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Geoscience and Remote Sensing, IEEE Transactions on

Issue 1  Part 1 • Date Jan 2000

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Displaying Results 1 - 25 of 33
  • The systematic behavior of water vapor estimates using four years of GPS observations

    Page(s): 324 - 329
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    The authors have used four years of Global Positioning System (GPS) data to study the amount of integrated water vapor (IWV) in the atmosphere. They find that the presence of certain radomes at some sites highly affects the water vapor estimates at other sites. These effects are eliminated by using a technique in which data from each station are processed individually View full abstract»

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  • Nonlinear inversion in electrode logging in a highly deviated formation with invasion using an oblique coordinate system

    Page(s): 25 - 38
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    Electrode logging as known in the oil industry is a method for determining the electrical conductivity distribution around a borehole or between two boreholes from the static-field (dc) measurements in the borehole. The authors discuss the reconstruction of the three-dimensional (3D) conductivity around a borehole in a highly deviated formation with invasion. At this moment, they have not included the borehole effect. To solve this problem, the full vector analysis is required. In most available algorithms, for the forward and inverse modeling of the resistivity data, the dipping bed environment is approximated using the staircase-discretization grid. In contrast, they have modeled the dipping-bed environment by introducing an oblique (nonorthogonal) coordinate system. By using the oblique coordinate system, they have gained some advantages over the usual approach. First, the use of the staircasing approximation for the dipping-bed environment can be avoided. This means that they reduce the discretization error, and they can suffice with less discretization points to obtain the results with the same degree of accuracy as the problem formulated in the Cartesian coordinate system. Secondly, the horizontally-symmetry constraints of the conductivity distribution can be included easily in the inversion procedure. Several numerical results are presented to demonstrate the performance of the inversion method using the synthetic “measured” data, which are generated by solving a forward-scattering problem numerically with the help of the conjugate gradient fast Fourier transform (CGFFT) method View full abstract»

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  • Detection of calibration drifts in spaceborne microwave radiometers using a vicarious cold reference

    Page(s): 44 - 52
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    The coldest possible brightness temperatures observed by a downward-looking microwave radiometer from space are often produced by calm oceans under cloud-free skies and very low humidity. This set of conditions tends to occur with sufficient regularity that an orbiting radiometer will accumulate a useful number of observations within a period of a few days to weeks. Histograms of the radiometer's coldest measurements provide an anchor point against which very small drifts in absolute calibration can be detected. This technique is applied to the TOPEX microwave radiometer (TMR), and a statistically significant drift of several tenths of a Kelvin per year is clearly detected in one of the channels. TMR housekeeping calibration data indicates a likely cause for the drift, as small changes in the isolation of latching ferrite circulators that are used in the onboard calibration-switch assembly. This method can easily be adapted to other microwave radiometers, especially imagers operating at frequencies in the atmospheric windows. In addition to detecting long-term instrument drifts with high precision, the method also provides a means for cross-calibrating different instruments. The cold reference provides a common tie point, even between sensors operating at different polarizations and/or incidence angles View full abstract»

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  • A nonlinear multispectral statistical CLEAN-based precipitation parameter-retrieval algorithm

    Page(s): 226 - 237
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    An iterative algorithm incorporating CLEAN deconvolution concepts for precipitation parameter retrieval using passive microwave imagery is presented. The CLEAN algorithm was originally designed to deconvolve single-channel radio astronomy images. In order to use CLEAN to retrieve precipitation parameters from multispectral passive-microwave imagery, extensions of the algorithm to accommodate nonlinear, multispectral, and statistical data mere designed and implemented. The primary advantage of the nonlinear multispectral statistical (NMS) CLEAN retrieval algorithm relative to existing algorithms is the use of high-resolution (high-frequency) imagery to guide the retrievals of precipitation parameters from lower resolution (Low-frequency) imagery. The NMS-CLEAN retrieval algorithm was used to estimate rain rate (RR) and integrated ice content (IIC) using simulated imagery of oceanic convection as would be observed from six channels of the proposed Advanced Microwave-Scanning Radiometer. Both the accuracy and structural detail of the retrieved rain rate were improved relative to the retrievals from a single-step, nonlinear, statistical algorithm. Reduced error and improved spatial resolution of a more minor magnitude was also seen in the integrated ice-content retrievals. This study also showed that spatially-simple storm structures resulted in better performance of the NMS-CLEAN retrieval algorithm View full abstract»

