Bradley C. Rundquist

The influence of canopy green vegetation fraction on spectral measurements over native tallgrass prairie

Abstract Spectral vegetation indices (SVIs) calculated from remotely sensed data are routinely used to monitor spatial and temporal changes in vegetation biophysical characteristics. The most commonly used SVI, the Normalized Difference Vegetation Index (NDVI), has been criticized because of its sensitivity to atmospheric conditions and substrate reflectivity, as well as its insensitivity to increases in vegetation biomass past particular thresholds. Yet, the use of NDVI remains widespread and is attractive because of the ease with which it is calculated. This article examines the utility of NDVI for monitoring the biophysical characteristic of green vegetation fraction (GVF) in comparison to other SVIs suggested as improvements. Statistical relationships between spectral response, presented in the form of SVIs, and GVF of a native tallgrass prairie canopy are explored. Broadband spectra were gathered from close-range during the 1999 growing season at the Konza Prairie Biological Station (KPBS), located in the Flint Hills region of Kansas, USA. Through simple regression analyses, spectra were related to GVF estimates derived from digital color photographs. SVIs evaluated are the NDVI, the Soil Adjusted Vegetation Index (SAVI), and the square of scaled NDVI (N*2). Results show that NDVI and N*2 were statistically related to GVF (R2 for NDVI=.77, N*2=.78) throughout the growing season. The least-squares line defining the relationship between N*2 and GVF approximated a 1:1 line. For June sample dates, all three SVIs were significant statistical predictors of GVF (R2 for NDVI=.89, N*2=.91, SAVI=.89). Regression coefficients for late-season sample dates were weaker, yet still significant in statistical terms (R2 for NDVI=.70, N*2=.70). While encouraging, these results suggest that further analyses are required to determine the usefulness of SVIs calculated from broadband devices for estimation of GVF when leaf litter dominates the scene.

Remote Detection of Prairie Pothole Ponds in the Devils Lake Basin, North Dakota

A decadal-scale wet spell in the closed Devils Lake basin of North Dakota has resulted in increases in the elevation and extent of the basins terminal lakes—Devils and Stump—as well as increases in the size and number of small prairie pothole ponds. Changes in lake surface area have been studied thoroughly, whereas the fluctuations in pond surface area have been virtually ignored. We use a subpixel classification technique in combination with a Landsat TM and ETM+ Band 5 (middle infrared; 1,550-1,750 nm) density slice to improve estimates of changes in the combined area of ponds in the basin for selected years between 1991 and 2002. The resulting information is a first step toward more accurate assessment of the impact of wetland flooding on the region.

Mesoscale Satellite Bioclimatology

This paper examines the strength of relationships between the Normalized Difference Vegetation Index (NDVI) and climatic data, when examined at the mesoscale. Mean monthly AVHRR NDVI data for 1988-1996 for the months of April through October for State of Kansas, its nine climatic divisions (CDs), and dominant land cover types within each CD were used. Corresponding climatic and water budget data were obtained or derived from National Climatic Data Center data. Temperature, precipitation, and NDVI deviations from normal were determined. Statistical analysis revealed significant relationships between NDVI and climatic variables, although strengths of the associations were modest. The highest correlation coefficient (r) for the state as a whole was 0.53, between NDVI and estimated actual evapotranspiration. When examined by climatic division or major land cover type, relationships between NDVI and a drought index were statistically significant in most cases and ranged from 0.30 to 0.56.

Terminal Lake Flooding and Wetland Expansion in Nelson County, North Dakota

The Devils Lake Basin of North Dakota, an interior drainage basin located within a dry, subhumid environment, has experienced pervasive flood conditions since the 1993 onset of a wet spell of unprecedented magnitude and duration. This unique natural-hazard environment has resulted in flooding from both the expansion of the surface area of the basins terminal lakes (Devils Lake and Stump Lake) and increases in the number and size of rural wetlands. To assess the relative extent of both terminal lake and rural wetland flooding, we focused on Nelson County, which contains Stump Lake and is representative of other counties in the basin. Remotely sensed data acquired by Landsat Thematic Mapper was used to map open-water extent in 2001, and results were compared to 1992 land-cover data provided by the United States Geological Survey (USGS). Our analysis indicates a 53% increase in the size of Stump Lake and a 426% increase in the area of rural wetland ponds. Stump Lake flooding is spatially restricted and has had limited impact upon the surrounding lakeshore environment. Rural wetland flooding is pervasive and has a deleterious effect upon the regions agricultural economic base.

The Effects of Climatic Factors on Vegetation Dynamics of Tallgrass and Shortgrass Cover

Abstract Climatic factors such as precipitation and temperature place primary controls on vegetation growth and development. The relationships between these factors and vegetation dynamics, as monitored using satellite remote sensing data, have been demonstrated on continental, regional and subregional scales. Most local studies have primarily focused on small areas immediately surrounding weather stations. Here, the effects of climatic “factors over intermediate‐scale sites of relatively homogenous vegetative land cover are examined. Two areas of Kansas are selected for study: the shortgrass Sandsage Prairie in the southwest and the Tallgrass Prairie National Preserve in the east‐central Flint Hills region. Within year and between year variation in vegetation in the context of climatic variability is examined on these sites using NOAA AVHRR data. Large increases in the strength of association between vegetative response (NDVI) and one‐month lagged precipitation as compared to same month correlations are demonstrated. This does not bode well for the use of AVHRR NDVI as a “real‐time” drought monitoring tool.

Geographic distributions of motor neuron disease mortality and well water use in U.S. counties.

Abstract Objective: We recently reported that U.S. mortality rates for motor neuron disease (MND) at the level of the state are associated with well water use. However, data at the state level may not accurately reflect data at the individual level. We therefore examined the association between MND mortality and well water use utilizing data from smaller geographic units that may better reflect exposure and disease at the individual level. Methods: We used data on age-adjusted MND mortality rates at the level of the county, obtained from the CDC, and corresponding data on the prevalence of well water use, obtained from the U.S. Geological Survey. Data were analyzed by multivariate linear regression and by Getis-Ord Gi*, a measure of spatial clustering. Results: Age-adjusted mortality rates for MND in 923 U.S. counties were significantly correlated with the prevalence of well water (p < 0.0001). ‘Hot spots’ of MND mortality were significantly associated with ‘hot spots’ of well water use (p < 0.0005). Conclusions: These findings support the hypothesis that an agent present in well water plays an etiologic role in ALS. Further study of water use among individuals with ALS is warranted.

Land Cover Change and Associated Trends in Surface Reflectivity and Vegetation Index in Southwest Kansas: 1972-1992

Abstract Land cover is an important component of the earth system. Human induced surface alteration can affect earth systems directly, through loss or degradation of ecosystems, or indirectly through impact on the climate and biogeochemical cycles necessary to sustain life on earth. The significance of the earths surface has made land use/land cover change an important issue in global change research. Alteration of land cover occurs at a variety of spatial scales, but as with many environmental change issues, the impacts of surface changes are often conceptualized at the global scale. In this study, we investigate the effects of land cover change on total reflected radiation and the Normalized Difference Vegetation Index (NDVI) in a 10,000 km2 local area in the High Plains of southwestern Kansas. Landsat MSS data from five years of record within the twenty‐year period 1973 to 1992 were classified into cool season crop, warm season crop, and pasture/prairie. Mean values of summer reflectance and NDVI from each cover type and for the study area as a whole were then analyzed for systematic change over the study period. Both reflectivity and vegetation index increased during the study period, although causes for the increase appear to be different. Results suggest that changes in mean surface reflectance in the study site are strongly influenced by land cover change, whereas changes in NDVI are more closely linked to 50‐day antecedent precipitation.

A Survey of Ethics Content in College-Level Remote Sensing Courses in the United States

Abstract Easier access to submeter imagery has fueled debates over ethical uses of remote sensing. Some have called for ethics instruction to counter undesired uses of the technology. Here, this article reports the results of a survey examining attitudes related to teaching ethics in remote sensing. It was found that 52 percent of respondents teaching remote sensing include ethical use discussions. Agreement on the importance of ethics instruction is statistically associated with the year the instructor received their degree, the highest degree awarded by their department, the number of remote sensing courses offered at their institution, and their prior exposure to ethical debates in remote sensing.

Spectral characterization of the invasive shrub saltcedar (Tamarix spp.) in North Dakota

A large infestation of the invasive shrub saltcedar (Tamarix ramosissima and Tamarix chinensis) was first detected east of the Montana–North Dakota border in 2001. Saltcedar has since spread from Montana along the Yellowstone and Missouri River corridors into the Lake Sakakawea region of west-central North Dakota, and has currently halted its progress at the reservoirs Garrison Dam. A receding lake level since 2001, the result of a moderate regional drought, has allowed saltcedar to quickly invade newly exposed shoreline. The infestation in some locations is severe, and there is concern among the lake managers that, left unchecked, the shrub will move upland and displace native species, degrade shoreline aesthetics, and damage wildlife habitat. Eradication efforts are underway, yet there is much interest among land managers in North Dakota in characterizing saltcedar spectrally to assist future remote detection efforts, especially in areas that are difficult to access on foot. To this end, close-range hyperspectral data collection was conducted on three dates during the 2003 growing season. This study reports the findings of close-range sensor data analyses.

Fully Engaging Students in the Remote Sensing Process Through Field Experience

Field data collection is often crucial to the success of investigations based upon remotely sensed data. Students of environmental remote sensing typically learn about the discipline through classroom lectures, a textbook, and computer laboratory sessions focused on the interpretation and processing of aircraft and satellite data. The importance of field validation of the data and products derived from them is rarely demonstrated through a field experience. Exercises designed for two separate courses are described: one at the undergraduate level and one at the graduate level. Through the comparison of pre- and post-test results, it was concluded that efforts to engage students in remote sensing data collection significantly benefits their understanding of the physical basis of environmental remote sensing (radiation/Earth surface interaction).