Abstract
The introduction of high-resolution Sentinels combined with the use of high-quality digital agricultural parcel registration systems is driving the move towards at-parcel agricultural monitoring. The European Union’s Common Agricultural Policy (CAP) has introduced the concept of CAP monitoring to help simplify the management and control of farmers’ parcel declarations for area support measures. This study proposes a proof of concept of this monitoring approach introducing and applying the concept of ‘markers’. Using Sentinel-1- and -2-derived (S1 and S2) markers, we evaluate parcels declared as grassland in the Gelderse Vallei in the Netherlands covering more than 15,000 parcels. The satellite markers—respectively based on crop-type deep learning classification using S1 backscattering and coherence data and on detecting bare soil with S2 during the growing season—aim to identify grassland-declared parcels for which (1) the marker suggests another crop type or (2) which appear to have been ploughed during the year. Subsequently, a field-survey was carried out in October 2017 to target the parcels identified and to build a relevant ground-truth sample of the area. For the latter purpose, we used a high-definition camera mounted on the roof of a car to continuously sample geo-tagged digital imagery, as well as an app-based approach to identify the targeted fields. Depending on which satellite-based marker or combination of markers is used, the number of parcels identified ranged from 2.57% (marked by both the S1 and S2 markers) to 17.12% of the total of 11,773 parcels declared as grassland. After confirming with the ground-truth, parcels flagged by the combined S1 and S2 marker were robustly detected as non-grassland parcels (F-score = 0.9). In addition, the study demonstrated that street-level imagery collection could improve collection efficiency by a factor seven compared to field visits (1411 parcels/day vs. 217 parcels/day) while keeping an overall accuracy of about 90% compared to the ground-truth. This proposed way of collecting in situ data is suitable for the training and validating of high resolution remote sensing approaches for agricultural monitoring. Timely country-wide wall-to-wall parcel-level monitoring and targeted in-season parcel surveying will increase the efficiency and effectiveness of monitoring and implementing agricultural policies.
Highlights
Grasslands are an intrinsic part of European agriculture, and essential for global bio-geochemical cycling, biodiversity and climate change mitigation, providing a range of economic and environmental services [1]
In the remainder of this Introduction we will summarize the importance of grasslands, discuss the state-of-the art of high-resolution remote sensing, with respect to the Copernicus Sentinels and grasslands, the availability of open-access parcel-level crop type declarations in the European Union (EU), highlight the continued need for in situ data and field observations and discuss recent opportunities provided by street-level imagery
In this example, ploughing can be observed during the second half of March on the RGB composite (Figure 6), which corresponds exactly to the Bare Soil Index (BSI) time series (Figure 5). In this example, half of the parcel was observed to be bare on 14 March, and the remaining part was bare on 24 March
Summary
Grasslands are an intrinsic part of European agriculture, and essential for global bio-geochemical cycling, biodiversity and climate change mitigation (e.g., soil carbon stocks), providing a range of economic (e.g., feed) and environmental services [1]. Following the 2013 reform of the European Union’s (EU) Common Agricultural Policy (CAP) to make the direct payment system more environmentally friendly with the so-called ‘greening’ rules, farmers can receive direct payments for maintaining permanent grasslands. New opportunities for grassland monitoring are provided by the EU Copernicus program and the observations by the Sentinel-1 and -2 satellites. The combination of the Sentinels’ observations, which are freely accessible, and the increasingly accessible crop-type data at the parcel level enable new possibilities for EU crop monitoring. In the remainder of this Introduction we will summarize the importance of grasslands, discuss the state-of-the art of high-resolution remote sensing, with respect to the Copernicus Sentinels and grasslands, the availability of open-access parcel-level crop type declarations in the EU, highlight the continued need for in situ data and field observations and discuss recent opportunities provided by street-level imagery
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