ISSN:0143-1161    

DOI:10.1080/01431169508954470

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Low resolution polarimetric data gathered by the AirSAR system over the Feltwell U.K. agriculturaltestsite reveals Gaussian behaviour at C band for all vegetation types, but clear evidence of texture at longer wavelengths. The measurements are compared with the predictions of a polarimetric texture model based on a multivariate K distribution (which includes the Gaussian distribution as a special case), from which distributions of the inphase component, amplitude, amplitude ratio, phase difference and real hermitian product between channels are derived. Kolmogorov-Smirnov fits to these marginal distributions verify that C, Land P band observations over a range of vegetation types are consistent with the model, but there is evidence of the model breaking down in cereal fields at P band. The departure from Gaussian behaviour with increasing wavelength is strongest for cereals; less marked trends are observed for root vegetables, while forest appears Gaussian at all wavelengths. These results are unexpected, since texture is normally associated with high resolution, particularly in woodland. Moment based measures are investigated as indicators of distribution and as discriminators of vegetation type. The order parameter of the K distribution appears useful in both respects. These results help to clarify the information content of polarimetric data, but raise questions about how best to use the data (e.g., for classification), and are hard to reconcile with simple physical models.

ISSN:0143-1161    

DOI:10.1080/01431169508954471

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

During September 1991, April 1992 and June/July 1993, a NASA P–3 aircraft, equipped with a scanning laser altimeter, flew numerous transects of the Greenland ice sheet. The aeroplane location was measured precisely using dilTerential Global Positioning System (GPS) surveying techniques, allowing all altimetry data to be converted into measurements of ice-surface elevation relative to the Earth ellipsoid. Results from flight data indicate that icc-surface elevations can be reliably measured to an accuracy of ∼20cm (and possibly to ∼s lOcm) over baselines of more than seven hundred kilometres.

ISSN:0143-1161    

DOI:10.1080/01431169508954472

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Passive microwave satellite data provide extremely important information about the climate and surface conditions in the often cloudy high latitude regions of the Earth. Available since 1978, multichannel passive microwave data have great potential for long term climate monitoring. In order to ensure consistent data sets for such long term monitoring, the relations between the microwave brightness temperatures from similar sensors on successive satellite platforms must be understood. In this study the 19,22. and 37GHz channels of the Defense Meteorological Satellite Program (DMSP) F8 and F11 Special Sensor Microwave Imager (SSMI) instruments are compared. While the analysis shows that the two data sets are highly correlated with correlation coefficients greater than 0·98. the consistency between the two data sets can be improved by applying small corrections in the order of I deg K. Two sets of regression coefficients are provided for adjusting the F11 data to the F8 baseline.

ISSN:0143-1161    

DOI:10.1080/01431169508954473

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In accordance with the distorted Born approximation, a wave approach is developed for the volume attenuation and backscattering coefficients associated with the foliage layer in forests at L- and P-bands. Since the foliage layer is not the dominant layer in forest modelling at longer wavelengths, the orientations of scatterers are assumed to be uniformly distributed. As a result, the ensemble average electric polarizability of scatterers becomes isotropic, generating both volume attenuation and backscattering independent of polarization. It is shown that multiple scattering efTects due to both near and far scatterers are insignificant. It is demonstrated that the total leaf biomass, the mean leaf volume, leaf shape and the dielectric constant are key parameters for the model.

ISSN:0143-1161    

DOI:10.1080/01431169508954474

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Synthetic aperture radar (SAR) images of the ocean surface can show evidence of the sheltering elTects of barriers, such as islands, on the incoming long ocean waves. In the presence of high background noise in SAR images, these elTects arc not always observed by visual inspection. As shown in this paper, they can be determined most effectively in the spectral domain. From the ERS–1 SAR data of 17 October 1991, we noticed that two separate swell components almost perpendicular to each other were incident on the Semidi Islands in the Gulf of Alaska. By spectral analysis, the shadow zone associated with each wave component can be identified. The distribution of an equivalent dilTraetion coefficient has been estimated at the Ice of the Chowiet Island which has a sharp tip. It has been compared to that obtained from the Sommerfeld solution of dilTraction for a semi-infinite barrier. The SAR data shows a similar dilTraction pattern to the model solution but has a slower fall-off into the geometric shadow zone.

ISSN:0143-1161    

DOI:10.1080/01431169508954475

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This study assessed the ability of Landsat Thematic Mapper (TM) sensor data to discriminate among three damage categories of Norway spruce in the Krusne Hory mountains using dichotomous logit regressions. Moderate and light damage stands, being the most spectrally similar, were separated with 83 per cent accuracy using TM1, TM4 and TM7. Moderate and heavy categories were best separated by TM3 (accuracy=88 per cent). Light and heavy damage classes were separated with up to 95 per cent accuracy. Ratios and indices did not improve the regression accuracies. The regression equations, when used to classify three categories of damage, accurately classified 71–75 per cent of Norway spruce stands.

ISSN:0143-1161    

DOI:10.1080/01431169508954476

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

NOAA-AVHRR data are examined for their potential application in assessing primary productivity in the arid rangelands of Central Australia. Field measurements of herbage biomass are correlated with four indices derived from NOAA-II Normalized Difference Vegetation Index (NDVI) data. Pre-flight and sensor degradation calibrations of bands 1 and 2 and atmospheric correction techniques are also tested.Regional herbage production can be readily estimated using backgroundadjusted maximum NDVI values for a growth season, with NDVI data derived from sensor degradation calibrations of bands 1 and 2 and corrected for atmospheric effects by band 4– band 5 temperature differences (T4– T5,). Correlations between temporal sums of NDVI and herbage biomass data are relatively poor and unsuitable for herbage assessment in Central Australia.

ISSN:0143-1161    

DOI:10.1080/01431169508954477

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Crop Normalized Difference Vegetation Index (NDVI) time profiles and crop acreage estimates were derived from the application of linear mixture modelling to Advanced Very High Resolution Radiometer (AVHRR) data over a test area in the southern part of the Pampa region, Argentina. Bands 1 and 2 from seven AVHRR scenes (June to January 1991) were combined to produce fraction images of winter crops, summer crops and pastures.A Landsat Thematic Mapper (TM) scene of the region was classified and superimposed to the AVHRR Local Area Coverage (LAC) data by means of a correlation technique. Each class signature was extracted by regressing the AVHRR response on the cover types proportions, estimated from Landsat-TM data, over sets of calibration windows. The crop NDVI profiles were hence derived from the class signatures in bands 1 and 2. These profiles appeared consistent with the cover types, but variability depending on the set of windows was noted.The assessment of the class signatures was indirectly accomplished through the subpixel classifications of the AVHRR data, performed using the different sets of class spectra.Although some discrepancies between AVHRR and Landsat–TM estimates were observed at the individual window level, the classification results compared quite well on a regional scale with Landsat–TM estimates: crop acreage was estimated to an overall accuracy ranging from 89 to 95 per cent according to the spectra used in the classification. Definitely, the proposed methodology should permit a better exploitation of the temporal resolution of AVHRR data in both the areas of yield prediction and vegetation classification. Furthermore, the perational application of such a methodology for crop monitoring will undoubtedlybe facilitated with the coming sensor systems such as the ModerateResolution Imaging Spectroradiometer (MODIS), the SPOT Vegetation Monitoring Instrument or the ‘Satelite Argentino Cientifico’ (SAC–C).

ISSN:0143-1161    

DOI:10.1080/01431169508954478

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Data from the Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA–10 satellite was collected over Indiana for the 1987 and 1988 growing seasons. A Normalized Difference (NDVI) transformation was applied to the data. Over 45 fields representing 8 soil associations were sampled to assess the effects of the 1988 drought on the development of natural and cultivated vegetation. The results show the effect of the lack of available moisture to the plants and its effect on the response measured by the AVHRR sensor.

ISSN:0143-1161    

DOI:10.1080/01431169508954479

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor