ISSN:0143-1161    

DOI:10.1080/01431169408954204

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Ground-based measurements on the Pasterze Glacier and the Kleines Fleisskees, located in the eastern Alps of Austria, have shown that these glaciers have receded significantly. Landsat Thematic Mapper (TM) data of these glaciers were acquired in August of 1984,1986,1988 and 1990, and have been studied in detail. The 1984–1990 retreat of the Pasterze Glacier has been measured using digital TM data, but the 1984–1988 retreat of the Kleines Fleisskees has not been observed using the TM data because the magnitude of recession between 1984 and 1988 was small relative to the resolution of the TM data. Significant increases in the area of exposed ice (icc facies) on both the Pasterze Glacier and the Kleines Fleisskees were observed and measured using TM data acquired in early August from 1984 to 1988. The area of the Pasterze Glacier and Kleines Fleisskees basins, as measured using TM data, is 20·8±1·02km2and 1·56±0·188 km2, respectively. The percentage of the Pasterze Glacier comprised of bare ice increased from 23 per cent in August of 1984 to 36 per cent in August of 1988. Data from nearby meteorological stations show no significant new snowfall during the months of July and early August in 1984, 1986 or 1988 prior to the Landsat overpasses, to obliterate the delineation of the ice facies. The Kleines Fleisskees was also measured using the same TM scene. 40 per cent of this glacier consisted of the ice facies in 1984, and 59 per cent in 1988. Field measurements show that both the Pasterze Glacier and the Kleines Fleisskees have been losing mass for more than 100 years.

ISSN:0143-1161    

DOI:10.1080/01431169408954205

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Microwave radiometers have been used with success in the past for the retrieval of ocean surface and atmospheric parameters. However,for the most effective use of the measurements provided by these instruments, it is neeessary that performant inversion algorithms be available. Existing algorithms have already proved their usefulness but are often based on statistical regressions on the measurements from some particular experiment or on artifical data sets. Progress towards better performances still remains possible. We have developed an iterative retrieval procedure based on a physical scattering and propagation model for observing the ocean surface and the intervening atmosphere. A correction for scattering by the roughened sea surface is proposed and introduced in a previouslydeveloped contracted form of the radiative transfer equation. This correction is modelled for a range of frequencies from 5 to 40GHz, and represented in the form of a polynomial expansion depending on two parameters only: the total atmospheric attenuation, and the wind friction velocity. Results of inversions on simulated measurements obtained with this approximate model are presented and discussed.

ISSN:0143-1161    

DOI:10.1080/01431169408954206

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The focused and non-focused image-forming methods for airborne synthetic aperture radar (SAR) are investigated. The more precise receiving signal model which includes not only traditional additive noise but the multiplicative noise which is the consequence of the aircraft's velocity and height fluctuations is developed. Results of numerical calculations of the root-mean-square (rms) errors of the set of principal image parameters as functions of the additive noise variance and multiplicative noise standard deviation for several weighting windows and the histograms of the distributions of some image parameters are presented.

ISSN:0143-1161    

DOI:10.1080/01431169408954207

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Surface elevation of terrain can be estimated from interferometric synthetic aperture radar (INSAR) observations from satellites. In this paper, we compare a satellite SAR estimate of surface elevation with a digital elevation map (DEM) compiled by the USGS from survey data. To compare the elevation obtained from SAR with a DEM, a new registration method is developed to register the SAR images with the DEM. To convert the DEM into the same format as the SAR data, a phase difference image is generated from the DEM according to SAR imaging geometry. The mean squared error between the simulated phase difference and the measured phase difference is minimised using a downhill simplex minimization algorithm. Registration parameters such as orientation, range and azimuth offsets are obtained in the minimization process. Elevation data generated from the Seasat SAR over an area west of Yellowstone National Park are compared with a DEM using the proposed registration algorithm. The root mean squared (rms) error between the computed elevation and the DEM is found to be 6·0 per cent of the total terrain variations in the image. Layover effects and other error sources are also explored in the paper.

ISSN:0143-1161    

DOI:10.1080/01431169408954208

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A novel algorithm is used to estimate the noise level in polarimetric SAR image data channels, by using the measured signature of an idealized surface with Bragg Scattering. This estimated noise level can then be used to correct the measured backscatter signatures from polarimetricSAR image data.

