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Pacific Southwest Research Station
Tahoe Science Projects supported by SNPLMA
Mapping hard and soft impervious cover in the Lake Tahoe Basin using LiDAR and multispectral images: a pilot study of the Lake Tahoe Land Cover and Disturbance Monitoring Plan
Jarlath O'Neil-Dunne, Spatial Informatics Group, LLC
Conversion of land to impervious cover threatens the environmental quality of the Lake Tahoe Basin (LTB) (Bailey 1974) by reducing water percolation into the soil and increasing runoff, and thus sediment, nutrient, and pollutant transfer into Lake Tahoe (Arnold and Gibbons 1996). If impervious cover, both hard (e.g., paved or roofed areas) and soft (e.g., degraded or compacted soil) reaches unsustainable or irreversible levels, the environmental goals or "thresholds" central to management efforts within the basin and set forth by the Lake Tahoe Restoration Act will be negatively affected. Therefore, effective management and monitoring of impervious surfaces within the LTB requires an impervious cover data set that is detailed, accurate, and meaningful. We propose to leverage existing investments in high resolution multispectral imagery, Light Detection and Ranging (LiDAR), and vector GIS data to map and quantify impervious cover for the LTB. We will use a repeatable and cost-effective analytical methodology, centered on Object-Based Image Analysis (OBIA) techniques, to map hard and soft impervious cover. This approach will overcome the limitations of previous mapping efforts that did not differentiate between impervious cover classes or ensure that impervious surfaces were properly connected, both of which are vital to management and modeling efforts. The end product will be a spatially detailed, accurate, attribute-rich, and realistic map of impervious cover within the LTB. In order to make the data accessible to other scientists, resource managers, and decision makers, this map and corresponding information will be delineated and summarized by ownership (e.g., parcels), environmental gradients/boundaries (e.g., watershed, soil type, soil capability class) and political boundaries (e.g., counties). Finally, we will pilot implement the proposed "Lake Tahoe Land Cover and Disturbance Monitoring Plan" (SIG 2009) using the derived impervious surface cover. The results from this pilot and the newly derived impervious cover input data will be compared to the previous assessment to gauge strengths and weaknesses between approaches and, if warranted, recommend ways to retrofit the previous assessment to the new approach.
Relation to Other Research Including SNPLMA Science Projects
To date, some forms of degraded soils and soft cover have been mapped, but are not currently monitored in the Tahoe Basin; however, researchers working with the Tahoe Regional Planning Agency previously used a comprehensive approach to analyze high resolution satellite images and found hard cover in 2002 was at or above allowable limits in the most vulnerable land/soil types. However, as previously stated, these calculations were based on the satellite images available at the time derived from "passive" remote sensing techniques, potentially leading to underestimates of impervious area observed in forested areas. The recent acquisition and availability of basin-wide LiDAR and WorldView-2 images, in conjunction with our proposed methodology, allows for a current and more precise assessment of both hard and soft cover. In addition, this type of imagery is considered ideal for long-term monitoring and allows for pilot implementation of the Lake Tahoe Land Cover and Disturbance Monitoring Plan.
Expected date of final products:
|Last Modified: Mar 28, 2013 02:52:08 PM|