## 2 Study Area and Data
### Phenological In-Situ Data  
Phenological data from 2019 to 2021 of three major crops (winter wheat, sugar beet and corn) were obtained from Germany's national meteorological service (DWD; in Ger  
Figure 1: Overview of the study area spanning across three federal states in Germany. White stars indicate DWD phenological stations, and pink plus signs represent the phenological field sites used in this study. The black grid lines show the Sentinel-2 Analysis Ready Data (S2-ARD) acquisitions used in this study, with the background representing the number of observations in 2019 (as shown in the colour bar). Circles illustrate examples of the sampling design of agricultural field samples of three crops (winter wheat, corn, sugar beet) within a 5 km radius around three randomly selected DWD phenological stations for three years (2019, 2020, 2021). man: Deutscher Wetterdienst), which operates a phenological observation network across Germany with hundreds of stations, as shown in (Figure 1) [10]. Volunteer observers report 160 phenological phases of wild and cultivated plants immediately or annually, which are directly related to the main growth stages according to the Biologische Bundesanstalt, Bundessortenamt and CHemical Industry (BBCH) system [45]. Each crop was observed in a different number of stations, depending on the abundance and agrometeorological relevance of the respective crop type. And each phase of observation associated with a certain DWD station was considered representative of the crops that fall within a maximum radius of 5 km of its location, as shown in Figure 1). It should be noted that the distribution of phenological stations is uneven, both across regions with varying environmental conditions and within regions with similar crop suitability. Moreover, the number and placement of observations fluctuate from year to year due to crop rotation practices [46]. DWD records from two years (2019-2020) were used to parameterize the phenological estimation, while the records for the year 2021 were used for the validation issue. Furthermore, we used additional in-situ BBCH information (2018-2022), with one portion collected from the \"PatchCrop\" experimental site managed by the Leibniz Centre for Agricultural Landscape Research [47] and another portion obtained through the PIAF database of the Plant Protection services of the German federal states where PIAF stands for the planning, information and evaluation system for trials in agriculture, viticulture, horticulture and agricultural research. PIAF is supervised by the Institute for Strategies and Technology Assessment at JKI. These data will be used to further investigate the accuracy of phenological estimates, as they provide field-based information on the timing of all phases of BBCH estimations for several crops. Restricted by the availability of data, we utilise these data that are exclusively accessible for this study within the federal LS and BB states. Table 1 lists all the phenological phases that were taken into consideration for the three main crops examined in this study based on DWD and BBCH, as well as a polar graph illustrating the distribution of each phase for each crop in our study areas from 2019 to 2021 as well as the number of in-situ observations.