Replacing human interpretation of agricultural land in Afghanistan with a deep convolutional neural network

ABSTRACT

Afghanistan’s annual opium survey relies upon time-consuming human interpretation of satellite images to map the area of potential poppy cultivation for statistical sample design. Deep Convolutional Neural Networks (CNNs) have shown ground-breaking performance for image classification tasks by encoding local contextual information, in some cases outperforming trained analysts. In this study, we investigate the development of a CNN to automate the classification of agriculture from medium-resolution satellite imagery as an alternative to manual interpretation. The residual network (ResNet50) CNN architecture was trained and validated for delineating the agricultural area using labelled multi-seasonal Disaster Monitoring Constellation (DMC) satellite imagery (32 m) of Helmand and Kandahar provinces. The effect of input image chip size, training sampling strategy, elevation data, and multi-seasonal imagery were investigated. The best-performing single-year classification used an input chip size of 33 × 33 pixels, a targeted sampling strategy and transfer learning, resulting in high overall accuracy (94%). The inclusion of elevation data marginally lowered performance (93%). Multi-seasonal classification achieved an overall accuracy of 89% using the previous two years’ data. Only 25% of the target year’s training samples were necessary to update the model to achieve >94% overall accuracy. A data-driven approach to automate agricultural mask production using CNNs is proposed to reduce the burden of human interpretation. The ability to continually update CNN models with new data has the potential to significantly improve automatic classification of vegetation across years.

Acknowledgements

The authors would like to thank the UK Natural Environment Research Council (NERC) for providing the funding for this project. The authors would also like to acknowledge the United Nations Office on Drugs and Crime (UNODC) for providing support during this research.

Disclosure statement

The authors declare no conflict of interest.

Data availability statement

The data used in this study are subject to licensing restrictions or are confidential. For more information see doi:10.17862/cranfield.rd.13228634.

Additional information

Funding

This research was supported by the UK Natural Environment Research Council (NERC) sponsored Data, Risk and Environmental Analytical Methods (DREAM) Centre for Doctoral Training [NERC Ref: NE/M009009/1].