*4.2. Qualitative Relationship between High Wind Speed and Lodged Fields*

To qualitatively check if there is a relationship between high wind speed and lodged fields, we overlaid Figures 5b and 7b with the wind speed map (Figure 2). These overlay is shown in Figure 9a,b respectively. The result showed that our estimated lodged fields followed areas with increased wind speed (Figure 9a,b). In particular, areas with wind speed of 80+ mph captured most of our estimated severely and moderately lodged fields while areas with wind speed of 60+ mph captured few lodged fields.

**Figure 9.** Example of (**a**) ratio map (Figure 5b) and (**b**) severity map (Figure 7b) overlaid with wind speed map in Figure 2.

#### *4.3. Reliability of the Approach Employed in Mapping Lodging*

To qualitatively access the performance of the Derecho lodged area mapped, we acquired eight ground truth data from field observation along the interstate I-80W. Due to limited amount of ground truth data collected, we were unable to perform extensive quantitative analysis of our method. While overlaying the eight ground truth points acquired with our lodged map, we observed that each point overlaid perfectly on an area that was lodged (Figure 10).

Furthermore, we compared an example of the lodged change detection map generated from Sentinel-1A ratio image and optical Landsat-8 ratio image by using our classification approach. The Landsat-8 ratio image was generated from the green band of pre-lodging event image acquired on 10 July 2020, and the post-lodging event image acquired on 11 August 2020 (Figure 11).

We chose the green band over every other band of Landsat-8 because the green band has a larger dynamic range which allowed for better separation of lodged and un-lodged areas. As can be seen from Figure 12, the lodging map generated from Landsat-8 ratio image and the Sentinel-1A ratio image were able to clearly detect lodging. While our approach was able to classify the Sentinel-1A ratio image into severely lodged and moderately lodged fields, we were unable to do so in the Landsat-8 ratio image. This observation showed that Sentinel-1A radar sensor has the advantage in reflecting the structural changes of lodging fields, while the Landsat-8 optical sensor only has the advantage in detecting the biochemical changes of lodging fields. All in all, for this study, we believe that the obvious feature for lodging is the structural change and the distribution pattern of lodged fields (severe and moderate) from Sentinel-1A image were similar to the distribution pattern of the lodged fields in the Landsat-8 image.

**Figure 10.** Location of field observations for (**a**) all the eight points and (**b**) a zoomed location for three points. (**c**) Photo for one of the field observations in "b".

**Figure 11.** (**a**) Landsat-8 pre-lodging event image acquired on 10 July 2020. (**b**)Landsat-8 post-lodging event image acquired on 11 August 2020. (**c**) Ratio image generated between 10 July 2020 and 11 August 2020.

**Figure 12.** Severity map generated from (**a**) Sentinel-1A and (**b**) Landsat-8.