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  • Determining land-surface parameters from the ERS wind scatterometer

    Page(s): 126 - 140
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The ERS-1 wind scatterometer (WSC) has a resolution cell of about 50 km but provides a high repetition rate (less than four days) and makes measurements at multiple incidence angles. In order to retrieve quantitative geophysical parameters over land surfaces using this instrument, a method is presented that applies a mixed-target modeling approach to estimate subpixel fractional vegetation cover at a regional scale. The model represents the footprint area as a combination of part dense, homogeneous vegetation and part bare soil (with homogeneous roughness and dielectric properties). Inversion of this model is then carried out using a retrieval procedure that incorporates a priori information in a quantitative manner The method is applied to the estimation of fractional cover over an area in Africa using WSC data from 1992 to 1995. Retrieved parameters are also compared to ground measurements made in the area during the 1992 HAPEX-Sahel campaign. The procedure illustrates the applicability of WSC data for measuring geophysical parameters over land and offers the potential of deriving a physically-based alternative to empirical indices for estimating regionally-variable parameters View full abstract»

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  • Dual-polarized Ku-band backscatter signatures of hurricane ocean winds

    Page(s): 73 - 88
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    The Ku-band dual-polarized backscatter signatures of ocean surfaces are described in this paper with the airborne scatterometer measurements collected in the Hurricane Ocean Wind Experiment in September 1997. The data collected from flights over Hurricane Erika provide a direct evidence that there are wind direction signals in the vertically and horizontally polarized Ku-band backscatter of ocean surfaces under the influence of hurricane force winds. At 46° incidence angle, the vertically polarized backscatter acquired at the upwind direction increases by about 1 dB as the wind speed increases from 22 m·s-1 to 35 m·s-1, while the horizontally polarized backscatter appears to be twice as sensitive with a change of about 2 dB. At 35 m·s-1 wind speeds, the difference between upwind and crosswind observations of vertically polarized backscatter is about 1.5 dB, smaller than the 2 dB difference for the horizontally polarized backscatter. This demonstrates that the horizontal polarization has a greater sensitivity to wind speed and direction than the vertical polarization in the high wind regime. The data also suggest that the upwind and downwind asymmetry of Ku-band backscatter decreases with increasing wind speed and can fall below 0 dB at small incidence angles (<35°) for the vertical polarization. A combined interaction of the geometric optics scattering and the short wave modulation by long waves is proposed to interpret this phenomenon and appears to agree with the dependence of the signature on incidence, wind speed, and polarization. The aircraft flight data support the feasibility of dual-polarized Ku-band radar for hurricane ocean wind measurements, although the data do suggest a reduced wind speed and direction sensitivity in the high wind regime. Also, the differing polarization backscatter signatures-suggest the relative contributions of various surface scattering mechanisms. An improved Ku-band GMF is described View full abstract»

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  • An imaging algorithm of objects embedded in a lossy-dispersive medium for subsurface radar-data processing

    Page(s): 296 - 303
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    A robust and high-resolution two-dimensional (2D) imaging algorithm is proposed for retrieving the shape of conductive objects embedded in a uniform lossy and dispersive medium. The target is modeled in terms of the location of points that represents the enter contour of the object, together with the parameters of the medium. A nonlinear least-squares fitting is applied to the estimated scattered waveform to adjust the model parameters. The estimated waveform is computed using the extended ray-tracing method, which incorporates the edge-diffraction waves. The performance of the algorithm is examined with numerical simulations and test-site experiments. The simulation with clutters also revealed the robustness of the algorithm even under fairly strong clutter environments View full abstract»

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  • Comparing the ocean color measurements between MOS and SeaWiFS: a vicarious intercalibration approach for MOS

    Page(s): 184 - 197
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    The Modular Optoelectronic Scanner (MOS) was launched in the spring of 1996 on the Indian IRS-P3 satellite. With the successful launch of NASA's Sea-viewing Wide Field of-view Sensor (SeaWiFS) in the summer of 1997, there are now two ocean color missions in concurrent operation, and there is interest to compare data from these two sensors. In this paper, we describe our efforts to retrieve ocean-optical properties from both SeaWiFS and MOS using consistent methods. We first briefly review the atmospheric correction, which removes more than 90% of the observed radiances in the visible, and then we describe how the atmospheric-correction algorithm used for the SeaWiFS data can be modified for application to other ocean color sensors. Next, since the retrieved water-leaving radiances in the visible between MOS and SeaWiFS are significantly different, we developed a vicarious intercalibration method to recalibrate the MOS spectral bands based on the optical properties of the ocean and atmosphere derived from the coincident SeaWiFS measurements. Furthermore, because of the strange calibration behavior of the MOS 750 nm band, we modified the atmospheric correction such that the MOS 685 and 868 nm bands can also be used. We present and discuss the MOS-retrieved, ocean-optical properties before and after the vicarious calibration using both the MOS 685 and 750 nm coupled with 868 nm bands in comparison with results from SeaWiFS and demonstrate the efficacy of this approach. We show that it is possible and efficient to vicariously intercalibrate sensors between one and another View full abstract»

