Canadian Forest Service Publications
Good practices for estimating area and assessing accuracy of land change. 2014. Olofsson, P.; Foody, G.M.; Herold, M.; Stehman, S.V.; Woodcock, C.E.; Wulder, M.A. Remote Sensing of Environment 148: 42–57.
Issued by: Pacific Forestry Centre
Catalog ID: 35450
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The remote sensing science and application communities have developed increasingly reliable, consistent, and robust approaches for capturing land dynamics to meet a range of information needs. Statistically robust and transparent approaches for assessing accuracy and estimating area of change are critical to ensure the integrity of land change information.We provide practitionerswith a set of “good practice” recommendations for designing and implementing an accuracy assessment of a change map and estimating area based on the reference sample data. The good practice recommendations address the three major components: sampling design, response design and analysis. The primary good practice recommendations for assessing accuracy and estimating area are: (i) implement a probability sampling design that is chosen to achieve the priority objectives of accuracy and area estimationwhile also satisfying practical constraints such as cost and available sources of reference data; (ii) implement a response design protocol that is based on reference data sources that provide sufficient spatial and temporal representation to accurately label each unit in the sample (i.e., the “reference classification” will be considerably more accurate than the map classification being evaluated); (iii) implement an analysis that is consistent with the sampling design and response design protocols; (iv) summarize the accuracy assessment by reporting the estimated error matrix in terms of proportion of area and estimates of overall accuracy, user's accuracy (or commission error), and producer's accuracy (or omission error); (v) estimate area of classes (e.g., types of change such as wetland loss or types of persistence such as stable forest) based on the reference classification of the sample units; (vi) quantify uncertainty by reporting confidence intervals for accuracy and area parameters; (vii) evaluate variability and potential error in the reference classification; and (viii) document deviations from good practice that may substantially affect the results. An example application is provided to illustrate the recommended process.
Plain Language Summary
Land change maps depict changes in land status (e.g. wildfire, forest disturbance, urban expansion, etc.). Area estimation is one application of land change maps. Several agencies use this information for creating policy, reporting and financial compensation (e.g. countries reporting under the Kyoto protocol and governments creating policies on deforestation and incentives for reduction in greenhouse gases). The accuracy of the information derived from change maps must be statistically sound and transparent. Practitioners use accuracy assessments to identify map quality and accuracy of change maps and area estimates. This paper provides map users and producers with good practice recommendations for designing and implementing accuracy assessment and area estimation methods. The article outlines design and analysis protocol for the three major components of accuracy assessments – sampling design, response design, and analysis. It also provides an example that illustrates the recommended process for an accuracy assessment. The authors intend the recommendations to be used as guidelines, and to be amended and updated as remote sensing technology improves and evolves.