USGS - science for a changing world

Significant Topographic Changes in the United States

Data Processing Methods and Procedures

Data Processing Methods
Data Processing Methods and Procedures

SRTM – NED Vertical Differencing

Accuracy Assessment of Elevation Data

Significant Change Thresholds

Filtering of Elevation Difference Mask to Identify True Topographic Changes

Tabulation of Statistics Characterizing the Extent of Topographic Change
Given that the primary input datasets, NED, SRTM, and NLCD, each have a spatial resolution of 30 meters and the fact that the study area covers the conterminous United States, a considerable amount of data processing was required to detect and quantify areas of significant topographic change.

The NED and SRTM data are each supplied as 1x1-degree tiles defined by lines of latitude and longitude, and these tiles provided a convenient and useful scheme for organizing and processing the input data. A total of 934 1x1-degree tiles cover the conterminous United States (see figure below). Even though the NED, SRTM, and NLCD were partitioned into 1x1-degree tiles for processing efficiency, each dataset is truly seamless—there are no artificial discontinuities across the tile boundaries. Data processing was accomplished with standard geographic information system (GIS) and statistical software tools and was automated as much as possible with scripted command files to standardize the procedures.

934 1x1-degree tiles used for organizing and processing input data
934 1x1-degree tiles used for organizing and processing input data.

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Page Last Modified: December 08, 2015