Are There Sufficient Landsat Observations for Retrospective and Continuous Monitoring of Land Cover Changes in China?

Zhou Zhou,You You,Shen Shen,Zhao Zhao,Xiao Xiao,Liu Liu,Metternicht Metternicht,Dong Dong

doi:10.3390/rs11151808

Abstract

Unprecedented human-induced land cover changes happened in China after the Reform and Opening-up in 1978, matching with the era of Landsat satellite series. However, it is still unknown whether Landsat data can effectively support retrospective analysis of land cover changes in China over the past four decades. Here, for the first time, we conduct a systematic investigation on the availability of Landsat data in China, targeting its application for retrospective and continuous monitoring of land cover changes. The latter is significant to assess impact of land cover changes, and consequences of past land policy and management interventions. The total and valid observations (excluding clouds, cloud shadows, and terrain shadows) from Landsat 5/7/8 from 1984 to 2017 were quantified at pixel scale, based on the cloud computing platform Google Earth Engine (GEE). The results show higher intensity of Landsat observation in the northern part of China as compared to the southern part. The study provides an overall picture of Landsat observations suitable for satellite-based annual land cover monitoring over the entire country. We uncover that two sub-regions of China (i.e., Northeast China-Inner Mongolia-Northwest China, and North China Plain) have sufficient valid observations for retrospective analysis of land cover over 30 years (1987–2017) at an annual interval; whereas the Middle-Lower Yangtze Plain (MLYP) and Xinjiang (XJ) have sufficient observations for annual analyses for the periods 1989–2017 and 2004–2017, respectively. Retrospective analysis of land cover is possible only at a two-year time interval in South China (SC) for the years 1988–2017, Xinjiang (XJ) for the period 1992–2003, and the Tibetan Plateau (TP) during 2004–2017. For the latter geographic regions, land cover dynamics can be analyzed only at a three-year interval prior to 2004. Our retrospective analysis suggest that Landsat-based analysis of land cover dynamics at an annual interval for the whole country is not feasible; instead, national monitoring at two- or three-year intervals could be achievable. This study provides a preliminary assessment of data availability, targeting future continuous land cover monitoring in China; and the code is released to the public to facilitate similar data inventory in other regions of the world.

Highlights

With increasing human activities in recent decades [1], anthropogenic land cover changes are more frequent and intensive [2], especially in nations with economies in transition
Scene-based analyses of Landsat data availability have been conducted in previous studies
Zhu et al [26] documented that selecting Landsat images with less than 10% cloud cover for continuous land cover change detection results in omitting more than 50% of the total clear observations

Summary

Introduction

With increasing human activities in recent decades [1], anthropogenic land cover changes are more frequent and intensive [2], especially in nations with economies in transition. China is a case in point of a country undergoing rapid and dramatic changes in land cover since the adoption of the Reform and Opening-up policy in 1978 [3,4], which drove rapid development of the economy, industrialization, and urbanization [5]. Multi-temporal satellite remote sensing allows the observation of land cover change over time [11]. Prior researches showcase the contribution of these data to map and monitor the trajectory of land cover changes in China. Liu et al [12] produced time series of land use/cover datasets of China (NLCD-China) from 1990 to 2015 at a five-year interval, using Landsat and Chinese satellite imagery; Gong et al [9,10] generated the 2010 and 2017 global land cover maps (FROM-GLC30, 30-m spatial resolution) from Landsat TM/ETM+ imagery and the 2017 global land cover map (FROM-GLC10, 10-m spatial resolution) using the Sentinel-2 imagery; Chen et al [13] released the global land cover maps at 30-m spatial resolution (GlobeLand30) for the years 2000 and 2010 using Landsat TM/ETM+ imagery; and Wu et al [14] produced land cover maps of China (ChinaCover) at 30-m spatial resolution for 2000 and 2010 using Landsat TM/ETM+ and HJ-1 imagery

Methods

Findings

Discussion

Conclusion