Abstract
With the increasing temporal resolution of medium spatial resolution data, seasonal features are becoming more readily available for land cover characterization. However, in the tropical regions, images can be severely contaminated by clouds during the rainy season and fires during the dry season, with possible effects to seasonal features. In this study, we evaluated the performance of seasonal features based on an annual Landsat time series (LTS) of 35 images for land cover characterization in West Sudanian savanna woodlands. First, the burnt areas were detected and removed. Second, the reflectance seasonality was modelled using a harmonic model, and model parameters were used as inputs for land cover classification and tree crown cover prediction using the random forest algorithm. Furthermore, to study the sensitivity of the approach to the burnt areas, we repeated the analyses without the first step. Our results showed that seasonal features improved classification accuracy significantly from 68.7% and 66.1% to 76.2%, and decreased root mean square error (RMSE) of tree crown cover predictions from 11.7% and 11.4% to 10.4%, in comparison to the dry and rainy season single date images, respectively. The burnt areas biased the seasonal parameters in near-infrared and shortwave infrared bands, and decreased the accuracy of classification and tree crown cover prediction, suggesting that burnt areas should be removed before fitting the harmonic model. We conclude that seasonal features from annual LTS improved land cover characterization performance, and the harmonic model, provided a simple method for computing annual seasonal features with burnt area removal.
Highlights
Land cover is an essential variable that affects and connects various aspects of human and physical environment, and is critical for the study of ecosystems, climate change, and biodiversity [1,2].The remote sensing approaches to characterize land cover include classification of land cover types and prediction of land cover attributes as continuous variables [3]
Our results show that seasonal features provide significantly better land cover classification and
Our results show that seasonal features provide significantly better landwhich cover classification and tree crown cover prediction accuracy in comparison to single date images, is in agreement treewith crown cover prediction accuracy in comparison to single date images, which is in agreement a number of studies from different parts of the world [7,40,41,42], including savannas [20,36,43], with a number studies from different parts of the world
Summary
Land cover is an essential variable that affects and connects various aspects of human and physical environment, and is critical for the study of ecosystems, climate change, and biodiversity [1,2]. The remote sensing approaches to characterize land cover include classification of land cover types and prediction of land cover attributes as continuous variables [3]. Several land cover attributes, such as tree crown cover, tree height, and species composition can be considered simultaneously. Tree crown cover is a commonly used attribute in land cover classification legends [4], definitions of vegetation types [5], and often mapped by remote sensing as a continuous variable [6,7]. Depending on the definition of forest, large areas of savanna woodlands, shrublands, and agroforestry parklands in West Africa qualify as forest [9]
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