(s): 885 - 888
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    An approach has been found to generate two-dimensional non-Gaussian surfaces with known height densities and surfaces with known height densities and surface correlation functions. Four types of surfaces with various combinations of Gaussian and non-Gaussian height densities and correlation functions are generated. Statistical properties of the generated surfaces are computed and shown to agree with the specified properties. The surface height density function of the generated surface is found to depend upon the number of filter weights chosen and the density function of input random numbers. The results are pertinent to the study of electromagnetic-wave scattering by rough surfaces View full abstract»

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  • Multifrequency sounding results of laboratory simulated homogeneous and two-layer Earth models

    Publication Year: 1988 , Page(s): 749 - 752
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    Scale model studies have established that layered Earth structures can be resolved by central frequency sounding (CFS) through a combination of parametric and geometric approaches. In view of the utility of scale model studies, which often improve the approach towards interpretation of field data, experimental work was carried out for CFS and compared with dipole frequency sounding (DFS) to establish the resolution pattern of CFS on laboratory simulated models. Results presented for homogeneous and two-layer Earth models for the conductive substratum agree well with the actual parameter values of the models View full abstract»

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  • Invertible canopy reflectance modeling of vegetation structure in semiarid woodland

    Publication Year: 1988 , Page(s): 809 - 825
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1168 KB)  

    The Li-Strahler canopy reflectance model, driven by Landsat Thematic Mapper (TM) data, provided regional estimates of tree size and density in two bioclimatic zones in West Africa. This model exploits tree geometry in an inversion technique to predict average tree size and density from reflectance data using a few simple parameters measured in the field (spatial pattern, shape, and size distribution of trees) and in the imagery (spectral signatures of scene components). The model was tested in sparse woodland and wooded grassland in the Sahelian and Sudanian bioclimatic zones in West Africa View full abstract»

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  • The complex dielectric constant of Iraqi soils as a function of water content and texture

    Publication Year: 1988 , Page(s): 882 - 885
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    Measurements of the complex dielectric constant ε of several soil samples have been carried out at 10 GHz as a function of moisture content Wc and particle-size distribution (PSD). Measurements performed on the moist samples showed a strong dependence on the PSD. At a particular moisture value, both real and imaginary terms of ε are found to be directly proportional to the sand content and inversely proportional to the clay content of the samples. An empirical model based on the PSD and the individual samples of W c is developed using the least-square technique View full abstract»

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  • Velocity filters for multiple interference attenuation in geophysical array data

    Publication Year: 1988 , Page(s): 741 - 748
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    The problem of velocity filtering a record of seismic data with the objective of extracting a desired signal by attenuating the coherent interferences traveling at different velocities is considered. A two-dimensional (N-input (N-M+1)-output) processing scheme is used where the (N-M+1) output traces are generated from the N-input traces by multichannel processing of overlapping subsets of M-input races. Each output is generated by using a vector of multichannel arrays filters designed to attenuate multiple coherent interference and random noise. The two-dimensional frequency-wavenumber expression corresponding to the proposed multiple-input-multiple-output processing scheme is derived so that it can be implemented using the two-dimensional fast Fourier transform. Two illustrative examples are included View full abstract»

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  • Real-time textural edge detection by incoherent spatial Gaussian bandpass filtering

    Publication Year: 1988 , Page(s): 839 - 849
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    A technique for textural edge detection using an acoustooptic two-pupil heterodyne scanning system is proposed. A textural region is modeled as a frequency-modulated tonal domain. Boundary extraction between two textures is discussed based on an extension of tonal edge detection by bandpass filtering in the frequency domain. The textural edge detection can be achieved optically by using two offset Gaussian pupils in the two-pupil scanning system. Its performance is discussed along with the experimental results 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