Showing papers in "International Journal of Remote Sensing in 1994"
TL;DR: In this paper, a coarse spatial resolution (one by one degree) data set of monthly NDVI values for 1987 was used to explore the methodological issues of identifying land cover types that are spectrally distinct and applicable at the global scale, accounting for phasing of seasons in different parts of the world, validating results in the absence of reliable information on global land cover, and acquiring high quality global data sets of satellite sensor data for input to land cover classifications.
Abstract: Phenological differences among vegetation types, reflected in temporal variations in the Normalized Difference Vegetation Index (NDVI) derived from satellite data, have been used to classify land cover at continental scales. Extending this technique to global scales raises several issues: identifying land cover types that are spectrally distinct and applicable at the global scale; accounting for phasing of seasons in different parts of the world; validating results in the absence of reliable information on global land cover; and acquiring high quality global data sets of satellite sensor data for input to land cover classifications. For this study, a coarse spatial resolution (one by one degree) data set of monthly NDVI values for 1987 was used to explore these methodological issues. A result of a supervised, maximum likelihood classification of eleven cover types is presented to illustrate the feasibility of using satellite sensor data to increase the accuracy of global land cover information, a...
1,010 citations
TL;DR: In this article, the authors describe a computationally fast and accurate technique for the atmospheric correction of satellite measurements in the solar spectrum, which is based on a set of equations with coefficients which depend on the spectral band of the sensor.
Abstract: This paper describes a computationally fast and accurate technique for the atmospheric correction of satellite measurements in the solar spectrum. The main advantage of the method is that it is several hundred times faster than more detailed radiative transfer models like 5S and that it does not require precalculated look-up tables. The method is especially useful for correcting the huge amounts of data acquired by large-field-of-view high-repetitivity sensors, like the ones on board polar orbiting and geostationary meteorological satellites. The technique is based on a set of equations with coefficients which depend on the spectral band of the sensor. Semi-empirical formulations are used to describe the different interactions (absorption, scattering, etc.) of solar radiation with atmospheric constituents during its traverse through the atmosphere. Sensor specific coefficients of each equation are determined using a best fit technique against the computations of the 5S code (Simulation of Satelli...
803 citations
TL;DR: Red edge was found valuable for assessment of plant chlorophyll concentration and LAI, and therefore nutritional status and water stress also affected drre, but only when the stress was well developed.
Abstract: Some red edge parameters in the first derivative reflectance curve (wavelength, amplitude and area of the red edge peak) were studied to evaluate plant chlorophyll content, biomassand RelativeWater Content (RWC).Plants of Capsicum annuum and Phaseolus vulgaris under different nitrogen and water availabilities, and plants of Gerbera jamesonii with different hydric status were studied. A high correlation was found between chlorophyll content and the wavelength of the red edge peak (λre ), and between LAI (leaf area index)and the amplitude of the red edge peak (drr e ), but the area of the red edge peak (σ680–780 nm) was the best estimator of LAI. Thus, red edge was found valuable for assessment of plant chlorophyll concentration and LAI, and therefore nutritional status. Water stress also affected drre, but only when the stress was well developed.
781 citations
TL;DR: A maximum likelihood classifier to segment polarimetric SAR data according to terrain types has been developed based on the Wishart distribution, which can be applied to multifrequency multi-look polarimetry SAR data, as well as 10 SAR data containing only intensity information.
Abstract: Multi-look polarimetric SAR (synthetic aperture radar) data can be represented either in Mueller matrix form or in complex covariance matrix form. The latter has a complex Wishart distribution. A maximum likelihood classifier to segment polarimetric SAR data according to terrain types has been developed based on the Wishart distribution. This algorithm can also be applied to multifrequency multi-look polarimetric SAR data, as well as 10 SAR data containing only intensity information. A procedure is then developed for unsupervised classification. The classification error is assessed by using Monte Carlo simulation of multilook polarimetric SAR data, owing to the lack of ground truth for each pixel. Comparisons of classification errors using the training sets and single-look data are also made. Applications of this algorithm are demonstrated with NASA/JPL P-, L- and C-band polarimetric SAR data.
717 citations
TL;DR: In this paper, the authors evaluated the ratio of leaf reflectance within narrow wavebands (2nm) as indicators of plant stress and determined the wavelength regions in which reflectance was most affected by 8 stress agents among 6 plant species.
Abstract: Ratios of leaf reflectances that were measured within narrow wavebands (2nm) were evaluated as indicators of plant stress. Wavebands used in ratio computation were based on earlier studies that determined the wavelength regions in which reflectance was most affected by 8 stress agents among 6 plant species. Several ratios, such as reflectance at 695 nm divided by reflectance at 670 nm (R695/R670), were affected by some but not all stress agents. However, R695/R420, R605/R760, R695/R760 and R710/R760 were significantly greater (p≤0·05) in stressed compared with non-stressed leaves for all stress agents. The ratios that most strongly indicated plant stress were reflectance at 695 nm divided by reflectance at 420 nm or 760 nm.
663 citations
TL;DR: In this article, a satellite-based 1° by 1° normalized difference vegetation index (NDVI) data set has been processed to derive land surface parameters for general circulation models of the atmosphere (GCMs).
Abstract: A satellite-based 1° by 1° normalized difference vegetation index (NDVI) data set has been processed to derive land surface parameters for general circulation models of the atmosphere (GCMs). Prior to calculation of the land surface parameters, corrections were applied to the source NDVI data set to account for (i) obvious anomalies in the data time-series, (ii) the effect of variations in solar zenith angle, (iii) data dropouts in cold regions where a temperature threshold procedure designed to screen for clouds also eliminates cold land surface points, and (iv) persistent cloud cover in the tropics. An outline of the procedures for calculating land surface parameters from the corrected NDVI data set is given, and a brief description is provided of source material that was used in addition to the NDVI data. The data sets summarized in this paper should represent improvements over prescriptions currently used in land surface parameterizations in that the spatial and temporal dynamics of key land ...
522 citations
TL;DR: A reprocessing of 12 years of global data from the Advanced Very High Resolution Radiometers on board the afternoon-viewing NOAA series satellites (NOAA-7, 9, and 11) is taking place as part of the NASA/NOAA Pathfinder project as discussed by the authors.
Abstract: A reprocessing of 12 years of global data from the Advanced Very High Resolution Radiometers on board the afternoon-viewing NOAA series satellites (NOAA-7, 9, and 11) is taking place as part of the NASA/NOAA Pathfinder project. A Pathfinder AVHRR land data set is being produced which is composed of global, 8 km NDVI with associated reflectances, brightness temperatures, solar and scan geometry, and cloud estimation. This data set is being processed using the best available methods in order to produce a consistent time series of data of unprecedented quality. Methods used in processing include a cross-satellite calibration, navigation using an orbital model and updated ephemerides, and correction for Rayleigh scattering. The data will be available to the community as both daily and composite data, and analysis of this long time series is expected to provide insight into terrestrial processes, seasonal and annual variability, and methods for handling large volume data sets.
511 citations
TL;DR: The MODIS land team (MODLAND) as mentioned in this paper developed a suite of global land products for EOSDIS implementation, including spectral albedo, land cover, spectral vegetation indices, snow and ice cover, surface temperature and fire.
Abstract: The Moderate Resolution Imaging Spectroradiometer (MODIS) will be the primary daily global monitoring sensor on the NASA Earth Observing System (EOS) satellites, scheduled for launch on the EOS-AM platform in June 1998 and the EOS-PM platform in December 2000. MODIS is a 36 channel radiometer covering 0·415-14·235 μm wavelengths, with spatial resolution from 250 m to 1 km at nadir. MODIS will be the primary EOS sensor for providing data on terrestrial biospheric dynamics and process activity. This paper presents the suite of global land products currently planned for EOSDIS implementation, to be developed by the authors of this paper, the MODIS land team (MODLAND). These include spectral albedo, land cover, spectral vegetation indices, snow and ice cover, surface temperature and fire, and a number of biophysical variables that will allow computation of global carbon cycles, hydrologic balances and biogeochemistry of critical greenhouse gases. Additionally, the regular global coverage of these var...
417 citations
TL;DR: The Global Land 1 km data set project as mentioned in this paper represents an international effort to acquire, archive, process, and distribute 1 km AVHRR data of the entire global land surface in order to meet the needs of the international science community.
Abstract: The global land 1 km data set project represents an international effort to acquire, archive, process, and distribute 1 km AVHRR data of the entire global land surface in order to meet the needs of the international science community. A network of 26 high resolution picture transmission (HRPT) stations, along with data recorded by the National Oceanic and Atmospheric Administration (NOAA), has been acquiring daily global land coverage since 1 April 1992. A data set of over 30000 AVHRR images has been archived and made available for distribution by the United States Geological Survey, EROS Data Center and the European Space Agency Under the guidance of the International Geosphere Biosphere programme, processing standards for the AVHRR data have been developed for calibration, atmospheric correction, geometric registration, and the production of global 10-day maximum normalized difference vegetation index (NDVI) composites. The major uses of the composites are related to the study of surface vegeta...
383 citations
TL;DR: In this article, two approaches to estimating sub-pixel land cover composition are investigated, a linear mixture model and a regression model based on fuzzy membership functions, and significant correlation coefficients, all > 0·7, between the actual and predicted proportion of a land cover type within a pixel were obtained.
Abstract: Mixed pixels occur commonly in remotely-sensed imagery, especially those with a coarse spatial resolution. They are a problem in land-cover mapping applications since image classification routines assume ‘pure’ or homogeneous pixels. By unmixing a pixel into its component parts it is possible to enableinter alia more accurate estimation of the areal extent of different land cover classes. In this paper two approaches to estimating sub-pixel land cover composition are investigated. One is a linear mixture model the other is a regression model based on fuzzy membership functions. For both approaches significant correlation coefficients, all >0·7, between the actual and predicted proportion of a land cover type within a pixel were obtained. Additionally a case study is presented in which the accuracy of the estimation of tropical forest extent is increased significantly through the use of sub-pixel estimates of land-cover composition rather than a conventional image classification.
370 citations
TL;DR: A nine-year (1982-1990) global normalized difference vegetation index (NDVI) data set with a spatial resolution of 1° by 1° and a temporal resolution of one month was compiled for use in climate studies.
Abstract: A nine-year (1982–1990) global normalized difference vegetation index (NDVI) data set with a spatial resolution of 1° by 1° and a temporal resolution of one month was compiled for use in climate studies. This data set was derived from higher resolution (5–8 km) monthly continental NDVI data sets that have been processed and archived by the Global Inventory Monitoring and Modelling Studies (GIMMS) group at NASA/Goddard Space Flight Center. The continental GIMMS NDVI data sets were calculated from Global Area Coverage (GAC) data collected at daily intervals by the Advanced Very High Resolution Radiometer (AVHRR) onboard the NOAA-7, -9 and -11 satellites The global 1° by 1° NDVI data set was produced to calculate land surface parameters for use within general circulation model J of the atmosphere (GCM). In view of this quantitative application, an evaluation is given of the representation by the NDVI data of the spectral properties of vegetation at the landsurface. Errors are defined as deviations f...
TL;DR: In this article, an analytical model was developed to address timing to peak NOVI response and total duration of response to daily precipitation for vegetation under water-limited growth conditions (e.g., in arid or semi-arid environments).
Abstract: This paper describes how NOVI responds to daily precipitation for vegetation under water-limited growth conditions (e.g., in arid or semi-arid environments). An analytical model was developed to address timing to peak NOVI response and total duration of NOVI response to a rainfall event with the passage of time. The model also describes how effectively the vegetation uses precipitated water. A case study in the Sandhills area of Nebraska, with NOVI calculated from Landsat-MSS images, showed that the model can accurately portray NOVI time series, and then can be used to derive some useful information about relations of NOVI and precipitation. For the vegetation in the test area, we found that the peak vegetative response to a precipitation event shifts from about 14 days after the rainfall event at the beginning of a growing season to 25 days at the late stage of the season, and then shifts back to 12 days at the end of the season. The duration of response, similar to the peak response in behavior...
TL;DR: In this paper, a split-window equation for land surface temperature is derived, yielding T = T4 + A(T4 − T5) + B(e), where T is the true surface temperature, T4 and T5 are the brightness temperatures measured in AVHRR channels 4 and 5.
Abstract: A split-window equation is derived for land surface temperature, yielding T = T4 + A(T4 − T5) + B(e), where T is the true surface temperature, T4 and T5 are the brightness temperatures measured in AVHRR channels 4 and 5, A is a coefficient related to the atmospheric transmittances in AVHRR channels 4 and 5, being dependent on the atmosphere type and independent on surface emissivity, and B(e) takes into account the emissivity effect, which depends on both the channel surface emissivities (e4 and e5) and the atmosphere type. The atmospheric dependence of split-window coefficients, A and B(e), is discussed by means of satellite measurements simulations and in situ data. It is shown that linear, global-scale algorithms can produce inaccurate estimates of surface temperature when they are applied to areas of reduced atmospheric variability. A simple, non-linear split-window algorithm has been proposed, in which A = a0+ a1(T4− T5). The constants a0and a1 have been calculated from a set of in situ and ...
TL;DR: In this article, the authors used theoretical modelling applied to calibrated SAR data to explain the radar backscatter from the forest canopy under study, which was found to be an optimal frequency band for forest observations.
Abstract: In recent years, there has been an increasing interest in the use of radar data for observations of forest ecosystems. In particular, it was shown that the intensity of SAR images at L band was proportional to the forest aboveground biomass. More recently, the analysis of NASA/ JPL SAR data over the Landes forest “south-west France” revealed strong correlation between P-band backscatter and biomass of pine trees and related characteristics “tree age, height, diameter”. Also, similar relations have been obtained on two different forests “maritime pine at Landes forest, France, and loblolly pine at Duke forest, U.S.A.”. This paper presents a step further in the understanding of the observations. using theoretical modelling applied to calibrated SAR data to explain the radar backscatter from the forest canopy under study. The study is presented at P band, which was found to be an optimal frequency band for forest observations. It was found that the H H return is physically related to both trunk and ...
TL;DR: Experience has demonstrated that even for a relatively simple sensor such as the AVHRR, the task of creating global data set is fraught with difficulties and that a number of iterations have been necessary despite considerable efforts in the specification of users' requirements.
Abstract: The Advanced Very High Resolution Radiometer (AVHRR) has become one of the most important sensors for monitoring the terrestrial environment at resolutions of 1 km to very coarse resolutions of 15 km and greater. To make these data suitable for scientific and other applications considerable effort has been devoted to the creation of global data sets. Experience has demonstrated that even for a relatively simple sensor such as the AVHRR, the task of creating global data set is fraught with difficulties and that a number of iterations have been necessary despite considerable efforts in the specification of users' requirements Four types of data processing streams, overlapping in time, have occurred in the creation of global data sets from the AVHRR. The first three data processing streams were all based on the reduced resolution, Global Area Coverage (GAC) data set, which is collected globally every day. In the first data processing stream a much reduced data set was created in the form of the Glob...
TL;DR: In this paper, a change detection method is applied to three remotely-sensed indicators of land-surface conditions (vegetation index, surface temperature and spatial structure) in order to improve the capability to detect and categorize subtle forms of land cover change.
Abstract: Change-vector analysis in multi-temporal space is a powerful tool to analyse the nature and magnitude of land-cover change. The change vector compares the difference in the time-trajectory of a biophysical indicator for successive time periods. This change detection method is applied to three remotely-sensed indicators of land-surface conditions—vegetation index, surface temperature and spatial structure—in order to improve the capability to detect and categorize subtle forms of land-cover change. It is tested in a region of West Africa, using multi-temporal Local Area Coverage imagery obtained by the Advanced Very-High Resolution Radiometer on NOAA-9 and NOAA-II orbiting platforms. The three indicators show a low degree of redundancy and detect different land-cover change processes, which operate at different time scales. Change vector analysis is being developed for application to the land-cover change product to be produced using NASA's Moderate-Resolution Imaging Spectroradiometer instrument,...
TL;DR: In this article, the authors proposed that a global data set of the land surface is created from remotely sensed data from the Advanced Very High Resolution Radiometer (AVHRR) to support a number of IGBP's projects.
Abstract: Examination of the scientific priorities for the International Geosphere Biosphere Programme (IGBP) reveals a requirement for global land data sets in several of its Core Projects. These data sets need to be at several space and time scales. Requirements are demonstrated for the regular acquisition of data at spatial resolutions of 1 km and finer and at high temporal frequencies. Global daily data at a resolution of approximately 1 km are sensed by the Advanced Very High Resolution Radiometer (AVHRR), but they have not been available in a single archive. It is proposed, that a global data set of the land surface is created from remotely sensed data from the AVHRR to support a number of IGBP's projects. This data set should have a spatial resolution of 1 km and should be generated at least once every 10 days for the entire globe. The minimum length of record should be a year, and ideally a system should be put in place which leads to the continuous acquisition of 1 km data to provide a base line d...
TL;DR: In this paper, the U.K.-Earth Observation Data Centre uses waveform retracking and slope correction for ocean and land altimeter data analysis over ice sheets and shelves.
Abstract: The analysis of altimeter data over non-ocean surfaces is complicated by the effects of topography and the dielectric properties of the surface. The philosophy behind the processing (for the U.K.-Earth Observation Data Centre) of altimeter data over ice sheets and shelves is explained and a description of the function and performance of the algorithms used is provided. The methods available for waveform retracking and slope correction, which represent the primary difference between ocean and land altimeter data analysis, are discussed in detail. Results from their operation with Seasat altimeter data and a simulated surface profile are provided to indicate their likely performance with ERS-1 data. The contents and structure of the ice sheet data product is described and its intended applications discussed. Future modifications and calibration/validation of the data are also considered.
TL;DR: In this article, an inversion algorithm based on a simplified radiative transfer model was proposed to estimate the characteristics of atmospheric aerosols by the use of the path radiance in two TM bands rather than a priori assumed.
Abstract: Most of the atmospheric correction methods proposed in the literature are not easily applicable in reaJ cases. The most sophisticated models frequently require inputs which are not commonly available, whilst traditional simple dark object subtraction techniques do not generally give real reflectance values. In the present work an atmospheric correction method applicable to Landsat-TM data is described, which requires only inputs that are commonly available and the presence in the imaged scenes of some dark surfaces in TM bands 1 (blue) and 3 (red). The method consists of an inversion algorithm based on a simplified radiative transfer model in which the characteristics of atmospheric aerosols are estimated by the use of the path radiance in two TM bands rather than a priori assumed. On the basis of this information, which is crucial for determining the atmospheric properties, the retrieval of real reflectances from TM images is possible. The method can be applied to all TM scenes in which some dar...
TL;DR: In this article, the authors compared estimates of regional biomass and LAI for a tallgrass prairie site derived from ground data versus estimates derived from satellite data and showed important differences in the relationships between Kauth-Thomas greenness (from TM), LAI, biomass and the various terrain variables.
Abstract: We compared estimates of regional biomass and LAI for a tallgrass prairie site derived from ground data versus estimates derived from satellite data. Linear regression models were estimated to predict LAI and biomass from Landsat-TM data for imagery acquired on three dates spanning the growing season of 1987 using co-registered TM data and ground measurements of LAl and biomass collected at 27 grassland sites. Mapped terrain variables including burning treatment, land-use, and topographic position were included as indicator variables in the models to acccount for variance in biomass and LAI not captured in the TM data. Our results show important differences in the relationships between Kauth-Thomas greenness (from TM), LAI, biomass and the various terrain variables. In general, site-wide estimates of biomass and LAI derived from ground versus satellite-based data were comparable. However, substantial differences were observed in June. In a number of cases, the regression models exhibited signific...
TL;DR: In this paper, a signal processing technique is presented and applied to annual patterns of the Global Vegetation Index (GVI) derived from the Advanced Very High Resolution Radiometer (AVHRR) to examine the frequency distribution of the multi-temporal signal.
Abstract: A signal processing technique is presented and applied to annual patterns of the Global Vegetation Index (GVI) derived from the Advanced Very High Resolution Radiometer (AVHRR) to examine the frequency distribution of the multi-temporal signal. It is shown that frequencies of the signal are linked to integrated GVI, seasonal variability and subseasonal variability of the land cover type. These characteristics are used to derive a land cover classification.
TL;DR: In this article, the authors discuss the routine monitoring of sea ice using the ERS-1 radar altimeter and review the processing adopted at the U.K. EODC.
Abstract: Sea ice presents a serious impediment to both shipping and off-shore operations in the polar regions. Since sea ice conditions can change within a matter of hours, near real time monitoring is required. Airborne data are available in some areas, but collection is expensive and coverage limited. Satellite images can provide wider coverage, but cloud cover, darkness and the need for rapid processing and dissemination can limit their use. Information on sea ice cover over longer periods is needed for global climate monitoring. Microwave sensors provide the most practical means of monitoring global sea ice cover since they can operate both at night and day and observe through clouds. Previous studies have concentrated on the use of passive microwave data.Here we discuss the routine monitoring of sea ice using the ERS-1 radar altimeter. The low data rate and somewhat simple nature of the data, lend themselves to the mapping of global sea ice cover and to operational applications.We review the processing adopted at the U.K. EODC.
TL;DR: In this paper, the authors show how vegetation cover index values derived from multi-temporal remotely-sensed data can be used in association with spatial models of grazing impact on landscapes to identify grazing-induced land degradation.
Abstract: Land degradation is difficult to assess in arid rangelands because of short-term variations in rainfall, landscape diversity and the problems of sampling very large areas. This paper shows how vegetation cover index values derived from multi-temporal remotely-sensed data can be used in association with spatial models of grazing impact on landscapes to identify grazing-induced land degradation. The method assumes that grazing effects decrease with distance from water and that temporary grazing impacts largely disappear as vegetation responds to major rainfalls. Grazing gradients (i.e., systematic changes in vegetation cover with distance from water) which remain indicate long term damage. Simple grazing gradients involve changes in average cover with distance from water and include normal, inverse and composite types, complex grazing gradients show systematic changes in cover variance with distance from water and develop where soil and runoff are being redistributed. Although complex grazing gradi...
TL;DR: In this article, the most commonly used methods have been applied to a time-series of 63 AVHRR day time images for the whole of West Africa for the 1991-1992 dry season.
Abstract: Data from the Advanced Very High Resolution Radiometer (AVHRR) have been used for the detection of fires in various ecosystems throughout the world. In this study the most commonlyused methods have been applied to a time-series of 63 AVHRR day time images for the whole of West Africa for the 1991–1992 dry season. The West African region includes ecosystems ranging from dry Sahelian grasslands to moist tropical forests. Furthermore, these ecosystems show considerable seasonal variability. Existing methods were found to be inadequate for fire detection for the whole region becauseof the spatial and temporal heterogeneity of the region's environments. A number of changes were made to the established methods and the new fire detection procedure was applied to the time-series. Field verification and interpretation of the results in the context of the main ecological divisionsof the regionshowed the new method to give good results for all ecosystems throughout the season. Finally, interpretation of fir...
TL;DR: In this paper, the authors used very high-resolution radiometer data from 1980 to 1992 to determine the boundary between the Sahara Desert and the Sahel Zone of Africa using daily advanced very high resolution radiometers.
Abstract: A programme of global arid and semi-arid land monitoring is currently underway at NASA/Goddard Space Flight Center using meteorological satellite data to detect possible climatic change as manifested by changes in arid and semi-arid land extent. This has resulted in the processing and interpretation of a large amount of satellite data from the NOAA-series of polar-orbiting satellites. Techniques are described and preliminary results presented for determination of the boundary between the Sahara Desert and the Sahel Zone of Africa using daily advanced very high resolution radiometer data from 1980–1992. Some of the techniques may be of interest to other researchers who are or will be using large multi-year data sets derived from coarse-resolution satellite data to investigate large-scale land surface questions.
TL;DR: In this paper, the spectral responses of algal chlorophyll and water, under natural sunlight with varying suspended sediment concentrations (SSC), were investigated, and the relationship between reflectance and SSC satisfies the expression: d2R(λ)/dS2 < 0.
Abstract: The purpose of this paper is to investigate the spectral responses of algal chlorophyll and water, under natural sunlight with varying suspended sediment concentrations (SSC). Twenty levels of SSC with each of two sediment types were generated, ranging from 50 to 1000 mgl−1, in 75101 of water containing chlorophyll-a concentrations of 718 μgl−1 and 295 μgl−1. Results indicate that suspended sediments do not eliminate the prominent spectral patterns of algal chlorophyll, even as SSC reached 1000 mgl−1. Between 400 and 900 nm, the relation between reflectance and SSC satisfies the expression: d2R(λ)/dS2<0. The effects of varying SSC on the positions and magnitudes of pronounced chlorophyll features were investigated. The ratio between the NIR and red wavelengths was totally independent of SSC. Thus, our finding supports using it as an index for measuring chlorophyll in natural surface water containing suspended sediments.
TL;DR: In this article, ground-based measurements on the Pasterze Glacier and the Kleines Fleisskees, located in the eastern Alps of Austria, have shown that these glaciers have receded significantly.
Abstract: Ground-based measurements on the Pasterze Glacier and the Kleines Fleisskees, located in the eastern Alps of Austria, have shown that these glaciers have receded significantly. Landsat Thematic Mapper (TM) data of these glaciers were acquired in August of 1984,1986,1988 and 1990, and have been studied in detail. The 1984–1990 retreat of the Pasterze Glacier has been measured using digital TM data, but the 1984–1988 retreat of the Kleines Fleisskees has not been observed using the TM data because the magnitude of recession between 1984 and 1988 was small relative to the resolution of the TM data. Significant increases in the area of exposed ice (icc facies) on both the Pasterze Glacier and the Kleines Fleisskees were observed and measured using TM data acquired in early August from 1984 to 1988. The area of the Pasterze Glacier and Kleines Fleisskees basins, as measured using TM data, is 20·8±1·02km2 and 1·56±0·188 km2, respectively. The percentage of the Pasterze Glacier comprised of bare ice inc...
TL;DR: In this paper, the upper limit of the PAR conversion efficiency as a function of woody biomass for forest vegetation was determined, which was about 3·5gMJ-1 at very low values of stem biomass.
Abstract: Terrestrial net primary production (NPP) may be determined from remotely-sensed vegetation indices by estimating the amount of photosynthetically active radiation (PAR) absorbed by vegetation. Studies from the literature were used to determine the upper limit of the PAR conversion efficiency (e) as a function of woody biomass for forest vegetation. Without climatic or other limitations, the upper limit was about 3·5gMJ-1 of absorbed PAR at very low values of stem biomass. Because of increased maintenance respiration with increasing woody biomass, the upper limit decreased to 2·0g MJ-1. Therefore, global estimates of NPP based on vegetation indices should include a classification among established forest, young forest and non-forest ecosystems to account for differences in e.
TL;DR: In this paper, the authors evaluated the usefulness of Landsat-TM digital data as a tool for discrimination and mapping of reef zones, using canonical variate analysis and minimum spanning trees.
Abstract: Coral reefs exhibit patterns of zonation. In this study we have evaluated the usefulness of Landsat-TM digital data as a tool for discrimination and mapping of reef zones. Classification, on bands 1, 2 and 3, and grouping of classes into reef zones was carried out with the aid of canonical variate analysis and minimum spanning trees. Thirteen reef zones can be identified and mapped, at a spatial scale relevant to their dimensions, with confidence. These zones can be further subdivided and mapped as spatially coherent subzones, in order to provide detailed information regarding the density of coral cover on the reef flat. In addition, the canonical variate analysis provides the basis for the aggregation of classes into sub-zones on interpreted primary productivity gradients, which is of relevance to coral reef management, monitoring and research.
TL;DR: The salt affected soils of Etah, Aligarh, Mainpuri and Mathura districts have been mapped into S 1: < 10 per cent of the area covered by salts, S 2: 10-30 per cent, S 3: 30-50 per percent, S 4: 50-75 per... as mentioned in this paper.
Abstract: The salt affected soils of Etah, Aligarh, Mainpuri and Mathura districts have been mapped into S1: < 10 per cent of the area covered by salts, S2: 10–30 per cent, S3: 30–50 per cent, S4: 50–75 per ...