Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observations
Long historical records and free accessibility have made Landsat data valuable for time-series analysis. However, Landsat time-series analysis is restricted for coastal areas due to the lack of sufficient numbers of clear images. The generation of synthetic Landsat images using model-fitting methods...
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| Format: | Article |
| Language: | English |
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Taylor & Francis Group
2024-12-01
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| Series: | GIScience & Remote Sensing |
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| Online Access: | https://www.tandfonline.com/doi/10.1080/15481603.2024.2421574 |
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| author | Chao Sun Jialin Li Yongchao Liu Tingting Pan Ke Shi Xinyao Cai |
| author_facet | Chao Sun Jialin Li Yongchao Liu Tingting Pan Ke Shi Xinyao Cai |
| author_sort | Chao Sun |
| collection | DOAJ |
| description | Long historical records and free accessibility have made Landsat data valuable for time-series analysis. However, Landsat time-series analysis is restricted for coastal areas due to the lack of sufficient numbers of clear images. The generation of synthetic Landsat images using model-fitting methods is accepted as an effective means of overcoming this problem. But for coastal areas, available observations are typically sparse and irregular, leading to ill-fitted models that distort synthetic Landsat images. In this study, we propose a linear harmonic model with different orders and implement it on an annual basis to generate synthetic Landsat images based on the Google Earth Engine (GEE) platform. First, we incorporated the available observations from adjacent years and filtered them by season to address the problems of data sparsity and irregularity. Then, we combined the threshold segmentation and ridge regression approaches to address the fake cloud problem, which sometimes contaminates synthetic Landsat images in summer. All cloud-free real Landsat images from five typical sites along China’s coasts during 1986–2020 were used to evaluate the accuracy and robustness of the synthetic Landsat images generated using our proposed methods. The principal results are as follows: (1) the R2 value of the linear harmonic model averaged across different Landsat bands and land cover types was 0.640, and the model was especially successful in simulating the surface reflectance in near NIR bands in forest and grassland areas; (2) 81.1% of the synthetic Landsat images covered by fake clouds were effectively restored, and there was the particular need to remove fake clouds for the synthetic Landsat images at low latitudes; (3) The mean absolute error for our synthetic Landsat images was 0.015, with the rate of 0.124; this was achieved under the clear-sky probability of only 36% and the average number of annual observations below 9, indicating a good performance. Compared with the continuous change detection and classification (CCDC) and seasonal median composite (SMC) methods, our proposed method offers advantages in both the accuracy and integrity of synthetic Landsat images. Our proposed method for synthesizing images also has potential for application to global coastal areas and other satellite datasets. |
| format | Article |
| id | doaj-art-dc7f4fe59f8742c58e330c9aa424542b |
| institution | Kabale University |
| issn | 1548-1603 1943-7226 |
| language | English |
| publishDate | 2024-12-01 |
| publisher | Taylor & Francis Group |
| record_format | Article |
| series | GIScience & Remote Sensing |
| spelling | doaj-art-dc7f4fe59f8742c58e330c9aa424542b2024-12-06T13:51:50ZengTaylor & Francis GroupGIScience & Remote Sensing1548-16031943-72262024-12-0161110.1080/15481603.2024.2421574Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observationsChao Sun0Jialin Li1Yongchao Liu2Tingting Pan3Ke Shi4Xinyao Cai5Department of Geography & Spatial Information Techniques, Ningbo University, Ningbo, Zhejiang Province, P. R. ChinaDepartment of Geography & Spatial Information Techniques, Ningbo University, Ningbo, Zhejiang Province, P. R. ChinaDepartment of Geography & Spatial Information Techniques, Ningbo University, Ningbo, Zhejiang Province, P. R. ChinaDonghai Academy, Ningbo University, Ningbo, Zhejiang Province, P. R. ChinaDepartment of Geography & Spatial Information Techniques, Ningbo University, Ningbo, Zhejiang Province, P. R. ChinaDepartment of Geography & Spatial Information Techniques, Ningbo University, Ningbo, Zhejiang Province, P. R. ChinaLong historical records and free accessibility have made Landsat data valuable for time-series analysis. However, Landsat time-series analysis is restricted for coastal areas due to the lack of sufficient numbers of clear images. The generation of synthetic Landsat images using model-fitting methods is accepted as an effective means of overcoming this problem. But for coastal areas, available observations are typically sparse and irregular, leading to ill-fitted models that distort synthetic Landsat images. In this study, we propose a linear harmonic model with different orders and implement it on an annual basis to generate synthetic Landsat images based on the Google Earth Engine (GEE) platform. First, we incorporated the available observations from adjacent years and filtered them by season to address the problems of data sparsity and irregularity. Then, we combined the threshold segmentation and ridge regression approaches to address the fake cloud problem, which sometimes contaminates synthetic Landsat images in summer. All cloud-free real Landsat images from five typical sites along China’s coasts during 1986–2020 were used to evaluate the accuracy and robustness of the synthetic Landsat images generated using our proposed methods. The principal results are as follows: (1) the R2 value of the linear harmonic model averaged across different Landsat bands and land cover types was 0.640, and the model was especially successful in simulating the surface reflectance in near NIR bands in forest and grassland areas; (2) 81.1% of the synthetic Landsat images covered by fake clouds were effectively restored, and there was the particular need to remove fake clouds for the synthetic Landsat images at low latitudes; (3) The mean absolute error for our synthetic Landsat images was 0.015, with the rate of 0.124; this was achieved under the clear-sky probability of only 36% and the average number of annual observations below 9, indicating a good performance. Compared with the continuous change detection and classification (CCDC) and seasonal median composite (SMC) methods, our proposed method offers advantages in both the accuracy and integrity of synthetic Landsat images. Our proposed method for synthesizing images also has potential for application to global coastal areas and other satellite datasets.https://www.tandfonline.com/doi/10.1080/15481603.2024.2421574Landsattime seriesmodel fittingsparse and irregular observationsfake clouds |
| spellingShingle | Chao Sun Jialin Li Yongchao Liu Tingting Pan Ke Shi Xinyao Cai Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observations GIScience & Remote Sensing Landsat time series model fitting sparse and irregular observations fake clouds |
| title | Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observations |
| title_full | Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observations |
| title_fullStr | Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observations |
| title_full_unstemmed | Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observations |
| title_short | Synthesizing Landsat images using time series model-fitting methods for China’s coastal areas against sparse and irregular observations |
| title_sort | synthesizing landsat images using time series model fitting methods for china s coastal areas against sparse and irregular observations |
| topic | Landsat time series model fitting sparse and irregular observations fake clouds |
| url | https://www.tandfonline.com/doi/10.1080/15481603.2024.2421574 |
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