By Topic

Geoscience and Remote Sensing, IEEE Transactions on

Issue 5 • Date Sept. 1998

Filter Results

Displaying Results 1 - 19 of 19
  • Introduction To The Special Section On The Electromagnetic Properties Of Sea Ice

    Page(s): 1631
    Save to Project icon | Request Permissions | PDF file iconPDF (14 KB)  
    Freely Available from IEEE
  • Full text access may be available. Click article title to sign in or learn about subscription options.
  • The use of ground-penetrating radar with a cooperative target

    Page(s): 1821 - 1825
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    A cooperative target (CT) is proposed to enhance the ground-penetrating radar (GPR) signal-to-clutter ratio (SCR) for buried man-made targets. Applications include tagging high-value buried structures and monitoring microtunneling equipment. Results are presented for a time-domain CT, a dipole antenna connected to an unterminated delay line. By using several independent time-domain CTs, strategically arrayed about a target, the rotational aspect of the target can also be obtained. Finally, harmonic generation is demonstrated as a technique for a frequency-domain CT View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Laboratory measurements of sea ice: connections to microwave remote sensing

    Page(s): 1716 - 1730
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    The connections between laboratory measurements and remote-sensing observations of sea ice are explored. The focus of this paper is on thin ice, which is more easily simulated in a laboratory environment. The authors summarize results of C-band scatterometer measurements and discuss how they may help in the interpretation of remote-sensing data. They compare the measurements with observations of thin ice from ERS and airborne radar data sets. They suggest that laboratory backscatter signatures should serve as bounds on the interpretation of remote-sensing data. They examine these bounds from the perspective of thin ice signatures, the effect of temperature, and surface processes, such as frost flowers and slush on these signatures. Controlled experiments also suggest new directions in remote-sensing measurements. The potential of polarimetric radar measurements in the retrieval of thickness of thin ice is discussed. In addition to the radar results, the authors discuss the importance of low-frequency passive measurements with respect to the thickness of thin ice View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Forward electromagnetic scattering models for sea ice

    Page(s): 1655 - 1674
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Recent advances in forward modeling of the electromagnetic scattering properties of sea ice are presented. In particular, the principal results include the following: (1) approximate calculations of electromagnetic scattering from multilayer random media with rough interfaces, based on the distorted Born approximation and radiative transfer (RT) theory; (2) comprehensive theory of the effective complex permittivity of sea ice based on rigorous bounds in the quasi-static case and strong fluctuation theory in the weakly scattering regime; (3) rigorous analysis of the Helmholtz equation and its solutions for idealized sea ice models, which has led in the one dimensional (1D) case to nonlinear generalizations of classical theorems in Fourier analysis. The forward models considered incorporate many detailed features of the sea ice system and compare well with experimental data. The results have advanced the general theory of scattering of electromagnetic waves from complex media as well as homogenization theory, which relates bulk properties of composite media to their microstructural characteristics. Furthermore, the results have direct application to microwave remote sensing and serve as the basis for inverse algorithms for reconstructing the physical properties of sea ice from scattering data View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • EMPOSI Database

    Page(s): 1794
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (8 KB)  

    First Page of the Article
    View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The role of snow on microwave emission and scattering over first-year sea ice

    Page(s): 1750 - 1763
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    Investigates the geophysical and thermodynamic effects of snow on sea ice in defining the electromagnetic (EM) interaction within the microwave portion of the spectrum. The authors combine observational evidence of both the physical and thermodynamic characteristics of snow with direct measurements of scattering and emission at a variety of frequencies. They explain their observational results using various “state-of-the-art” forward scattering and emission models. Results show that geophysical characteristics of snow effect emission above about 37 GHz and above 5 GHz for active microwave scattering. They understand these effects to be driven by grain size and its contribution to volume scattering in both passive and active interactions within the volume. With snow cover, the Brewster angle effect is not significant and there is a gradual rise in emission from 10 to 37 GHz. They find emissivity to be dominated by direct emission from saline ice through the snow layer. Hence, the influence of grain size is small but the trend is clearly a drop in total emission as the grain size increases. They find that the role of the volume fraction of snow on emission and scattering is a complex relationship between the number density of scatterers relative to the coherence of this scattering ensemble. At low volume fractions, they find that independent scattering dominates, resulting in an increase in albedo and the extinction coefficient of the snow with frequency. The thermodynamic effects of snow on microwave scattering and emission are driven by the role that thermal diffusivity and conductivity play in the definition of brine volumes at the ice surface and within the snow volume. Prior to the presence of water in liquid phase within the snow volume, they find that the indirect effects are dominated by an impedance matching process across the snow-ice interface. They find that the complex permittivity at the snow-ice interface is considerably higher than over the bare ice surface View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modeling light propagation in sea ice

    Page(s): 1743 - 1749
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    This paper outlines the process by which it is possible to begin with the physical properties of sea ice (such as the size distributions of brine pockets and air bubbles), then predict the optical absorption and scattering properties of the ice, and finally use these inherent optical properties in radiative transfer models to predict light propagation within the ice. Each step of this entire process is illustrated by application to a comprehensive data set of sea ice physical and optical properties. Agreement is found between measured and modeled beam spread functions (bsfs), albedos, and transmittances View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Saline ice thickness retrieval under diurnal thermal cycling conditions

    Page(s): 1731 - 1742
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    An inverse scattering algorithm is presented that reconstructs ice growth under thermal cycling conditions by using time-series active microwave measurements. The algorithm uses a direct scattering model consisting of a physically based electromagnetic model that accounts for thermal and electromagnetic properties of ice and combined volume and surface scattering effects as well as a one-dimensional (1D) thermodynamic model of saline ice growth that includes thermal interactions with the atmosphere. The combined thermodynamic-electromagnetic scattering model is applied to interpret the United States Army Cold Regions Research and Engineering Laboratory, Hanover, NH, 1994 experimental observations (CRRELEX'94) on both the ice growth and the diurnal cycles in C-band polarimetric backscatter. The crucial part of the inversion algorithm is the use of sequentially measured radar data together with the direct scattering model to retrieve the sea ice parameters. The algorithm was applied to CRRELEX'94 data and successfully reconstructed the evolution of ice growth under a thermal cycling environment. This work shows that the inversion algorithm using time-series data offers a distinct advantage over algorithms using individual microwave data set View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A model for altimeter returns from penetrable geophysical media

    Page(s): 1784 - 1793
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The radar altimeter is a well-understood instrument for monitoring the world's oceans. There has been a recent effort to extend altimeter techniques to the study of the world's ice sheets. To this end, several authors have developed average altimeter waveform models that incorporate pulse-penetration effects to varying degrees. In this paper, the authors extend these models to more adequately account for the effects of surface roughness and subsurface inhomogeneities on the average scattered waveform. This leads to a waveform model that is useful in analyzing altimeter returns obtained over a wider range of geophysical media, such as snow, ice, and foliage, which are characterized by strong subsurface inhomogeneities. Representative results of applying this extended model to airborne altimeter measurements made over various regions of the Greenland ice sheet in September 1991 are provided View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Evolution of electromagnetic signatures of sea ice from initial formation to the establishment of thick first-year ice

    Page(s): 1642 - 1654
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    The spatial and temporal distribution of new and young sea ice types are of particular interest because of the influence this can exert on the heat and mass balance of the polar sea ice. The objective of the present work is to characterize the temporal evolution of the electromagnetic (EM) signatures of sea ice from initial formation through the development of first-year (FY) ice on the basis of the temporal variations in the physical properties of the ice. The time series of young sea ice signatures, including microwave emissivity, radar backscatter, and visible and infrared spectral albedo, has been measured at successive stages in the growth and development of sea ice, both under laboratory and field conditions. These observations have been accompanied by studies of the physical properties that influence the interaction between radiation and the ice. This has resulted in a consistent data set of concurrent multispectral observations that covers essentially all phases of the development of the different types of sea ice from initial formation to thick FY ice. Mutually consistent theoretical models covering the entire wavelength range of the observations are applied to selected cases and successfully match the observations. Principal component analysis (PCA) of the data set suggests combinations of the set of frequencies to effectively distinguish among different stages in the temporal evolution of the sea ice View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improved determination of the sea ice edge with SSM/I data for small-scale analyses

    Page(s): 1795 - 1808
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    A method to derive the sea ice edges from the 37- and 85-GHz channels of the spaceborne Special Sensor Microwave/Imager (SSM/I) with higher resolution than operational ice concentration analyses is developed. A combined ice-atmosphere model to evaluate atmospheric influences showed that under clear sky conditions the error of the ice edge position is 3.1 km on average. The method performs well up to total liquid water content (TWC) of 125 g/m2 and overestimates the ice extent when TWC increases up to 250 g/m2. The algorithm is suitable to classify open water, the interior ice pack, and thin ice (nilas) or low ice concentrations caused by a mixture of open water and pancake ice. Simulations showed that interpolation and resolution-matching techniques may improve the retrieval results with emphasis on interpolation. Validation of the algorithm with high-resolution infrared data shows errors of the ice edge on average less than 5 km. Comparison with the NASA Team ice concentration algorithm in the Weddell Sea, Antarctica, shows best agreement with the contour line of 33% ice concentration. The suitability of the method for mesoscale investigations is demonstrated with a time series of a meander structure in the marginal ice zone (MIZ) View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electromagnetic and physical properties of sea ice formed in the presence of wave action

    Page(s): 1764 - 1783
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Estimating the magnitude of brine flux to the upper ocean requires an ability to assess the dynamics of the formation of sea ice in a region. Brine storage and rate of expulsion is determined by the environmental conditions under which the sea ice forms. In this paper, the physical and electromagnetic properties of sea ice, formed under wave-agitated conditions, are studied and compared with results obtained from ice formed under quiescent conditions. Wave agitation is known to have a profound effect on the air-ice interface and internal ice structure. A variety of sensors, both active and passive, optical and microwave, were used to perform this characterization. Measured electromagnetic parameters included radar backscatter, microwave emission, and spectral albedo in the visible and infrared. Measured physical properties included ice structure, brine and temperature distribution, profiles of the vertical height of the air-ice interface, and ice formation processes. Results showed that emission, backscatter, and albedo all take different signature paths during the transformation from saline water to young sea ice and that the paths depend on sea surface state during ice formation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Inverse electromagnetic scattering models for sea ice

    Page(s): 1675 - 1704
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    Inverse scattering algorithms for reconstructing the physical properties of sea ice from scattered electromagnetic field data are presented. The development of these algorithms has advanced the theory of remote sensing, particularly in the microwave region, and has the potential to form the basis for a new generation of techniques for recovering sea ice properties, such as ice thickness, a parameter of geophysical and climatological importance. Moreover, the analysis underlying the algorithms has led to significant advances in the mathematical theory of inverse problems. In particular, the principal results include the following. (1) Inverse algorithms for reconstructing the complex permittivity in the Helmholtz equation in one and higher dimensions, based on layer stripping and nonlinear optimization, have been obtained and successfully applied to a (lossless) laboratory system. In one dimension, causality has been imposed to obtain stability of the solution and layer thicknesses can be obtained from the recovered dielectric profile, or directly from the reflection data through a nonlinear generalization of the Paley-Wiener theorem in Fourier analysis. (2) When the wavelength is much larger than the microstructural scale, the above algorithms reconstruct a profile of the effective complex permittivity of the sea ice, a composite of pure ice with random brine and air inclusions. A theory of inverse homogenization has been developed, which in this quasistatic regime, further inverts the reconstructed permittivities for microstructural information beyond the resolution of the wave. Rigorous bounds on brine volume and inclusion separation for a given value of the effective complex permittivity have been obtained as well as an accurate algorithm for reconstructing the brine volume from a set of values. (3) Inverse algorithms designed to recover sea ice thickness have been developed. A coupled radiative transfer-thermodynamic sea ice inverse model has accurately reconstructed the growth of a thin, artificial sea ice sheet from time-series electromagnetic scattering data View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effects of topography on mechanisms of radar backscatter from coniferous forest and upland pasture

    Page(s): 1830 - 1834
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Multifrequency, polarimetric airborne synthetic aperture radar (SAR) data of a Sitka spruce plantation and moorland area on upland terrain in the United Kingdom are studied to quantify the effects of topography on mean backscatter and the relative importance of volume, surface, and double-bounce scattering mechanisms as estimated using a simple decomposition scattering model View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Field observations of the electromagnetic properties of first-year sea ice

