Automated feature extraction for prospection and analysis of monumental earthworks from aerial LiDAR in the Kingdom of Tonga

Recent LiDAR (Light Detection and Ranging) survey in Tonga has documented a dense and complex archaeological landscape, particularly on the principal island of Tongatapu. Among the features revealed by the LiDAR are a profusion of earthen mounds, most of which are associated with residence, sporting, or burial in the period 1000-1850 CE. For identification and mapping of the mounds we use and evaluate two automated feature extraction (AFE) techniques, object-based image analysis and an inverted pit-filling algorithm ("iMound"). Accuracy of these methods was measured using an F1-score (harmonic mean of precision and recall). Variable AFE results indicate that continual and iterative fine-tuning is required. Successful mapping of some 10,000 mounds on Tongatapu reveals a distinct spatial structure that relates to traditional land division and tenure.