## 6 Conclusions  
Dense time series and fine spatial resolution remote sensing images (e.g., 30-m) are urgently needed for monitoring detailed land surface dynamics. In this study, new time series 30-m imagery products with 8-day, 16-day and monthly time intervals were generated using the 2-day revisiting HJ-1A/B observations. Building on automated orthorectification and cloud masking algorithms previously developed for HJ data, this study demonstrates the feasibility of using HJ-1A/B images to produce 30-m composites which can reflect the vegetation dynamics in a heterogeneous area over eight days, 16 days and one month.  
Quality assessment was performed by comparing the HJ composites with the well-verified WELD and MODIS products. HJ composites have no data gaps and have substantially less cloud contamination than WELD data. Good agreements were found between the monthly WELD and HJ TOA reflectance for eight months (January to April, September to December) with a mean R for blue, green, red and near-infrared bands of 0.5539, 0.6695, 0.7361, and 0.7716, respectively. An obviously lower R\({}^{2}\) value was found for the scatter plots in May, June, July and August when more clouds and data gaps appeared in WELD in this period. HJ showed a better temporal coherence than WELD according to the time series analysis of the TOA NDVI profile. The comparison between HJ and MODIS revealed that the HJ composites are comparable to MODIS data over areas consisting of large patches of homogeneous surface types, but can provide 30-m spatial details for fragmented landscapes. Mean residual cloud cover percentage statistics indicated that the mean residual clouds for 8-day, 16-day and monthly HJ composites were 16.37%, 4.79%, and cloud free, respectively. It is believed that the HJ composites are comparably high-quality products in terms of both temporal profile and radiometric consistency.  
Generally, the compositing efforts conducted in this study illustrate that the compositing of HJ-1A/B observations can provide datasets at dense temporal resolution and fine spatial resolution, and it overcomes the difficulty of less clear-sky observations. However, as there are some unsolved problems such as the precise atmospheric correction and BRDF normalization for HJ-1A/B images, the methodology only partially exploited the temporal information by using the TOA reflectance measures. More explicit utilization of the consistent surface reflectance will further enhance the quality of composited products.  
This study was funded jointly by the National Natural Science Foundation project of China (41271433, 41571373), the International Cooperation Key Project of CAS (Grant No. GJHZ201320), the International Cooperation Partner Program of Innovative Team, CAS (Grant No. KZZD-EW-TZ-06), the \"Hundred Talents\" Project of Chinese Academy of Sciences (CAS). We are grateful to all the contractors, image providers and the anonymous reviewers for their valuable comments and suggestions.  
All authors have made major and unique contributions. [PERSON] processed the major data sources, developed the algorithm, and drafted the preliminary version of this paper. [PERSON] designed the framework of this research work, and finished the final version of this paper. [PERSON] performed the data collection and preprocessing. [PERSON] assisted in the comparison and validation work, and manuscript revision.  
The authors declare no conflict of interest.