OLCI Terrestrial Chlorophyll index
OLCI Terrestrial Chlorophyll Index
The OLCI Terrestrial Chlorophyll Index is the main variable included in the otvi.nc file.
The OLCI Terrestrial Chlorophyll Index (OTCI) is produced globally at 300 m spatial resolution for land from OLCI data on the SENTINEL-3 mission and is designed to be a continuation of the MERIS Terrestrial Chlorophyll Index derived from MERIS data.
The ENVISAT MERIS Terrestrial Chlorophyll Index (MTCI) was designed to monitor vegetation condition through an estimation of chlorophyll content using reflectance in the red edge region of the reflectance spectra. Unlike conventional vegetation indices which are based on the normalised difference between reflected solar radiation in red and near-infra-red wavebands, MTCI makes use of the shift of the red edge where absorption drops dramatically as wavelength increases. The use of red shift allows the MTCI product to remain responsive to high chlorophyll content which would saturate conventional vegetation indices. The OTCI is a chlorophyll index similar to the MTCI, defined by:
Rband12, Rband11, Rband10 are the reflectances in bands centred at 753, 709 and 681 nm.
In order to avoid meaningless values and numerical problems, input spectra shall be screened first for clouds, water and non-vegetated land surfaces. Some simple spectral tests are then computed. The expected accuracy of the product is also estimated during this processing and the Rayleigh correction is applied before computing the OTCI parameter.
NOTE: the Rayleigh correction accounts for actual channels central wavelength (smile), local atmospheric pressure conditions, and latitudinal variation of the Rayleigh optical thickness at standard pressure.