CEOS LPV DIRECT V2.1: A database of upscaled LAI, FAPAR and Fcover values for satellite biophysical product validation

Ground references of high quality are needed to validate satellite-based products. The DIRECT V2.1 database compiles Leaf Area Index (LAI), fraction of absorbed photosynthetically active radiation (FAPAR) and fraction of vegetation cover (FCover) averaged values over a 3 km x 3 km area. The ground data was upscaled using high spatial resolution imagery following CEOS WGCV LPV (so called CEOS LPV) LAI validation good practices (Fernandes et al., 2014) to properly account for the spatial heterogeneity of the site. Ground measurements performed during several international Cal/Val activities, including VALERI, BigFoot, SAFARI-2000, CCRS, Boston University, were compiled by S. Garrigues (Garrigues et al., 2008) in the DIRECT database, and later ingested in the CEOS LPV OLIVE tool (Weiss et al., 2014) for accuracy assessment.

F. Camacho reviewed DIRECT to remove those sites without understory measurements (Camacho et al., 2013) and after that expanded the database adding the ImagineS network of sites (Camacho et al., 2021). DIRECT V2.1 is the last update including 44 new sites from China (Fang et al., 2019; Song et al., 2021) and 2 more sites from ESA FRM4Veg project (Brown et al., 2021).

The CEOS LPV DIRECT V2.1 database constitutes a major effort of the international community to provide ground reference for the validation of satellite-based LAI and FAPAR ECVs, with a total of 176 sites around the world (7 main biome types) and 280 LAI values, 128 FAPAR and 122 FCOVER values covering the period from 2000 to 2021.

Data description

LAI, LAIeff, FAPAR and FCOVER upscaled values over 3 km x 3 km.

LAI_NoUnderstory, refers to sites where only overstory was measured and thus are not recommended for accuracy assessment of satellite products.

File contents

A Header " Sites":

General information for each site (coordinates, landcover, method, reference)

For each variable:

# number of the site (site description in Sites)

Lat_cen, latitude centre of 3km x 3km

Lon_cen, longitude centre of 3km x 3km

Site name, name of the site

Date, MM/DD/YYYY

Mean, average value over 3km x 3km

Uncert, uncertainty over 3 km x 3km (STD)