*2.2. Remote Sensing Time Series*

Sentinel-2 products with Level-2A bottom of atmosphere (BOA) reflectance data were downloaded from the Copernicus Open Access Hub [36]. The proposed RTSR method is applicable to the complete set of spectral bands, but only five bands have been selected here in order not to overload the section on results and the figures. The spectral bands B2, B3, B4, and B8 were selected based on their superior spatial resolution (10 m). These bands only cover the visible to near infrared part of the electromagnetic spectrum. They were therefore complemented with spectral band B12, to also cover the short-wave infrared. The proposed method can apply to other data sources, if a vegetation index can be calculated and the assumption that relatively high vegetation index values can be considered as trustworthy

holds. In practice, this will be for most optical remote-sensing imagery with a red and near infrared band. Here, the NDVI was calculated using the red (B4) and near infrared (B8) bands:

$$\text{NDVI} = \frac{\text{B8} - \text{B4}}{\text{B4} + \text{B8}} \tag{1}$$

The ground sampling distance (GSD) of the bands in the visual and near infrared is 10 m, whereas the GSD of band B12 in the short wave infrared is 20 m. All selected bands were resampled to 10 m based on the nearest neighbor to obtain a regular gridded data cube. In addition to the spectral bands, Sentinel-2 products are delivered with a scene classification (SCL) band, which is an output of the Sen2Cor atmospheric correction processor [37]. It distinguishes 11 classes including information on clouds and cloud shadows. The products downloaded covered all acquisitions from beginning of December 2018 to the end of January 2020 with a cloud cover of less than 70%. A subset of eight acquisitions for one of the test sites in France under various atmospheric conditions is shown in Figure 2.

**Figure 2.** True color images (bands B4, B3, B2) for a subset of the time series acquired with Sentinel-2 under various atmospheric conditions (selected acquisition dates: 23 May 2019, 7 June 2019, 12 June 2019, 7 July 2019, 17 July 2019, 6 August 2019, 16 August 2019, 21 August 2019). The red square area corresponds to an agriculture field near Montpellier, France (43◦39 53.64N, 3◦54 47.88E).
