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  • 1
    Publication Date: 2023-06-21
    Description: The GPS satellite transmitter antenna phase center offsets (PCOs) can be estimated in a global adjustment by constraining the ground station coordinates to the current International Terrestrial Reference Frame (ITRF). Therefore, the derived PCO values rest on the terrestrial scale parameter of the frame. Consequently, the PCO values transfer this scale to any subsequent GNSS solution. A method to derive scale-independent PCOs without introducing the terrestrial scale of the frame is the prerequisite to derive an independent GNSS scale factor that can contribute to the datum definition of the next ITRF realization. By fixing the Galileo satellite transmitter antenna PCOs to the ground calibrated values from the released metadata, the GPS satellite PCOs in the z-direction (z-PCO) and a GNSS-based terrestrial scale parameter can be determined in GPS + Galileo processing. An alternative method is based on the gravitational constraint on low earth orbiters (LEOs) in the integrated processing of GPS and LEOs. We determine the GPS z-PCO and the GNSS-based scale using both methods by including the current constellation of Galileo and the three LEOs of the Swarm mission. For the first time, direct comparison and crosscheck of the two methods are performed. They provide mean GPS z-PCO corrections of −186 ± 25 mm and −221 ± 37 mm with respect to the IGS values and +1.55 ± 0.22 ppb (parts per billion) and +1.72 ± 0.31 in the terrestrial scale with respect to the IGS14 reference frame. The results of both methods agree with each other with only small differences. Due to the larger number of Galileo observations, the Galileo-PCO-fixed method leads to more precise and stable results. In the joint processing of GPS + Galileo + Swarm in which both methods are applied, the constraint on Galileo dominates the results. We discuss and analyze how fixing either the Galileo transmitter antenna z-PCO or the Swarm receiver antenna z-PCO in the combined GPS + Galileo + Swarm processing propagates to the respective freely estimated z-PCO of Swarm and Galileo.
    Description: Chinese Government Scholarship http://dx.doi.org/10.13039/501100010890
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:526 ; GNSS ; PCO ; Galileo ; Terrestrial scale ; LEOs
    Language: English
    Type: doc-type:article
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  • 2
    Publication Date: 2021-08-18
    Description: Abstract
    Description: The differences of atmospheric delays (Atmospheric ties) are theoretically affected by the height differences between antennas at the same site and the meteorological conditions. However, there is often a discrepancy between the expected zenith delay differences and those estimated from geodetic analysis. The purpose of this experiment is to investigate the possibility effects that could caused biases on GNSS atmospheric delays at co-location site.
    Description: Methods
    Description: We set up the experiment on the rooftop of the A20 building at Telegrafenberg, the campus of GFZ, Potsdam, Germany. This experiment used four Septentrio choke-ring antennas (SEPCHOKE B3E6) and Septentrio PolaRx5 receivers. We installed the antenna A201 at the highest place. A202 and A203 were placed lower than A201 with two meters and four meters height differences, respectively. Antenna A204 was installed on the same level as A203 but installed with radome (SPKE). Moreover, the meteorological sensor (Vaisala WXT530) was installed to record air pressure, temperature, and relative humidity. The GNSS data were processed by using EPOS.P8 software with Precise Point Positioning (PPP) approach. The GFZ Final orbits and clock products were used in the processing. The zenith total delays and total gradients were hourly estimated. The station coordinates were estimated daily. Results of an experiment are reported in Kitpracha et al. (2021).
    Keywords: Atmospheric ties ; GNSS co-location experiment ; Atmospheric delays ; Earth Remote Sensing Instruments 〉 Passive Remote Sensing 〉 Positioning/Navigation 〉 GNSS
    Type: Dataset , Dataset
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  • 3
    Publication Date: 2022-04-25
    Description: Abstract
    Description: Long-term tide gauge records provide valuable insights to sea level variations, but interpretation requires an accurate determination of the associated vertical land motion. Within the Tide Gauge Benchmark Monitoring Working Group of the International GNSS Service, we performed a dedicated reprocessing (1994-2020) for GNSS stations co-located with tide gauges. Based on 341 stations the GFZ contribution to the third TIGA reprocessing provides vertical land motion rates for 230 stations at or close to recently active tide gauges. We limited the processing to GPS observations.
    Description: Methods
    Description: To ensure the highest accuracy, we used the classical network approach with ambiguity fixing according to Ge et al. (2005) but without orbit determination. Therefore, we introduced the orbit and clock products provided in the GFZ repro3 solution (Männel et al., 2020, 2021). The processing strategy follows the current geodetic IERS conventions (https://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn36.htm) and the IGS repro3 settings (http://acc.igs.org/repro3/repro3.html). The processing is described in detail in our dedicated Analysis Center Notes (ftp://isdcftp.gfz-potsdam.de/gnss/products/tiga3/gfz_tiga3.acn). In line with repro3 we applied the antenna correction file igsR3_2077.atx where the GPS transmitter offsets were adjusted to the pre-launch calibrated Galileo PCOs provided by EUSPA. The derived station coordinates are thus given in the consistently derived IGSR3 reference frame whose terrestrial scale differs by around 1.2 ppb from the ITRF2014 scale as described in IGS-mail 8026 (https://lists.igs.org/pipermail/igsmail/2021/008022.html). More details are presented in the associated publication (Männel et al., 2022). Despite daily coordinates, we also estimated hourly zenith total delays and daily gradients to account for tropospheric delays. The results are provided in the following formats: • troposphere delays and gradients (GFZ1R3TFIN_〈YYYY〉〈DDD〉0000_01D_01H_TRO.TRO.gz, data format: tro: https://files.igs.org/pub/data/format/sinex_tro_v2.00.pdf), • station coordinates (GFZ1R3FIN_〈YYYY〉〈DDD〉0000_01D_01D_SOL.SNX.gz,data format: snx: https://www.iers.org/IERS/EN/Organization/AnalysisCoordinator/SinexFormat/sinex.html), The file naming follows the IGS Long Product Filename Convention (http://acc.igs.org/repro3/Long_Product_Filenames_v1.0.pdf). All files are .gz compressed.
    Keywords: GNSS ; tide gauge ; station coordinates ; vertical land motion ; TIGA ; Earth Remote Sensing Instruments 〉 Passive Remote Sensing 〉 Positioning/Navigation 〉 GPS ; EARTH SCIENCE 〉 OCEANS 〉 COASTAL PROCESSES 〉 LOCAL SUBSIDENCE TRENDS ; EARTH SCIENCE 〉 OCEANS 〉 COASTAL PROCESSES 〉 SEA LEVEL RISE ; EARTH SCIENCE 〉 SOLID EARTH 〉 GEOMORPHIC LANDFORMS/PROCESSES 〉 TECTONIC PROCESSES 〉 ISOSTATIC UPLIFT ; In Situ/Laboratory Instruments 〉 Gauges 〉 TIDE GAUGES
    Type: Dataset , Dataset
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