Estimation of Forest Area and Canopy Cover Based on Visual Interpretation of Satellite Images in Ethiopia

Zerihun Asrat,Terje Gobakken,Habitamu Taddese,Ingunn Burud,Erik Næsset,Hans Ørka

doi:10.3390/land7030092

Abstract

Forests, particularly in the tropics, are suffering from deforestation and forest degradations. The estimation of forest area and canopy cover is an essential part of the establishment of a measurement, reporting, and verification (MRV) system that is needed for monitoring carbon stocks and the associated greenhouse gas emissions and removals. Information about forest area and canopy cover might be obtained by visual image interpretation as an alternative to expensive fieldwork. The objectives of this study were to evaluate different types of satellite images for forest area and canopy cover estimation though visual image interpretation, and assess the influence of sample sizes on the estimates. Seven sites in Ethiopia with different vegetation systems were subjectively identified, and visual interpretations were carried out in a systematical design. Bootstrapping was applied to evaluate the effects of sample sizes. The results showed that high-resolution satellite images (≤5 m) (PlanetScope and RapidEye) images produced very similar estimates, while coarser resolution imagery (10 m, Sentinel-2) estimates were dependent on forest conditions. Estimates based on Sentinel-2 images varied significantly from the two other types of images in sites with denser forest cover. The estimates from PlanetScope and RapidEye were less sensitive to changes in sample size.

Highlights

Forests constitute the largest terrestrial ecosystem, and they provide a variety of services and functions [1,2]
For PlanetScope imagery, 85% of the images used were from May 2017, and only 2.4% were from March and earlier
Most of the images were acquired during the dry season (December–May), except for 13% of the images from RapidEye, which were acquired in October and November

Summary

Introduction

Forests constitute the largest terrestrial ecosystem, and they provide a variety of services and functions [1,2]. One of the services that forests offer is carbon sequestration; approximately. 2.5 billion tons carbon are absorbed annually [3,4,5]. Despite their contributions to carbon sequestration, much of the world’s forests, tropical forests, are suffering from severe deforestation and degradation, contributing to increased carbon emission [5,6,7]. About 12% of the total anthropogenic carbon emissions come from deforestation [5,8]. The pressure from deforestation and degradation on forests is larger in tropical, developing countries due to heavy dependence on the resource for livelihoods [9].

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Conclusion