ISSN:0143-1161    

DOI:10.1080/01431169208904094

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

There exist several techniques for the measurement of directional ocean wave spectra. The most conventional technique is the employment of pitch-roll buoys but a disadvantage of this technique is that it measures at a fixed point. Another promising technique is the use of airborne or spaceborne radars. We present here results of a comparison between the data from an airborne radar, which is measuring near vertical incidence, and measurements of directional wave spectra obtained by means of a pitch-roll buoy and processed by using the Long-Hasselmann iterative algorithm. Although preliminary, these results constitute a step towards the employment of the airborne radar based on the Radar Ocean Wave Spectrometer (ROWS) principle as defined by Jackson (1981), as a validation tool for spaceborne synthetic aperture radars.

ISSN:0143-1161    

DOI:10.1080/01431169208904095

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

It has been known that the emission from row crops strongly depends on the direction of vegetation row structures relative to the polarization of radiometric receiving antenna. The purpose of the paper is to develop an emission model to interpret the existing emission data of row crop canopy and to aid in understanding the emission process for a row structured vegetation layer or other anisotropically-emitting medium. The vegetation layer of row crops is modelled as a random slab embedded with small thermally emitting spheroids with major axis aligned parallel to the row crop direction. The effects of geometric row structure of vegetation layer can be accounted for by assuming that each thermally-emitting object such as a leaf is aligned to a certain preferred direction. The vegetation canopy is a tenuous medium at microwave frequency so that it is possible to use the radiative transfer theory in emission model. The total emission from the canopy is given in a simple algebraic form based on the zero-order radiative transfer theory. The single scattering albedo for a spheroid and its phase function are derived in order to use in the radiative transfer-based emission computation. The effects of layer azimuthal dependence on emission are accounted for by using an anisotropic albedo in the transfer theory. The developed emission theory favourably compares with the brightness temperature measured over the soybeans canopy, and verifies that a maximum emission reception occurs when the receiving antenna polarization state is perpendicular to the row direction. The emission theory may also find applications in the interpretation of optical and infrared emission data taken from an anisotropic thermal medium.

ISSN:0143-1161    

DOI:10.1080/01431169208904096

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Models that relate composite reflectance to its components are useful for inferring crop growth information from measured scene reflectance. Radiation measurements in Thematic Mapper bands (TM1, TM2, TM3, and TM4) were made from cotton, soybean, sunflower and grain sorghum at three stages of growth and used to evaluate three reflectance models. Two models, AIRM1 and AIRM2, assumed that scene components contribute in an additive independent manner to composite reflectance. The third model, TRIM, assumes that radiation transmitted through the canopy interacts with bare soil in two scene components. The AIRM2 and TRIM models divide the composite reflectance into canopy, bare soil, and shadow components, but AIRM1 considers only canopy and bare soil. Ranking of models in order of decreasing accuracy for predicting composite reflectance in bands TM3 and TM4 was AIRM2, TRIM, and AIRM1. The AIRM1 and AIRM2 models estimated average TM3 reflectance at full plant cover between 1 and 4 per cent for all crops. Their estimations in band TM4 were 60 per cent for cotton, soybean, and sunflower with grain sorghum being 50 percent.

ISSN:0143-1161    

DOI:10.1080/01431169208904097

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Multi-resolution and multi-temporal remote sensing data (SPOT-XS and AVHRR) were evaluated for mapping local land cover dynamics in the Sahel of West Africa. The aim of this research was to evaluate the agricultural information that could be derived from both high and low spatial resolution data in areas where there is very often limited ground information. A combination of raster-based image processing and vector-based geographical information system mapping was found to be effective for understanding both spatial and spectral land-cover dynamics. The SPOT data proved useful for mapping local land-cover classes in a dominantly recessive agricultural region. The AVHRR-LAC data could be used to map the dynamics of riparian vegetation, but not the changes associated with recession agriculture. In areas where there was a complex mixture of recession and irrigated agriculture, as well as riparian vegetation, the AVHRR data did not provide an accurate temporal assessment of vegetation dynamics.