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  • Practical methods for rapid and accurate computation of interferometric spectra for remote sensing applications

    Page(s): 169 - 183
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    The apodization of an interferogram corresponds to a linear transformation in spectral space between unapodized and apodized radiances. Many apodization functions have well-behaved numerical inverse transformations, and we show an analytic inverse for the Hamming apodization function. The inverse transformation has many practical uses for remote sensing applications and can also be used theoretically to show the equivalence between unapodized spectra and properly apodized spectra. The inverse transformation, which is a representation of the discrete convolution theorem, can be used to readily convert computed apodized spectra to spectra computed for other symmetric apodization functions (including unapodized), which may have poorer characteristics with regard to calculating channel-transmittance parameters or radiances. We also show a quantitative method for comparing apodization functions of different mathematical forms View full abstract»

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  • Raman lidar calibration for the DMSP SSM/T-2 microwave water vapor sensor

    Page(s): 141 - 154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    Campaigns were conducted at the Pacific Missile Range Facility, Barking Sands, Kauai, investigating Raman lidar as a method to improve calibration of the DMSP SSM/T-2 microwave water vapor profiling instrument. Lidar mixing ratios were calibrated against AIR and Vaisala radiosondes and the calibration was tested in the vicinity of clouds. Above 6 km, radiosondes reported anomalously low relative humidity in the vicinity of clouds. Lidar measurements were confirmed by using an electro-optical shutter, which provided correct measurement of relative humidity at cloud bases above 6 km. Radiative transfer calculations applied to the lidar data closely matched signals observed in the SSM/T-2 atmospheric channels. Forward calculations for surface sensitive channels disagreed with SSM/T-2 and SSM/I observations. Fine scale surface roughness and localized orographic drying are tentatively suggested as explanations. Cloud effects were ruled out as a significant source of discrepancy View full abstract»

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  • Quantitative performance evaluation of the lossless compression approach using pole-zero modeling

    Page(s): 39 - 43
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB)  

    A technique for lossless compression of seismic signals is proposed. The algorithm employed is based on the equation-error structure, which approximates the signal by minimizing the error in the least square sense and estimates the transfer characteristic as a rational function or equivalently, as an autoregressive moving-average process. The algorithm is implemented in the frequency domain. The performance of the proposed technique is compared with the lossless linear predictor and the differentiator approaches for compressing seismic signals. The residual sequence of these schemes is coded using arithmetic coding. The suggested approach yields compression measures (in terms of bits per sample) lower than the lossless linear predictor and the differentiator for compressing different classes of seismic signals View full abstract»

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  • Multispectral image feature selection for land mine detection

    Page(s): 304 - 311
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    The authors' system uses a camera that acquires registered images in six spectral bands and a supervised-learning algorithm to detect metal and plastic land mines. Results show that even with a small sample size, the detection performance is good and holds promise for future work with larger data sets View full abstract»

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  • A coherent scattering model to determine forest backscattering in the VHF-band

    Page(s): 238 - 248
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    A coherent scattering model to determine the forest radar backscattering at VHF frequencies (20-90 MHz) has been developed. The motivation for studying this frequency band is the recent development of the CARABAS Synthetic Aperture Radar (SAR). In order to model the scattering from branches and trunks, homogeneous dielectric cylinders placed above a semi-infinite di-electric ground have been analyzed. An analytical approach, where the theoretically exact currents induced in an infinite cylinder are truncated, has been compared to a numerical solution using the finite difference time domain (FDTD) method. If the first-order coherent ray tracing is included in the analytical approach, the results match well with the numerically exact FDTD solution. The results show that, in order to determine the VHF-backscattering from a forest stand, the coherent ground interaction is an important part and has to be considered. In this paper, modeling results are in good agreement with CARABAS measurements View full abstract»

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  • Simulation of interferometric SAR response for characterizing the scattering phase center statistics of forest canopies

    Page(s): 115 - 125
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    A coherent scattering model for tree canopies is employed in order to characterize the sensitivity of an interferometric SAR (INSAR) response to the physical parameters of forest stands. The concept of an equivalent scatterer for a collection of scatterers within a pixel, representing the vegetation particles of tree structures, is used for identifying the scattering phase center of the pixel whose height is measured by an INSAR. Combining the recently developed coherent scattering model for tree canopies and the INSAR Δk-radar-equivalence algorithm, accurate statistics of the scattering phase-center location of forest stands are obtained numerically for the first time. The scattering model is based on a Monte Carlo simulation of scattering from fractal-generated tree structures, and therefore is capable of preserving the absolute phase of the backscatter. The model can also account for coherent effects due to the relative position of individual scatterers and the inhomogeneous extinction experienced by a coherent wave propagating through the random collection of vegetation particles. The location of the scattering phase center and the correlation coefficient are computed using the Δk-radar equivalence simply by simulating the backscatter response at two slightly different frequencies. The model is successfully validated using the measured data acquired by JPL TOPSAR over a selected pine stand in Raco, MI. A sensitivity analysis is performed to characterize the response of coniferous and deciduous forest stands to a multifrequency and multipolarization INSAR in order to determine an optimum system configuration for remote sensing of forest parameters View full abstract»

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  • Estimation of soil-type heterogeneity effects in the retrieval of soil moisture from radiobrightness

    Page(s): 312 - 315
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    The authors estimate the magnitude of the beam-filling error due to soil-type heterogeneity in the determination of sensor-footprint average soil moisture (θ¯f) retrieved from remote L-band radiometer measurements. Sets of randomly chosen soils are given uniform initial wetness and are subjected to atmospheric drying over 15 days in a numerical model. Results indicate that soil heterogeneity contributes less than 0.7% volumetric soil-moisture error (0.007 mwater3/msoil3) View full abstract»

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  • The normalized radar cross section of the sea at 10° incidence

    Page(s): 64 - 72
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    Measurements of the normalized radar cross section of the sea at K u band at an incidence angle of 10° were performed from a manned airship off the Oregon coast in September and October of 1993. The cross section at this incidence angle is often assumed to have little dependence on windspeed and direction. Their measurements, however, indicate that at windspeeds below 6-7 m/s, the cross section is in fact dependent on these quantities, and the azimuthal modulation can reach values on the order of 5-8 dB. Comparisons of the measured values with the predictions of the quasispecular scattering model are presented. The theory is shown to be accurate in predicting the azimuthal modulation and the strength of the backscatter if the effects of swell are included or if measured wind directions are ignored and the upwind direction is forced to be near the maximum cross section. Values of mean-square wind-wave slope and effective-reflection coefficient required to obtain these fits are very close to those obtained by previous investigators. In particular, mean-square wind-wave slopes are about 70-80% of those of Cox and Munk (1954) because the radar responds only to facets larger than about 10 cm, with smaller ripples acting to reduce the reflection coefficient. If swell is included, they find that mean-square slopes in the direction of the swell, that are as much as ten times the measured swell slopes, are required to fit the model to the cross-section data at low windspeeds. They suggest that this may be due to high-order effects of the hydrodynamic modulation of short waves by the swell. They believe that this explanation is more likely than assuming that wind directions were incorrectly measured View full abstract»

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  • The relationship between the matched-filter operator and the target signature space-orthogonal projection classifier

    Page(s): 283 - 286
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    An operator called the target signature space-orthogonal projection classifier (TSC) was recently introduced. The author shows that the TSC is actually a scaling of the familiar matched-filter operator. It is also proved that scaling the matched-filter operator does not alter its receiver operating characteristic (ROC) curve. Therefore, the TSC has the same performance as the matched-filter operator but requires more computations View full abstract»

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  • Potential and limitations of RADARSAT SAR data for wet snow monitoring

    Page(s): 316 - 320
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    Based on Canadian Satellite (RADARSAT) synthetic aperture radar (SAR) images and simulations from a radar-backscattering model, the authors determined that conventional wet snow-mapping algorithms should perform optimally for a snowpack with a liquid-water content ⩾3%, at low incidence angle (θ=20-30°) and for a rather smooth surface (rms height ⩽2.1 mm) View full abstract»

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  • Dispersion analysis of crack-waves in an artificial subsurface fracture using two crack models

    Page(s): 3 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    The authors investigated crack-wave dispersions in an artificial subsurface fracture both experimentally and numerically using a wavelet analysis and two crack models. Crack-waves are seismic modes that propagate along a fracture. The dispersion characteristics of crack-waves depend on the geometry and physical properties of a fracture. The authors measured crack-waves at an artificial subsurface fracture in Higashi-Hachimantai Hot Dry Rock model field, Japan. This subsurface fracture is at a depth of about 370 m. During a measurement, they injected water into the fracture and changed the interface conditions of the fracture. A wavelet analysis provided the dispersion of the arrival times of crack-waves. The crack-waves showed positive velocity dispersion; i.e., low frequency components arrived later. As wellhead pressure increased due to water injection, the dispersion characteristics changed. A low-velocity-layer (LVL) model and a crack-stiffness model were examined to explain crack-wave dispersion. In the LVL model, rock layers with a low velocity surround a fluid layer. There is no contact between the LVLs. On the other hand, the crack-stiffness model considers crack stiffness due to contact between asperities on fracture surfaces. The arrival-time curves calculated by the crack-stiffness model showed a good fit to the measured values. As wellhead pressure increased, crack stiffness decreased and thickness of a fluid layer increased. In contrast, the LVL model did not adequately duplicate the measured data View full abstract»

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  • Improved resolution backscatter measurements with the SeaWinds pencil-beam scatterometer

    Page(s): 89 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The SeaWinds scatterometer was launched on the NASA QuikSCAT spacecraft in June 1999 and is planned for the Japanese ADEOS-II mission in 2000. In addition to generating a global Ku-band backscatter data set useful for a variety of climate studies, these flights will provide ocean-surface wind estimates for use in operational weather forecasting. SeaWinds employs a compact “pencil-beam” design rather than the “fan-beam” approach previously used with SASS on Seasat, NSCAT on ADEOS-I, and the AMI scatterometer on ERS-1, 2. As originally envisioned and reported, the resolution of the SeaWinds backscatter measurements were to be antenna-beamwidth limited. In order to satisfy an emerging demand for higher resolution backscatter data, however, the SeaWinds signal-processing design has been significantly modified. Here, the various options considered for improving the resolution of the SeaWinds measurements are discussed, and the selected hardware modification (the addition of deramp processing for range discrimination) is described. The radar equation specific to a rotating pencil-beam scatterometer with digital range filtering is developed, and the new challenges associated with calibrating the resulting improved resolution measurements are discussed. A formulation for assessing the variance of the measurements due to fading and thermal noise is presented. Finally, the utility of improved resolution SeaWinds measurements for land and ice studies is demonstrated by simulated enhanced-resolution imaging of a synthetic Earth backscatter scene View full abstract»

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  • Metamorphic signature of snow revealed in SSM/I measurements

    Page(s): 53 - 63
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    Brightness temperatures (19, 22, 37, 85 GHz) measured by the special sensor microwave/imager (SSM/I) are analyzed using data from the snow monitoring network within the former Soviet Union during the 1987-1988 winter period. It is shown that in the beginning of winter, the SSM/I measurements display the classical snow scattering signature, i.e., the brightness temperatures decrease with increasing depth, and the largest decrease occurs at the highest frequency. Dramatic deviations from this pattern are observed in the middle of winter, where the brightness temperature approaches a minimum and then begins to increase despite the fact that the snow depth remains constant or continues to grow. The two-stream radiative transfer model is combined with results from dense media theory to help explain the phenomenon. Model results suggest that the increase in brightness temperature is due to a decrease of the single scattering albedo as the snowpack ages. This decrease of the albedo is related to changes in the snow crystalline structure due to metamorphism. Consequences for the interpretation of satellite measurements and development of algorithms for deriving snow water equivalent are discussed View full abstract»

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  • Area-based results for mine detection

    Page(s): 12 - 24
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    The cost and the closely related length of time spent in searching for mines or unexploded ordnance (UXO) may well be largely determined by the number of false alarms. False alarms can result in time consuming digging of soil or in additional multisensory tests in the minefield. The authors consider two area-based methods for reducing false alarms. These are: (a) the previously known “declaration” technique and (b) the new δ technique, which they introduce. They first derive expressions and lower bounds for false-alarm probabilities as a function of declaration area and discuss their impact on receiver operation characteristic (ROC) curves. Second, they exploit characteristics of the statistical distribution of sensory energy in the immediate neighborhood of targets and of false alarms from available calibrated data, to propose the δ technique, which significantly improves discrimination between targets and false alarms. The results are abundantly illustrated with statistical data and ROC curves using electromagnetic-induction sensor data made available through DARPA from measurements at various calibrated sites View full abstract»

