Curtis M. Edmonds

A Landscape Approach for Detecting and Evaluating Change in a Semi-Arid Environment

Vegetation change in the American West has been a subject of concern throughout the twentieth century. Although many of the changes have been recorded qualitatively through the use of comparative photography and historical reports, little quantitative information has been available on the regional or watershed scale. It is currently possible to measure change over large areas and determine trends in ecological and hydrological condition using advanced space-based technologies. Specifically, this process is being tested in a community-based watershed in southeast Arizona and northeast Sonora, Mexico using a system of landscape pattern measurements derived from satellite remote sensing, spatial statistics, process modeling, and geographic information systems technology. These technologies provide the basis for developing landscape composition and pattern indicators as sensitive measures of large-scale environmental change and thus may provide an effective and economical method for evaluating watershed condition related to disturbance from human and natural stresses. The project utilizes the database from the North American Landscape Characterization (NALC) project which incorporates triplicate Landsat Multi-Spectral Scanner (MSS) imagery from the early 1970s, mid 1980s, and the 1990s. Landscape composition and pattern metrics have been generated from digital land cover maps derived from the NALC images and compared across a nearly 20-year period. Results about changes in land cover for the study period indicate that extensive, highly connected grassland and desertscrub areas are the most vulnerable ecosystems to fragmentation and actual loss due to encroachment of xerophytic mesquite woodland. In the study period, grasslands and desertscrub not only decreased in extent but also became more fragmented. That is, the number of grassland and desertscrub patches increased and their average patch sizes decreased. In stark contrast, the mesquite woodland patches increased in size, number, and connectivity. These changes have important impact for the hydrology of the region, since the energy and water balance characteristics for these cover types are significantly different. The process demonstrates a simple procedure to document changes and determine ecosystem vulnerabilities through the use of change detection and indicator development, especially in regard to traditional degradation processes that have occurred throughout the western rangelands involving changes of vegetative cover and acceleration of water and wind erosion.

Modeling runoff response to land cover and rainfall spatial variability in semi-arid watersheds.

Hydrologic response is an integrated indicator of watershed condition, and significant changes in land cover may affect the overall health and function of a watershed. This paper describes a procedure for evaluating the effects of land cover change and rainfall spatial variability on watershed response. Two hydrologic models were applied on a small semi-arid watershed; one model is event-based with a one-minute time step (KINEROS), and the second is a continuous model with a daily time step (SWAT). The inputs to the models were derived from Geographic Information System (GIS) theme layers of USGS digital elevation models, the State Soil Geographic Database (STATSGO) and the Landsat-based North American Landscape Characterization classification (NALC) in conjunction with available literature and look up tables. Rainfall data from a network of 10 raingauges and historical stream flow data were used to calibrate runoff depth using the continuous hydrologic model from 1966 to 1974. No calibration was carried out for the event-based model, in which six storms from the same period were used in the calculation of runoff depth and peak runoff. The assumption on which much of this study is based is that land cover change and rainfall spatial variability affect the rainfall-runoff relationships on the watershed. To validate this assumption, simulations were carried out wherein the entire watershed was transformed from the 1972 NALC land cover, which consisted of a mixture of desertscrub and grassland, to a single uniform land cover type such as riparian, forest, oak woodland, mesquite woodland, desertscrub, grassland, urban, agriculture, and barren. This study demonstrates the feasibility of using widely available data sets for parameterizing hydrologic simulation models. The simulation results show that both models were able to characterize the runoff response of the watershed due to changes of land cover.

Airborne laser fluorosensor survey of the Columbia and Snake rivers: simultaneous measurements of chlorophyll, dissolved organics and optical attenuation

Abstract An airborne laser fluorosensor has been used to make concurrent, near-continuous (microscale) profiles of chlorophyll-a, dissolved organic carbon (DOC) and the beam attenuation coefficient along the Columbia and Snake rivers. Cross-reference between profiles is used to expose anomalies and explain ambiguities encountered in their interpretation. The unique potential for remote sensing of DOC concentrations is based on a strong correlation with the fluorescence of dissolved organic matter (DOM). Similarly, the reciprocal of the remotely sensed water Raman emission is shown to be a reliable predictor of the beam attenuation coefficient. Profiles of a 734 km segment of the lower Snake and Columbia rivers obtained during peak discharge revealed a number of interesting features. In particular, the chlorophyll-a fluorescence data suggested the existence of subsurface chlorophyll-a maxima in the reservoirs formed by the eight dams of the Columbia-Snake Inland Waterway, and the absence of variability in ...

A Landscape Ecology Assessment of the Tensas River Basin

A group of landscape ecological indicators were applied to biophysical data masked to the Tensas River Basin. The indicators were used to identify and prioritize sources of nutrients in a Mississippi/Atchafalaya River System sub-basin. Remotely sensed data were used for change detection assessment. With these methods, we were able to look at land use practices over the past twenty years in the Tensas River Basin of Louisiana. A simple land use classification was applied to multispectral scanner (MSS) data from 1972 and 1991. The landscape analysis methods described in this paper will show how to use these methods to assess the impact of human land use practices that are being implemented to improve environmental quality. Landscape assessment methods can be used as a simple, timely, cost effective approach for monitoring, targeting, and modeling ecosystem health in watersheds. Although this study was conducted in the southeast, the methods described in this paper may be applicable to western landscapes.

Short- and long-term memory effects in intensified array detectors: influence on airborne laser fluorosensor measurements

Phosphorescence and thermoluminescence memory effects in the phosphors of image intensifiers have been examined as they relate to the performance of intensified optical multichannel analyzers. Although most users of these devices may not need to be concerned with or aware of these secondary effects, their influence on an airborne laser fluorosensor application is shown to be significant. The magnitude of these strongly coupled effects, which are very sensitive to experimental conditions, has been modeled for a specific application, and algorithms are presented that can be used to remove these effects from airborne measurements of laser-induced fluorescence spectra of aquatic and terrestrial targets. It is a straightforward matter to adopt these procedures to other situations involving different gating routines, repetition rates, and diode group sizes.

Airborne UV-DIAL Urban Plume Measurements

This paper presents and interprets continuous profile measurements of ozone and particulate density of urban origin obtained remotely with the EPA airborne ultraviolet differential absorption lidar (UV-DIAL) from studies conducted in southeastern Michigan (greater Detroit area) during May 1992 and in the Houston, Texas, Gulf Coast area in summer 1993.