Remote sensing of vegetation dynamics in agro-ecosystems using SMAP vegetation optical depth and optical vegetation indices

TL;DR

This paper presents a novel method to derive vegetation optical depth from SMAP microwave data, enabling improved monitoring of crop phenology and water content in agro-ecosystems without relying on optical data.

Contribution

It introduces an inversion approach for SMAP data to estimate vegetation optical depth independently, enhancing agricultural monitoring and ecological studies.

Findings

L-band VOD correlates with biomass and water content.

Microwave and optical data provide complementary insights.

VOD serves as an ecological indicator for biosphere studies.

Abstract

The ESA's SMOS and the NASA's SMAP missions, launched in 2009 and 2015, respectively, are the first two missions having on-board L-band microwave sensors, which are very sensitive to the water content in soils and vegetation. Focusing on the vegetation signal at L-band, we have implemented an inversion approach for SMAP that allows deriving vegetation optical depth (VOD, a microwave parameter related to biomass and plant water content) alongside soil moisture, without reliance on ancillary optical information on vegetation. This work aims at using this new observational data to monitor the phenology of crops in major global agro-ecosystems and enhance present agricultural monitoring and prediction capabilities. Core agricultural regions have been selected worldwide covering major crops (corn, soybean, wheat, rice). The complementarity and synergies between the microwave vegetation signal, sensitive to biomass water-uptake dynamics, and optical indices, sensitive to canopy greenness, are explored. Results reveal the value of L-band VOD as an independent ecological indicator for global terrestrial biosphere studies.