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  • Precipitation detection by the TOPEX/Poseidon dual frequency radar altimeter, TOPEX microwave radiometer, Special Sensor Microwave/Imager and climatological shipboard reports

    Page(s): 205 - 213
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    The athors evaluate the ability of a dual-frequency radar (C and Ku band) altimeter to detect rain events. A TOPEX/Poseidon (T/P) altimeter rain flag for the year 1994 is compared to collocated rain rate (RR) from the Defense Meteorological Satellite Program's Special Sensor Microwave Imager (DMSP SSM/I), as processed to the TOPEX/Poseidon passive radiometer's (TMR) liquid-water content, and to a 34-year climatology of shipboard present-weather reports compiled by G. W. Petty (1995). The altimeter-SSM/I analysis is couched in terms of the tradeoff between the probability of a false positive and the probability of a failure to detect rain. The authors show that the ability of the SSM/I and TMR datasets to detect precipitation are closer to each other than to either the altimeter or the shipboard climatology, and this difference is accentuated at latitudes poleward of 45°. They argue that the different footprint sizes explain only part of this discrepancy. They propose that the difference at high latitudes is caused by the altimeter data's sensitivity to snow. In order to detect precipitation (as opposed to detecting bad altimetric values or out-of-range altimetric corrections), a TMR-only flag with liquid-water content of 600 μm recovers too few rain events, 400 μm is close to climatological moderate-to heavy intensity rains, and 200 μm is close to rain of any intensity. For the same purpose, a combined altimeter and TMR flag, with a TMR threshold of 100 μm and with the Ku radar cross section 1.5 standard deviations below an average Ku/C curve, gives the best match for climatological precipitation of any intensity class View full abstract»

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  • A fuzzy-possibilistic scheme of study for objects with indeterminate boundaries: application to French Polynesian reefscapes

    Page(s): 257 - 270
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    This communication describes the study of an ecological system using remote-sensing data and image-analysis tools derived from possibility theory. Possibility theory enables the construction of membership functions using a multisource fusion algorithm. The sources of information are the sampled training stations. The authors test to see if the possibilistic algorithm is able to provide results with an accuracy at least equal to that provided by traditional probabilistic-classification algorithms. Then, for each pixel, they analyze the hierarchy of membership degrees output by the fusion to study the spatial structure of an ecosystem composed of objects that lack precise boundaries. They characterize patches or gradients, boundary rates, and transition states. As an example, a scheme of analysis for underwater reefscapes at Moorea Island, French Polynesia, is proposed. The nonparametric multisource fusion method has an accuracy of 82% (overall normalized-percentage agreement), while a probabilistic maximum-likelihood classifier has an accuracy of 73%. The analysis of the hierarchy of membership degrees indicates that almost 25% of Moorea Island lagoon is heterogeneous, composed of real boundaries, transition states, and fragmented zones View full abstract»

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  • Infrared tomographic system for monitoring the two-dimensional distribution of atmospheric pollution over limited areas

    Page(s): 155 - 168
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    In this paper, we analyze the feasibility and performance of a particular tomographic system for atmospheric pollution monitoring over limited areas (e.g., urban areas). Such a system exploits attenuation-based infrared measurements of the average concentration of the fundamental molecular species of pollutants along rectilinear paths. First, the paper demonstrates the feasibility of an apparatus based on semiconductor infrared laser diode transmitters and passive retroreflectors, capable of measuring the average concentration of pollutants along rectilinear paths with 2-km maximum length, by exploiting their infrared absorption properties. For each gaseous species of interest, the optimal wavelength is then singled out, with the purpose of applying the derivative method for measuring the corresponding average atmospheric concentration. The optimal wavelengths are determined based on both absorption data of atmospheric components and plausible ranges of variation of their concentration. Finally, we present simulations carried out to evaluate the reconstruction of spatial-concentration fields of several air pollutants obtained through a tomographic-inversion algorithm exploiting simultaneous attenuation measurements made along different infrared links. Two different network topologies for such measurements are considered 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.

 

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Meet Our Editors

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