摘要:

A series of radiative transfer calculations is performed to study the potential of using Sun-stimulated chlorophyll fluorescence for the detection of phytoplankton. Calculated radiance spectra including the fluorescence peak agree well with measurements. We found that the Sun-stimulated natural fluorescence of chlorophyll-a is a good predictor for phytoplankton, even in waters with varying suspended matter and yellow substance concentrations. An increase in chlorophyll concentration of 1 mg m−3causes an increase in fluorescence of about 0·05Wm−2sr−1μm−1, when a fluorescence efficiency factor of 0·3 per cent was assumed. The vertical stratification of chlorophyll affects the fluorescence signal, for example, the fluorescence is reduced to 30 per cent, if the phytoplankton is below 2 m depth instead of reaching the water surface.

ISSN:0143-1161    

DOI:10.1080/01431169008955166

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Sun-stimulated chlorophyll fluorescence is a small but significant property of phytoplankton which can be detected using remote-sensing techniques. Besides the influence of oceanic properties, chlorophyll fluorescence is masked by atmospheric extinction. While an increase in chlorophyll concentration of 1 mg/m3causes an increase in the upwelling radiances of about 0·03Wm−2sr−1μm−1just above the water surface and due to the chlorophyll fluorescence, the upward radiances measured at λF= 685nm and at the top of the atmosphere ranges from 8 to 20Wm−2sr−1μm−1for realistic atmospheric turbidity variations and a solar zenith distance of Θs= 50·7°. Additionally, the fluorescence, peaking at λF= 685nm with a half-width of about 10 nm, is reduced by the absorption of O2and H2O. However, the fluorescence signal is nearly unaffected, when wavelengths λ≥686nm are exluded and a spectral interval of ΔλF= 5nm is used for the radiance measurements.

ISSN:0143-1161    

DOI:10.1080/01431169008955167

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Radiative transfer calculations for remote sensing of coastal waters by airborne lidar and satellite radiometer have been compared in order to answer the question, whether an airborne lidar may be used instead ofin situmeasurements from ships to calibrate a satellite radiometer. The radiative transfer of laserlight measuring the Raman-scattering of water molecules, the fluorescence of chlorophyll-aand the fluorescence of yellow substance or Gelbstoff is simulated by the lidar equations while the radiance to a satellite radiometer is calculated with an ocean-atmosphere model based on the matrix-operator method. Including multiple scattering in the lidar equations, an eigenvalue analysis shows that three oceanic constituents (chlorophyll-a, nonchlorophyllous particles and Gelbstoff) can be separated measuring the backscattered laserlight at three wavelengths from a height of 100 to 200m. Changes in the concentration of all three substances are detected with higher accuracy with an airborne lidar than with a radiometer even at the same height. A comparison of different algorithms indicates that the common blue-green algorithms fail in coastal waters due to the variability of several oceanic constituents, which influence the colour of sea water. In this case, algorithms using the sun-induced chlorophyll-afluorescence at 685 nm, are superior to blue-green algorithms. Airborne lidar measurements of the chlorophyll-afluorescence at 685 nm, normalized by the Raman-signal at 650 nm, are as good asin situdata and can be used to calibrate satellite measurements of chlorophyll-a.

ISSN:0143-1161    

DOI:10.1080/01431169008955168

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Active and passive remote sensing techniques for measurement of oceanic constituents have been compared using the ADRIA'84 dataset. A new method has been developed to retrieve the amount of nonchlorophyllous particles by airborne lidar measurements at three wavelengths. If the lidar measurements of chlorophyll-aand Gelbstoff are calibrated byin situmeasurements, the fluorescence efficiencies can be estimated, Specific extinction coefficients for chlorophyll-aand nonchlorophyllous particles for the northern Adriatic Sea have been derived by comparingin situand underwater irradiance measurements with radiative transfer calculations, using the ocean-atmosphere model by Fischer (1983). For the Coastal Zone Colour Scanner (CZCS), an algorithm for chlorophyll-ameasurements was derived. The comparison with chlorophyll-alidar measurements shows that different scales are resolved by both instruments. The CZCS-chlorophyll-aconcentrations are influenced by Gelbstoff and nonchlorophyllous particles. It is possible to use airborne lidar measurements of chlorophyll-afor calibrating spaceborne radiometers, if the fluorescence efficiency of chlorophyll-ais known and if the lidar itself is calibrated. The comparison between Advanced Very High Resolution Radiometer (AVHRR) sea surface temperatures and CZCS measurements indicates that mesoscale structures in the ocean are much better indicated by measurements in the visible spectrum. Mesoscale structures are often masked by the warming of the ocean top layer when measuring in the infrared.

ISSN:0143-1161    

DOI:10.1080/01431169008955169

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Wave height measurements made during the year November 1986 to November 1987 by the radar altimeter on the US Geosat satellite are used to map the seasonal variations in the global wave climate. The largest significant wave heights are found in winter in the Southern Ocean with only a slight reduction during the southern summer. In the North Atlantic and North Pacific the significant wave heights are lower and there is a larger variation between summer and winter.

ISSN:0143-1161    

DOI:10.1080/01431169008955170

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In Synthetic Aperture Radar (SAR) interferometry from a satellite, the altimetric information is obtained from the phase difference of two focused complex images gathered by the same sensor in two passes along parallel or crossing orbits. The altimetric resolution of such a system improves when the satellites displacement is increased in the cross-track direction. The maximum allowed displacement, limited by speckle noise, increases with the spatial resolution of the SAR image. Excluding the additive noise, we show that the achievable vertical resolution is better than the slant range resolution times the cosine of the off-nadir angle for about 99 per cent of the image points. As an example, an altimetric map of the Panamint Valley area is calculated using repeated passes of the Seasat satellite. The effect of the additive noise is visible when the cross-track distance of the two orbits is low.

ISSN:0143-1161    

DOI:10.1080/01431169008955171

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A major factor limiting the usefulness of airborne scanner imagery such as ATM has been the inability of conventional geometric correction procedures to remove high frequency distortion induced by platform and relief effects. An algorithm is described which uses matching Delaunay triangles to achieve a form of geometric correction that can cope with high frequency distortion. Early experimental results show that the procedure has the capacity to correct images which exhibit very complex patterns of distortion.

ISSN:0143-1161    

DOI:10.1080/01431169008955172

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Information on grassland quality is required to assess the impact of agricultural policy in Europe. Field methods are time-consuming and local in scope, but may provide a basis from which to extrapolate using remotely sensed data. For thirty-eight fields in the Lorraine region of France floristic descriptions, agricultural observations, biomass, ground radiometric data and SPOT HRV data were collected during June, July and September 1986 and April 1987. Agronomical and phytosociological classifications of grassland management type and by inference grassland quality, yielded similar results but the phytosociological method was preferred as it could be quantified. Ground radiometric data and SPOT HRV data for all four seasons were used successfully to discriminate grassland quality but stratification by grassland quality did not increase the degree of correlation between remotely sensed data and vegetation amount. This research highlights the potential that exists for using SPOT HRV data, in conjunction with a phytosociological classification of grassland quality, to classify and then monitor, the quality of grasslands in Europe.

ISSN:0143-1161    

DOI:10.1080/01431169008955173

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The imaging frequency and synoptic coverage of the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) make possible for the first time a phenological approach to vegetation cover classification in which classes are defined in terms of the timing, the duration and the intensity of photosynthetic activity. This approach, which exploits the strong, approximately linear relationship between the amount of solar irradiance absorbed by plant pigments and shortwave vegetation indices calculated from red and near-infrared reflectances, involves a supervised binary decision tree classification of phytophenological variables derived from multidate normalized difference vegetation index (NDVI) imagery. A global phytophenological classification derived from NOAA global vegetation index imagery is presented and discussed. Although interpretation of the various classes is limited considerably by the quality of global vegetation index imagery, the data show clearly the marked temporal asymmetry of terrestrial photosynthetic activity.

ISSN:0143-1161    

DOI:10.1080/01431169008955174

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The relative effectiveness of Landsat Thematic Mapper (TM) derived normalized difference vegetation index (NDVI) and short-wave infrared/near infrared index (SWIR/NIR) for measuring different types of damage in several forest communities was examined and compared. Study areas included: (1) Twin Mountain, New Hampshire, a site with well-defined fir waves; (2) Camels Hump mountain, Vermont, a site undergoing well-documented coniferous forest decline; and (3) a predominantly deciduous region seriously impacted by pear thrips in southern Vermont and north-western Massachusetts. Results indicated that the SWIR/NIR was excellent in distinguishing between high and low conifer damage for both fir wave and forest decline sites. The NDVI was less satisfactory in these conifer-dominated sites. High and low deciduous damage sites were easily separable using both NDVI and SWIR/NIR. The NDVI also allowed excellent separation between medium and low deciduous damage. Results from this study suggest that both indices are appropriate for global-scale monitoring of vegetation, with the SWIR/NIR being suitable for monitoring both deciduous and coniferous conditions and the NDVI being appropriate for monitoring broadleaf conditions.

ISSN:0143-1161    

DOI:10.1080/01431169008955175

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor