ISSN:0143-1161    

DOI:10.1080/014311697216766

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In strong sunglint areas the brightness temperatures in channel 3 (3.7 mu m) and channel 4 (11 mu m) of the Advanced Very High Resolution Radiometer (AVHRR) have been found to differ by more than 27 degK. In the worst case, where there is a large amount of water vapour, as in the tropics, the difference in atmospheric effects in these two channels is only about 3 degK. Therefore, most of the observed temperature difference must be due to specular reflection of the solar radiation. Although detection of intense sunglint has been reported by others their analysis was in terms of digital numbers which cannot reveal if the detector is saturated. Using brightness temperatures rather than digital numbers, it is shown that the magnitude of sunglint contribution cannot be fully quantified because the 3.7 mu m sensor is saturated. There are two independent lines of evidence which show the saturation of the detector: ( i ) In the absence of sunglint there is a periodic noise in channel 3 of the NOAA-7 AVHRR which disappears in the strong sunglint zone and, ( ii ) the sunglint contributions in channel 1 (0.63 mu m) and channel 2 (0.93 mu m) of the AVHRR change in those areas where the sunglint in the 3.7 mu m channel remains constant. The observed saturation temperature is about 319 degK, whereas that calculated from the inflight calibration parameters is about 323degK. Assuming that the inflight calibration information is reliable, this discrepancy in the saturation temperature is explained by proving that the full quantization range of 0 to 1023 is not utilized. Therefore, saturation of the detector cannot be ascertained from the values of digital numbers.

ISSN:0143-1161    

DOI:10.1080/014311697216775

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We present the results of a field experiment in which the nearly complete bidirectional reflectance distribution function of Alaskan arctic tundra sites early in the growing season is measured by the PARABOLA instrument. The spectral hemispheric reflectances were computed by angular integration of these measurements for three wavebands: red (650-670nm), near-infrared (810-840nm) and shortwave infrared (1620-1690 nm). Total albedo was then estimated by weighting the spectral hemispheric reflectances by the fraction of total solar irradiance in three broadband spectral regions (300-700, 700-1300 and 1300-4000nm) and representing each spectral region by the narrowband PARABOLA measurements. These calculations resulted in albedo estimates with a mean relative error of 15.7 per cent as compared to pyranometer measured albedo. Since vegetation reflectance varies significantly over each of the three broadband regions, additional reflectance weighting factors were computed from a combination of high spectral resolution canopy reflectance data and corresponding computed spectral solar irradiance. This additional reflectance weighting resulted in a reduction in the mean relative error to 7.5 per cent relative to pyranometer measured albedo. It is noted that the three spectral bands of the PARABOLA instrument data reported here are similar to those of the spectral wavebands planned for future Advanced Very High Resolution Radiometer (AVHRR) sensors on National Oceanic and Atmospheric Administration (NOAA) satellites. Therefore the results and techniques presented here may be useful for future global albedo estimation utilizing AVHRR sensors. The analysis presented here may also be applied to albedo estimation from satellite sensors with higher spectral resolution and more complete spectral coverage, such as the future orbiting MODIS sensor, in which the errors of spectral reflectance weighting will be reduced considerably due to a more complete sampling of the reflected spectrum.

ISSN:0143-1161    

DOI:10.1080/014311697216784

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Land cover changes are measured at increasingly broader spatial scales. Yet understanding and modelling change processes with a satisfactory accuracy require fine scale observations. The objective of this study is to design and test a methodology to detect tropical deforestation 'hot spots' at broad spatial scales. This methodology is designed to allow concentration of the data collection and modelling of change processes only on the areas characterized by a high rate of change. The procedure is based on a hierarchical set of decision rules with selection criteria being first measured on an exhaustive basis at a global scale and then only for the areas retained in the first sorting, with increasingly selective constraints. The first set of criteria, i.e., proportions in key land cover, landscape fragmentation, and fire activities, were derived from subcontinental scale remote sensing data. Socio-economic variables were also measured at that scale. These different variables were combined over West Africa and the northern boundary of the Central African evergreen forest to identify potential tropical deforestation fronts. Different models were used to generate maps of deforestation hot spots. These were validated with data from the literature.

ISSN:0143-1161    

DOI:10.1080/014311697216793

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Land Cover Map of Great Britain consists of a mosaic of 30 classified map sections derived from 46 Landsat Thematic Mapper images captured between 1987 to 1990 (Fuller et al. 1994a). Some 88 per cent of Britain was mapped from combined summer (mid-May to late July) and winter (mid-October to mid-March) images. Persistent local cloud cover meant that 11 per cent of Britain was mapped using only single season imagery, and 1 per cent was not mapped. The target summer and winter periods had to be extended up to six weeks outside the ideal range for 32 per cent of Britain (Fuller et al. 1994b). Use of suboptimal imagery causes inconsistencies and inaccuracies between classifications. When data is summarized onto a coarser grid differences between sections can sometimes become intrusive where they join. For many users it is important to estimate any known bias and, as far as possible, compensate for it in summary statistics. For such users removing the ostensibly discontinuous image boundaries may produce summary maps with improved appearance and allow better integration with other data sets when trying to produce correlative statistics. We present a method which can be used to removed local bias in summary data due to known misclassifications in the original data.

ISSN:0143-1161    

DOI:10.1080/014311697216801

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In the framework of an investigation about frost damage that occurred 1987 in Northern Greece a new index, the modified NDVI (mNDVI), was developed. Within a joint bilateral German-Greek-Cooperation project the Greek partner investigated SPOT images and the German partner mainly evaluated Landsat TM images to estimate frost damages in agriculture with a remote sensing approach. The first applications of the new mNDVI are described in this paper and show very promising results.

ISSN:0143-1161    

DOI:10.1080/014311697216810

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Miocene crustal extension in the south-western United States was accompanied by potassium metasomatism, a type of alteration marked by addition of large amounts of potassium at the expense of other constituents, notably sodium. The fluids responsible for the potassic alteration may have played a role in triggering extensional fault motion; one way to determine this is to compare the geographic distribution of the alteration to fault and sedimentary facies maps. Despite the large impact on rock composition, however, the alteration is visually subtle and difficult to map in the field. In this paper we present a preliminary alteration map of the Lemitar Mountains near Socorro, New Mexico, within the Rio Grande rift. This map was created from Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data. The potential to discriminate potassium metasomatism in Landsat Thematic Mapper satellite data is part of the motivation for this study, since such data are widely available. Although the potassic minerals do not exhibit spectral features in the visible and near-infrared, iron was mobilized during potassium metasomatism, and the distribution of haematite thus serves as a proxy for the potassium. Evidence supporting the proxy relationship between haematite and metasomatism include (a) published reports by previous workers stating that haematite is added to rocks during K-metasomatism; (b) limited chemical evidence that samples collected from areas displaying a distinctive spectral response are strongly metasomatized; (c) the presence of large amounts of haematite in metasomatized rocks, observed petrographically and with an EDAX microprobe; and (d) the coincidence of the southern edge of the K-anomaly in the Lemitar Mountains as defined by chemical analysis and the southernmost occurrence of the anomalous spectral response. No other significant source of haematite has been reported from this area. Manganese oxide, occurring as localized veins or as rock varnish, is black in colour and highly absorptive, resulting in a distinctly different spectral response than the metasomatism-related haematite. This work shows that K-metasomatism can be mapped using AVIRIS data. The spectral response is not subtle, and can be observed in Landsat Thematic Mapper data; it is likely that K-metasomatism can be mapped, at least to some significant degree, from the Landsat data. Ongoing work is focusing on calibrating the strength of the spectral response to the intensity of alteration.

