摘要:

Coarse spatial resolution, high temporal frequency satellite data from the NOAA/AVHRR system are presented to demonstrate their utility for monitoring vegetation seasonal dynamics. The techniques for processing and analysing the data are outlined and examples are given for selected applications at a range of scales. Normalized difference vegetation index images are presented for the entire globe and for the continents of Africa, South America and south-east Asia, with descriptions of the seasonal dynamics of major vegetation formations as portrayed by the transformed AVHRR data. Monitoring of forest clearance in Brazil, the productivity of African grasslands, Indian tropical forest and Chinese agriculture are selected for discussion. The paper concludes that coarse-resolution satellite data provide a valuable tool for vegetation mapping and monitoring at regional and global scales.

ISSN:0143-1161    

DOI:10.1080/01431168508948281

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

By combining the surface energy balance equation with the vertical transport equations for latent and sensible heat, crop temperatures can, in principle, be transformed into instantaneous evapotranspiration values. To obtain 24 hour values the TERGRA model of Soer can be applied.

ISSN:0143-1161    

DOI:10.1080/01431168508948282

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A two-stream approximation model of radiative transfer is used to calculate values of hemispheric canopy reflectance in the visible and near-infrared wavelength intervals. Simple leaf models of photosynthesis and stomatal resistance are integrated over leaf orientation and canopy depth to obtain estimates of canopy photosynthesis and bulk stomatal or canopy resistance. The ratio of near-infrared and visible reflectances is predicted to be a near linear indicator of minimum canopy resistance and photosynthetic capacity but a poor predictor of leaf area index or biomass.

ISSN:0143-1161    

DOI:10.1080/01431168508948283

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The relationships between reflectance in the LANDSAT Thematic Mapper (TM) bands and grass canopy characteristics were studied. Data were collected from a total of 107 tall fescue (Festuca arundinacia) plots (0·2 m2) during the 1983 growing season. Canopy height, percentage cover, total wet biomass, total dry biomass, plant water and leaf area index were correlated with spectral data obtained from a Barnes Modular Multiband Radiometer. The near-infrared wavelength region corresponding to TM band 4 appeared to be the best estimator of total wet biomass (r = 0·80) and canopy height (r =0·82). Percentage canopy cover had the highest correlation coefficients with TM band 7 (r = −0·95) and TM bands 1, 2 and 3 (r≥0·93). All canopy variables showed a curvilinear relationship with the spectral bands, except canopy cover, which showed a near linear relationship, for the biomass range in this study. Linear transformations were obtained using natural logarithms of the grass canopy variables and the spectral bands. Band ratios were more significant than individual bands when correlated with the canopy variables. The relationship between the normalized difference transformation and total wet biomass was linear for low biomass situations. The normalized difference values were constant for high biomass levels. Redundancy was found in several of the canopy variables and several of the spectral variables. Principal component transformations were effective in reducing the seven spectral bands to two principal components, while maintaining nearly all of the variance of the seven bands.

ISSN:0143-1161    

DOI:10.1080/01431168508948284

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Actual and degraded LANDSAT-4 Thematic Mapper (TM) data were analysed to examine the effect of spatial resolution on the performance of a per pixel, maximum-likelihood classification algorithm. Analysis of variance (ANOVA) and a balanced, three-factor, eight-treatment, fixed-effects model were used to investigate the interactions between spatial resolution and two other TM refinements, spectral band configuration and data quantization. The goal was to evaluate quantitatively the effects of these attributes on classification accuracies obtained with all pixels (pure pixels plus mixed pixels) and on accuracies obtained with pure pixels alone.

ISSN:0143-1161    

DOI:10.1080/01431168508948285

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Remote sensing image classification with the maximum-likelihood decision rule leads to a computational cost that depends quadratically on the number of bands in the data. Moreover, the data has to be modelled beforehand by sets of multivariate normal distributions if acceptable classification accuracies are to be obtained. A new algorithm is presented with a cost linearly proportional to the number of bands. Being based upon a combination of linear classifiers it is not dependent upon a priori parametric modelling of the data. Instead it partitions the measurement space in a piecewise-linear fashion leading to high accuracies at low cost, particularly for multitemporal data.

ISSN:0143-1161    

DOI:10.1080/01431168508948286

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A simple method for reducing the effect of cloud on satellite thermal imagery, while preserving full temperature and spatial resolution, is presented. The method makes use of the correlation between apparent thermal and visible radiances in an area contaminated by thin or patchy (subpixel) cloud. The method was developed for ocean images where the cloud is present over an area of low uniform albedo in the visible spectral region, but advantages are also demonstrated in processing Arctic images containing some sea ice cover.

ISSN:0143-1161    

DOI:10.1080/01431168508948287

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Clouds above the ocean are detected with three thermal-infrared channels of the AVHRR on board NOAA-7. A classification into low, middle and high clouds is possible. As only spectral and not spatial information is used, it is possible to analyse each pixel individually. The classification has been developed with a radiative transfer model for clouds adapted to the spectral domain of the NOAA-7 infrared channels. The ruling parameter is the ratio between scattering and extinction. The spectral optical depth has slightly less influence, while different anisotrophy of scattering for individual types of clouds is not important. Two parameters are best suited to classifying clouds, namely, brightness temperature in channel 5(12·0 μm) and the difference of brightness temperature between channel 3 (3·7μm) and channel 4 (10·8 μm). The algorithm to classify clouds with thresholds referring to the standard atmosphere ‘autumn 45° north’ is applied to actual satellite data.

ISSN:0143-1161    

DOI:10.1080/01431168508948288

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The Along-Track Scanning Radiometer (ATSR) is a planned ERS-1 payload for accurate sea-surface temperature measurements under two different incidence angles from a conical scan. It is investigated whether it can additionally be used for cloud stereoscopy and wind determinations as proposed by DFVLR for the Stereo Line Scanner (SLS). Although not designed for these types of measurements the ATSR seems very useful for a pilot experiment with only a lower resolution than proposed for the SLS.

ISSN:0143-1161    

DOI:10.1080/01431168508948289

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431168508948291

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor