Combination of GNSS and InSAR measured at co-located geodetic monitoring sites

Global Navigation Satellite Systems (GNSS) can provide a temporally dense set of geodetic coordinate observations in three dimensions at a limited number of discrete measurement points on the ground. Compared to this, the Interferometric Synthetic Aperture Radar (InSAR) technique gives a spatially dense set of geodetic observations of ground surface movement in the viewing geometry of the satellite platform, but with a temporal sampling limited to the orbital revisit of the satellite. Using both of these methods together can leverage the advantages of each to derive more accurate, validated surface displacement estimates with both high temporal and spatial resolution. In this paper, we discuss the properties of both techniques with a view to combined usage for improving future national datums. We apply differential GNSS processing to data observed at a local geodetic network in the Sydney region as well as time series InSAR analysis of Radarsat-2 data. We compare and validate surface displacements resulting from the two techniques at 21 geodetic monitoring sites equipped with GNSS and radar corner reflectors (CRs). The resulting GNSS/InSAR displacement time series agree at the level of 5 to 10 mm. This case study shows that co-located GNSS/CR sites are well-suited to compare and combine GNSS and InSAR measurements. An investigation of potential multipath effects introduced by the CRs attached directly to GNSS monumentation found that daily site coordinates are affected at a level below 0.1 mm. The GNSS/CR sites may hence serve as a local tie for future incorporation of InSAR into national datums. This will allow frequent updates of national geodetic networks and corresponding datums by using the large-scale and spatially dense information on surface displacements resulting from InSAR analyses

In-depth verification of Sentinel-1 and TerraSAR-X geolocation accuracy using the Australian Corner Reflector Array

This article shows how the array of corner reflectors (CRs) in Queensland, Australia, together with highly accurate geodetic synthetic aperture radar (SAR) techniques—also called imaging geodesy—can be used to measure the absolute and relative geometric fidelity of SAR missions. We describe, in detail, the end-to-end methodology and apply it to TerraSAR-X Stripmap (SM) and ScanSAR (SC) data and to Sentinel-1interferometric wide swath (IW) data. Geometric distortions within images that are caused by commonly used SAR processor approximations are explained, and we show how to correct them during postprocessing. Our results, supported by the analysis of 140 images across the different SAR modes and using the 40 reflectors of the array, confirm our methodology and achieve the limits predicted by theory for both Sentinel-1 and TerraSAR-X. After our corrections, the Sentinel-1 residual errors are 6 cm in range and 26 cm in azimuth, including all error sources. The findings are confirmed by the mutual independent processing carried out at University of Zurich (UZH) and German Aerospace Center (DLR). This represents an improve�ment of the geolocation accuracy by approximately a factor of four in range and a factor of two in azimuth compared with the standard Sentinel-1 products. The TerraSAR-X results are even better. The achieved geolocation accuracy now approaches that of the global navigation satellite system (GNSS)-based survey of the CRs positions, which highlights the potential of the end-to-end SAR methodology for imaging geodesy

(Schw)Ehre, wem (Schw)Ehre gebührt : Festschrift zur Verabschiedung von Prof. Dr.-Ing. Dr. h.c. Bernhard Heck

Die Festschrift zur Verabschiedung von Prof. Bernhard Heck enthält 41 Beiträge aus dem Freundeskreis, der Kollegenschaft sowie von ehemaligen Promovierenden. Der Schwerpunkt der Arbeiten liegt auf den Gebieten der Physikalischen und Satellitengeodäsie sowie der Geodynamik und spiegelt das vielfältige Wirken von Bernhard Heck wider. Abgerundet wird die Schrift durch Beiträge zur Ausbildung am Geodätischen Institut des KIT und zur Stellung der Geodäsie im gesellschaftlichen Kontext

Practical Considerations before Installing Ground-Based Geodetic Infrastructure for Integrated InSAR and cGNSS Monitoring of Vertical Land Motion

Continuously operating Global Navigation Satellite Systems (cGNSS) can be used to convert relative values of vertical land motion (VLM) derived from Interferometric Synthetic Aperture Radar (InSAR) to absolute values in a global or regional reference frame. Artificial trihedral corner reflectors (CRs) provide high-intensity and temporally stable reflections in SAR time series imagery, more so than naturally occurring permanent scatterers. Therefore, it is logical to co-locate CRs with cGNSS as ground-based geodetic infrastructure for the integrated monitoring of VLM. We describe the practical considerations for such co-locations using four case-study examples from Perth, Australia. After basic initial considerations such as land access, sky visibility and security, temporary test deployments of co-located CRs with cGNSS should be analysed together to determine site suitability. Signal to clutter ratios from SAR imagery are used to determine potential sites for placement of the CR. A significant concern is whether the co-location of a deliberately designed reflecting object generates unwanted multipath (reflected signals) in the cGNSS data. To mitigate against this, we located CRs >30 m from the cGNSS with no inter-visibility. Daily RMS values of the zero-difference ionosphere-free carrier-phase residuals, and ellipsoidal heights from static precise point positioning GNSS processing at each co-located site were then used to ascertain that the CR did not generate unwanted cGNSS multipath. These steps form a set of recommendations for the installation of such geodetic ground-infrastructure, which may be of use to others wishing to establish integrated InSAR-cGNSS monitoring of VLM elsewhere

Status of the Global Observing System for Climate

Status of the Global Observing System for Climat