# Relating Sentinel-1 Interferometric Coherence to Moving Events on Grasslands
## 1 Introduction
In [17], the Radarsat-2 C-band HH/VV (horizontal transmit, horizontal receive/vertical transmit, vertical receive) intensity ratio was shown to be related to the ploughing of winter wheat, but management practices like grazing, moving, and mixed management on grasslands could not be discriminated. [PERSON], [PERSON], and [PERSON] [18] analysed the relationship of COSMO-SkyMed X-band, ENVISAT ASAR, and ALOS PALSAR backscatter values to the Normalized Differential Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), and soil moisture index (MI) values without ground truth measurements, and concluded that at paddock scale, X-band HH backscatter could be useful for the detection of grazing or mowing activities on pastures during peak season on non-rainy dates. Mowing events on grasslands were specifically studied using PolSAR by [PERSON] et al. in 2013 [19] and 2016 [20], demonstrating that several C-band and X-band polarimetric parameters are sensitive to mowing events in cases where the grass was left on the ground after the event. However, the combination of VV and VH (vertical transmit, horizontal receive) polarized channels offered by the Sentinel-1 means that the PolSAR approach is problematic, as most of the PolSAR methods require fully polarimetric or dual polarimetric co-pol data. Additionally, use of backscatter from one channel (e.g., VV) is problematic, due to variations caused by changing meteorological conditions and vegetation orientation effects [21]. On the other hand, InSAR-based approaches have shown potential for change detection in vegetation, and the regularity of Sentinel-1 data is well-suited for InSAR applications. Early advances in the detection of abrupt changes in vegetation with InSAR were made in the forest domain. In [22], it was shown that clear-cuts have higher interferometric coherence values than forests, in line with observations comparing forested and bare areas in [23]. The approach has been shown to apply for agricultural monitoring as well. High coherence values due to backscattering from the ground were linked to ploughed bare fields and low vegetation height in [24; 25]. A similar approach, but for the detection of moving events on grasslands, has been studied by [PERSON] et al. [26; 27], where it was demonstrated how 1-day X-band interferometric coherence is much higher for moved grasslands when compared to grasslands covered by vegetation. However, meteorological effects play an important role in the interpretation of interferometric coherence [28; 29; 30], including over bare ground [31]. As one of the sources of change, precipitation may cause temporal decorrelation, complicating interpretation. The aim of this paper is to describe the relationship between the C-band SAR 12-day repeat pass temporal interferometric coherence and moving events of grasslands. The study was performed in Central Estonia. We mainly focus on the impact that temporal separation between a moving event and interferometric acquisitions has on the coherence values. Additionally, we analyse the effect of precipitation on the coherence, as the importance of accounting for meteorological effects in the correct interpretation of this parameter has been previously demonstrated. A more comprehensive understanding of the relationship between coherence and moving events would allow for the evaluation of the feasibility of using this parameter for future moving detection applications. The paper is organised as follows. In Section 2, we present the data used in the study that includes SAR acquisitions, field survey information, and the description of the data processing chain. Section 3 is devoted to presenting the results and discussion about the relationship between the interferometric coherence and moving events. Additionally, the influence of precipitation on the relationship is analysed. Finally, conclusions are listed in Section 4.