ISSN:0143-1161    

DOI:10.1080/014311697219231

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/014311697219240

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Crater lakes on active volcanoes act as heat and chemical traps, and are amenable to surveillance from space. By use of all seven spectral bands, the Landsat Thematic Mapper (TM) can simultaneously measure: (i) lake surface temperature, (ii) lake surface area, and (iii) lake colour which is related to water chemistry. Use of the total instrument in this way enhances its utility for volcano surveillance. This work examines TM data for crater lakes at the following volcanoes: Ruapehu (New Zealand), Taal (Philippines), Kawah Ijen and Kelut (Indonesia), Poas (Costa Rica), and Apoyeque and Jiloa (Nicaragua). Observatory data indicate that lake surface temperatures derived by TM band 6 are typically 1-4°C less than contemporaneously measured bulk temperatures, probably due to the skin effect, the difference between water bulk and surface temperature. For Ruapehu, TM band 6 hotspots coincide approximately with known upwelling sites above volcanic vents on the lakebed. Field observations at Kawah Ijen show that the skin effect (< 3°C) is strongly correlated with windspeed: wind gusts peaking at ≈ 5m s−1caused rapid decreases in surface temperature of ≈ 0.5-1.0°C. These fluctuations are small compared with the magnitude of volcanogenic changes in lake temperature and do not reduce the utility of infrared surveillance. TM-derived water surface spectral reflectances indicate high concentrations of suspended chemical sediment in the most active crater lakes: Ruapehu, Poás and Ijen. For Ruapehu, imaged on two dates, the later scene reveals an upwelling slick, bright in bands 5 and 7, possibly composed of hollow sulphur spherules emitted from a subaqueous vent. The Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) and Enhanced Thematic Mapper (ETM +) both due for launch in 1998, will offer improved capabilities for remote surveillance of crater lakes.

ISSN:0143-1161    

DOI:10.1080/014311697219259

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The concentration of soil phosphorus and pH correlated significantly with Landsat TM and Compact Airborne Spectrographic Imager (CASI) data, terrain position and aspect. Band ratios of the infrared and visible wavelengths are particularly significant for phosphorus. Exchangeable soil cations (that is calcium and sodium), as well as electrical conductivity, correlated less strongly with CASI and TM, but the correlations were statistically significant. Magnesium, potassium, and pH were significantly correlated with TM data, but not with the CASI data. pH and phosphorus were significantly correlated with terrain position. Three factors may individually, or in combination, be causing these results: illumination differences caused by terrain, direct reflectance of soil, or differences in vegetation (due to the influence of the soil on vegetation). A review of the literature appears to support the latter as the most likely causal factor. The results are important for establishing whether forest soils may be mapped using only remotely-sensed data, digital terrain data, or a combination.

ISSN:0143-1161    

DOI:10.1080/014311697219268

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The use of satellite remote sensing in Malaysian forestry and its potential are discussed under three headings (1) Application of satellite remote sensing in Malaysian forestry; (2) Current efforts in remote sensing research application; (3) Potentials of remote sensing techniques in monitoring logging operations and forest change; and remote sensing as a tool in rehabilitation and reforestation. It is concluded that there is a high potential of satellite remote sensing application in Malaysia, especially with the Landsat and SPOT data supported with aerial photographs. This is due to its fast delivery of relevant, timely and accurate information needed for sustainable forestry and a sound management decision.

ISSN:0143-1161    

DOI:10.1080/014311697219277

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A unique remotely sensed data set derived for a temperate mixed grassland in the central United States was used to test the comparability of a suite of satellite and aircraft sensors, and to characterize temporal variability in the normalized difference vegetation index (NDVI), retrieved surface radiant temperature (Ts), and surface biophysical variables. The temporal evolution of atmospherically corrected NDVI images through two growing seasons was found to be consistent among sensors. Maximum NDVI compositing of AVHRR data compared favourably with Landsat TM and SPOT-HRV, despite large variations in individual band reflectances with viewing geometry. Surface radiant temperatures retrieved from the various sensors, including aircraft TM-simulators, were also comparable, and in good agreement with surface measurements after radiometric calibration and atmospheric correction (2.7°C rmse). The relationship between NDVI andTswas determined largely by vegetation and environmental conditions (e.g., leaf area index and soil moisture), and was thus related to the partitioning of energy fluxes. The NDVI/Tsslopes were also affected by acquisition time, but were not significantly different among sensors over the growing season. These results suggest that data from different sensors can be used to augment spatial and temporal characteristics of datasets, when calibrated and corrected. Such capability diminishes the trade-off of spatial resolution at the expense of temporal resolution (and vice versa), thus allowing observation of short-term variations in biospheric processes.

