# Coarse-Resolution Satellite Images Overestimate Urbanization Effects on Vegetation Spring Phenology
## 5 Conclusion  
It is not well known whether satellite-based time series with coarse resolutions can accurately detect urbanization effects on vegetation spring phenology. This study fills this research gap. In light of our results, we found that the difference between vegetation spring phenology in rural and urban at different spatial resolutions are not coincident, and specifically, the rural-urban difference is amplified with coarser spatial resolutions. A possible reason for this inconsistency is that coarse images tend to have more mixed pixels with higher diversity in terms of spring phenology dates, which leads to the detected vegetation spring phenology being earlier than the real situation.  
Figure 13: Comparison of vegetation spring phenology extracted from two different datasets: (**a**) resampled Sentinel-Landsat (500 m) and (**b**) MODIS (500 m).  
We suggest that future studies that explore the urban vegetation phenology use satellite images with a spatial resolution as high as possible. According to the findings of our study, it is better to use satellite images in which most vegetation pixels are \"pure\" to reduce the uncertainty in spring phenology detection. Specifically, in cities like Beijing, satellite images with spatial resolution finer than 30 m are superior when exploring urbanization effects on vegetation spring phenology. However, current available satellite-based vegetation index time series cannot be compatible with high temporal and high spatial resolution. Recently, a fused dataset, Harmonized Landsat-8 Sentinel-2 (HLS) product with 5-day and 30 m spatial resolution, was used directly for studying urbanization effects on vegetation phenology, but the spatial coverage was limited at this time. Alternatively, we can fuse data from multiple satellites by various spatiotemporal data fusion algorithms. This study also provides a detailed procedure to generate high-quality time series by fusing images from two satellites (i.e., Sentinel-2 and Landsat-8) that can be adopted in future studies.  
Conceptualization, J.T., X.Z. and J.C.; Methodology, J.T. and X.Z.; Software, J.T.; Validation, J.T.; Formal Analysis, J.T. and X.Z.; Investigation, J.T.; Resources, J.T.; Data Curation, J.T.; Writing-Original Draft Preparation, J.T.; Writing-Review & Editing, X.Z., J.W., M.S. and J.C.; Visualization, J.T.; Supervision, X.Z.; Project Administration, X.Z.; Funding Acquisition, X.Z. All authors have read and agreed to the published version of the manuscript.  
This study was funded by the National Natural Science Foundation of China (project no.41701378), Research Grants Council of Hong Kong (project no.25222717), and Research Institute for Sustainable Urban Development, the Hong Kong Polytechnic University (project no. 1-BBWD).  
We thank [PERSON] for improving the quality of this paper.  
The authors declare no conflict of interests. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.