The Netherlands has been actively managing its groundwater table for centuries, and much of the Dutch agricultural sector is based in drained peatlands called polders. The polders are separated into parcels which are rectangular plots surrounded by drainage ditches. It has been observed that groundwater levels are the most significant driver of soil surface height variation in the region . It has been hypothesized that groundwater management regimes in these regions are causing them to irreversibly subside at a rate which is faster than sea level rise [2, 3].
Direct observation of surface motion of this region has so far not been possible with distributed scatterer (DS) InSAR due to high levels of noise in these grass-covered fields and rapid deformation between consecutive SAR acquisitions . These rapid shifts can frequently result in phase unwrapping errors when typical DS processing techniques are used. Additionally, relating the observed InSAR time series with respect to an absolute reference frame has not been possible due to the decoupling of point scatterer (PS) and DS processing techniques, and the lack of a well-defined reference benchmark. To understand the scope of the effects of subsidence in these regions, and subsequently act on it, scientists and policymakers need to know the subsidence rates in absolute terms, so that they may be compared to other locations, or other hazards such as sea level rise.
We adopt a novel multilooking strategy which uses parcels as the basic unit of measure for a DS InSAR monitoring system. This is a natural choice, as the land cover and water table are almost always consistent over a given parcel. Our approach has several advantages over traditional multilooking strategies, as it simultaneously groups pixels together which are physically acted upon by the same mechanism, while also providing a many-fold increase in the effective number of looks. This significantly reduces measurement noise and ensures that
all the pixels being multilooked are tied to the same ergodic process, which a typical boxcar filter will not do, even when coupled with a statistical homogeneity test.
These multilooked phases can now be treated as virtual point scatterers; they are assigned a location corresponding to the centroid of the parcel in question, and imported into the Delft Persistent Scatterer Interferometry (DePSI) system for time-series analysis as 2nd order points . This allows us to take advantage of the robust point scatterers (PS) in the image to form a 1st order network of points for atmospheric phase screen (APS) removal, trend removal and variance component estimation. This mixed system allows for the simultaneous monitoring of both agricultural zones and the built environment.
Via the connection to the 1st order network, we are able to make an arc connection to the Integrated Geodetic Reference Station (IGRS)  in the region. These stations are comprised of a corner reflector, a GPS receiver and other geodetic instrumentation which will allow us to make a direct connection from the observed parcel movement to an absolute geodetic reference frame.
In our contribution we will present the first results of parcel-multilooked DS estimation performed within this mixed scatterer framework of the region surrounding Zegveld, The Netherlands based on Sentinel-1 data. Following the parameter estimation in DePSI, we select an IGRS in the region of interest as the InSAR reference point, and transform the relative displacement time series into an absolute frame using the co-located GPS measurements.
 S. van Asselen, G. Erkens, and F. de Graaf, “Monitoring shallow subsidence in cultivated peatlands,” Proceedings of the International Association of Hydrological Sciences, vol. 382, pp. 189–194, 2020.
 G. Erkens, M. J. van der Meulen, and H. Middelkoop, “Double trouble: subsidence and co2 respiration due to 1,000 years of dutch coastal peatlands cultivation,” Hydrogeology Journal, vol. 24, no. 3, pp. 551–568, 2016.
 T. Hoogland, J. van den Akker, and D. Brus, “Modeling the subsidence of peat soils in the dutch coastal area,” Geoderma, vol. 171-172, pp. 92 – 97, 2012. Entering the Digital Era: Special Issue of Pedometrics 2009, Beijing.
 Y. Morishita and R. F. Hanssen, “Deformation parameter estimation in low coherence areas using a multisatellite insar approach,” IEEE Transactions on Geoscience and Remote Sensing, vol. 53, no. 8, pp. 4275–4283, 2015.
 F. van Leijen, Persistent Scatterer Interferometry based on geodetic estimation theory. PhD thesis, TU Delft, 2014.
 R. F. Hanssen, “A radar retroreflector device and a method of preparing a radar retroreflector device", U.S. Patent No. 2018236215, 2018.