Arnold, D.

Jäggi, A.

Kobel, C.

English

Bern Open Repository and Information System (BORIS)

source: https://doi.org/10.48350/180386 | downloaded: 15.5.2023C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 1Astronomical InstituteUniversity of BernSidlerstrasse 5CH-3012 BernImpact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingC.Kobel, D.Arnold, A.JäggiC.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 2Introduction• Jason-3– Altimetry satellite• Altitude: 1331 km• Inclination: 66°• Period: 112 minutes• CNES, NASA’s JPL and GSFC provide orbit solutions• Perform POD using Bernese GNSS Software• Pre-Launch PCV is available• PCV map to be computed using residual stacking• Jason-3 operates in different attitude modes– Fixed-yaw– Yaw-steering• Attitude mode changes if 𝛽 = ± 15° (Yaw-steering to Fixed-yaw and vice versa• Yaw-flip takes place if 𝛽 = 0°https://eoportal.org/web/eoportal/satellite-missions/j/jason-3 (image credit: CNES)C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 3PCV map determinationMake use of GPS measurements and POD results to estimate the PCV mapUsing the Bernese GNSS Software this is done using a residual stacking approach.For the different attitude modes separate PCV maps are derivedTwo different orbit parametrizations were usedo Reduced-dynamic (RD): 3 constant accelerations per arc (one per spatial component) + 240 piecewise constant empirical accelerations per arc (every 6 minutes in Radial, Along- and Cross-track direction) constrained to 5 𝑛𝑚/𝑠2o Dynamic (NG): 160 piecewise constant empirical accelerations per arc (every 6 minutes in Along- and Cross-track direction) constrained to 0.5 𝑛𝑚/𝑠2 + one scaling parameter for radiation pressure per arcThis results in 8 different PCV maps.(Yaw-Steering+fixed-Yaw)*(forwards+backwards)*(2*orbit parametrization)  = 8C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 4Coverage of GPS measurements in antenna frameDepending on the attitude mode there is an incomplete coverage in the antenna frame.This is mainly visible when comparing forward and backward orientation. This results from the differences in the acquisition or loss of the signal at the beginning or end of a pass of a GPS satellite.The reason for this is the 15° tilted GPS antenna of Jason-3. Two S/N thresholds : one value (Sa) for acquisition and another value (Sb) for loss, and Sa>Sb. In the satellite reference frame, the acquisitions are in a visibility cone smaller than the losses. Additionally, some added delays in the acquisition, as the receiver needs a certain time to lock correctly, eliminate the 0.5 phase ambiguity, etc...(Flavien Mercier, personal communication)C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 5Jason-3 attitude modesView in nadir-directionTimeC.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 6Different PCV mapsAttitude modeParametrizationYaw-steering forward (YSF) Fixed-yaw forward (FYF) Fixed-yaw backward (FYB) Yaw-steering backward (YSB)Reduced-dynamic:No explicit non-gravitationalforce modelling,240 piecewise constantempirical accelerations per arc, 3 contant accelerationsper arcDynamic:Non-gravitational forcemodelling, 160 piecewiseconstant empiricalaccelerations per arc, 1 scaling parameter forradiation pressure per arcC.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 7PCV maps comparisonsThe PCV maps are compared with relation to the map resulting from the yaw-steering forward attitude mode.Parametrization1: Reduced-dynamicParametrization2: DynamicPronounceddifferences are visible when comparing YSF to YSB.The resulting PCV maps of the dynamicPOD do not show such large variations. The comparison YSF to FYF shows the mostsignificant pattern.C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 8PCV offset removalIt is possible to remove phase center offsets (PCO) from the PCV maps using least squares adjustement.𝜙′ 𝛼, 𝑧 = − sin 𝛼 ∗ sin 𝑧 ∗ 𝐸 − cos 𝛼 ∗ sin 𝑧 ∗ 𝑁 − cos 𝑧 ∗ 𝑈Where 𝜙′(𝛼, 𝑧) is the PCV map, 𝛼 and 𝑧 are azimuth and zenith angle respectively, 𝐸,𝑁 and 𝑈 are the components of theoffset vector.To account for the different, incomplete coverages of the antenna for different attitude modes, an elevation cut-off of 30 degrees was used for the removal of possible induced offsets.The offsets which are determined for all the PCV maps result to:(E/N/U)[mm] Yaw-steering forward Fixed-yaw forward Fixed-Yaw backward Yaw-sterring backwardParametrization 1Reduced-dynamic-0.042 ± 0.0106.684 ± 0.0094.324 ± 0.0020.680 ± 0.010 2.964 ± 0.0092.903 ± 0.0021.913 ± 0.0100.613 ± 0.0104.068 ± 0.0022.722 ± 0.011-3.571 ± 0.010 3.298 ± 0.002Parametrization 2Dynamic-2.403 ± 0.008-7.229 ± 0.0070.487 ± 0.002-0.772 ± 0.009 4.004 ± 0.0083.245 ± 0.002-2.203 ± 0.007 -3.970 ± 0.006-0.937 ± 0.0013.550 ± 0.008-8.971 ± 0.0080.065 ± 0.002C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 9PCV offset removalThe PCV maps are compared to the map resulting from the yaw-steering forward attitude mode. Before the comparisontakes place, possible offsets were removed, as described on the previous slide.Parametrization1: Reduced-dynamicParametrization2: DynamicIt is visible, thatthe PCO removalleads todifferences in thePCV maps of verylow amplitude.This result isvisible in all thePCV mapcomparisonswhen a PCO isremoved before.The inference of this result is that apart from different induced offsets, the phase center variation pattern for all theestimated maps is very similar. C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 10Orbit comparisons of different attitude modesMean ± STD [mm]RD YSF -5.8 ± 6.9RD FYF 0.2 ± 6.8RD FYB -12.9 ± 7.3RD YSB -7.9 ± 5.8NG YSF -0.5 ± 4.2NG FYF -0.3 ± 4.2NG FYB -0.1 ± 4.3NG YSB -0.9 ± 4.1Systematic differences are visible in the orbit comparisons. For (RD) YSF, FYB and YSB an offset to the JPL solution in radial direction is present. It is evident that the NG solutions have a better agreement with the JPL solutions than the RD solutions.C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 11Orbit comparisons of different attitude modesIt is visible, that NG YSF and NG FYB show a higher agreement to the JPL solution than the others. Additionally, theconsistency of the offsets to the JPL solutions for the RD and the NG solutions is evident. The standard deviations for the RD solutions is larger than for the NG solutions for all the attitude modes.Mean ± STD [mm]RD YSF 6.3 ± 10.5RD FYF -12.2 ± 10.0RD FYB 10.6 ± 10.8RD YSB -10.1 ± 7.7NG YSF 4.2 ± 5.6NG FYF -13.3 ± 5.5NG FYB 2.4 ± 5.6NG YSB -10.9 ± 5.2C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 12Orbit comparisons of different attitude modesVisible are the systematic differences in the orbit comparison in the Cross-track direction. The NG YSF solution shows thebest agreement to the JPL solution. The use of non-gravitational force modelling (NG solutions) leads to smaller meanvalues in the orbit comparisons. The systematics for the different attitude modes is similar for the two parametrizations (RD and NG). Mean ± STD [mm]RD YSF 15.6 ± 7.2RD FYF 9.4 ± 6.0RD FYB -14.0 ± 6.0RD YSB -11.0 ± 7.3NG YSF 2.0 ± 5.8NG FYF 8.1 ± 5.4NG FYB -9.5 ± 5.2NG YSB -4.1 ± 6.6C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 13Orbit quality of different attitude modesA POD is performed where the Pre-Launch PCV is used for all the attitude modes. This solution is also compared to an external solution (CNES). This serves the investigation whether the systematics in orbit differences from the previousslides is only visible when individual PCV maps are used for the POD. Additionally, this serves as a reference for thecomparisons, since the comparison is to another solution than on the previous slides. It is evident that, depending on the betaangle (which reflects thedifferent attitude modesaccording to slide 2), systematics are presentin the orbit comparisons. Therefore, one canconclude, that makinguse of individual maps forthe POD for different attitude modes is not the(main) reason for thesystematic orbitdifferences.C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 14Orbit quality of different attitude modesSLR validation of the reduced-dynamic solutions based on individual PCV maps for the different attitude modes.The SLR validation showsdifferent mean values for theattitude modes. (RD)FYF has the smallest meanvalue. (RD)YSB is the best solutionaccording the the standarddeviation.One can see that the variationof the quality of the solutionsfor the different attitude modesis significant.C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 15Orbit quality of different attitude modesSLR validation of the dynamic solutions based on individual PCV maps for the different attitude modes.A notable results of the SLR validation of the NG solutions isthat the mean values for YSF and FYF are similar, as well asthe ones for YSB and FYB. Therefore, a systematicdifference between forward and backward orientation of thesatellite is visible.  Whencomparing the individual standard deviations of theattitude modes of the NG solutions to the results for theRD case (previous slide), it isevident that the NG solutionsare of better quality.C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 16Orbit quality of different attitude modesThe solution where the same PCV was used for the POD for all the attitude modes is SLR validated. The PCV computation is based on data from all the attitude modes from the year 2019. The mean values are more similarthan the ones for RD and NG on theprevious slides. Important is, thatno systematics is present in thecomparison of the different orientations or attitude modes. The solutions for the YSB show thesmallest mean value and standarddeviation.Comparing to the results from theprevious slides, one can conclude, that, in terms of the SLR validation, making use of an individual PCV mapfor every attitude mode does improvethe orbit quality for of the attitudemodes, namely YSF (smallermean),FYF (smaller mean and STD)  and YSB (smaller mean and STD).C.Kobel: Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modelingEGU, 27.April. 2021Slide 17Summary and Conclusion➢ Different PCV maps result when data from different attitude modes are used, whereas a common pattern can berecognized in all the PCV maps. A PCO removal from the different PCV maps shows that the real physical PCV inducedby the satellite environment can be captured well using the residual stacking approch. However, the PCV maps areaffected by different induced PCOs, which leads to sytematic differences. ➢ Orbit differences to an external solution show that the systematics between the PCVs are also visible on orbit level, resulting in different mean offsets for the different spatial components and attitude modes.➢ These orbit differences show that using non-gravitational force modelling leads to more consistency with regard to theexternal solution. This may be due to the reason that the external solution is also based on dynamic orbit modelingapproaches.➢ An SLR validation allows to conclude that the dynamical parametrization leads to orbit solution of superior quality. This coincides with the results of better orbit agreement to external reference solutions and less variety in the PCV maps.➢ The result indicates that it is of importance to take into account the different attitude modes for the PCV mapcomputation. 

Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modeling

https://boris.unibe.ch/180386/1/Presentation_EGU21_Jason3_PCV.pdf

Impact of different attitude modes on Jason-3 precise orbit determination and antenna phase center modeling

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