ISSN:0143-1161    

DOI:10.1080/01431169408954209

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The significance of several key multi-frequency, polarimetric back-scatter parameters extracted from calibrated and noise-corrected NASA/JPL DC-8 SAR data are examined. The data were collected during the 1989 MAESTRO-1 campaign over the Flevoland agricultural test site. Calibration uncertainty estimates are used to specify minimum separations between features. Thirteen different backscatter types were identified from the test site data, including eleven different crops, one forest and one water area. Using the parameters with the highest separation for a given class, a hierarchical algorithm was developed to classify the entire image. All three frequencies and all polarizations were used to construct the rules for the classifier. Results indicate that multi-frequency, polarimetric radar backscatter signatures can be useful in classifying several different ground cover types in agricultural areas.

ISSN:0143-1161    

DOI:10.1080/01431169408954210

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Vector radiative transfer theory is used to model the scattered intensity from a layer of randomly oriented particles over a periodic rough surface. To account for the periodic nature of row-structured vegetation, the number density of particles within the layer is assumed to be varying periodically in the horizontal direction. Using Fourier series expansions and orthogonality properties, the radiative transfer equation is solved for the transformation matrix relating the incident and scattered intensities, from which the backscattering coefficient of the layer can be computed for any incidence direction and polarization configuration. The experimental component of this investigation consisted of radar observations at 1–5,4–75, and 9–5 GHz made by a truck-mounted system for a field of corn under three conditions: (a) full, which means that the corn plants were in their natural state, (b) defoliated, which was accomplished by stripping off the leaves and removing them, thereby leaving behind only bare vertical stalks, and (c) bare soil, which corresponds to the soil surface after having removed the stalks. The soil surface is modelled as a composite consisting of a deterministic periodic component and a random roughness component. A two-scale polarimetric scattering model is formulated and used to compare with the experimental observations. Excellent agreement between theory and measurements is realized as a function of both incidence and azimuth angles at all three microwave frequencies. The canopy model was then applied to the corn canopy under the two other conditions: stalks alone and full canopy. The model results were compared with radar backscatter measurements made for each of three look directions, including perpendicular and parallel to the row direction and at 45° relative to the row direction. For the stalk canopy, it was observed that the quasi-periodic arrangement of the stalks within the row enhances the backscatter at L-band when looking perpendicular to the row direction, which is attributed to a coherent-scattering effect associated with the stalks. A heuristic approach is used to model the quasi-periodic structure of the stalks by deriving a coherency factor which multiplies the first-order radiative solution for randomly located stalks. A similar coherency factor was also introduced for the leaves of the full canopy. The modified model was found to provide good agreement with experimental observations at L-band for all polarizations and at all look directions.

ISSN:0143-1161    

DOI:10.1080/01431169408954211

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The present study deals with the mapping of forest basal cover and biomass using IRS data. IRS-LISS-I data were classified into forest types and crown cover categories. A stand biomass was computed for selected sites using density, basal cover data and biomass estimation equations. Allometric relations were developed between crown cover and basal cover and between crown cover and biomass. Using these relations basal cover and biomass were computed for each crown cover class of each forest type. The classes having identical biomass were merged together. Total biomass for each forest type was computed by using mean values and the aerial extent. The average total above-ground biomass density between forest types ranged between 52–36tha-1∥Plantations) and 371–08tha-1(Sal forest). The estimates of the study compared well with the estimates for 19 sites computed through conventional techniques. The method described in the present study is expected to play a significant role in global biomass estimations.

ISSN:0143-1161    

DOI:10.1080/01431169408954212

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The effect of nitrogen fertilization and water stress on the spectral signature of winter wheatTriticum aestivumcv. Astral were measured with a field radiometer over two years. Spectral reflectance of the canopy has been related to the most indicative physiological parameters (nitrogen and photosynthctic pigment content, biomass, leaf area and LAI), but only a few of these parameters can be estimated independently of plant treatment.The normalized difference vegetation index seems the most powerful spectral combination with which to estimate the total area of plant leaves and LAI. The nitrogen content of plants can also be related to a linear combination of green and red canopy reflectances independently of plant treatment. Relations between canopy reflectance and other physiological parameters are not independent of plant treatment.

ISSN:0143-1161    

DOI:10.1080/01431169408954213

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor