Abstract
The Ocean and Land Colour Instrument (OLCI) on-board Sentinel-3 (2016–present) was designed with similar mechanical and optical characteristics to the Envisat Medium Resolution Imaging Spectrometer (MERIS) (2002–2012) to ensure continuity with a number of land and marine biophysical products. The Sentinel-3 OLCI Terrestrial Chlorophyll Index (OTCI) is an indicator of canopy chlorophyll content and is intended to continue the legacy of the Envisat MERIS Terrestrial Chlorophyll Index (MTCI). Despite spectral similarities, validation and verification of consistency is essential to inform the user community about the product’s accuracy, uncertainty, and fitness for purpose. This paper aims to: (i) describe the theoretical basis of the Sentinel-3 OTCI and (ii) evaluate the spatiotemporal consistency between the Sentinel-3 OTCI and the Envisat MTCI. Two approaches were used to conduct the evaluation. Firstly, agreement between the Sentinel-3 OTCI and the Envisat MTCI archive was assessed over the Committee for Earth Observation Satellites (CEOS) Land Product Validation (LPV) core validation sites, enabling the temporal consistency of the two products to be investigated. Secondly, intercomparison of monthly Level-3 Sentinel-3 OTCI and Envisat MTCI composites was carried out to evaluate the spatial distribution of differences across the globe. In both cases, the agreement was quantified with statistical metrics (R2, NRMSD, bias) using an Envisat MTCI climatology based on the MERIS archive as the reference. Our results demonstrate strong agreement between the products. Specifically, high 1:1 correspondence (R2 >0.88), low global mean percentage difference (−1.86 to 0.61), low absolute bias (<0.1), and minimal error (NRMSD ~0.1) are observed. The temporal profiles reveal consistency in the expected range of values, amplitudes, and seasonal trajectories. Biases and discrepancies may be attributed to changes in land management practices, land cover change, and extreme climatic events occurred during the time gap between the missions; however, this requires further investigation. This research confirms that Sentinel-3 OTCI dataset can be used along with the Envisat MTCI to provide a data coverage over the last 20 years.
Highlights
Chlorophyll plays a key role in the chain of reactions that convert solar radiation, carbon dioxide, and water molecules into chemical energy and plant biomass [1]
To assess the temporal consistency of Sentinel-3 OLCI Terrestrial Chlorophyll Index (OTCI) and Envisat MERIS Terrestrial Chlorophyll Index (MTCI) values over specific validation sites, pixel extractions were obtained from Level-2 Sentinel-3 OTCI and third reprocessing (3RP) Envisat MTCI data over 37 validation sites, representing a variety of land cover types, regions, and species (Table S1)
This product provides continuity to the related land products derived from Envisat MTCI
Summary
Chlorophyll plays a key role in the chain of reactions that convert solar radiation, carbon dioxide, and water molecules into chemical energy and plant biomass [1]. Leaf chlorophyll concentration (LCC) is used as an indicator of photosynthetic capacity and productivity, plant phenology, and nutrition status [2,3,4]. Natural vegetation exposed to pronounced seasonal variation in climatic conditions (e.g., temperate deciduous forests) experiences increases in chlorophyll as leaves unfold and reach maturity, and decreasing levels during autumn senescence due to breakdown and reabsorption of pigments. Information on the spatial and temporal distribution of chlorophyll can help to improve our understanding of vegetation response to climate and support carbon modelling and food security
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
