Impact case study database

Research at the University of Southampton made a key contribution to the European Copernicus programme’s capability to monitor global vegetation by (i) providing near real-time data on global vegetation chlorophyll content that are routinely distributed to users by the ESA, and (ii) establishing an operational validation procedure for vegetation monitoring products. Both of these contributions are vital to meeting the objectives of the Copernicus land monitoring services programme to provide geographical information on the status of vegetation cover to a broad range of users in the field of terrestrial environmental applications, including those in agriculture, food security and forest management.

ESA used Dash’s algorithm to develop a new vegetation data product, the OLCI Terrestrial Chlorophyll Index (OTCI). OTCI is based on the Sentinel-3 satellite’s Ocean and Land Imaging spectrometer (OLCI) instrument, and replaced MTCI after MERIS ceased operation in 2012. User demand for a replacement product, coupled with evidence of the Southampton algorithm’s robustness, led ESA to include the ‘red edge’ detection capability offered by OTCI within the mission requirements document for the Copernicus Sentinel-3 satellite programme. Since Sentinel 3 was launched in October 2016, ESA has used OTCI as a near real-time, global data product on vegetation chlorophyll content. Dash’s group authored the user guide and algorithm description [ 5.2]. The OTCI is currently (February 2021) the only near-real time, global operational product estimating terrestrial vegetation chlorophyll content. An operational data product is one that ESA has committed to deliver long-term and in near-real time, guaranteeing users its continued and timely production. It is distributed to users free of charge through the Copernicus programme. As ESA states ‘the unique capability of the OTCI algorithm to exploit the red edge position, thus providing accurate information on very high level of chlorophyll contents which cannot be performed by other sensors, put Europe and the European Space Agency and Copernicus Programme in a unique and leading position for monitoring the state of vegetation all over the world” [ 5.1].

During 2017 alone, 2.44 pebibytes (> 1000 terabytes) of Sentinel 3 OTCI data were downloaded from Copernicus’ dissemination system [ 5.3]. Copernicus programme users have deployed OTCI to monitor and manage terrestrial ecosystems, including estimating forest and crop health. As ESA stated “ The innovative product (OTCI) that was developed by Dash’s team now contributes to an overall observation system that allows us to better understand how our planet is evolving and how it is responding to climate change and at the same time allows us to better understand climate change itself” [ 5.1] .

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 on the ground-based validation of satellite-derived vegetation data products [ 3.3, 3.4] led to Dash’s group writing an Algorithm Theoretical Basis Document for the European Commission specifying validation procedures for three other vegetation products – leaf area index, LAI; fraction of vegetation cover, FVC; and fraction of absorbed photosynthetically active radiation, FAPAR [ 5.4]. Dash’s group led the validation of the vegetation component [ 5.5] and from 2017, conducted one of the largest and most comprehensive ground validation exercises globally, processing ground data across the world to determine the products’ accuracy as part of ESA’s Sentinel-3 Validation Team. In 2017, ESA noted ‘Feedback from the Sentinel-3 Validation Team meeting provided essential information to ESA and EUMETSAT to progress with the evolution and improvement of Sentinel-3's core data products’ [ 5.5]. The validation data are now being routinely used by the European Commission (EC) to ensure the operational products meet user requirements. The EC has noted that they ‘… reproduce well the changes due to drought and wet conditions in Europe, as well as the realism of the temporal variation over specific events around the globe’ [ 5.6]. Since 2017, the EC has delivered these three products – LAI, FVC, FAPAR – through the Copernicus programme to users worldwide. They are used by more than 6,000 organisations and users worldwide for a wide range of applications ranging from monitoring biodiversity to drought surveillance [ 5.7]. For example, the EC’s Joint Research Centre uses Copernicus FAPAR and LAI product as key inputs to the Europe-wide Monitoring Agriculture ResourceS (MARS) crop early warning programme [ 5.8], which supports the Common Agricultural Policy and food security assessments worldwide.

In addition to ensuring the quality of the three satellite-based vegetation products [ 5.4], the Copernicus programme has distributed the ground-based GBOV validation data set produced by Dash’s group since October 2018. The GBOV data are the largest ground data set for in-depth quality assessment of any satellite-derived vegetation product. Since their release in 2019, they have been downloaded by more than 300 users worldwide [ 5.9]. Through such downloads, users have applied Southampton’s ground data to accuracy assessment of other satellite-derived vegetation data products (e.g. those from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) sensor) alongside the data products distributed through the Copernicus programme [ 5.10].

Meanwhile, users have also benefitted significantly from implementing Dash’s chlorophyll algorithms independently of ESA. For example, in 2018 the World Bank reviewed the performance of algorithms for their prediction of crop yields from satellite data and recommend use of MTCI for countrywide maize crop yield estimates in Uganda, noting ‘the superior performance of MTCI is noteworthy’ [p. 17] and ‘The large boost in performance when using MTCI with Sentinel2 therefore more than outweighed any loss in accuracy from using coarser resolution’ [ 5.11].

The MTCI and OTCI algorithms developed at the University of Southampton thus formed the basis for innovative and robust data products for global vegetation monitoring which help the European Commission to deliver part of its flagship Copernicus programme. These data products provide accurate and timely information for users to monitor and manage both crops and our terrestrial biosphere.