Publication Details

Category Text Publication
Reference Category Journals
DOI 10.1016/j.jag.2024.103910
Licence creative commons licence
Title (Primary) Quantitative assessment of various proxies for downscaling coarse-resolution VOD products over the contiguous United States
Author Zhong, S.; Fan, L.; De Lannoy, G.; Frappart, F.; Zeng, J.; Vreugdenhil, M.; Peng, J. ORCID logo ; Liu, X.; Xing, Z.; Wang, M.; Li, X.; Wang, H.; Wigneron, J.-P.
Source Titel International Journal of Applied Earth Observation and Geoinformation
Year 2024
Department RS
Volume 130
Page From art. 103910
Language englisch
Topic T5 Future Landscapes
Keywords Active microwave; Passive microwave; Vegetation optical depth (VOD); Sentinel-1; Optical indices
Abstract Vegetation Optical Depth (VOD), a vegetation parameter that quantifies the extinction effect of microwaves penetrating the canopy, plays a crucial role in global-scale biomass monitoring and climate change research. However, the spatial gridding of existing long-term VOD products is relatively coarse (approximately 25 km), with restrictions on their application at a regional scale. High-resolution active-microwave proxies and optical vegetation indices can potentially be used to disaggregate coarse-resolution VOD, but it is unclear which proxy is optimal. In this paper, the Normalized Difference Vegetation Index (NDVI) and active-microwave proxies (VH, VV, and cross-polarization ratio CR) from Sentinel-1 were quantitatively assessed with VOD products at various frequencies (L-/C-/X-VOD) across the contiguous United States (U.S.). The results showed that VH (R = 0.80) and NDVI (R = 0.77) exhibit a high spatial correlation with L-VOD products. For temporal correlation, NDVI had the highest overall performances with all VOD products, but good correlations were also achieved with CR and, to a lesser extent, VH. Further comparisons of the performance between Brightness Temperature (TB) and VOD revealed that while TB displayed a strong temporal correlation with active-microwave proxies, its spatial correlations with such proxies were low. In contrast, VOD had good correlations both temporally and spatially with active-microwave proxies (e.g., VH). These evidences suggested that the downscaling of VOD using the combination of VH and other proxies could be an alternative promising method to estimate high-resolution VOD.
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Zhong, S., Fan, L., De Lannoy, G., Frappart, F., Zeng, J., Vreugdenhil, M., Peng, J., Liu, X., Xing, Z., Wang, M., Li, X., Wang, H., Wigneron, J.-P. (2024):
Quantitative assessment of various proxies for downscaling coarse-resolution VOD products over the contiguous United States
Int. J. Appl. Earth Obs. Geoinf. 130 , art. 103910 10.1016/j.jag.2024.103910