## 4 Current Status and Identified Needs
### Level 2 Bio-Geophysical Land Products
The CGLS systematically provides global estimation of LAI at 1/3 km resolution derived from Proba-V [144] and now from Sentinel-3 observations. * Terrestrial Chlorophyll Content. Chlorophyll is one of the most important foliar biochemicals, where the content within a vegetation canopy is related positively to both the productivity of the vegetation and the depth and width of the chlorophyll absorption feature in the reflectance spectra [23]. The S3 OTCI product, which is based on the legacy MERIS Terrestrial Chlorophyll Index (MTCI) algorithm, provide information on the chlorophyll content of vegetation (amount of chlorophyll per unit area of ground). This is a combination of information on area of leaves per unit area on ground (LAI) and the chlorophyll concentration of those leaves [23; 24]. * Sun-Induced Fluorescence (SIF) is considered the most direct remote sensing signal to track photosynthetic activity and its dynamics [145; 146]. The ESA FLEX mission aims to observe SIF in order to monitor the photosynthetic activity of different biomes and their interannual changes related to climate variability [13; 14]. There is currently no active network to support systematic and global validation of SIF. ESA has been supporting the development of dedicated ground-based instrument for this purpose, called Fluorescence Box (Flox) [147; 148], and is planning to deploy these instruments in various locations in order to properly support FLEX Cal/Val activities. There is, in principle, a considerable number of reference data available for validating satellite-based estimation of these bio-geophysical variables. This in situ data is typically gathered during field campaigns or operationally collected in the frame of existing permanent sites and distributed as part of regional and continental networks. However, the main challenge is that these geophysical variables are not directly measured in the field, but rather inferred from indirect observations (see, in particular, fAPAR). Furthermore, the procedures for making the field measurements and for sampling the region of interest generally differ, which can cause large discrepancies over heterogeneous vegetated surfaces when comparing the point data to the collocated satellite-based observations. This lack of common Cal/Val best practices is limiting our ability of synergistically exploiting the currently available ground-based data for the global validation of satellite-derived terrestrial ECVs [41]. Furthermore, a wide range of potentially complementary Cal/Val initiatives are on-going or are planned under different umbrellas (ESA, EC, CEOS), but there is a lack of an integrated solution, since synergies across current and future missions and cross-fertilization among existing Cal/Val projects are largely under-exploited, with resulting duplication of efforts and increase of costs. Within this section, we review the current status and highlight the remaining needs in terms of infrastructure and methodologies for the validation of land bio-geophysical products. The needs identified in the text are listed with derived recommendations in the Table 4 at the end of the section.