## 2 Materials and Methods
### Crop LAI and Above-Ground Biomass Collection from the SMAPVEX16-MB Field Campaign  
In this study, ground measurements of AGB are from the SMAPV Validation Experiment 2016 in the Carman/Elm Creek region of southern Manitoba, Canada (SMAPVEX16-MB). This experiment was conducted to support NASA's SMAP satellite post-launch calibration/validation activities [58]. Figure 2 shows the location of the SMAPVEX16-MB experiment and the distribution of the AGB sampling plots. A total of 50 fields were selected for sampling in this campaign, with each field covering an area of 800 m \(\times\) 800 m.  
Figure 1: A diagram of the data processing flow for mapping crop biomass using Sentinel-2 data and the Boreal Ecosystems Productivity Simulator (BEPS). These 50 fields represent the dominant crops within the study area. According to the AAFC Annual Crop Inventory, soybeans, spring wheat and canola accounted for approximately 70% of crops grown in the study area, with corn, oats, and other field beans accounting for approximately 17% of the study area in 2016. These sites are within a region of approximately 26 km \(\times\) 48 km. Field sampling was conducted on 13 different dates, 13, 15, 18, 20, 27, and 28 June and 5, 6, 11, 12, 17, 20, and 21 July. Each field had 16 sampling locations for soil moisture, although data on crop vegetation were collected from only 6 of these sites (Locations 2, 3, 10, 11, 13 and 14). The objective during SMAPVEX16-MB was to collect crop data approximately once per week during the experiment. Given this goal, each field was sampled 5 times for the purpose of characterizing crop growth. This strategy resulted in 380 data points to be compared with GPP simulated at 20 m resolution from Sentinel-2 data. Figure 2: The geographical location of the SMAPVEX16-MB field campaign and distribution of 50 sampling fields overlaid on the crop type map. The study area is located in southern Manitoba, Canada. (**a**) The location of SMAPVEX16-MB in Canada; (**b**) the distribution of sampling fields; and (**c**) the regular location of 16 sampling sites within each field. During sampling, all above-ground crop biomass was cut at the soil surface, placed in plastic bags to prevent water loss, and immediately transported to a portable field lab for weighing. For crops with wide row spacing (corn and beans), 5 plants were harvested in each of two rows. Biomass (g) per unit area (m\({}^{2}\)) was determined using wet and dry weights and plant density. For narrowly placed crops (canola, oats and wheat), all biomass was collected within a 0.5 x 0.5 m square. After wet weights were determined, plants were transported to a drying room. Here plants were left for approximately one week, until stable dry weights determined that plants had completely dried. The weights of these samples were further calibrated using samples dried by an oven (60 \({}^{\circ}\)C for 48 h). This dataset includes samples for six crop types, i.e., oat, soybean, wheat, corn, canola and black bean. A complete description of biomass collection is detailed at [[https://nsidc.org/data/SV16M_V/versions/1](https://nsidc.org/data/SV16M_V/versions/1)]([https://nsidc.org/data/SV16M_V/versions/1](https://nsidc.org/data/SV16M_V/versions/1)) (accessed on 30 July 2019) and by [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [58]. The water content of plant organs varies with specific crop type and seasons; after the gross biomass is dried, the dry matter can be directly compared to the BEPS simulation of the net carbon assimilation. Along with biomass measurements, LAI was measured with hemispherical digital photos [59]. In this technique, a camera with a fish-eye lens captured photos of the crop canopy with the camera positioned at least 50 cm above or below the canopy. The camera was mounted on a pole if the picture was taken above the canopy. Seven photos were taken along two transects (14 photos in total) at three sampling sites for each of the fields.