## 3 Results
### Assessment of Time-Series SAR Data for Seeding and Harvest Date Mapping  
To illustrate the change due to field operations, colour images were generated and shown in Figure 8 for the period at the beginning of the season in May (May 6 and 18, May 18 and 30) and at the end of the growing season in late September to early October (September 15 and 27, and September 27 and October 9). The images to the left-hand side are made of two InSAR coherence images as the red and green channel, and a blank image (no variance) as the blue channel. The images to the right-hand side are made of the three VH backscattering coefficient as red, green and blue channel. From the images on the left, a field with red color is most likely representing no change during the first pair of SAR acquisition period (hence high coherence) and a change during the second pair of SAR acquisition period (low coherence), whereas green colour likely means that change happened during the first period but no change in the second period. Yellow colour means that coherence is consistently strong and that no structural change happened during both periods. Progression of seeding and harvest in a region can thus be visually evaluated this way through sequential color composition of InSAR coherence images. Images composited with the VH (Figure 8b,d) do not show contrast colour for the changes, but they do highlight the difference between agricultural fields and forests, particularly for the spring image in which crop fields are shown with dark tone, reflecting low biomass or low surface roughness conditions of crop fields in contrast to forests.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Correct** & \(\pm\)**1 Cycle** & **Fail** & **Total** & **\%Correct** \\ \hline Seeding & 57 & 4 & 6 & 67 & 85 \\ Harvest & 43 & 25 & 9 & 77 & 56 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results for seeding and harvest detection.  
Figure 8: Mapping of change through InSAR coherence at the start May 6–May 18–May 30 (**a,b**) and end lower, September 15, September 27, and October 9 (**c,d**) of the season. Maps to the left are generated using two consecutive InSAR coherence images and one blank image as RGB channels (**a,c**), and maps to the right are made using the three VH backscattering intensity images sequentially as RGB channels (**b,d**).  
To further demonstrate the capability of time-series InSAR coherence and VH backscattering coefficient for identification of crop seeding and harvest dates, the aforementioned algorithm was applied to the SAR data to map crop seeding date at the pixel level. First, crop pixels were identified using a simple threshold approach, i.e., average VH in April \(<-25\) dB and average VH on July 29 and August 10 \(>-21\) dB. This step can effectively exclude the forest (higher VH in April) and water (lower VH in mid-season) pixels in subsequent analysis. Residual speckle noise has caused certain degree of false identification shown as crop pixels on non-agricultural lands. The mapping results are shown in Figure 9 covering five periods for both seeding (Figure 8a,b) and harvest (Figure 8c,d) dates, determined by SAR acquisition dates. The proportion of pixels being identified as seeded or harvested during each time period is also given in Figure 9.  
In the study area, crops were seeded mostly in May to early June, with only about 10% of the fields seeded later than June 11. For harvest event, about 16% happened during the period from August 10 to 22, mostly wheat and some other summer cereal crops. For harvest, about 30.2% of the fields were harvest between the two satellite acquisitions from August 22 to September 15. Due to heavy rain at the time of the satellite overpass on September 3, the SAR image was contaminated and hence not used in the analysis. Another 30% of harvest happened between September 27 and October 9, and the rest of the 13% were harvest after October 9.