ISSN:0143-1161    

DOI:10.1080/01431169208904098

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A structured approach to land cover mapping, involving different stages of field work and processing of remote sensing data, is presented. The Processing of TM data of one acquisition date was done by Analysing the Digital data-Structure (PAD) to produce optimum imagery for land-cover mapping of the Atlantic zone in Costa Rica.

ISSN:0143-1161    

DOI:10.1080/01431169208904099

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

SPOT multispectral (XS) and Landsat Thematic Mapper (TM) digital data were studied in an attempt to evaluate the use of this data in detailed assessments of forest conditions. Forest type, basal area, and age class information were collected from 256 sample sites within an intensively managed 80000acre experimental forest in North Carolina, U.S.A. A comparison of the SPOT and TM data with the sample site information showed that XS3, the near-infrared waveband, and TM bands 2, 3, 4, 5, and 7 were significantly correlated with basal area. Age class was not found to be significantly correlated with any of the three SPOT XS wavebands. TM bands 2, 3, 4, 5, and 7 were, however, shown to be significantly correlated with age class. Although significant, the correlation coefficients between the TM or SPOT waveband data and basal area or age class were low (<0.65).

ISSN:0143-1161    

DOI:10.1080/01431169208904100

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Spectral reflectance curves in the 400-1110 nm range have been obtained from two-year-old Norway spruce seedlings exposed to varying levels of ozone and acid mist during their two years of growth in controlled environmental chambers. The trees were exposed to l00ppb ozone, 140ppb ozone and 140ppb ozone plus acid mist, while the control group were exposed to filtered air. Two spectral parameters are used to indicate the impact of these pollutants, namely the level of the infrared plateau and the position of the red edge. The infrared plateau has been found to have a higher reflectance as pollutant concentrations increase. This is thought to infer changes within the internal structure of the leaves. The red edge has been found to shift by up to l8 nm at the point of maximum red-edge slope. From both these parameters it is apparent that damage from ozone levels of between 100 and 140 ppb is detectable. This is especially so when the plants are concurrently exposed to acid mist.

ISSN:0143-1161    

DOI:10.1080/01431169208904101

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A simple and logical technique was developed to display and quantify forest change using three dates of satellite imagery. The normalized difference vegetation index (NDVI) was computed for each date of imagery to define high and low vegetation biomass. Colour composites were generated by combining each date of NDVI with either the red, green, or blue (RGB) image planes in an image display monitor. Additive colour logic was used to interpret forest change (forest harvest and regeneration) across the landscape on the three dale NDVI colour composite. Harvest and regeneration area were quantified by applying a modified parallelepiped classification creating an RGB-NDVI image with 27 classes that were grouped into nine major forest change categories. Road construction, harvest and regeneration status on old clearcuts can be monitored by interpretation of the additive colour observed at any site. Aerial photographs and stand history maps obtained from a major forest industrial landowner were compared with the forest changes indicated by the RGB-NDVI image. The utility of the RGB-NDVI technique for supporting forest inventories and updating forest resource information systems are presented and discussed.

ISSN:0143-1161    

DOI:10.1080/01431169208904102

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The canopy radiation model EXTRAD was used to quantify the accuracy of leaf area index (LAI) estimations from vegetation indices (Vis), derived from green and infra-red crop reflectance. The Vis were the infra-red/ green (IR/GR) ratio, the normalized difference vegetation index (NDVI), the perpendicular vegetation index (PVI) and the weighted difference vegetation index (WDVI). The accuracy of LAI estimation was calculated in relation to variation in leaf green and infra-red colour, leaf angle distribution, soil background and illumination conditions. The theoretical calculations were supported with a field experiment on sugar-beet.

ISSN:0143-1161    

DOI:10.1080/01431169208904103

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor