Enhanced monitoring of terrestrial vegetation from space

The research challenge

The condition and productivity of vegetation is controlled by chlorophyll content and concentration within a vegetation canopy. Reliable estimation of vegetation chlorophyll content is vital for forest and agricultural service providers who monitor crop yields, plant health, seasonality, carbon fluxes and carbon sequestration. Accurate and near-real-time estimates of vegetation chlorophyll content can therefore inform timely response to poor harvests or plant disease outbreaks, whilst estimates of global chlorophyll content enable improvements in carbon flux modelling and evaluation of vegetation response to climate change.

Image above right: Showing the global distribution of vegetation chlorophyll content. Areas around rainforest and agriculture activities in Europe and China shows high level of chlorophyll. (Data: Copernicus programme, image process: Harry Morris)

Our solution

The Southampton team developed an algorithm which used imagery from the European Space Agency’s (ESA’s) Medium Resolution Imaging Spectrometer (MERIS) satellite sensor to calculate an estimate of vegetation chlorophyll content, called the MERIS Terrestrial Chlorophyll Index (MTCI) . When the satellite carrying the MERIS sensor unexpectedly failed in 2012, ESA identified a continued need to provide users with ongoing data on vegetation canopy chlorophyll content. Dash therefore led research to develop and validate a second vegetation chlorophyll content product (OTCI) using data from ESA’s Sentinel-3A optical sensor (launched in 2016). This was the first time ESA had produced a dedicated operational global vegetation product. Subsequent research by the Southampton team and others, such as Copernicus Institute of Sustainable Development , has demonstrated the superiority of MTCI over alternative satellite-derived products in estimating vegetation chlorophyll content and monitoring vegetation condition. The team has also developed new procedures for validating satellite-derived vegetation chlorophyll content products , including using analysis of time-series data , and established for the first time a framework for operational validation of Copernicus land products using ground-based observations for validation (GBOV) .

Image right: The image, captured on 26 June 2019, shows a patchwork of agricultural fields dominate the landscape. Ukraine’s main grain crops are winter wheat, spring barley and corn. (contains modified Copernicus Sentinel data (2019), processed by ESA)

What was the impact?

Southampton’s research has made two key contributions to the European Copernicus programme’s capability to monitor global vegetation:

1. The provision of near real-time data on global vegetation chlorophyll content which are routinely distributed to users by ESA

- ESA used Dash’s algorithm to develop a new vegetation data product, the OLCI Terrestrial Chlorophyll Index (OTCI) , replacing the MTCI after MERIS ceased operation in 2012. Since the Copernicus Sentinel 3 satellite was launched in October 2016, ESA has used the OTCI as a near real-time global data product on vegetation chlorophyll content; it is currently (July 2021) the only product offering this spatial, temporal and thematic coverage.

- During 2017 alone, 2.44 pebibytes (> 1000 terabytes) of Sentinel 3 OTCI data were downloaded from Copernicus’ dissemination system.

- Copernicus programme users have deployed OTCI to monitor and manage terrestrial ecosystems, including estimating forest and crop health.

2. Establishing an operational validation procedure for vegetation monitoring products.

- To ensure the quality of their operational data products meets the expected user requirements, in 2016 the European Commission established a new service called the Ground-Based Observations for Validation (GBOV). Southampton’s research has been key to this, including: specification of validation procedures for three vegetation products – leaf area index (LAI), fraction of vegetation cover (FVC), and fraction of absorbed photosynthetically active radiation (FAPAR); validation of the vegetation component; and design and implementation of one of the largest and most comprehensive ground validation exercises globally.

- LAI, FVC, FAPAR are used by more than 6,000 organisations and users worldwide , for applications ranging from monitoring biodiversity to drought surveillance e.g. the EC’s Joint Research Centre uses the products as key inputs to the Europe-wide Monitoring Agriculture ResourceS (MARS) crop early warning programme , which supports the Common Agricultural Policy and food security assessments worldwide.

- Since their release by the Copernicus programme in 2019, the GBOV data produced by Southampton have been downloaded by more than 300 users worldwide .

Independently from ESA, other users have also benefitted significantly from implementing the team’s chlorophyll algorithms e.g. the World Bank recommended use of MTCI for countrywide maize crop yield estimates in Uganda .

Associated projects

The European Space Agency - Sentinel

Ground-Based Observations for Validation (GBOV) of Copernicus Global Land Products