What are the most effective methods for assessing digital elevation model accuracy?

1 Sources of DEM errors

DEMs can be derived from various sources, such as aerial photogrammetry, satellite imagery, lidar, radar, or contour maps. Each source has its own advantages and disadvantages, and may introduce different types of errors in the DEM. For example, the level of detail of the DEM depends on the size of the grid cells or pixels that represent the elevation values; a higher resolution means a finer detail but also a larger data volume and processing time. Additionally, the number and distribution of elevation points that are used to generate the DEM affect its accuracy and smoothness; a higher density means a better coverage but also a higher cost and complexity. Furthermore, different interpolation methods have different assumptions and limitations which may produce different results. In addition, factors such as projection, datum, scale, and orientation can affect the geometric accuracy of the DEM when transforming from the source coordinate system to the target coordinate system. Finally, factors such as atmospheric conditions, illumination, shadows, vegetation, and surface roughness can introduce noise and errors in the elevation data when deriving from optical or radar sensors.

2 Methods of DEM accuracy assessment

Assessing the accuracy of DEMs can be done in two ways: internal and external. Internal methods, such as error propagation, visual inspection, and statistical analysis, use the information from the source data or the DEM itself to evaluate its quality. External methods, such as ground truthing, check points, and error matrix, use independent data or reference standards to compare with the DEM. Error propagation estimates potential errors in the DEM based on errors in the source data and interpolation method. Visual inspection involves examining the DEM for any obvious errors or anomalies. Statistical analysis uses descriptive or inferential statistics to summarize and analyze elevation values in the DEM. Ground truthing involves collecting field measurements of elevation at selected locations. Check points use a set of elevation points from another source to compare with the DEM. Error matrix classifies elevation values into discrete categories and compares them with categories in a reference standard. All these methods can help assess the accuracy of DEMs and provide valuable insights for improving its quality.

3 Criteria for choosing the best method

Choosing the best method for assessing the accuracy of DEMs can be tricky, as each method has its own strengths and weaknesses. To make the best choice for your needs, consider the purpose, availability, and accuracy of the method. For instance, if you want to identify and correct errors in the DEM, an internal method such as visual inspection or error propagation may be preferable. On the other hand, if you want to validate and report on accuracy, an external method such as ground truthing or check points may be more suitable. Additionally, if you need a quantitative and objective measure of accuracy, an external method like check points or error matrix may be best. However, if you need a qualitative and subjective measure of accuracy, an internal method like visual inspection or statistical analysis may be more effective. It's important to remember that accuracy assessment is not a one-time task; it should be performed throughout the lifecycle of the DEM from its creation to its application. By following these criteria, you can select the most effective method for assessing your DEM's accuracy and ensure that it is used with confidence.

4 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?