    Page(s): 1705 - 1715
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    An interdisciplinary field experiment was conducted during April and May of 1994 at Point Barrow, AK, to investigate the relationship between the electromagnetic and physical-biological properties of first-year sea ice. Electromagnetic signatures of bare and snow-covered first-year ice were measured over a broad spectral range, including ultraviolet through near-infrared albedo, microwave emissivity, and radar backscatter. Observations indicated that the scattering of visible light varied significantly with depth in response to changes in the size and orientation of the ice crystals and in the number of brine and air inclusions. The scattering of visible light was greatest in the surface layer where there were numerous inclusions, and crystals tended to be small and randomly oriented. Changes in albedo over small horizontal distances were found to be related to surface layer conditions, including the number of air bubbles and particulate levels. Even for bare ice, transmittances were small with peaks in the blue-green. Scattering exceeds absorption throughout the snow and ice except in the skeletal layer colonized by bottom ice algae. Passive microwave emissivities showed a substantial difference between snow-covered and snow-free sites due to the effects of impedance matching at longer frequencies and volume scattering at higher frequencies produced by the snow, Spatial variability in the emissivity was quite small except at 90 GHz, where the emissivity was most sensitive to the amount of depth hoar. Radar backscatter coefficients were 5-6 dB larger for oblique viewing angles over snow-covered ice View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A broad spectral, interdisciplinary investigation of the electromagnetic properties of sea ice

    Page(s): 1633 - 1641
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    This paper highlights the interrelationship of research completed by a team of investigators and presented in the several individual papers comprising this Special Section on the Office of Naval Research (ONR), Arlington, VA, Sponsored Sea Ice Electromagnetics Accelerated Research Initiative (ARI). The objectives of the initiative were the following: (1) understand the mechanisms and processes that link the morphological and physical properties of sea ice to its electromagnetic (EM) characteristics; (2) develop and verify predictive models for the interaction of visible, infrared, and microwave radiation with sea ice; (3) develop and verify inverse scattering techniques applicable to problems involving the interaction of EM radiation with sea ice. Guiding principles for the program were that all EM data be taken with concurrent physical property data (salinity, density, roughness, etc.) and that broad spectral data be acquired in as nearly a simultaneous fashion as possible. Over 30 investigators participated in laboratory, field, and modeling studies that spanned the EM spectrum from radio to ultraviolet wavelengths. An interdisciplinary approach that brought together sea ice physicists, remote-sensing experts (in fill measurements), and forward and inverse modelers (primarily mathematicians and EM theorists) was a hallmark of the program. Along with describing results from experiments and modeling efforts, possible paradigms for using broad spectral data in developing algorithms for analyzing remote-sensing data in terms of ice concentration, age, type, and possibly thickness are briefly discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiclass spectral decomposition of remotely sensed scenes by selective pixel unmixing

    Page(s): 1809 - 1820
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    Linear pixel unmixing is a straightforward and efficient approach to the spectral decomposition of multichannel remotely sensed scenes. A main drawback to its utilization in operational cases, however, is that the number of spectral components that can be correctly treated must be less or equal to the scene dimensionality (the so-called “condition of identifiability”). To overcome the limitations deriving from this condition, a two-step strategy is currently proposed for application to each scene pixel. Provided that many spectral end-members are available, a subset with a prefixed number of end-members that optimally decompose the candidate pixel is first selected by a procedure based on the Gramm-Schmidt orthogonalization process. This restricted subset is then employed for conventional linear pixel unmixing. The final result is the decomposition of the multispectral scene into all the end-members considered while reducing the residual errors deriving from interclass spectral variability. The new procedure has been tested in three case studies representative of different environmental situations and data sets. The results of these experiments, compared to those of a conventional procedure, show that the new method identifies more clearly the spectral signal associated to all scene components and significantly reduces (20-30%) the residual error of the decomposition process. This is confirmed by further tests using synthetic scenes that are linear combinations of known end-members. In these cases, the reduction of the residual error by the new method is much higher (up to 70-80%) and the abundance images produced are more accurate estimates of the real components View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On nonparametric edge detection in multilook SAR images

    Page(s): 1826 - 1829
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    Nonparametric alternatives based on the Wilcoxon-Mann-Whitney statistics are evaluated for edge detection in synthetic aperture radar (SAR) images. First, the power of the nonparametric test is compared to that of the ratio-of-averages detector. Then, a nonparametric change-point test is evaluated to identify the true edge position inside a fixed window View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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