ISSN:0143-1161    

DOI:10.1080/01431169308954006

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

There is an urgent need to inventory and monitor indicators of biological diversity, such as species richness. Remotely-sensed data provide a means to accomplish part of this task, but there has been no comprehensive scientific framework to guide its effective application. Here we propose a remote sensing research agenda designed to improve the quality and quantity of information available for testing scientific hypotheses, monitoring, and conservation planning. Biodiversity should be more fully incorporated into ongoing Earth system science and global change programmes, with remote sensing featured as a prominent data acquisition and analysis tool.

ISSN:0143-1161    

DOI:10.1080/01431169308954007

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Frequent cloud cover and logistical constraints hamper biophysical remote sensing studies in arctic locations, resulting in a general lack of information regarding relationships between biophysical quantities and the spectral reflectance of arctic vegetation communities. An experiment was conducted on the north slope of Alaska to characterize relationships between the spectral reflectance of three tussock tundra communities (moist tussock, dry heath and water track) and the above ground biomass and vegetation composition of each community. Hand-held radiometric and ground reference data were collected three times during the 1989 growing season. The normalized difference vegetation index (NDVI) was regressed on above ground photosynthetic and non-photosynthetic biomass quantities and individual blue, green red and near-infrared spectral reflectances and the NDVI were regressed on vegetation cover type fractions. Up to 51 per cent of the variance in the NDVI was explained by the amount of photosynthetic biomass in the moist tussock and dry heath communities while no significant relationship was established between the NDVI and non-photosynthetic biomass. Vegetation cover types had a substantial effect on the observed spectral reflectances and NDVI of each of the three communities. A secondary objective of the study was to determine whether the ratio of photosynthetic to non-photosynthetic biomass could be determined using simple point quadrat estimates of these fractions. No substantial relationship was established between the harvested and point quadrat estimates of the biomass fractions.

ISSN:0143-1161    

DOI:10.1080/01431169308954008

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The single scattering albedo and optical depth of typical savanna vegetation in Botswana (Africa) have been determined by inverse modelling using satellite observed microwave signatures and surface soil moisture. Soil emissivity was modelled using a multi-layer radiative transfer model. The study is based on large scale surface moisture data and Nimbus/SMMR 6·6 GHz and 37 GHz dual polarized brightness temperatures over a 3-year period. As compared to the optical depths, the derived single scattering albedos displayed only minor seasonal variations, whereas the values fit well within the range reported in the literature from laboratory and field experiments. Both 6·6 and 37 GHz optical depths were found to be significantly related to NDVI-values derived from NOAA/AVHRR.

ISSN:0143-1161    

DOI:10.1080/01431169308954009

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We present new remote sensing indices of plant water status: the ratio between the reflectance at 970 nm, one of the water absorption bands, and the reflectance at a reference wavelength, 900 nm (R970/R9000; the first derivative minimum in this near-infrared region (dNIRminimum) and the wavelength where this minimum is found ( λNIRminimum). In order to evaluate them, we carried out three experiments. Daily irrigated gerbera plants were allowed to dry until almost wilting and then daily irrigation was restarted; pepper and bean plants were grown for four months submitted to two different irrigation treatments; and bean detached leaves were submitted to progressive dehydration whereas pressure-volume curves were being carried out.

ISSN:0143-1161    

DOI:10.1080/01431169308954010

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The effect of sensor degradation in the Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2 on the Normalized Difference Vegetation Index (NDVI) has been established. Three models have been developed that adjust NDVI for sensor degradation without recourse to component channel 1 and 2 data. The models have been verified with data obtained by the AVHRR on board of NOAA-7, -9 and -11. Two models provide accurate results in some cases, but perform less well in others. A third model is applicable to all cases investigated, and estimates the effect of sensor degradation with a maximum RMS error of 0·002NDVI. The remaining error depends on surface characteristics and the magnitude of sensor degradation, and cannot be accounted for without the component channel 1 and 2 data.

ISSN:0143-1161    

DOI:10.1080/01431169308954011

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Coastal salt-affected land is subject to variation in area as well as magnitude with time because of influence of coastal processes. In order to take corrective and protective measures, it is essential to have accurate information about such an area in the form of maps. Using conventional ground methods, mapping of such an inhospitable area is not only difficult and time-consuming but also expensive, laborious, and associated with vagaries of weather. Hence an attempt has been made to use remote sensing techniques for the purpose of preparing a map of one of the coastal areas of Gujarat state, providing information about the extent and magnitude of salt-affected land.

ISSN:0143-1161    

DOI:10.1080/01431169308954012

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Recently, a number of studies have investigated the use of the 37 GHz channels of the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) for vegetation monitoring and for studying synergisms between the SMMR and the NOAA Advanced Very High Resolution Radiometer (AVHRR). The approaches are promising but raise a number of issues concerning interpretation of the results, specifically on the relative effects of vegetation and other surface and atmospheric characteristics on the observed signal. This article analyses the 37 GHz Microwave Polarization Difference Temperature (MPDT) in terms of its sensitivity to surface and atmospheric parameters. For this, a radiative transfer model is used which indicates some limitations of the MPDT index and suggests the importance of accounting for atmospheric effects in the data analysis. An alternative approach to the MPDT, including lower SMMR frequencies than 37 GHz, is discussed.

ISSN:0143-1161    

DOI:10.1080/01431169308954013

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Data measured by microwave radiometers are brightness temperatures, from which, using algorithms, geophysical parameters are retrieved. Errors in these parameters can be due either to the algorithms or to instrumental deficiencies affecting the brightness temperatures. Only geophysical data can be validated directly since dedicated meteorological experiments cannot be performed frequently enough or in a sufficient number of places during the satellites lifetime. To achieve such a global validation, we propose to use global meteorological model analyses, which contain the information of all routine observations after checking their quality. In this article, we test this approach by comparing Nimbus-7/SMMRgeophysical data with ECMWF model analyses. Data from five months in 1979 are examined, and deviations between both data sets are analysed in terms of satellite or model errors. This comparison revealsSMMRproblems inSSTand surface wind data, and local model errors in the precipitable water. Therefore, a good knowledge of model behaviour is necessary for using its analyses in satellite data validation, yet it appears as a useful tool, working at scales ranging from regional to global, and in time, from a particular event to a season or more.

ISSN:0143-1161    

DOI:10.1080/01431169308954014

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new method of processing synthetic aperture radar (SAR) data was originally developed by a group of geophysicists, who use seismic migration to generate seismic images of the Earth. Called here ω—κ migration, it has several advantages over more traditional methods of forming SAR images; they all arise because this method provides a mathematically exact solution to the imaging problem, in that the emitted waves are not being treated as plane waves. This paper discusses how migration processing can be applied to chirped radars; how it applies to spotlight data; and how to correct for non-uniform motions of the SAR platform.

ISSN:0143-1161    

DOI:10.1080/01431169308954015

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor