Synergistic Use of Sentinel-1 and Sentinel-2 to Map Natural Forest and Acacia Plantation and Stand Ages in North-Central Vietnam

Ben Spracklen,Dominick V Spracklen

doi:10.3390/rs13020185

Abstract

Many remote sensing studies do not distinguish between natural and planted forests. We combine C-Band Synthetic Aperture Radar (Sentinel-1, S-1) and optical satellite imagery (Sentinel-2, S-2) and examine Random Forest (RF) classification of acacia plantations and natural forest in North-Central Vietnam. We demonstrate an ability to distinguish plantation from natural forest, with overall classification accuracies of 87% for S-1, and 92.5% and 92.3% for S-2 and for S-1 and S-2 combined respectively. We found that the ratio of the Short-Wave Infrared Band to the Red Band proved most effective in distinguishing acacia from natural forest. We used RF on S-2 imagery to classify acacia plantations into 6 age classes with an overall accuracy of 70%, with young plantation consistently separated from older. However, accuracy was lower at distinguishing between the older age classes. For both distinguishing plantation and natural forest, and determining plantation age, a combination of radar and optical imagery did nothing to improve classification accuracy.

Highlights

The global area of forest plantations increased from 167 Mha in 1990 to 278 Mha in2015 [1]
Our study focuses on North-Central Vietnam, where there has been a large increase in plantation forests
Harvest causes a significant reduction in backscatter, with mean ± standard deviation values for the VH band falling from −12.1 ± 0.6 dB pre-harvest to −14.5 ± 1.2 dB immediately after harvest

Summary

Introduction

The global area of forest plantations increased from 167 Mha in 1990 to 278 Mha in2015 [1]. The global area of forest plantations increased from 167 Mha in 1990 to 278 Mha in. Forest plantations can reduce logging pressure on natural forests through providing an alternative source of timber. Conversion of natural forest to plantation is a major driver of forest loss [2]. Assessments [3] of forest cover often make no distinction between natural forest and planted forest, so that countries can report increased forest area despite the ongoing loss of natural forest and conversion of natural forest to plantation. Natural forests and plantation forests differ in their ability to store and sequester carbon [4], and to support biodiversity [5,6,7], and local livelihoods [8]. An ability to distinguish plantation and natural forests using remote sensing would be of great value by allowing the accurate monitoring of natural forest loss and plantation expansion

Methods

Results

Discussion

Conclusion