ISSN:0143-1161    

DOI:10.1080/014311697217585

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Lidar monitoring of surface waters is usually applied to fluorescent substances like phytoplankton, yellow substances and oil. A lidar method is introduced which allows the measuring of the total attenuation coefficient at the laser wavelength considering also nonfluorescent substances besides fluorescent ones. Two signals are measured: first the total fluorescence lidar signal L, which is characterized by long path-lengths of the laser radiation in the water column, and second, the fluorescence F, which originates from the first layers immediately below the water surface. A simple experiment in the laboratory was performed using a nitrogen laser. Water samples containing algae and varying amounts of humic and ligninesulfonic acids were investigated. Synchronously the attenuation coefficients were measured. The F/L ratio yielded the total attenuation at the laser wavelength. Good correlations between the conventional and the lidar-derived attenuation coefficients were achieved described by squared correlation coefficients of R2 > 0.95. The F/L ratio seems to be a good tool in lidar monitoring of waters.

ISSN:0143-1161    

DOI:10.1080/014311697217594

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We analyse a new optical method to detect and utilize underwater acoustic signals from above the ocean surface. The method is based on scattering of modulated laser light by natural inhomogeneities (hydrosoles, bubbles, turbulence, etc.) whose concentration oscillates in a vertically propagating sound wave. Measurement of the Doppler shifted modulation frequency in the scattered light may be used both for monitoring of the upper ocean sound speed profile and for communication with underwater objects.

ISSN:0143-1161    

DOI:10.1080/014311697217602

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The performance of a high resolution tristatic minisodar is evaluated over an area of complex topography using a 30m high meteorological mast equipped with cup anemometers and bivanes. The instrumentation was in operation at the Moni Toplou Wind Park (Island of Crete, Greece) and the comparison covered a range of high wind speed and different meteorological conditions during day and night-time periods. The Sodar measurements of mean wind speed and direction for 15 min time segments agreed with the in situ measurements although an underestimation of the wind speed is evident. On the other hand the standard deviations of the wind speed and direction as estimated by Sodar gave poor agreement with the in situ instrumentation.

ISSN:0143-1161    

DOI:10.1080/014311697217611

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The availability of remote sensing data with improved spatial, spectral and radiometric resolution is now available to fully exploit their potential for a specific application subject to the relative merits and the limitations of each sensor's data. Presented here is a case study where Landsat MSS and TM; and SPOT MLA data for part of the Bijapur district, southern India, which were acquired on the same day, have been evaluated for mapping eroded lands. The approach involves the geometric registration of all three data to a common map grid using tie points and third order polynomial transform; and resampling the MSS and TM data to a 20m by 20 m pixel dimension and radiometric normalization. Thematic maps showing eroded lands were generated on a micro-VAXbased DIPIX system using a maximum likelihood classifier. Accuracy estimates were made for the thematic maps following stratified unaligned random sampling technique, and subsequently, computing overall accuracy and Kappa coefficient. Spectral separability and classification accuracy was maximum from SPOT-MLA data followed by a combination of Landsat MSS band 1, SPOT-MLA band 2 and Landsat TM band 4; Landsat TM, a combination of Landsat MSS, TM and SPOT MLA; and Landsat MSS data.

ISSN:0143-1161    

DOI:10.1080/014311697217620

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper, high resolution, remotely-sensed data are investigated as a source of management information for moorland vegetation communities on a hypothetical farm in a marginal farming area of Scotland. A hybrid technique for vegetation mapping is adopted. This involves unsupervised machine classification of spectral variation in digitally enhanced air photographs and satellite imagery, together with visual interpretation of the imagery in both the laboratory and the field. This technique enables relative estimates of annual gross biomass production, for a range of vegetation types, to be obtained. The data are integrated into a simple heather moorland management model (HMMM), to produce potential sheep-stocking capacities under a range of management scenarios, the possible financial implications of these scenarios are also assessed.

ISSN:0143-1161    

DOI:10.1080/014311697217639

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Attention worldwide has been focused on the need to assess the appropriateness of land management strategies especially where these occur near sensitive areas of wildlife habitat. This work considers the use of mainly Thematic Mapper data in providing an assessment of the relative impact of different land management strategies on the natural vegetation cover in part of the sensitive Okavango area in Botswana. Supervised classification (maximum likelihood) techniques when used on six-band TM imagery showed that differential degradation was prevalent in land management areas, especially where these are separated by fencelines with an overall accuracy 72 per cent. Marginally more degradation is evident in a controlled hunting area adjacent to the Game Reserve, relative to a communal grazing area. Band transform analyses indicate that distinctive changes in cover type and density frequently take place over boundaries or fencelines separating land management areas. Some degradation in the controlled hunting area appears related to the influence of faultlines on the distribution of soil, hence plant community types. In other cases the pattern of degradation is distributed randomly between the Game Reserve and the cordon fence. Reasons for this unusual distribution pattern may lie in the restriction of movement of migratory wildlife species southwards by the cordon fence separating communal grazing from hunting land uses. A more appropriate management strategy may lie in the prediction of wildlife movements, prior to the erection of cordon fences.

ISSN:0143-1161    

DOI:10.1080/014311697217648

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

MVI (Maximum Value Interpolated) is a new proposed method in NDVI profiles maximization instead of MVC (Maximum Value Composite). The MVI method consists of recording not only the NDVI maximum value within a period (e.g., a month), but also the day when that value was recorded. Through simple linear interpolation between these points it is possible to detect, for each time period, a representative NDVI value. Through a profile simulation method it is possible to show that the new method allows a significant error reduction compared with the MVC method.

ISSN:0143-1161    

DOI:10.1080/014311697217657

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Models of regional CO exchange processes in arctic tundra environ2 ments using landscape characteristics may need to incorporate spatial and temporal variations in the depth to the permafrost layer because it influences soil drainage, aeration, decomposition, and nutrient availability. However this depth, or the depth of the active layer (DAL), will have to be estimated indirectly since it is not practical to make a large number of ground measurements on a regular basis. Previous research has demonstrated that spatial variations in DAL are strongly related to aboveground vegetation production in sub-arctic tundra. Since aboveground vegetation production in Alaskan arctic tundra has been related to the Normalized Difference Vegetation Index (NDVI), it was hypothesized that spatial variations in NDVI would follow variations in DAL in these environments. Studies were conducted on the North Slope of Alaska during the summers of 1994 and 1995 to determine the feasibility of estimating DAL at multiple spatial scales using the NDVI. Experiments were performed at sites with distinctly different topographic relief using hand-held and satellite spectral radiometric data and ground measurements of DAL. Overall, our results suggest that there is no relation between NDVI and DAL in areas with little variation in relief. However, in areas where topography strongly controls the flow and redistribution of water, NDVI did account for approximately 40 per cent of the variability in DAL.

ISSN:0143-1161    

DOI:10.1080/014311697217666

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An investigation into the impact of the maximum Normalized Difference Vegetation Index (NDVI) and the maximum surface temperature (Ts) compositing procedures (MaN and MaT respectively) upon retrieved NDVI and Ts values extracted from forested areas located across eight months of cloud screened European AVHRR data is described. NDVI values are found to be significantly higher and generally less variable when they are extracted from MaN rather than from MaT composites and Ts values are found to be significantly higher and generally less variable when they are extracted from MaT rather than from MaN composites. The impact of these differences is illustrated within the context of a European forest/non-forest classification that uses both NDVI and Ts data. Higher potential forest/non-forest classification accuracies are found using NDVI data extracted from the MaN composites and Ts data extracted from the MaT composites than from any other combination of composited data. The findings indicate that inappropriate selection of a compositing procedure may have a significant impact upon the subsequent application of NDVI and/or Ts data.

ISSN:0143-1161    

DOI:10.1080/014311697217675

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor