# Comparison of EPIC-Simulated and MODIS-Derived Leaf Area Index (LAI) across Multiple Spatial Scales
## Methods
### LAI Data (In Situ LAI and Upscaling, MODIS LAI, EPIC LAI)  
#### 2.2.1 In Situ LAI Measurements and Upscaling  
Sampling data was collected within the quadrat, a 100 \(\times\) 100 m grid (Figure 2A), delineated by five 100 m east-to-west (E-W) oriented transects separated 20 m apart in a north-south (N-S) direction. Sampling point locations (25) were interspersed between these transects, separated 20 m apart. Secondary sampling units (i.e., sub-plots) comprised of 2-3 intersecting transects 50 and/or 100 m in length which were distributed randomly within the LAI research site extent (Figure 2B) [31]. One quadrat was placed within the Appomattox, Hertford, and Umstead LAI research sites. Four quadrats were located within the Fairystone site to account for the variability of terrain and aspect. Quadrat locations were chosen randomly within four 0.5 km sections (NW, NE, SE, SW) within the 1.0 km research sites (Figure 3). At each LAI research site, overstory and understory forest measurements (i.e., height, diameter, stocking, crown closure, LAI) were made using both fixed area and point sampling methods as described in [31]. LAI was estimated for both deciduous and coniferous forest canopies from two indirect optical measurements: (1) the Tracing Radiation and Architecture of Canopies analyzer (TRAC) optical sensor and (2) digital hemispherical photography (DHP) [31; 36; 37; 38]. The modified Beer-Lambert light extinction function was used to solve for LAI [1; 31]. TRAC and DHP measurements were recorded across all four research sites for the following dates: Fairystone (1 May 2002, 25 June 2002, 4 September 2002), Appomattox (5 March 2002, 23 May 2002), Umstead (23 April 2002, 21 October 2002), and Hertford (5 March 2002). Measurements were not taken in the thinned pine at Appomattox (5 March) and the unthinned pine at Umstead (9 May). Pine LAI for both dates was estimated by comparing relative differences of SR LAI between 2002 data collects at each site, then reducing/increasing a known in situ LAI value by this percent difference. In situ LAI was upscaled to a 1.0 km resolution coincident with the MODIS grids to create LAI reference maps (LAI-RM) at all four LAI research sites for MODIS LAI comparisons (Mc5 and Mc6) (Figure 4). USGS three-band natural color orthoimagery and cloud-free 30 m Landsat 5 (L5) Thematic Mapper and Landsat 7 (L7) Enhanced Thematic Mapper+ data were acquired from the USGS EarthExplorer repository for all four research sites with selections as close to the in situ collection dates as possible. L5 and L7 satellites have been active since 1983 (L5) and 1999 (L7), with L5 decommissioned  
Figure 2: Plot design for (**A**) 100 m \(\times\) 100 m quadrat and (**B**) 50 m or 100 m sub-plot. Tracing Radiation and Architecture of Canopies (TRAC) measurements were made along the east-west 100 m transects (lines) and the 45\({}^{\circ}\) and 135\({}^{\circ}\) 50 m transects (lines) for both the quadrat and the sub-plot. Hemispherical photographs were captured at 20 m intervals (dots) within each quadrat and at the 0, 25, and 50 m marks of the sub-plot transects. in 2013. Both satellites acquire spectral data (0.45-2.35 \(\upmu\)m) at a 30 m spatial resolution over six bands, along with one thermal band (10.40-12.50 \(\upmu\)m) at 120 m (L5) and 60 m (L7). L5 and L7 imagery was clipped to the 1.0 km research sites coincident with the MODIS LAI Mc5 and Mc6 grids. LC percentages were calculated via heads-up digitization of the natural color leaf-off high-resolution (0.61 m) USGS orthoimagery using ArcMap. The normalized difference vegetation index (NDVI) was calculated from available L5 or L7 data for the hardwood forest stand type and regressed against the in situ LAI values. If correlations were acceptable (r\({}^{2}\) > 0.30), then LAI would be predicted via the regression model, otherwise the in situ LAI would be used. For loblolly pine, we employed the simple ratio (SR) LAI algorithm [39], with the SR LAI values calibrated to the in situ LAI measurements, then upscaled to the 1.0 km resolution.