ISSN:0143-1161    

DOI:10.1080/014311697216829

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

NOAA AVHRR images taken in 1994 have been used as a primary reference in the regional selection of areas suitable for aquaculture activities in Baie des Chaleurs (eastern Canada). The sea surface temperature extracted from these images has allowed both a qualitative and quantitative analysis of thermal events that occurred during the period of observations. Other in situ measurements, such as salinity, current speed and chlorophyll pigments have been analysed in such a manner as to identify the space-time variability of surface water characteristics. This information has been analysed within Idrisi . The different layers enabled a preliminary regional aquaculture suitability index map of Baie des Chaleurs to be produced. According to this index (defined between 0 and 1), a zone of an aquaculture potential situated between an index of 0.5 to 0.75 was delineated over a regional surface area of about 300 km2. This location was foreseeable since it shows high chlorophyll pigment concentrations, providing good enviromental conditions for high biological productivity. Resume. L'utilisation des images de texture dans l'analyse numerique de donnees de teledetection necessite une caracterisation quantitative de cette texture. Diverses methodes sont utilisees, certaines caracterisent la distribution spatiale des niveaux de gris qui est alors utilisee comme outil de segmentation d'une image en parametres de texture, d'autres approches d'analyse de texture sont basees sur l'extraction des parametres structuraux des images satellitaires. Nous proposons dans cet article une approche structurale d'analyse de texture permettant la generation d'images derivees caracterisant les differents aspects d'organisation spatiale des images de teledetection. Cette approche est basee sur le concept d'unite de texture. Elle permet le calcul d'un nouveau spectre de texture multiniveaux sur une fenetre de l'image et enfin la generation des images derivees des statistiques de ce spectre. Les images generees decrivent les caracteristiques de symetrie, d'orientation absolue et relative de la texture. La methode developpee a ete testee sur des images de Landsat TM sur une region du Sud algerien. L'evaluation des resultats a ete faite par rapport aux donnees cartographiques, cartes et photographies aeriennes.

ISSN:0143-1161    

DOI:10.1080/014311697216838

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Three different 'soft' classifiers (fuzzy c-means classifier, linear mixture model, and probability values from a maximum likelihood classification) were used for unmixing of coarse pixel signatures to identify four land cover classes (i.e., supervised classifications). The coarse images were generated from a 30m Thematic Mapper (TM) image; one set by mean filtering, and another using an asymmetric filter kernel to simulate Multi-Spectral Scanner (MSS) sensor sampling. These filters collapsed together windows of up to 11 11 pixels. The fractional maps generated by the three classifiers were compared to truth maps at the corresponding scales, and to the results of a hard maximum likelihood classification. Overall, the fuzzy c-means classifier gave the best predictions of sub-pixel landcover areas, followed by the linear mixture model. The probabilities differed little from the hard classification, suggesting that the clusters should be modelled more loosely. This paper demonstrates successful methods for use and comparison of the classifiers that should ideally be extended to a real dataset.

ISSN:0143-1161    

DOI:10.1080/014311697216847

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Atmospheric water vapour plays a key role in the climatology of the Earth. It has traditionally been measured using radiosondes for reasons of instrumental simplicity but these offer limited opportunities for spatial and continuous measurements of dynamic water vapour changes over large areas of the Earth's atmosphere. Efforts have recently turned to using satellite remote sensing instruments with different spectral and spatial capabilities to derive measurements of total water vapour content in atmospheric columns or simply precipitable water. The merging of remote sensing data with different spectral and spatial capabilities can result in large biases when independent measurements are not nested correctly to produce the final product. Consequently, such merging of data must take into account the intrinsic time dynamics of measured parameters. In this paper, the impact of atmospheric water vapour dynamics on the merging of satellite-based retrieval of precipitable water estimates is investigated by comparing independent measurements obtained at different spatial resolutions from the High Resolution Infrared Sounder (HIRS) and the Advanced Very High Resolution Radiometer (AVHRR). Correlations are used to infer optimal merging parameters depending on the observational conditions. The authors conclude that the merging technique reproduces HIRS-based retrievals in cloud-free and partly cloudy locations from AVHRR soundings.

ISSN:0143-1161    

DOI:10.1080/014311697216856

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor