Derived Vegetation Indices Research Articles

The distribution of ticks (Acari: Ixodidae) of domestic livestock in Portugal

This paper introduces the first countrywide faunistic study of the tick parasites on ruminants in Portugal. The aim of this study was to map accurately the distribution of the ticks Dermacentor marginatus, Rhipicephalus (Boophilus) annulatus, R. bursa, Hyalomma m. marginatum, H. lusitanicum and Ixodes ricinus in Portugal. Additional information about the abiotic preferences of these species has been obtained through the use of abiotic (temperature- and vegetation-derived) variables have been recorded from remotely sensed information at a nominal resolution of 1.1 km(2). A further aim was the development of predictive models of distribution using Classification and Regression Trees (CART) methodologies. Four species (R. annulatus, R. bursa, D. marginatus and H. m. marginatum) are mostly restricted to south-eastern parts of the country, under hot and dry climate conditions of Mediterranean type. H. lusitanicum has been collected almost only in the southern half of Portugal. I. ricinus has a very patchy distribution and is mainly associated with vegetation of Quercus spp., found in southern zones of the country, but it is present also in the more humid western part. A variable number of abiotic variables, mainly temperature derived, are able to describe the preferences of the tick species. It is remarkable that variables derived from maximum values of the Normalized Derived Vegetation Index (yearly or summer-derived) only apply to discriminate areas where I. ricinus has been collected. CART models are able to map the distribution of these ticks with accuracy ranging within 75.3 and 96.4% of actual positive sites.

Using ground-based multispectral radiometry to detect stress in wheat caused by greenbug (Homoptera: Aphididae) infestation

Greenbug ( Schizaphis graminum (Rondani)) outbreaks appear in the Great Plains almost every year and have had significant economic impacts on wheat and sorghum yields. Early detection of greenbug infestation becomes a critical part of integrated pest management (IPM) for wheat and sorghum production. We conducted a pilot study to determine the feasibility of using remote sensing techniques to detect stress in wheat caused by greenbug infestation. The purpose of this study was to characterize greenbug-induced stress in wheat using a hand-held radiometer. Reflectance data and derived vegetation indices from the 16 bands of the radiometer were analyzed statistically (SAS PROC MIXED). Results show that it is possible to detect greenbug-induced stress in wheat using a hand-held radiometer. The band centered at 694 nm and the vegetation indices derived from bands centered at 800 and 694 nm were identified as most sensitive to damage due to greenbug infestation. Broad Landsat TM bands and derived vegetation indices also showed potential for detecting stress in wheat caused by greenbug infestation.

LANDUSE AND CROPPING PETTERN CLASSIFICATION USING SATELLITE DERIVED VEGETATION INDICES AND SURFACE METEOROLOGICAL DATA

The Huaihe River Lasin is vast granary in China, therefore landuse and cropping cycle information is important for water usage and hydrological analysis. In this study, landuse and cropping pattern classification in the Huaihe River Basin is produced from satellite derived vegetation indices (30sec resolution) and surface meteorological data. And agricultural statistic data of 187 prefectures in Henan Province is used for validation. Firstly, using some notable features in the NDVI and NDWI time series, all meshes (1320 × 600) are classified into 7 categories. Secondly, accumulated degree-days temperature data during growing period is calculated from NDVI time series and surface air temperature data, and it is used for cropping type classification. Lastly, VSW (Vegetation, Soil and Water) index is applied for evaluation of the mixed-cell effect. The results of this study show the importance of mixed-cell effect and the availability of VSW index for cropland classification.

The distribution and ecological 'preferences' of the tick Amblyomma cajennense (Acari: Ixodidae), an ectoparasite of humans and other mammals in the Americas.

The distribution and ecological 'preferences', in the Nearctic and Neotropical regions, of the prominent, pathogen-carrying tick Amblyomma cajennense (Fabricius) were reviewed, on the basis of the published literature, satellite imagery, and the examination of several tick collections. The tick has been collected from the southern U.S.A. (Texas and Florida) to northern Argentina, but is probably absent from Uruguay and southern Brazil (the few records of the species in these areas probably represent mis-identifications). The ecological conditions prevailing in the areas where the tick has been reported were characterized using remotely sensed data on temperature and vegetation stress (as indicated by the normalized derived vegetation index, or NVDI). In Mexico and the U.S.A., the species is found in areas where the mean temperature is around 13-16 degrees C and the NVDI is high. South of Venezuela, however, the tick is only common in zones where the mean temperature is 18-20 degrees C and the NVDI is again high. It is relatively low mean temperatures and differences in the seasonal patterns of rainfall that seem to limit the tick's colonization of areas to the north of its current distribution. Low temperatures also seem to be keeping the tick out of mountainous areas, such as the Sierra Madre in Mexico and the pre-Andean hills in Argentina. The southern distribution of A. cajennense is mainly restricted by relatively low temperatures and not by low humidity.

Optimal Landsat TM band combinations and vegetation indices for discrimination of six grassland types in eastern Kansas

Hyperspectral sensors can make narrow-band measurements for several hundred regions of the electromagnetic spectrum, and with increasing frequency, multi-dates of remotely sensed data are being used for Earth observation purposes. The use of more spectral bands is creating greater demand for larger computer storage capacity and faster data processors. This study evaluates the use of raw Thematic Mapper (TM) band combinations and several derived vegetation indices to determine optimal vegetation indices and band combinations for discriminating among six grassland management practices in eastern Kansas. Results showed that among the transformed dataset, the Greenness Vegetation Index was found to be the best for discriminating among grassland management types. When evaluating the raw TM bands, TM4 (NIR) was always selected in Discriminate Analysis as the best discriminating variable. There is no significant improvement in grassland discrimination by using a combination of the raw TM bands and the vegetation indices. Increasing the number of TM bands by using multiple dates of imagery will improve discrimination accuracy up to a point, but the use of too many bands (greater than 10 or 12) can actually decrease discrimination accuracy.

Climate warming and changes in habitat suitability for Boophilus microplus (Acari: Ixodidae) in Central America.

Remote sensing on the basis of AVHRR (advanced very high resolution radiometer) satellite imagery was used, together with standard geostatistical methods (cokriging), to estimate the distribution of habitat suitability (HS) for the tick Boophilus microplus (Canestrini) in Central America. Most attention was paid to the expected limits of tick distribution as well as the temperature and vegetation values responsible for different HS zones and their variability within the year. The highest HS extended through wide areas of southeastern United States, much of Mexico, and other countries of Central America. Areas with higher HS had relatively stable temperatures (within 20-25 C) throughout the year, and had a NDVI (normalized derived vegetation index) of around 0.4. These areas need to be targeted to ensure acaricide usage at optimum intervals and to avoid the formation of areas with enzootic instability. A seasonal analysis of the climate trend through the study period (1982-1999) revealed a warming cycle, together with a rise in NDVI index values. The main consequence of this trend is the gradual increase in unsuitability in areas where the tick is already established, with the establishment of new foci in zones currently too cold to support tick populations. The cooling periods of 1-2 yr that were observed between warming cycles may also lead to enzootic instability when warm zones cool to within the suitability range. As the model is remotely sensed, a continuous update of the B. microplus distribution could be performed, assuring maximum efficiency in developing management strategies.

Distribution, abundance, and habitat preferences of Ixodes ricinus (Acari: Ixodidae) in northern Spain.

Ixodes ricinus (L.) was collected by standard dragging in 2,082 different sites in 18 broad vegetation categories in northern Spain to explore the influence of vegetation on its abundance. Of these, 785 sites were surveyed in 1995, 636 in 1996, and 661 in 1997. The impact of habitat features on differences in tick numbers is addressed. The tick was present in low numbers in areas of old, heterogeneous coniferous forests. Ticks appeared to prefer sites that had substantial secondary plant growth such as river canopies, heterogeneous Pinus uncinata forests, mixed forests, and deciduous heterogeneous woods. Highest tick abundance was recorded for sites that contained Quercus spp., as well as for mixed old forests that had many ecotones. I. ricinus was absent in open habitats, homogeneous young coniferous forests, and open hillsides. These differences were attributed to greater shrub cover and litter depth, which created more favorable microclimatic conditions for tick survival. The abundance of I. ricinus nymphs was not homogeneous in sites within the same habitat category and vegetation physiognomy at these sites did not appear to cause differences in tick abundance. Analysis of variance (ANOVA) indicated that variation in tick abundance could be explained by the exposure of the sampled site, at least for some zones within deciduous forest categories. However, this factor did not explain the variation observed in other habitats. Temperature and vegetation (normalized derived vegetation index) features were recorded daily by remotely sensed imagery throughout the study period and the data were used to obtain long-term mean and maximum values of the physical parameters considered. Multiple regression analysis performed between these long-term abiotic factors and nymphal abundance in positive sites showed high relationship (R2 coefficients) for every habitat category and explained >50% of the variation in tick abundance.

Optical–Biophysical Relationships of Vegetation Spectra without Background Contamination

For a better evaluation of the accuracy of VIs in estimating biophysical parameters, a “true” VI value attributed only to the vegetation signal and free of any contamination is needed. In this article, pure vegetation spectra were extracted from a set of open and closed canopies by unmixing the green vegetation signal from the background component. Canopy model-simulation and reflectances derived from graph-based linear extrapolation were used to unmix and derive a “true” vegetation signal, equivalent to a perfect absorber (free boundary) canopy background reflectance condition. Optical–biophysical relationships were then derived for a variety of canopy structures with differences in foliage clumping, horizontal heterogeneity, and leaf type. A 3-dimensional canopy radiative transfer model and a hybrid geometric optical-radiative transfer model (GORT) were used to simulate the directional-hemispherical reflectances from agricultural, grassland, and forested canopies (cereal and broadleaf crop, grass, needleleaf, and broadleaf forest). The relationships of the extracted red and near-infrared reflectances and derived vegetation indices (VIs) to various biophysical parameters (leaf area index, fraction of absorbed photosynthetically active radiation, and percent ground cover) were examined for the pure vegetation spectra. The results showed normalized difference vegetation index (NDVI) relationships with biophysical parameters to become more asymptotic over the pure vegetation condition. The extraction of pure vegetation signals had little effect on the soil-adjusted vegetation index (SAVI), which had values equivalent to those obtained with the presence of a background signal. NDVI values were fairly uniform across the different canopy types, whereas the SAVI values had pronounced differences among canopy types, particularly between the broadleaf and cereal/needleleaf structural types. These results were useful not only in selecting suitable vegetation indices to characterize specific canopy biophysical parameters, but also in understanding a “true” VI behavior, free of background noise.

Variability of Laboratory Measured Soil Lines of Soils from Southeastern Brazil

Linear relationships (soil lines) between the conventional red (R) and near-infrared (NIR), and between unconventional NIR reflectance bands were investigated for the effects of spectral positioning and widths of approximately simulated bands of some broad- and narrow-band sensors, and for the influence of the chemical constituents and moisture in the samples. The investigation was based on laboratory spectra of air-dried samples from soil profiles from southeastern Brazil, an experiment for the chemical removal of organic matter, and on a wetting process of the soil samples. The relationships were evaluated for a general soil line and for the individual lines of some soil types, under air-dried condition, through the determination of the line parameters, dispersion statistics, and principal components analysis (PCA). Soil lines obtained with broad or narrow NIR bands positioned at shorter wavelengths, and consequently at smaller distance differences between the pair of bands, presented better fitted lines than the ones obtained with NIR bands located at longer wavelengths and at larger distances. Compared with the broad bands, spectrally better positioned narrow NIR/R bands produced closely similar results because of the propitious effect of the larger bandwidth. However, unconventional NIR/NIR bands presented better fitted lines than the R/NIR bands. The inherent interplay between organic matter and iron oxides is accountable for the variability in the linear parameters of the individual lines. The general line for the samples considered is composed of nonparallel segments of the different soil types, with a tendency for an increased obliquity in the low albedo soils. Soil types with very low albedo present line slope values below 1, poor correlations, but small root mean square (RMS) values, whereas soil types with moderate and high albedo present line slope values above 1, strong correlations, and large RMS values. The former is rich in organic matter and iron oxides whereas the latter has more transparent components, such as quartz, or less opaque substances. However, in soil types with a lesser content of organic matter, the iron spectral features are enhanced and variations in the shape of the spectra are produced because of the larger reflectance increase in the R band than in the NIR interval. The maximum spectral contrast resulting from this compositional interplay is assessed when the NIR band is positioned at longer wavelengths. Similarly, soil wetting introduces nonlinear spectral changes that also affect the characteristics of the soil lines. The analysis of field measured reflectance spectra derived from an experiment designed to monitor the growth of a bean crop indicates that the shift of the NIR band towards shorter wavelengths produces not only better fitted soil lines but also stronger vegetation signals. The enhancement of the vegetation signal obtained with the displacement of the NIR band results from the steeper descending slope towards longer wavelengths of the NIR plateau observed in the vegetation spectra. The results place constraints on an unsupported choice of bands to derive vegetation indices, especially those of the advanced hyperspectral imaging sensors. The most recommended pair of NIR-R bands for crop vegetation indices is the one from LANDSAT-TM, closely followed by JERS-OPS and SPOT-HRV, or from narrow NIR-R bands positioned within these ranges at spectral intervals not affected by atmospheric attenuation.

Seasonal change in understory reflectance of boreal forests and influence on canopy vegetation indices

One objective of the Boreal Ecosystem‐Atmospheric Study (BOREAS) is to increase our understanding of the nature of canopy spectral bidirectional reflectance in the visible/near‐infrared regimes for open canopies typical of boreal forest stands. For such stands, the need to characterize the reflectance of the sunlit and shaded vegetated understory is critical. These variables are subject to temporal variability due to differences in species phenology and foliar display as well as diurnal and seasonal changes in solar illumination through a seasonally varying upper canopy foliar area. To provide for this need, a multiteam field effort was mounted to measure the nadir midday understory reflectance for the flux tower sites during 1994 BOREAS field campaigns between February and October, specifically during the winter focused field campaign (FFC‐W), the spring thaw focused field campaign (FFC‐T), and the three intensive field campaigns (IFC‐1, IFC‐2, and IFC‐3) between June and September, which sample vegetation phenological change. This was accomplished by measuring at near‐solar noon the sunlit and shaded nadir reflectance of the understory along a surveyed leaf area index (LAI) transect line at each flux tower site. Site‐to‐site comparisons of understory reflectance spectra reveal stand differences that become more significant as the season progresses. Mean midday understory reflectance spectra were observed to be remarkably consistent over the season for young jack pine stands, followed by somewhat increased variability for mature jack pine, and significant seasonal variability for black spruce stands. Derived vegetation indices for understories are generally consistent with extrapolations of previous relationships of canopy spectral vegetation indices (VIs) versus leaf area index to zero LAI. Inclusion of these “zeroLAI” understory‐derived indices significantly enhance the correlation in the linear VI‐LAI relationships.

Soil Impact on Satellite Based Vegetation Monitoring in Sahelian Mali

Soil Impact on Satellite Based Vegetation Monitoring in Sahelian Mali

Correlation of rangeland cover measures to satellite‐imagery‐derived vegetation indices

Abstract Using field data from the U.S. Army's land inventory and monitoring program, a study was conducted to examine the utility in estimating the quantity of vegetation cover with satellite imagery across a large and complex rangeland. The study area used for this investigation was the U.S. Army's Yakima Training Center in central Washington. The Land Condition‐Trend Analysis (LCTA) program at Yakima Training Center has 202 permanent plots located in a randomly stratified manner across the installation. The principle measures taken along the transects were canopy cover and ground cover. Landsat Thematic Mapper imagery collected in May and August of 1992 was used in the analyses. The satellite data coincided with the beginning and end of the field data collection period and were used to derive various vegetation indices including Ratio, TVI, SAVI, and MSAVI. Analysis of correlation of rangeland cover measures and satellite imagery derived vegetation indices were performed. Correlation between the vegeta...

Proposal and investigation of a method for estimating surface energy balance in regional forests using TM derived vegetation index and observatory routine data

Abstract Taking forest areas specified according lo information on the National digital land data, the vapour pressure deficit at leaf temperature and the degree of stomatal opening were presumed using the vegetation index of forest areas derived from Landsat TM data. Assuming the principle of Monin-Obukhov similarity is correct, a new method for calculating the latent and sensible heat fluxes of regional forests was proposed taking into account the difference in Leaf Area Index. The relation of the increase of latent heat flux with the vegetation index was obtained, and the plane distribution of latent and sensible heat fluxes in large areas is calculated.

Ground based measurements for interpretation of vegetation indices over developing countries

Satellite derived vegetation indices (VIs) are valuable tool to evaluate the role of vegetation in the exchange of radiation, momentum and heat during atmosphere-biosphere interactions. Besides accurate description of land, vegetation dynamics and ecological conditions, VIs can be used for estimating primary productivity, drought monitoring, crop yield prediction, detecting weather impacts and other events relevant to ecology and agricultural productivity. However, the true potential of VIs can only be realised if it is supported and validated through concurrent field experiments. The scaling problems between wide ranging atmospheric processes to small space, space-time biophysical phenomena can also be resolved through satellite derived VIs backed-up by ground truth experiments. Sensor calibration, atmospheric-geometric correction, radiance to parameters calculation, etc., are some crucial technical issues which could be addressed through ground experiments. Complex, multidisciplinary and resource intensive nature of ground experiments in support of satellite derived VIs interpretation call for meaningful international cooperation. This is inevitable in view of evolving scientific solutions to global environmental problems.

Integrating reconstructed scatterometer and advanced very high resolution radiometer data for tropical forest inventory

A scientific effort is currently underway to assess tropical forest degradation and its potential impact on Earth's climate. Because of the large continental regions involved, Advanced Very High Resolution Radiometer (AVHRR) imagery and its derivative vegetation index products with resolutions between 1 and 12 km are typically used to inventory the Earth's equatorial vegetation. Archival AVHRR imagery is also used to obtain a temporal baseline of historical forest extent. Recently however, 50-km Seasat-A Scatterometer (SASS) Ku-band imagery (acquired in 1978) has been reconstructed to ≈ 4-km resolution, making it a supplement to AVHRR imagery for historical vegetation assessment. In order to test the utility of reconstructed Ku-band scatterometer imagery for this purpose, seasonal AVHRR vegetation-index and SASS images of identical resolutions were constructed. Using the imagery, discrimination experiments involving 18 vegetation categories were conducted for a central South America study area. The results of these experiments indicate that AVHRR vegetation-index images are slightly superior to reconstructed SASS images for differentiating between equatorial vegetation classes when used alone. However, combining the scatterometer imagery with the vegetation-index images provides discrimination superior to any other combination of the data sets. Using the two data sets together, 90.3% of the test data could be correctly classified into broad classes of equatorial forest, degraded woodland/forest, woodland/savanna, and caatinga .

Estimating soil moisture from 6·6 GHz dual polarization, and/or satellite derived vegetation index

Abstract Eight and a half years (January 1979 to August 1987) of Scanning Multichannel Microwave Radiometer (SMMR) data taken at a frequency of 6·6 GHz for both day and night observations at both polarizations were processed, documented and used to study the relationship between brightness temperature (TB) and antecedent precipitation index (API) in a wide range of vegetation index (normalized difference vegetation index (NDVI) varies from 0·2 to 0·6) in the mid-west and southern United States. In general, this study validates the model structure for soil wetness developed by Choudhury and Golus. For NDVI greater than 0·45 the resultant microwave signal is substantially affected by the vegetation. The night-time observations by both polarizations gave a better correlation between TB and API. The horizontal polarization is more sensitive to vegetation. For the least and greatest vegetated areas, nighttime observations by vertical polarization showed less scatter in the TB versus API relation. A non-linear ...

Estimation of the Earch Environment by Remote Sensing Technology.

The way of human existence on the earth is largely influenced by the changes in earth environment and how to manage and conserve it is very important to human beings. Recently, however, the earth environment is destroyed by El Nino phenomena, desertification, greenhouse effect, destruction of ozone layer, acid rain, etc. Then the investigation and research of the earth environment by remote sensing technology are attracting world attention. It is also applied to the research of vegetation (agriculture and forest), ocean land use, civil engineering, disaster prevention, atmosphere, geographical information, etc. A method to derive vegetation indices used to know activation of green vegetation is introduced. These indices are also used to detect desertification phenomena. From the viewpoint of environment, human beings living in natural environment must adapt themselves to the environment without changing it.

Evaluating landsat thematic mapper derived vegetation indices for estimating above-ground biomass on semiarid rangelands

Ground data from the Central Plains Experimental Range in northeast Colorado and Landsat satellite images of that area acquired in August 1989, June 1990, and September 1990 were used to evaluate the level of association that can be expected from a univariate model relating spectrally derived vegetation indices (difference, ratio, and normalized difference vegetation indices) and dried green vegetation biomass. The vegetation indices were related to the ground sample estimates using a sample point, spectral class, and greenness strata approach. No strong relationships were found between the vegetation indices and sample estimates of dried green biomass using the sample point approach. The spectral class approach produced significant results only for the June 1990 sample period ( r=0.96). Significant relationships were found for the August 1989, June 1990, and September 1990 samples periods ( r 2=0.95, 0.71, and 0.95, respectively) when the data were aggregated by greenness strata. The high degree of association between green biomass and the NDVI, obtained when the data were combined into greenness strata, indicated that it is possible to predict green biomass levels on semiarid rangelands using univariate regression models.

Satellite assessment of drought impact on native plant communities of southeastern New Mexico, U.S.A.

Low spatial resolution imagery from a polar orbiting meteorological satellite was utilized to detect short-term drought effects on native plant communities in southeastern New Mexico, U.S.A. rangelands. A spectrally derived Vegetation Index was compared to the Palmer Drought Severity Index, Crop Moisture Index, and monthly precipitation departures for a wet year (1988) and a dry year (1989). Differences between years as well as between plant communities were assessed. Plant communities consisting primarily of grass species were the most spectrally responsive to variation in precipitation, while forested areas were least affected.

Evaluating hand‐held radiometer derived vegetation indices for estimating above ground biomass

Abstract The potential for using vegetation indices developed from remote sensing devices, such as the GSFC Mark‐II hand‐held radiometer, to evaluate biomass has been examined in a number of studies. Relationships range from very good (r2=0.96) to very poor (r2=0.029). One problem with most of the studies is that the data were only collected during a single year, therefore, the usefulness of the relationships within and between years is difficult to evaluate. This study examined the usefulness of vegetation indices, calculated from data gathered by the GSFC Mark‐II radiometer, in assessing the amount of biomass on native grasslands. Vegetation indices derived from data gathered over two years (1989 and 1990) and during four periods throughout each growing season indicate that the ratio between near‐infrared and red spectral responses (ratio vegetation index) performed better then either the difference between the two bands or the normalized difference vegetation indices. Poor relationships were observed (...