Citation:

Jarnagin, S T., D B. Jennings, D W. Ebert, R S. Lunetta, AND J G. Lyon. A TECHNIQUE FOR ASSESSING THE ACCURACY OF SUB-PIXEL IMPERVIOUS SURFACE ESTIMATES DERIVED FROM LANDSAT TM IMAGERY. Chapter 19, Ross Lunetta & John Lyon (ed.), Remote Sensing and GIS Accuracy Assessment. Taylor & Francis Books, Inc., Boca Raton, FL, (2004).

Impact/Purpose:

Overarching Objectives and Links to Multi-year Planning

This research directly supports long-term goals established in ORD's multi-year research plans related to GPRA Goal 2 (Water Quality) and Long Term Goal WQ-2 Assessment of aquatic systems impairment. Relative to the GRPA Goal 2 Water Quality multi-year plan, this research will "provide tools to assess and diagnose impairment in aquatic systems and the sources of associated stressors" and "provide the tools to restore and protect aquatic ecosystems and to forecast the ecological, economic, and human health outcomes of alternative solutions" (Water Quality Long Term Research Goals 2 and 3).

Subtask 1 - Impervious Surface Evaluation

This subtask addresses the development of impervious surfaces estimators for local to regional scale assessments of watersheds and their landscape relationship to stream ecology. The amount of impervious surface area in a watershed is a key indicator of landscape change. As a single variable, it serves to integrate a number of concurrent interactions that directly influence a watershed's hydrology, stream chemical quality, and in-stream habitat. It is our working hypothesis that impervious surface area within a watershed, as an independently mapped predictor variable, can be used to generally track a range of watershed ecological parameters (e.g., NPS pollution, biological integrity, TMDLs) that are of concern to local, state and federal environmental managers. The specific objectives of this research are: 1) to quantitatively evaluate the varying remote sensing methods used in mapping impervious surfaces at multiple scales (local to regional), and 2) to relate the varying levels of impervious surface area in watersheds to the environmental condition of multiple water resource endpoints such as streamflow, temperature, and biota.



Subtask 2 -- Landscape Assessments and Evaluations of Best Management Practices: Watershed Demonstrations

Best Management Practices (BMP) encompass a range of strategies to reduce water pollution related to urban and agricultural activities. EPA, through Section 319(h) of the Clean Water Act [PL 92-500], provides grants to states to implement BMPs in areas with suspected or known water-quality problems. Grants for implementation of BMPs have not been tracked or monitored to document their effectiveness. Although effectiveness can be measured in many different ways, one straightforward but important measure is existence. Implementation of BMPs is a voluntary process and actual implementation is not always executed (Nowak 1992). The primary objective of this project is to assess the feasibility of using high-resolution aerial photography and other remotely sensed data to identify the existence of BMPs that were planned under the 319 program. An additional objective is to evaluate the effectives of BMPs implemented by examining monitoring data from about 5 sites in the OW National NPS monitoring system.

There are several potential benefits to determining the feasibility of using the aerial photography for identifying BMPs: 1) since BMP implementation is voluntary and some may not be implemented due to a variety of social and economic factors (Nowak 1992), remote detection of BMPs can provide data to estimate the ratio of BMPs implemented to BMPs planned; 2) remote detection of BMPs provides validation data that can be input into EPA's Grants Reporting and Tracking System (GRTS), and 3) remote monitoring of BMPs over time could be used to develop data on BMP lifespans, providing important data related to social- and cost-effectiveness.

Subtask 3 -- TMDL Non-point Source Assessment Tool

This subtask involves the development of a software tool to assess the potential risks of water bodies to exceed TMDL threshold values established by States. When completed, the tool will allow the user to evaluate watersheds over entire regions. The too

Description:

We developed a technique for assessing the accuracy of sub-pixel derived estimates of impervious surface extracted from LANDSAT TM imagery. We utilized spatially coincident
sub-pixel derived impervious surface estimates, high-resolution planimetric GIS data, vector--to-
raster conversion -methods and raster GIS overlay methods to derives a level of agreement
watershed, a small (14 km2) sub-watershed in the mid-Atlantic physiographic region. From the planimetric data we produced a per-pixel truth estimate of impervious surface percent as a means for from LANDSAT TM imagery- The spatial technique allows for multiple accuracy assessment approaches. Results showed that even though per-pixel based estimates of the accuracy of the sub-pixel data were poor (Error Matrix Overall Accuracy = 28.41, Kappa coefficient of agreement = 0. 185), the accuracy of the impervious surface percentage estimated using whole- area and rank correlation approaches were much more accurate (Relative Percent Correct =70.85, Spearman correlation = 0.608). Our findings suggest that per-pixel based approaches to the accuracy assessment of sub-pixel classified data need to be approached with some caution. Per-pixel based approaches may underestimate the actual whole-area accuracy of the material-of- interest map, as derived from sub-pixel methods, when applied over large geographic areas raster overlay technique easily extracted the data necessary to derive these assessments. The suited for the assessment of data at the sub-pixel level, it can be utilized - or altered - to derive the accuracy of any classified dataset where higher resolution digital truth data is available.

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