Mapping and Evaluation of NDVI Trends from Synthetic Time Series Obtained by Blending Landsat and MODIS Data around a Coalfield on the Loess Plateau

Feng Tian,Rasmus Fensholt,Kun Wang,Yunjia Wang,Yi Huang,Li Zhang

doi:10.3390/rs5094255

Abstract

The increasingly intensive and extensive coal mining activities on the Loess Plateau pose a threat to the fragile local ecosystems. Quantifying the effects of coal mining activities on environmental conditions is of great interest for restoring and managing the local ecosystems and resources. This paper generates dense NDVI (Normalized Difference Vegetation Index) time series between 2000 and 2011 at a spatial resolution of 30 m by blending Landsat and MODIS (Moderate Resolution Imaging Spectroradiometer) data using the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM) and further evaluates its capability for mapping vegetation trends around a typical coalfield on the Loss Plateau. Synthetic NDVI images were generated using (1) STARFM-generated NIR (near infrared) and red band reflectance data (scheme 1) and (2) Landsat and MODIS NDVI images directly as inputs for STARFM (scheme 2). By comparing the synthetic NDVI images with the corresponding Landsat NDVI, we found that scheme 2 consistently generated better results (0.70 < R2 < 0.76) than scheme 1 (0.56 < R2 < 0.70) in this study area. Trend analysis was then performed with the synthetic dense NDVI time series and the annual maximum NDVI (NDVImax) time series. The accuracy of these trends was evaluated by comparing to those from the corresponding MODIS time series, and it was concluded that both the trends from synthetic/MODIS NDVI dense time series and synthetic/MODIS NDVImax time series (2000–2011) were highly consistent. Compared to trends from MODIS time series, trends from synthetic time series are better able to capture fine scale vegetation changes. STARFM-generated synthetic NDVI time series could be used to quantify the effects of mining activities on vegetation, but the test areas should be selected with caution, as the trends derived from synthetic and MODIS time series may be significantly different in some areas.

Highlights

With an area of 648,700 km2, the Chinese Loess Plateau is home to about 108 million people [1]
The total number of pixels in the Normalized Difference Vegetation Index (NDVI) trends derived from the synthetic time series is nearly 70-times larger than in those derived from the MODIS time series, which equals the ratio of per pixel area between MODIS and Landsat images
The mean values of NDVImax slopes of both trends were nearly the same, with 0.0009 for those derived from synthetic time series and 0.0007 for those derived from MODIS time series

Summary

Introduction

With an area of 648,700 km, the Chinese Loess Plateau is home to about 108 million people [1]. It is one of the largest regions with severe soil erosion in the world [2]. It is important to assess the effects of coal mining activities on the local environment. One solution to this issue is to compare the changes in vegetation productivity, which is recognized as one of the key indicators of environmental conditions, between mined and non-mined areas [5].

Results

Discussion

Conclusion