ISSN:0143-1161    

DOI:10.1080/014311697219286

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This work presents a methodology to classify croplands using a multitemporal/historical dataset of images and ground ancillary data referring to three consecutive years. An image processing/geographic information system as well as a database management system (DBMS) were used to make the integration of these multisource data. In order to evaluate the usefulness of a database for crop classification, the area under study was digitally classified by two groups of interpreters, using two methodologies: (a) the proposed methodology using maximum likelihood classification assisted by an historical/multisource database, and (b) a conventional maximum likelihood classification only. Both results were compared using the Kappa statistics. The indices to both the proposed and the conventional digital classification methodologies were 0.669 (very good) and 0.472 (good), respectively. The use of the database rendered an improvement over the conventional digital classification. Furthermore, along with this study some problems related to multisource data integration are discussed.

ISSN:0143-1161    

DOI:10.1080/014311697219295

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In order to prevent soil loss and protect fertile lands from soil erosion, precise information on the nature, extent and magnitude of soil erosion is a prerequisite. In the study reported here, Landsat MSS, TM and Indian Remote Sensing Satellite (IRS-1A) Linear Imaging Self-scanning Sensor (LISS-II) data have been visually interpreted to derive qualitative information on both eroded lands and shifting cultivation areas. Three categories of eroded lands, namely (i) nil to slight, (ii) moderate, and (iii) severe to very severe were delineated. Opticalcum-digital enlargement of LISS-II data helped to pick up small pockets of eroded lands and shifting cultivation areas that were not discernible at a 1 :250 000 scale. Temporal variation observed in the extent and distribution of eroded lands is also discussed in detail.

ISSN:0143-1161    

DOI:10.1080/014311697219303

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Reliable estimates of carbon exchange between terrestrial ecosystems and the atmosphere due to land-use change have become increasingly important. One source of land-use change estimates comes from comparing multi-date remote sensing imagery, though the effect of land-cover classification errors on carbon flux estimates has not been considered to our knowledge. We evaluated the integration of a land-cover change detection methodology using Landsat MultiSpectral Scanner (MSS) imagery with a regional carbon budget analysis. This work includes the incorporation of image classification accuracy information into the carbon budget of our sample landscape. Our analysis indicates that the Los Tuxtlas, Mexico study region experienced an approximate net loss of 2.146 106tC from 1986 to 1990. A carbon loss value which does not include classification error estimates is 34 per cent less than the adjusted value.

ISSN:0143-1161    

DOI:10.1080/014311697219312

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Daily values of actual canopy transpiration were obtained by stemflow heat balance method (SFG) in drought-stressed, waterlogged, and periodically-irrigated soybean canopies (Glycine maxMerr.). Spectral and thermal infrared measurements and basic meteorological factors were obtained over the canopies under a wide range of sky conditions. The potential canopy transpiration (Trp) was found to be linearly correlated to the product of an instantaneous measurement of spectral vegetation index (SAVI) and daily sum of incoming solar radiation (Rs), asTrp=αSAVIRs. The proportionality constantαwas 0.28 for soybean canopies. On the basis of this simplified relation, a simple method was proposed to estimate the daily values of actual canopy transpiration (Tra). The method utilizes either instantaneous measurements of plant and air temperature differential (tplant- tair) or CWSI (Crop Water Stress Index) around mid-day as a major input. Bothtplant- tairand CWSI can be estimated by thermal remote sensing. Values of Tra estimated by models using the instantaneous measurements of either tplant tair or CWSI were found to be well correlated to those measured by SFG. Results showed that the simple model based on a combined use of spectral and thermal data would provide a basis for estimation of potential and actual daily transpiration with a few easily-available inputs.

ISSN:0143-1161    

DOI:10.1080/014311697219321

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor