ISSN:0143-1161    

DOI:10.1080/01431168908903968

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

High spectral resolution Airborne Imaging Spectrometer (AIS) data were acquired over 20 well-studied Wisconsin forest sites to evaluate the potential of remote sensing for estimating forest canopy chemistry. Intensive nutrient cycling research in these forests demonstrates that canopy lignin content is strongly related to measured annual nitrogen mineralization at the undisturbed sites and may serve as an accurate index for nitrogen cycling rates. Ground measurements were made of foliar biomass and canopy nitrogen and lignin content, the latter within two weeks of the AIS overflight. The spectral data were transformed using derivative techniques modified from laboratory spectroscopy. Stepwise regression assisted in determining combinations of wavelengths most highly correlated with canopy chemistry and biomass. Strong correlations between AIS data and total canopy lignin content in deciduous forests and canopy lignin concentration (total lignin/biomass) in both deciduous and coniferous stands indicate that imaging spectrometry can be used to estimate canopy lignin content and, from that, the spatial distribution of annual nitrogen mineralization rates.

ISSN:0143-1161    

DOI:10.1080/01431168908903969

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A relationship between the maximum-value composite and monthly mean normalized difference vegetation index (NDVI) is derived statistically using data over the U.S. Great Plains during 1986. The monthly mean NDVI is obtained using a simple nine-day compositing technique based on the specifics of the scan patterns of the NOAA-9 Advanced Very High Resolution Radiometer (AVHRR). The results indicate that these two quantities are closely related over grassland and forest during the growing season. It is suggested that in such areas a monthly mean NDVI can be roughly approximated by 80 per cent of the monthly maximum NDVI, the latter being a standard satellite data product. The derived relationship was validated using data for the growing season of 1987.

ISSN:0143-1161    

DOI:10.1080/01431168908903970

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Estimation of evapotranspiration from thermal infrared (IR)as been widely studied in recent years and in particular by methods using the simplified relation ETR − Rn = A − B(Ts−Ta) proposed by Jacksonet al.(1977) and thermal IR data from the NOAA satellite obtained near midday (local time). The representativeness of instantaneous temperature for computing daily fluxes is discussed and a one-layer model is presented for a developed crop. A new theoretical expression of the simplified relation which can be applied to developed crops is presented and the sensitivity of the parameters in this relation is examined.

ISSN:0143-1161    

DOI:10.1080/01431168908903971

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A numerical simulation has been constructed of the hydrodynamic modulation transfer function (HMTF) which defines the spatial and spectral properties of swell waves as observed by an imaging radar. While the simulation is based on the Alpers and Hasselmann (1978) two-scale modulation transfer model, it explicitly takes account of directional properties of the short-wave spectrum and does not necessarily assume an isotropic wind-wave spectrum. Several different spreading functions are modelled and it is demonstrated that an anisotropic wind wave field significantly distorts the HMTF. Depending on the wind direction relative to the radar azimuth, the effect can be to shift the direction and the wave number of the peak of the image spectrum relative to the true swell spectrum. The effect of fetch limitation on the wind-wave spectrum is also examined based on the JONSWAP spectrum, but the consequences of this for the HMTF imaging mechanism are found to be minimal.

ISSN:0143-1161    

DOI:10.1080/01431168908903972

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The relationship between reflectance and suspended sediment concentration (SSC) is dependent upon the wavebands sensed and the viewing geometry of the sensor. The laboratory experiment reported in this paper investigated these dependences. The reflectance in four wavebands (two visible and two near-infrared) of a large water-filled and wave-free tank were recorded as three variables were changed, namely SSC, sensor viewing angle and relative sensor azimuth. The strength of the positive relationship between reflectance and SSC was shown to vary with (i) wavelength, as the maximum reflectance and SSC class separability occurred at the longer visible wavelengths, and (ii) viewing geometry, as the reflectance/SSC asymptote was dependent upon both the angle and azimuth of the sensor. The optimum conditions for the sensing of SSC were concluded to be nadir in visible (0·55 and 0·65 μm) and near-infrared (0.75 μm) wavelengths.

ISSN:0143-1161    

DOI:10.1080/01431168908903973

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A three-component model of ocean colour is presented, that takes into account contributions of phytoplankton, non-chlorophyllous particles and dissolved organic matter. The model is based on theoretical considerations and is validated by comparison with observed reflectance spectra. It is then used to address the problem of estimating chlorophyll concentration in coastal (case 2) waters by remote sensing. Principal component analysis is carried out on a large number of reflectance spectra simulated using the model. The results indicate the possibility of chlorophyll retrieval in at least some case 2 waters. Retrieval becomes difficult in waters where the signal from small quantities of chlorophyll is drowned in the noise from large quantities of non-chlorophyllous particles and dissolved organic matter. Non-chlorophyllous particles are the most easy to recover, while dissolved organic matter appears to be the most difficult. The non-linearity of the system limits the possibility of a single algorithm to cover all ranges of variation. It appears possible to pass from full spectral data to five selected wavelengths without any loss in the retrieval efficiencies. The use of 400 nm-channel data in the algorithm, in addition to the data from the usual 440, 520 and 550nm channels, considerably increases the possibility of distinguishing phytoplankton from dissolved organic matter.

ISSN:0143-1161    

DOI:10.1080/01431168908903974

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

There is a need for cloud information with which to conduct validation of the International Satellite Cloud Climatology Project (ISCCP) cloud retrievals. The U.S. Air Force (USAF) nephanalysis is at present the only operational real-time global cloud analysis and the available archive from this offers a potential database for comparison with ISCCP retrievals. The performance of the USAF 3D (three dimensional) Nephanalysis during the month of July 1983, one of the months designated for validation/intercomparison, is examined here on a regional basis. The cloud field retrieved by the USAF Nephanalysis is examined in relation to features unique to the archive such as the inclusion, where appropriate, of conventional observations. A direct comparison with ground-based observations illustrates the effect of conventional data on the archive over a range of time scales. Examination of the Nephanalysis over difficult areas such as polar and desert regions reveals some of the problems pertinent to most current cloud algorithms. Comparisons between 3D Nephanalysis archives separated by 4 years (1979 and 1983) show interannual and synoptic effects and illustrate the evolution of this retrieval algorithm. The most obvious change is due to modifications to the technique employed for spreading conventional observations (surface and aircraft) into the satellite-based analysis. The more recent method results in input from isolated stations being more obvious in the final archive although the values reported are generally close to those in the surrounding satellite retrieval. Bogussing (the imposition of cloud amounts derived, at the time, by an analyst usually from geostationary satellite data) is another feature unique to the USAF Nephanalyses. These two characteristics mean that unsupervised (i.e. purely computer-based) comparison between real-time (RT) Nephanalysis and, for example, ISCCP would be unwise. On the other hand, the year-to-year consistency of the USAF retrieval algorithm, the clear lack of reference to previously determined climatological fields and the time and space resolution and continuity of the Nephanalysis product suggest that the USAF Nephanalysis offer a valuable data set for comparison with ISCCP provided that comparisons are undertaken with care.

ISSN:0143-1161    

DOI:10.1080/01431168908903975

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Temperatures estimated from 29 April 1986 Landsat Thematic Mapper (TM) data for the fire at the Chernobyl nuclear power plant are reassessed and a new range of distribution and temperatures of the hottest visible material is suggested. The detected shortwavelength infrared thermal radiance is interpreted to come from sources at around 1130-1430 K. occupying about 0·05 per cent of each of four ground resolution cells.

ISSN:0143-1161    

DOI:10.1080/01431168908903976

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431168908903977

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor