摘要:

In agriculture, soil moisture gradients near the surface are important. The objective of this study was to determine their impact on the estimation of the radar backscatter when using surface diffusion models. Two surface radar backscatter models were evaluated in a bare soil with soil moisture stratification induced by irrigation and evaporation. The models were the semi-empirical model (OM) and the Integral Equation Model (IEM). These models were coupled with a penetration depth model. Three approaches were used to calculate the reflectivity at the air-soil interface required by the models. The first one was based on the incoherent reflectivity contribution of each stratum. The second approach calculated the Fresnel reflectivity based on the mean complex dielectric constant over a fixed depth, and the third one computed the Fresnel reflectivity using the mean complex dielectric over the penetration depth of the incident signal. The estimations from the OM model were highly correlated with the observations for all combinations of incidence angles, frequencies and polarizations. However, the backscatter was systematically underestimated and bias increased with wavelength. The IEM provided the most accurate estimate but was sensitive to radar configuration and roughness. The two Fresnel reflectivity based approach tended to overestimate the backscatter in the drying sequence after intensive irrigation following field work. The incoherent reflectivity on the other end underestimated the backscatter in freshly dry disturbed soil. The sampling depth had to be chosen carefully when estimating the backscatter from the second approach, especially in Ku and L-bands. Resume. Les gradients hydriques pres de la surface jouent un role important en agriculture. L'objectif de cette etude etait de determiner leur impact sur l'estimation du signal radar par un modele de diffusion de surface. Deux modeles furent evalues dans un sol nu ou une stratification hydrique avait ete induite par irrigation et evaporation. Il s'agissait du modele semi-empirique (OM) et du modele de l'equation integrale (IEM). Ces modeles furent couples a un modele de penetration du signal. Trois approches furent retenus pour le calcul de la reflectivite a la surface requise par les modeles. La premiere etait basee sur la reflectivite incoherente qui tient compte de la contribution de chaque strate de sol. La second calculait la reflectivite de Fresnel a l'interface air-sol en utilisant la constante dielectrique complexe moyenne sur une profondeur de penetration fixe; la troisieme calculait la reflectivite de Fresnel a partir de la constante dielectrique moyenne sur la profondeur de penetration du signal. Les estimes du modele OM etaient fortement correles aux observations pour toutes les combinaisons d'angles d'incidence, de frequences et de polarizations etudiees. Cependant, les coefficients de retrodiffusion furent systematiquement sous-estimes et l'ecart augmenta avec la longueur d'onde. L'IEM fournit des resultats precis mais s'est revele sensible a la configuration du radar et a la rugosite. Les deux approches basees sur la reflectivite de Fresnel ont surestime le signal retrodiffuse dans la phase de dessechement qui a suivi une forte irrigation effectuee apres le travail du sol. L'approche basee sur la reflectivite incoherente a par contre sous-estime le signal retrodiffuse dans les sols secs fraichement laboures. La profondeur d'echantillonnage devrait etre choisi esoigneusement quand le coefficient de retrodiffusion est estime par la seconde approche, particulierement en bande Ku et L.

ISSN:0143-1161    

DOI:10.1080/014311697219330

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The zone of Tampico-Altamira to the north-east of Mexico has undergone considerable industrial development in the last 10 years. A great number of industries discharge their waste into the Panuco River and the sea, contaminating and altering the ecological balance of the area. Employing digital image analysis techniques and field data, two dates of thematic images in which changes in the spatial distribution of suspended solids from industrial discharges, were prepared. From the statistical properties of the defined classes, the best principal components were selected and were used as input to an Isodata clustering algorithm. Such components were derived from the band groups of the visible and the infrared. The images employed are from Landsat-5 (TM): of October 1990, and October 1992. The resulting classification was edited in such a way as to include the original image in the part corresponding to the mainland, and keeping the segmentation in sediment levels only in the coastal and lacunar zone. The images were georeferenced in UTM coordinates. The results show a complex system of hydrodynamic interaction between the Panuco River, the sea and the coastal lagoons.

ISSN:0143-1161    

DOI:10.1080/014311697219349

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This study focuses on a multitemporal spectral analysis of morphologic features of the Venice Lagoon. Principal Component Analysis, applied in a multidate merged rotation to standardized visible and infrared Landsat Thematic Mapper spectral bands, has allowed discrimination of differences in spatial distribution and spectral characteristics of the observed features. A comparative analysis has been carried out on the derived PC based on visual and statistical interpretation. Near- and medium-infrared bands are revealed to be suitable to return significant information in a very shallow water environment and under particular weather conditions. A map of part of the Northern Lagoon has been produced out of the first Principal Component of multitemporal TM4s.

ISSN:0143-1161    

DOI:10.1080/014311697219358

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Causes of geometric distortion in space shuttle imagery of targets on the Earth's surface are analysed. A mathematical model formulating the geometric distortion caused by the incidence angle and the local azimuth angle are derived, and the corresponding image processing scheme for orthorectification is developed. The method is used for rectifying two sequential space shuttle photographs of continental shelf waters off the coast of south-west Africa taken by the space shuttle Atlantis during mission STS-36 in March 1990. The results indicate that mismatches between coastline images in unrectified photographs and a standard map have been almost eliminated in the rectified photographs, and the two photographs also match each other very well. Application of the spatial Fourier transform to oceanic internal wave packet signals at a selected test site yields directional wavenumber spectra, from which components of the wave field, the dominant wavelength, and propagation directions are determined. Comparisons between wavelengths and propagation directions derived from the spectra of the same site on the rectified and unrectified photographs show that the average rectification ratio for wavelengths reaches 20 per cent, and for propagation directions 10 per cent, including a 20 per cent rectification ratio for the crossing angle of the internal waves.

ISSN:0143-1161    

DOI:10.1080/014311697219367

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The wavelet transform allows multi-resolution decomposition, analysis and reconstruction of remotely sensed images. This study attempts to demonstrate its ability for local or scale-dependent image enhancement using an ERS-1 SAR image. The performance of the proposed wavelet transform enhancement has been assessed with reference to the Fourier domain enhancement.

ISSN:0143-1161    

DOI:10.1080/014311697219376

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We present an analysis of ring-wave and scatterometer data from a water surface that was agitated by simulated rain. Water droplets of 2.8mm diameter impacted the water surface at almost terminal velocity, and the rain rates cover a wide range of conditions (5 to 200mm hr−1). Both the ring-wave energy and backscattered power from the GHz scatterometer increase asRincreases, but the growth rates slacken at higher rain intensities. Ring-wave frequency spectra and wavenumber spectra are well represented by log-Gaussian spectral models. The results can be used to guide development of microwave scattering models.

ISSN:0143-1161    

DOI:10.1080/014311697219385

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this Letter the results of applicability of Kirchhoff 's law as given by Salisbury and coworkers are discussed. In their paper, experimental evidence on the violation of Kirchhoff 's law for heterogeneous temperature regimes was given. In this Letter the hypothesis of the existence of a single 'sample temperature' resulting in measured emissivities which were less than the true values was demonstrated. Thus, the 'evidence' given by Salisbury and coworkers needs reviewing.

ISSN:0143-1161    

DOI:10.1080/014311697219394

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor