ISSN:0143-1161    

DOI:10.1080/01431169408954092

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The quality of SPOT imagery of the humid tropics is variable: frequently only the infrared band is usable. The following statistical conclusions were drawn from a comparison of SPOT and Landsat-TM imagery of Belize: (1) land systems, but not often land facets, can be demarcated; (2) where the quality is good, stereoscopic imagery is preferred for demarcating land systems; (3) after stereoscopy, spectral range appeared more important than ground resolution. Landsat-TM and the two SPOT modes could be used to demarcate plantation agriculture with an overall accuracy greater than 90 per cent, and there was no significant difference between them. Smallholder agriculture was demarcated significantly less reliably (70–90 per cent overall accuracy), for which the SPOT panchromatic mode was found to be more reliable than Landsat-TM at the 99 per cent probability level, but not significantly better than the SPOT multi-spectral mode. Visual interpretation was more reliable than automated classification for demarcating largeholder agriculture.

ISSN:0143-1161    

DOI:10.1080/01431169408954093

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A model for computing the albedos and BRDF (bidirectional reflectance distribution function) of inhomogeneous land surfaces consisting of two different components has been developed. An empirical equation, based on the model results, for calculating albedos of inhomogeneous land surfaces and avoiding errors caused by shadowing effect was set up.

ISSN:0143-1161    

DOI:10.1080/01431169408954094

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Seven years of data are used to examine the orbital characteristics of five NOAA satellites and the implication for using AVHRR data in climatological studies is investigated. Generally a steady drift from a nominally Sun-synchronous orbit results in the earlier arrival of even-numbered satellites and the later arrival of odd-numbered satellites. The most extreme example of drift, for the case of NOAA-6 resulted in a difference of average arrival time of 90 minutes over the operational lifetime of the satellite. Phasing results in a ±51 minute variation in arrival time. The combination of drift and phasing can have a significant effect on the use of AVHRR and other NOAA satellite data in climatological studies, particularly for the mid- and high-latitudes during the winter and summer solstices.

ISSN:0143-1161    

DOI:10.1080/01431169408954095

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A seven year archive of data is used to examine changes in the calibration of the AVHRR instruments carried on board the NOAA-5, -7, -8, -9 and -10 satellites. These changes are assessed from the point of view of using AVHRR data for climatological studies. Visible channels have no on-board calibration and the reported degradation of these channels suggests that visible data should only be used with great caution in climatological studies. Variations in infrared channel calibration are in the main associated with temperature changes on board the satellites. The on-board calibration procedures appear to cope adequately with these temperature changes.

ISSN:0143-1161    

DOI:10.1080/01431169408954096

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Measurements from the thermal infrared split window channels of the AVHRR sensor were investigated for their relationship to the total atmospheric water vapour amount over land surfaces. The difference in brightness temperature between the AVHRR channel 4 and 5 (10·3–11·3μm and 11·4–12·3μm respectively) was found to be a linear function of total precipitable water, for several stations in differing climatic regimes. For each individual location the total precipitable water was estimated with a standard error ranging from 0·22 to 0·48 cm for the complete range of conditions from wet to dry season or summer to winter. For mid-latitude continental locations there is very little influence of atmospheric aerosols on the relationship while for the African Sahel region the effect of large airborne particulates with a silicate component introduces a significant effect at large values of aerosol optical depth due to absorption. The influence of spectral emissivity variation in the split window region was also observed for arid regions where there is a significant quartz component to the soil. It is concluded that for regional retrieval of precipitable water, this technique provides sufficient accuracy for application to correction of near-infrared satellite data such as AVHRR channel 2 (0·71 –0·98 μm), however the site specific relation betweenT4-T5and PW needs to be established with independent PW measurements.

ISSN:0143-1161    

DOI:10.1080/01431169408954097

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The Normalized Difference Vegetation Index time series derived from NOAA satellite data relevant to the years 1986–1989 have been used to evaluate their usefulness for vegetation mapping purposes. Given the remote sensing information about all the available dates in a period, it is possible to define areas of homogeneous time NDVI profile through unsupervised classification procedures. In the discrimination process it is assumed that dynamic features of the vegetation with an evolution period shorter than one month can be neglected. Three different approaches are used: an unsupervised classification on Principal Components and on 6 and 12 months data.

ISSN:0143-1161    

DOI:10.1080/01431169408954098

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Land degradation is difficult to assess in arid rangelands because of short-term variations in rainfall, landscape diversity and the problems of sampling very large areas. This paper shows how vegetation cover index values derived from multi-temporal remotely-sensed data can be used in association with spatial models of grazing impact on landscapes to identify grazing-induced land degradation. The method assumes that grazing effects decrease with distance from water and that temporary grazing impacts largely disappear as vegetation responds to major rainfalls. Grazing gradients (i.e., systematic changes in vegetation cover with distance from water) which remain indicate long term damage. Simple grazing gradients involve changes in average cover with distance from water and include normal, inverse and composite types, complex grazing gradients show systematic changes in cover variance with distance from water and develop where soil and runoff are being redistributed. Although complex grazing gradients may involve little change in total cover with distance from water, they are symptomatic of a reduction in the proportion of forage present. The ability to recognize grazing gradients may greatly simplify range assessment procedures and may also improve satellite image based procedures for determining erosion risk.

ISSN:0143-1161    

DOI:10.1080/01431169408954099

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Mixed pixels occur commonly in remotely-sensed imagery, especially those with a coarse spatial resolution. They are a problem in land-cover mapping applications since image classification routines assume ‘pure’ or homogeneous pixels. By unmixing a pixel into its component parts it is possible to enableinter aliamore accurate estimation of the areal extent of different land cover classes. In this paper two approaches to estimating sub-pixel land cover composition are investigated. One is a linear mixture model the other is a regression model based on fuzzy membership functions. For both approaches significant correlation coefficients, all >0·7, between the actual and predicted proportion of a land cover type within a pixel were obtained. Additionally a case study is presented in which the accuracy of the estimation of tropical forest extent is increased significantly through the use of sub-pixel estimates of land-cover composition rather than a conventional image classification.

ISSN:0143-1161    

DOI:10.1080/01431169408954100

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A practical method of three-dimensional feature space iterative clustering (3D-FSIC) for image classification has been introduced, in which the clustering iteration is performed in three-dimensional feature space rather than scanning the image pixel by pixel. This method permits the cluster size and pixel frequency to be taken into account so that a more advanced decision rule, the optimal multiple point reassignment (OMPR) can be applied. The paper also provides a simple technique for splitting a cluster based on the first principal component without performing principal component transformation. Finally, a classification example using hue images as well as a discussion of the advantages of using hue images in the 3D-FSIC classification is given.

ISSN:0143-1161    

DOI:10.1080/01431169408954101

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor