ISSN:0143-1161    

DOI:10.1080/01431169308953979

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Most atmospheric parameters relevant to microbe dissemination into the atmosphere, including aerial transport and deposition, can be monitored by temperature and humidity, aerosols, clouds, precipitation, and wind through current meteorological and other satellite systems. A wide range of these parameters are already extracted and distributed operationally on a regional or global basis like cloudiness, cloud height, cloud motion, winds, surface temperature and atmospheric temperature profiles, and precipitation estimates, Some of these products like cloud motion, winds, and temperature profiles enter weather forecast models for initialization purposes. These models predict the global state of the atmosphere (some include precipitation and cloudiness) quite reliably for several days. Thus, an important part of the necessary technical framework for global disease spread and transmission monitoring exists.

ISSN:0143-1161    

DOI:10.1080/01431169308953980

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Three AVHRR-LAC data sets acquired in September 1990 and January 1991 were used to map the forest resources of Madagascar. The island was partitioned into four strata to include: (1) the western hardwoods, (2) the central grasslands, (3) the eastern rainforest, and (4) spiny forest. Each stratum was classified separately using AVHRR-LAC data in conjunction with 1984-1988 Landsat-MSS photoproducts. The results of AVHRR classification indicate that approximately 11 per cent of the island is covered by forest. Approximately 1 per cent of the island was obscured by clouds and could not be enumerated. Estimates of forest area, by stratum, follow: western hardwoods, 6697 km2; central grasslands, 2830km2; eastern rainforest 34167km2; and spiny forest, 17 224 km2. The total forest area on the 587041km2island is estimated to be 60918km2. The AVHRR forest map was compared to a mid 1970s land cover map which was developed using Landsat-MSS photoproducts. The average class agreement between the mid 1970s ground reference map and the 1990 AVHRR-LAC map was 78-2 per cent, the overall accuracy was 81-1 per cent. Areas identified as forest on the ground reference map on the 1990 AVHRR map agreed only 62 per cent of the time, however, that figure confounds AVHRR misclassifi-cation error with actual forest loss over the decade. Much of the per-pixel disagreement between the ground reference and AVHRR maps involved areas identified as forest in the 1970s and as nonforest in 1990. These results demonstrate that one kilometre spatial resolution satellite data may be used to provide a reconnaissance level survey of the forest resources of a region or subcontinent when used in conjunction with fine resolution data.

ISSN:0143-1161    

DOI:10.1080/01431169308953981

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The Santa Barbara microwave backscattering model for woodland vegetation with discontinuous tree canopies is described, with an emphasis on the construction of the model from probability-weighted sub-components. The modelling approach is to treat individual tree crowns as scatterers and attenuators, using the probabilities of scattering and attenuation to compute total backscatter. Four major model components are defined: surface backscattering, crown volume scattering, multi-path interactions between crown and ground, and double-bounce trunk-ground interactions. Each component is divided into subcomponents having distinct scattering and attenuation paths. The scattering of each subcomponent is computed and weighted by the probability of its occurrence. Total backscatter from a simulated woodland stand is computed by incoherent summation of the components. Recent revisions to the model have modified the subcomponent definitions and improved the probability formulation.

ISSN:0143-1161    

DOI:10.1080/01431169308953982

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

On a 1984-1989 series of ARTEMIS-NDVI data derived from the NOAA-AVHRR sensor a case study on crop monitoring and early crop yield forecasting was elaborated for the provinces of Burkina Faso. In order to remove residual effects of clouds and other atmospheric influences on 10-day maximum NDVI images, a conditional temporal interpolation method was applied. Various NDVI regression parameters were compared. For the seven northern provinces, a simple linear regression based on averaged maximum 10-daily or monthly NDVI values proved to be superior to regressions based on the integrated NDVt and on NDVI increments. Multiple regressions led to significantly higher correlation coefficients, but only towards the end of the growing season (up to r2= 087). The simple linear regression was also found valid for a part of the central and southern provinces. The yields of the majority of the provinces however was best approximated using one second-order polynomial equation. A test of the regressions on 1989 data showed a forecast error percentage of less than 15 per cent for half of the 30 provinces in August, approximately 2 months before harvest. In the other half of the provinces, high forecast errors occurred mainly due to a locust invasion, excessive rainfall in August and drought in September, after the time of the forecast. Therefore correction factors for the occurrence of extreme pest and other problems have to be included in the model in close cooperation with the relevant organizations. Some of these problems could however be assessed indirectly from the NDVI dynamics.

ISSN:0143-1161    

DOI:10.1080/01431169308953983

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Nel Primary Productivity (NPP) and Actual Evapotranspiration (AET) are key processes characterizing the vegetation activity. At a continental scale, Annual Net Primary Productivity (ANPP) and annual AET are related to the integrated Normalized Difference Vegetation Index (NDVI). When applied to the African continent, the ANPP/ZNDVI relation gives an estimation of the productivity with a precision comparable to those given by climate models. The estimation of annual AET is possible within climatic zones defined here by their Rain-Use Efficiencies (RUE). On the other hand, on a monthly basis, the AET/ SNDVI relations are less clear and are strongly dependent on the physiognomy of the vegetation community considered. These results show the limits of using ENDVI for estimating the elementary processes of terrestrial vegetation at a continental scale.

ISSN:0143-1161    

DOI:10.1080/01431169308953984

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A video-digitized, aerial colour-infrared photograph of a species-rich mire site was analysed to explore its information content with respect to ecologically important site characteristics, viz., species richness and structural diversity. First-order (mean and standard deviation) and texture measures (semivariance, angular second moment and inverse difference moment) were calculated for image windows representing 2 by 2 m vegetation quadrats. For each quadrat the number of herbaceous species (SPPH), the cumulative cover of herbaceous species (COVH) and moss (COVM) and a structure-diversity index (DIVC) were derived from the complete recordings of species composition and species cover per quadrat. The diversity index is made up of structure classes based on species morphology and maximum height. Stepwise regression was used for the explanation of the variance in these statistics observed between the quadrats. The additional value of the texture measures was assessed relative to a base model containing red and near-infrared only. COVH and DIVC appeared to be sufficient as descriptors of species richness and structural diversity; 30 and 60 per cent of the variance respectively is explained by the base model. The addition of semivariance resulted in an improved model only for SPPH and COVH. Biological and physical arguments are provided for explaining the behaviour of each statistic.

ISSN:0143-1161    

DOI:10.1080/01431169308953985

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Many sugar maple stands in the northeastern United States experienced extensive insect damage during the 1988 growing season. Chlorophyll data and high spectral resolution spectrometer laboratory reflectance data were acquired for multiple collections of single detached sugar maple leaves variously affected by the insect over the 1988 growing season. Reflectance data indicated consistent and diagnostic differences in the red edge portion (680-750 nm) of the spectrum among the various samples and populations of leaves. These included differences in the red edge inflection point (REIP), a ratio of reflectance at 740-720 nm (RE3/RE2), and a ratio of first derivative values at 715-705 nm (D715/D705), All three red edge parameters were highly correlated with variation in total chlorophyll content. Other spectral measures, including the Normalized Difference Vegetation Index (NDVI) and the Simple Vegetation Index Ratio (VI), also varied among populations and over the growing season, but did not correlate well with total chlorophyll content. Leaf stacking studies on light and dark backgrounds indicated REIP, RE3/RE2 and D715/D705 to be much less influenced by differences in green leaf biomass and background condition than either NDVI or VI.

ISSN:0143-1161    

DOI:10.1080/01431169308953986

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

C-band SAR and X-band SLAR radar backscattering data collected over an agricultural area in The Netherlands, during the Agriscatt 1987 campaign, were compared and analysed in relation to type and structural properties of soil cover. The C- and X-band data were found to be similar in major trends. The variation in field-average radar backscattering values, however, was smaller in the C-band than in the X-band. Some fields showed a strong look direction dependence while others showed a strong polarization dependence of the backscattering. From field observation and from a theoretical analysis, incorporating the different structures and spatial orientations of the canopies elements, it was shown that non-uniform azimuthal distribution was the main cause for this phenomenon. It was concluded that these different types of backscattering behaviour can be two aspects of a single physical mechanism.

ISSN:0143-1161    

DOI:10.1080/01431169308953987

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Multi-temporal, multi-frequency (1-2-17-25 GHz) radar data collected with the DUTSCAT airborne scatterometer over the Flevoland test site in the Agriscatt-1988 campaign, were analysed in relation to crop type and crop growth of mainly sugar-beet, potato and winter wheat. Two frequency ranges were distinguished that had specific backscattering behaviour: the low frequency L-band and the high frequencies X- to Ku2-band. The L-band had the largest relative content of variation on bare soils and was shown to penetrate potato canopy. The high frequencies, namely the X- to Ku2-bands, had the largest relative content of variation on crop covers and were shown to be relatively sensitive to canopy structure. These bands were (equally) well suitable for the separation between crop types. All bands were equally useful to indicate qualitatively the growth of beet and potato in the early growing season. The backscattering of wheat appeared not to be related to growth of the crop in any of the frequency bands. The theoretical backscattering model of Eom and Fung was evaluated for its ability to describe radar signatures of crops. It appeared that care should be taken with the representation of leaves as di-electric ellipsoids in the model, notably when the leaf surface is undulating (beet) or composed (potato)

ISSN:0143-1161    

DOI:10.1080/01431169308953988

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor