Aragón Ángel, María Ángeles

Hernández Pajares, Manuel

Juan Zornoza, José Miguel

Lee, C.C.

Liou, Y.-A.

Reinisch, B.W.

Sanz Subirana, Jaume

English

UPCommons

Improvement and validation of retrieved FORMOSAT-3/COSMIC electron densities using Jicamarca DPS

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 PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGEA. Aragón-Angel, Y.-A. Liou, C.-C. Lee,M. Hernández-Pajares, J.M. Juan, J. Sanz,B.W. ReinischImprovement and validation of retrieved FORMOSAT-3/COSMIC electron densities using Jicamarca DPS PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE2Outline1. RO: Classical Abel transform applied to L1 phase excess2. Clock calibration3. Improved Abel transform4. Results5. Topside estimation6. Future work7. Conclusions PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGEThe GPS receiver on the LEO observes the change in the delay of the signal path between the GPS  and the LEO satelliteThis change in the delay includes the effect of the atmosphere which delays and bends the signal GPSLEOElectron density from RO dataBending angleBasic observable:• Linear combination of    dual frequencies LI • Bending angle of L1Assumption ofL1&L2 same pathClock calibration PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE4vTαThe basic measurement is the phase path:From it, the excess phase is defined:The change rate of the excess phase, called excess Doppler, is what is going to become our input observable:L= ∫GPSLEOndsΔ L=L−∣r L E O−rGP S∣ΔD=d  ΔLdtThe projection of satellite orbital motion along signal ray-path produces a Doppler shift  at both the transmitter and the receiver. The fundamental observable is the signal Doppler shift, which is different than expected from only velocities due to the satellite and receiver clock drifts and the atmospheric bending of the signal (ionosphere and troposphere).Classical Abel transform applied to L1 excess phase  PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE5vTαThe projection of satellite orbital motion along signal ray-path produces a Doppler shift  at both the transmitter and the receiver. The fundamental observable is the signal Doppler shift, which is different than expected from only velocities due to the satellite and receiver clock drifts and the atmospheric bending of the signal (ionosphere and troposphere).Classical Abel transform applied to L1 excess phase a) In a vacuum b) In the presence of a medium, such as the ionosphere   PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGESingle Difference● LEO clock errors removed ● Use solved-for GPS clocks ● Advantage: Minimizes double difference errorsCalibration of the excess phaseTo compute accurate RO, need to remove the drifts of  GPS transmitter and LEO receiver clocks from the raw phase data.:Classically:With a LEO constellation deployed (FORMOSAT-3/COSMIC), complete double differencing coverage can be  provided avoiding the fiducial site.ΔD=d  ΔLdt PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE7The ionospheric free combination , Lc, has been used to remove the clock drift.Δα i∝Δf i∝d  ΔL i dt−dTdt Δf i∝ddt  ΔLi−T Bending angle: Calibration of excess phase delayAlternative approach for a two-frequency receiver: ddt ΔLC =dTdt0=f 12⋅Δf 1−f 22⋅Δf 2f 12−f 22 =ddt ΔLC−T  PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE8TroposphereBending angle: Calibration of excess phase delayThe ionospheric free combination, Lc, has been used to remove the clock drift. Typical example given below:Alternative approach for a two frequency receiver: Red: computed by double differencing Blue: computed from L1-Lc Height (km)Phase excess (m/s) PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE9Just the given occultation GPS data are processed. Recursive solution starting from the outer ray. i corresponds to the bending angle of the ray with  impact parameter pi. Signal Doppler shiftClassical Abel transform applied to bending anglesThe classical spherical symmetry hypothesis can be expressed as:Unknown to be solved is Ne PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE10Improved Abel transformA more general approximation than the spherical symmetry was assumed introduced by [Hernández-Pajares, Juan, Sanz (2000)] applied to the ionospheric combination LI:VTEC information externally providedShape functionNew unknown instead of NeProblem:  Electron density is equal for points at the same height but a RO footprint ~ 3000kmIGS Global Ionospheric Map (GIM) PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE Analysis of F-3/C derived Ne profiles at the dip equator Jan - Dec 2007 PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGEROJ DPSExperiment @ Jicamarca PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGEROJ DPSExperiment @ Jicamarca PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE Scenario:  - Time span: Jan 2007 until Dec 2007  - Jicamarca DPS location (+/- 3 degrees)Experiment PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE foF2 comparisons Manually calibrated density profiles from  Jicamarca DPS: - Spatial co-location (+/- 3 degrees)  - Time co-location: 15 minutes PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE LT effect on NmF2: Day Improved AbelA clear underestimation of the electron density profiles during daytime (LT) from F3-C data would be derived observing figure corresponding to Ne(F-3/C)-Ne(DPS). Nevertheless, the DPS topside Ne is overestimated   need to revisit the slabthickness in the model used.Ne(F-3/C) – Ne(DPS) PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE LT effect on NmF2: Night Improved AbelEven distribution of the differences btw the electron density profiles derived from F3-C data and Jicamarca DPS measurements during nighttime (LT)Ne(F-3/C) – Ne(DPS) PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGEoverestimationunderestimationImprovedAbelLT effect on NmF2 Comparison of the values of the electron density peaks btw the electron density profiles derived from F3-C data and Jicamarca DPS measurements PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE Some interesting profiles at JicamarcaExample of agreement between all measurements: F-3/C derived profiles (classic + impr.) and Jicamarca DPS data PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE Some interesting profiles at JicamarcaThe DPS does not provide any information regarding the behavior of the density profile below the foF2 peak  PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE Some interesting profiles at JicamarcaThe DPS does not provide any information regarding the secondary peak at F-layer: F3 peak referred in literature PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGEUpper ionospheric estimation PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE23 No upper ionospheric contribution considered √ Climatological model Extrapolation scheme Using the separability nature of the electron densityUpper ionosphere estimationExperiment:  One year data for 2007 of co-located DPS measurements at Jicamarca vs. FORMOSAT-3/COSMIC RO derived profiles of electron density. PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE24 No upper ionospheric contribution considered √ Climatological model Extrapolation scheme Using the separability nature of the electron densityUpper ionosphere estimation: NeQuick √No upper NeNeQuick PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE25Upper ionosphere estimation No upper ionospheric contribution considered √ Climatological model: NeQuick √ Extrapolation scheme Using the separability nature of the electron density: Exponential decay √No upper NeExtrapolation PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE26 No upper ionospheric contribution considered √ Climatological model Extrapolation scheme Using the separability nature of the electron densityUpper ionosphere estimation: NeQuick √: Exponential decay √∫F h d h=1F h1=1h1−hn [1−∑i=1n−2ΔF i⋅hi1−hn ]F h1=0 PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE27When using the Improved Abel Transform to retrieve electron densities from RO events, the value of the integral of the shape function along the RO path should theoretically be 1 (in practice, a value close to 1)Surprisingly, for the first processed FORMOSAT-3/COSMIC data belonging to the first two weeks of 2007, with more than 17.000 solved and accepted occultations, these integral values where far from being 1.Upper ionosphere estimation PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE28Distribution of the values of the shape function integral taking into account the different LEO spacecrafts.Upper ionosphere estimation PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE Upper ionosphere estimationThe shape function integral value gives a comparison btw VTEC GPS derived and VTEC RO derived. RO are mainly sensitive to IONO, not accounting for PLASMASPHERE.Since plasmasphere is more important during night, this fraction of VTEC is smaller during night rather than day. PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGE30ConclusionsThe results from this work show: Alternative way  to calibrate clocks by means of the ionospheric-free combination of carrier phases avoiding double differencing strategies (valid for ionospheric heights).  Analysis of an Implementation of Separability technique for the retrieval of electron densities from L1 excess phase at a very ionospheric variable location (mitigating the effect of co-location). The Improved Abel transform provides more accurate determination of foF2. Several strategies to account for the upper ionospheric content have been explored.  It has been shown that Radio Occultations are basically sensitive to the ionosphere rather than the plasmasphere. Hence, the electron content accounts for the iononospheric contribution. PhD. Defense, Barcelona, February 22 2010                                                                                                                          A. Aragón-AngelgAGE  Research group  of Astronomy and GEomaticsgAGEThank youGràcies!

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Improvement and validation of retrieved FORMOSAT-3/COSMIC electron densities using Jicamarca DPS

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