ISSN:0143-1161    

DOI:10.1080/01431168608948941

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431168608948942

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431168608948943

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Leaf structure and function are shown to result in distinctive variations in the absorption and reflection of solar radiation from plant canopies. The leaf properties that determine the radiation-interception characteristics of plant canopies are directly linked to photosynthesis, stomatal resistance and evapotran-spiration and can be inferred from measurements of reflected solar energy. The effects of off-nadir viewing and atmospheric constituents, coupled with the need to measure changing surface conditions, emphasize the need for multitemporal measurements of reflected radiation if primary production is to be estimated

ISSN:0143-1161    

DOI:10.1080/01431168608948944

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Red and near-infrared satellite data from the Advanced Very High Resolution Radiometer sensor have been processed over several days and combined to produce spatially continuous cloud-free imagery over large areas with sufficient temporal resolution to study green-vegetation dynamics. The technique minimizes cloud contamination, reduces directional reflectance and off-nadir viewing effects, minimizes sun-angle and shadow effects, and minimizes aerosol and water-vapour effects. The improvement is highly dependent on the state of the atmosphere, surface-cover type, and the viewing and illumination geometry of the sun, target and sensor. An example from southern Africa showed an increase of 40 per cent from individual image values to the final composite image. Limitations' associated with the technique are discussed, and recommendations are given to improve this approach

ISSN:0143-1161    

DOI:10.1080/01431168608948945

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Images at a resolution of 8 km are currently being generated for the whole of Africa, displaying the normalized difference vegetation index (NDVI). These images have undergone a process of temporal compositing to reduce the effects of cloud cover and atmospheric variation. When the NDVI is plotted against time, different cover types are shown to have characteristic profiles corresponding closely with their phenology. The resultant pattern of NDVI values displayed on the images is analysed in terms of the cover types present and local variations in rainfall. Comparison between images for 1983 and 1984 overall showed considerable similarities, but significant differences were observed in the northward extent of the greening wave in the Sahel, the greening up of the Kalahari Desert and East African communities. It is concluded that vegetation monitoring using NDVI images needs to be associated with scene stratification according to cover type

ISSN:0143-1161    

DOI:10.1080/01431168608948946

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A comparison is made of four AVHRR images of Ethiopia for August and September 1983and 1984, with reference to the drought conditions experienced during these 2 years

ISSN:0143-1161    

DOI:10.1080/01431168608948947

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

NOAA Advanced Very High Resolution Radiometer satellite data are applied to regional vegetation monitoring in East Africa. Normalized Difference Vegetation Index (NDVI) data for a one-year period from May 1983 are used to examine the phenology of a range of vegetation types. The integrated NDVI data for the same period are compared with an ecoclimatic zone map of the region and show marked similarities. Particular emphasis is placed on quantifying the phenology of theAcacia Commiphora bushlands.Considerable variation was found in the phenology of the bushlands as determined by the satellite NDVI, and is explained through the high spatial variability in the distribution of rainfall and the resulting green-up of the vegetation. The relationship between rainfall and NDVI is further examined for selected meteorological stations existing within the bushland. A preliminary estimate is made of the length of growing season using an NDVI thresholding technique

ISSN:0143-1161    

DOI:10.1080/01431168608948948

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Normalized difference vegetation index data derived from the Advanced Very High Resolution Radiometer on board the NOAA-7 satellite for the 1983 growing season for the Sahelian Zone of Niger are compared with biomass estimates derived from an empirical grassland productivity model. The model used daily rainfall data to estimate the potential biomass production for fourteen meteorological stations through the growing season. A good general correspondence (r = 0·75) was seen between the productivity model and the satellite-derived integrated NDV1, although specific differences were apparent between actual and potential biomass. The study shows the utility of high-temporal-resolution satellite data for monitoring grassland conditions at a local and regional scale and emphasizes the importance of a maximum value compositing approach to the analysis. The study also shows the potential of the satellite data for quantifying phenological characteristics of vegetation

ISSN:0143-1161    

DOI:10.1080/01431168608948949

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

NOAA-6 and NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) global-area coverage (4 km ground resolution) data were obtained at three-day intervals throughout each of the four-month periods covering the 1980, 1983 and 1984 growing seasons, between latitudes 10° and 22° North in the Democratic Republic of Sudan. Daily rainfall data for twelve meteorological stations spanning the Savanna Zone were analysed. Rainfall in Sudan during 1980 was below normal, but in 1983 and 1984 there were moderate and severe droughts. The satellite data were used to calculate normalized difference vegetation index (NDVI) values from the visible and near-infrared bands of the satellite data. These were processed into ten-day composite data sets using the AVHRR thermal-infrared channel as a cloud screen and a temporal compositing procedure that reduces cloud contamination and selects viewing angles closest to nadir.

ISSN:0143-1161    

DOI:10.1080/01431168608948950

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor