Monitoring vegetation condition using microwave remote sensing: the standardized vegetation optical depth index (SVODI)

Abstract. Vegetation conditions can be monitored on a global scale using remote sensing observations in various wavelength domains. In the microwave domain, data from spaceborne missions are available late 1970s onwards. From these observations, vegetation optical depth (VOD) estimated, which is an indicator of total canopy water content and hence above-ground biomass its moisture state. Observations VOD anomalies would thus complement indicators based visible near-infrared primarily ecosystem's photosynthetic activity. Reliable long-term state monitoring needs to account for varying number over time caused by changes satellite constellation. To overcome this, we introduce standardized index (SVODI), created combining estimates multiple passive sensors frequencies. Different frequencies sensitive different parts canopy. Thus, them into single makes this deviations any represented. SSM/I-, TMI-, AMSR-E-, WindSat- AMSR2-derived C-, X- Ku-band VODs merged probabilistic manner resulting condition spanning 1987 present. SVODI shows similar temporal patterns well-established health (VHI) derived thermal data. regions where availability main control growth, also meteorological drought scPDSI (self-calibrating Palmer severity index) soil ERA5-Land. Temporal relate climate oscillation indices SOI (Southern Oscillation DMI (dipole mode relevant regions. It further shown that occur VHI before they SVODI. The results demonstrate potential monitor condition, supplementing existing indices. comes with advantages disadvantages inherent sensing, such as being less susceptible cloud coverage solar illumination but at cost lower spatial resolution. generation not specific could therefore find applications other fields. products (Moesinger et al., 2022) open-access under Attribution 4.0 International Zenodo, https://doi.org/10.5281/zenodo.7114654.