Temperature Is Likely an Important Omission in Interpreting Vegetation Optical Depth

• Published in: Geophysical research letters 2024-08, Vol.51 (15), p.n/a
• Main Authors: Zhao, Meng, Humphrey, Vincent, Feldman, Andrew F., Konings, Alexandra G.
• Format: Article
• Language: English
• Subjects: Algorithms; Biomass; Canopies; Canopy; Depth; Diurnal; Ecohydrology; Mathematical models; Moisture content; Optical analysis; Optical thickness; Plant biomass; Plant cover; Plants; Plants (botany); Satellites; Temperature; Variation; Vegetation; Water content; Water depth
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL110094

Vegetation optical depth (VOD) satellite microwave retrievals provide significant insights into vegetation water content and responses to hydroclimatic changes. While VOD variations are commonly linked to dry biomass and live fuel moisture content (LFMC), the impact of canopy temperature (Tc) remains overlooked in large‐scale studies. Here, we investigated the impact of Tc on L‐band (1.4 GHz) and X‐band (10.7 GHz) VOD at diurnal and seasonal timescales. Synthetic benchmark VOD was created using realistic fields of Tc, LFMC, and biomass in an electromagnetic model. Perturbation experiments revealed that Tc strongly affects diurnal VOD variations at both L‐band and X‐band. Seasonally, while biomass emerges as the largest contributor to VOD variations in 70% (at X‐band) and 90% (at L‐band) of our study region, Tc and LFMC still play substantial roles. The findings stress the importance of refining retrieval algorithms to distinguish Tc, LFMC, and biomass effects for future VOD applications in ecohydrology. Plain Language Summary Satellite measurements known as vegetation optical depth (VOD) are sensitive to how much water plants contain (i.e., their hydration level). Because of this, VOD allows researchers to study how ecosystems respond to changes in weather, climate, and other factors. However, besides water, other variables like the temperature of the plants and their biomass can also change satellite VOD readings. In this study, we used computer simulations to examine how canopy temperature, relative water content, and plant biomass may affect these satellite readings. We found that canopy temperature has a surprisingly strong impact on VOD variations, especially at the diurnal timescale. Our results highlight the need to account for plant temperature influence in future VOD applications. Key Points A simulation approach was used to investigate how canopy temperature, live fuel moisture content, and dry biomass affect VOD variations The impact of canopy temperature on VOD variations is more substantial than previously assumed, both at diurnal and seasonal timescales To interpret VOD dynamics, algorithms should differentiate between temperature, live fuel moisture content, and biomass contributions