EOLAB Fiducial Reference Measurements of vegetation biophysical parameters

This database provides fiducial reference measurements (FRM) of key vegetation variables, including Leaf Area Index (LAI), Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), and Fraction of Green Vegetation Cover (FVC/FCOVER), together with related metrics such as the clumping index. The dataset includes measurements collected during several field campaigns over cropland sites in Spain (three sites) and one site in the Amazon Basin (Peru). Observations were derived from indirect optical methods, including digital hemispherical photography (DHP), LAI-2200 Plant Canopy Analyzer, and AccuPAR ceptometer, following ESA FRM4Veg protocols for both measurement and uncertainty estimation (see Brown et al., 2021; Camacho et al., 2024). Due to the use of indirect methods, LAI-related variables are reported as Green Area Index (GAI) for short canopies (crops, excluding fruit trees) and Plant Area Index (PAI) for tall canopies (forests), including both overstory and understory contributions. Similarly, FAPAR is represented by the Fraction of Intercepted PAR (FIPAR) absorbed by green vegetation. The current version comprises 189 sampling units across four sites. The dataset will be updated as new campaigns become available. Short Description of the sites: Moncada (Spain) – irrigated croplandMoncada is an agricultural area of approximately 4 × 4 km located near Valencia (Spain), within the “Horta de Valencia”, a Globally Important Agricultural Heritage System (GIAHS) recognized by the Food and Agriculture Organization (FAO). The area comprises around 6,000 small agricultural holdings (typically <1 ha) and thousands of individual plots. Approximately 80% of the area is devoted to fruit production, together with more than 50 irrigated vegetable crops (e.g. onion, artichoke, pumpkin, lettuce, cabbage and tiger nut). The site is mainly characterized by short crops, with only a limited presence of fruit trees.EOLAB conducted three field campaigns (May, July and November 2017), characterizing approximately 90 elementary sampling units (ESUs) using DHP. CAN-EYE outputs (bidirectional gap fractions) were subsequently used to derive uncertainties following FRM4Veg procedures. Barrax (Spain) – irrigated and rainfed croplandThe Las Tiesas experimental farm (39.0549°N, 2.1010°W), located near Barrax (Albacete, Spain), is a well-established site for calibration and validation (Cal/Val) activities. Established in 1999, it meets FRM requirements for satellite product validation, including flat and homogeneous fields, a variety of irrigated and rainfed crops, good accessibility, and a high probability of clear-sky conditions.During the CEOS Surface Reflectance Intercomparison Exercise for Vegetation (SRIX4Veg) campaign (18–21 July 2022), EOLAB conducted measurements using DHP, AccuPAR LP-80 and LAI-2200 Plant Canopy Analyzer. A total of 50 ESUs were characterized. Nules (Spain) – citrus orchardsA field campaign was conducted on 1 August 2024 at an agricultural site in Nules (39.8823°N, 0.1662°W), Castellón, Spain. The area includes approximately 500 ha of irrigated crops, of which ~94% correspond to citrus orchards (mainly orange and mandarin), a dominant crop type in the Mediterranean region. The site was selected for its relatively homogeneous land cover and to complement previous validation exercises with a new crop type.A total of 18 ESUs were characterized using DHP and AccuPAR LP-80. However, due to the row structure of the canopy, FCOVER derived from DHP was found to be unreliable (systematic underestimation due to limited angular sampling), and clumping index values derived from CAN-EYE were unrealistically low (0.3–0.5), leading to overestimated LAI. Therefore, only effective PAI is provided as a proxy for LAI, and FIPAR (at 10:30 local time) as a proxy for FAPAR. Chontachaka (Peru) – evergreen broadleaf forestA field campaign was conducted from 21 to 26 September 2024 in the Chontachaka Ecological Reserve (13.0290°S, 71.4784°W), Cusco, Peru, located in the buffer zone of Manu National Park (UNESCO World Heritage Site), one of the most biodiverse regions of the Amazon Basin. The site lies within the Manu River basin and spans elevations between 900 and 1200 m, within a broader altitudinal gradient ranging from lowland Amazon (~300 m) to Andean regions (>3000 m).The reserve covers approximately 200 ha and is characterized as tropical cloud forest, classified as evergreen broadleaf forest in the ESA CCI Land Cover 2022 product. A total of 39 ESUs were characterized using DHP, following a random sampling design due to the high structural complexity of the canopy. Measurements were acquired at the bottom of the canopy to derive total canopy properties. References: Brown, L.A.; Camacho, F.; García-Santos, V.; Origo, N.; Fuster, B.; Morris, H.; Pastor-Guzman, J.; Sánchez-Zapero, J.; Morrone, R.; Ryder, J.; et al. Fiducial Reference Measurements for Vegetation Bio-Geophysical Variables: An End-to-End Uncertainty Evaluation Framework. Remote Sens. 2021, 13, 3194. https://doi.org/10.3390/rs13163194 Camacho, F.; Martínez-Sánchez, E.; Brown, L.A.; Morris, H.; Morrone, R.; Williams, O.; Dash, J.; Origo, N.; Sánchez-Zapero, J.; Boccia, V. Validation and Conformity Testing of Sentinel-3 Green Instantaneous FAPAR and Canopy Chlorophyll Content Products. Remote Sens. 2024, 16, 2698. https://doi.org/10.3390/rs16152698