摘要:

A time series of 15 Thematic Mapper images was used to analyse the seasonal dynamics of soil spectral signatures in a fluvial corridor. A normalization method based on pseudo-invariant objects was used to compare data. The objective was to identify stable spectral patterns in order to characterize the spectral structure of the landscape. Results revealed that the existing geomorphic units could not be differentiated efficiently by spectral data. Strong spectral confusions persisted through time between most categories. However, several spectral patterns that remained stable through time were observed in the images. Ground investigations revealed that these patterns were characterized by the dominance of one or two soils elements (clay, silt or sand). They helped in the definition of a new typology of the fluvial landscape. A multidate composite image was created from several single images in order to concentrate the information on bare soils (more than 75 per cent of the area was covered). The classification of this image provided a good evaluation of the underlying soil spectral structure of the landscape usually masked by the vegetation cover.

ISSN:0143-1161    

DOI:10.1080/01431169408954214

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The salt affected soils of Etah, Aligarh, Mainpuri and Mathura districts have been mapped into S1: < 10 per cent of the area covered by salts, S2: 10–30 per cent, S3: 30–50 per cent, S4: 50–75 per cent and S5: > 75 per cent using an integrated approach of image interpretation. The dull white tone of salt affected and sandy soils have posed problems in their discrimination, onTMfalse colour composite, however, the problem of spectral similarity was solved through integration of interpretation of thermal data (10.4–12.5μm) withTM FCC(bands 2, 3, 4) interpretation. The discrimination of salt affected soils was significantly better on data between March and first week of April because of maximum contrast. Out of l-75m ha of the total geographical area, the salt affected soils account for 11–8 per cent. Another 16–2 per cent is likely to be affected with this problem if similar degraded conditions prevail there. The values of pH: 8–7 and ECe: 1–3 dsm-1of S1 soils group them into non saline and mildly alkali class. Similarly low ECe: 4–4dSm-1and high pH: 9–8 for S3 soils and high ECe: 24–0 dsm-1and very high pH: 10–7 of S4/S5 soils, placed the soils into alkali and sodic classes respectively. The gypsum requirement based on pH values varies from 1 to 15 tha-1.

ISSN:0143-1161    

DOI:10.1080/01431169408954215

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this paper we have analysed the effects of the different atmospheric species (water vapour, fixed gases and aerosols) and the surface emissivity on the split-window method for determining the sea surface temperature. The widely used split-window method is based on the differential absorption of water vapour in the atmospheric window 10.5ndash;12.5 μm. Other atmospheric species with absorption coefficients different to that of water vapour can then have a large influence on the split-window. The effect of gases, such as C02, N20, CH4, CO and 03, and maritime aerosols is evaluated by comparing the effect of the water vapour alone. To do this we simulated AVHRR measurements in channels 4 and 5 for a set of mid-latitude atmospheres using LOWTRAN 7 code. Our results indicated that the fixed gases have a negative effect on the split-window specially for dry atmospheres; in this case the error in retrieved temperatures was shown to increase by about 70 per cent with respect to that obtained considering water vapour only. The effect of maritime aerosols was parameterised in terms of the surface meteorological range and the path optical thickness was measured at 0.55 μm, which can be obtained from both visible channels of AVHRR. The total effect on the split-window appeared to be a linear function of the path optical thickness. On the other hand, we analysed the impact of sea surface emissivity showing that it is strongly dependent on the observation angle, especially for angles larger than 40°. In addition to this it has been shown that the emissivity effect depends on the atmospheric moisture. However, for angles lower than 40° the atmospherically averaged emissivity effect is close to zero. Finally we have given a correction algorithm accounting for all the studied effects, yielding an error estimated at 0–34 degK. over the simulated mid-latitude data set.

ISSN:0143-1161    

DOI:10.1080/01431169408954216

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the framework of the European Arctic Stratospheric Ozone Experiment (1991–1992) a scries of balloon ascents for ozone and temperature in situ measurements up to 35 km height have been performed at Athens, Greece (38° N, 24° E). This is the first time that such an intensive sounding campaign has been performed in Athens. The data collected for the vertical distribution of ozone and temperature have been compared with the satellite-derived reference models which provide the monthly latitudinal variations of vertical structure of both ozone and temperature. The comparison shows that at the middle stratosphere there is very good agreement between the Satellite Reference Model and the in situ ozone measurements. There is also very good agreement between the Satellite Reference Model and the in situ temperature measurements, thus confirming the recently published findings by Varotsos and Helmis.

ISSN:0143-1161    

DOI:10.1080/01431169408954217

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this work, the evaluation of the unsupervised classification by the matrix with the measures of similarity is being presented. This matrix has been created with the classified images of the same Landsat MSS image but classified with different unsupervised classifiers. Three classification measures of similarity and two clustering methods for each similarity measure were used. For the evaluation of these classifiers a matrix with the measures of similarity has been estimated, which gives the pairwise relations between image clusters, after classification. The results indicated that the optimum classifier for the sample area was the one that used the measure of similarity, that is the Euclidian distance.

ISSN:0143-1161    

DOI:10.1080/01431169408954218

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431169408954220

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor