Goal and context a new electron density extrapolation technique (VCET) for impact parameters of 500km up to the EPS-SG orbital height.

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1 Improved Abel Inversion and additional modeling of electron density fields: application to EUMETSAT Polar System Second Generation Miquel Garcia-Fernàndez(1,2), Manuel Hernandez- Pajares(1), Antonio Rius(3), Riccardo Notarprieto(4), Axel von Engeln(4) (1) UPC-IonSat, Barcelona, Spain, (2) Rokubun S.L., Barcelona, Spain, (3) Institut d Estudis Espacials de Catalunya (IEEC), Bellaterra, Spain, (4) EUMETSAT, Darmstadt, Germany,

2 Goal and context The new EUMETSAT Polar System 2 nd Generation (EPS-SG) satellites are designed for neutral atmospheric sounding. EPS-SG will provide as well an opportunity of ionospheric sounding, below impact parameters heights of 500km. Different aspects of the electron density retrieval and impact on EPS-SG are being studied in the EUMETSAT funded project ROPE. We are going to summarize one of them: a new electron density extrapolation technique (VCET) for impact parameters of 500km up to the EPS-SG orbital height. The Vary-Chapman Extrapolation Technique (VCET) is based on the scale height linear increase above hmf2. VCET has been assessed vs complete electron density profiles obtained in 4 representative scenarios of COSMIC- FORMOSAT-3 occultations, with an updated Improved Abel Transform Inversion technique.

3 EUMETSAT Polar System Second Generation (EPS-SG) satellites (following [*]) EPS-SG consists of two, parallel series of satellites (Metop-SG A and Metop-SG B), with an altitude of 817 km. The Metop-SG A series has the optical imaging, infrared and microwave sounding; aerosol imaging, and radio occultation missions Metop-SG B series is dedicated to microwave and sub-millimetre-wave imaging, scatterometry and radio occultation The plan is for a series of three satellites of each type (six in total) and a constellation deployment scenario allowing parallel operations of multiple satellites. [*] SystemSecondGeneration/EPSSGDesign/index.html

4 ROPE project The ongoing EUMETSAT funded study Ionospheric Radio- Occultation Profiling Evaluation and Test Data Generation (ROPE) performed by UPC-IonSAT & IEEC-ICE, is focused on: 1) Selecting a representative set of ionospheric profiles for a. Use in the generation of processor test data for the radio occultation instrument RO on the future EUMETSAT Polar System (EPS) Second Generation (EPS-SG) satellites. b. Assessing the impact of ionospheric irregularities on the RO obs. 2) Provides information on the impact of the EPS-SG RO baseline characteristics on the ionospheric retrieval: Feasibility of extrapolating the electron density from 500 km up to the EPS-SG orbit? 3) Update the Forward Module of the Radio Occultation Processing Package (ROPP-FM) for taking into account also the ionospheric contribution to the atmospheric refractivity.

5 1. Selecting a representative set of ionospheric profiles Generated with an updated version of the former Improved Abel Transform Inversion technique (IAI, Hernández-Pajares et al. 2000, García-Fernández et al. 2003). Four scenarios with COSMIC/FORMOSAT- 3 availability on high solar flux (#1,2), low solar flux (#3) and high space weather (#4) have been selected. Focus is on scenarios relevant to EPS-SG

6 Improved Abel transform Inversion 6

7 Updated IAI implementation The solving strategy of Abel transform inversion has been further improved during the project. A dual-layer tomographic topside electron content model, feed with LEO POD antenna raw GNSS data, is first estimated and to discount the electron content above the EPS-SG height. IAI is solved now by Least Mean Squares (LMS), instead of using the peel-onion iterative approach. This LMS-based approach, among other advantages (like the LMSconsistent estimation of the shape function error) to impose a bottomside smoothed constraint tending to zero for reducing the occurrence of artifact variability (at ionospheric heights below 70 km). Two-runs strategy: the first with poorest vertical resolution (e.g. 5 km) for estimating the L1-L2 carrier phase ambiguity, BI and the second, once BI is fixed, with higher vertical resolution. An improved screening procedure is applied as well to filter out unrealistic profiles.

8 Selected scenarios occultations after screening

9 2. How to fill up each electron density profile from 500 km up to the EPS-SG orbit First Step, profile estimation downwards 500 km: Shape Function (SF) / Electron Density (Ne) retrieval. An adaptation of last version of Improved Abel Integral Inversion (IAI) implementation to EPS-SG scenario will be done. Second Step, profile extrapolation upwards 500 km: Electron density profile extrapolation upwards within 500 km h h[eps-sg]. The identification, development and assessment of suitable electron density extrapolation techniques are presented here.

10 Second Step: Electron density extrapolation to 500 km h h[eps-sg] a) Summary of recently published Vary- Chapman electron density model to represent (fit) observed electron density profiles in radioccultations. b) Extrapolation and asessment of electron density profiles from below 500 km, up to the LEO height ( km), in the four scenarios selected for ROPE.

11 a) Summary of recently assessed Vary-Chapman electron density model in radiooccultation scenario. The Vary-Chapman model is most appropriate for describing the topside electron density than the standard Chapman model[*] [*] (based on an study performed during the last years and published two months ago Olivares-Pulido et al ).

12 Electron Density vertical profile Vary-Chap Models H depends on height (e.g. Nsumei et al., [2012]). 12

13 Observed vs Chapman model (typical example) Observed electron density typically overexceeds Chapman prediction at heights above F2 layer peak

14 Scale Height from GNSS RO data LLS fit (top side) LLS fit (bottom side) In general, solutions in the bottom side may have some computational issues due to the presence of local maxima below h_ (i.e. _ ). 14

15 Fit results: day 100,

16 Fraction of occultations with Scale Height linear fit with Pearson corr. coef. above 0.98 Total EDPs for each day (second column) and percentage of EDPs with sample Pearson coefficient above 0.98 (third column). 16

17 Details: Olivares-Pulido, G., M. Hernández-Pajares, A. Aragón-Angel, and A. Garcia- Rigo (2016), A linear scale height Chapman model supported by GNSS occultation measurements, J. Geophys. Res. Space Physics, 121, doi: /2016ja )

18 b) Extrapolation and asessment of electron density profiles from below 500 km, up to the LEO height ( km), in the four scenarios selected for ROPE. The Vary-Chapman Extrapolation Technique (VCET): The Vary-Chapman model presents a good performance for extrapolating the F2-peak topside electron density profile, in particular compared with Chapman model.

19 Electron Density models to compare in F2-peak topside extrapolation 3 classical Chapman models (from scale heights c. in 3 ways): Climatic (Cappellari[*]) topside scale height (available for our extrapolation problem). Average of topside scale heights (no suitable for extrapolation). Scale height from electron density profile VTEC and electron density peak (this could be adapted to extrapolation from GIM VTEC and PODplasmaspheric VTEC correction). VCET : Vary-Chapman model from scale heights (Hi) estimated independently and independently for each height, adjusted linearly from h=hmf2+100 km to min(hmf2+100km,500km), and extrapolated above. All of them take observed hmf2 & NmF2, below 500km. [*] H=(hmF2-50km)/3, see Feltens (2008), Cappellari et al. (1975).

20 Distribution of profile peak height in the 4 ROPE scenarios Only 2 of profiles with peak height above 500 km (correspond to very low values with irregularities and TID)

21 One typical example (not the best, not the worse) Region of interest where the ionospheric extrapolation is required (it will not observed from EPS-SG)

22 Difference regarding directly observed profile, in the extrapolation height range

23 Summary of results on the occultations in the 4 scenarios

24 Selected extrapolation approach: Linear Vary-Chapman model

25 Conclusions 1. The new Vary-Chapman based Extrapolation Technique of electron density (VCET), physically consistent with the linear temperature increase above hmf2, has been developed in ROPE. 2. VCET is based on Vary-Chapman linear model, and it is suitable for extrapolating the future EPS-SG profiles above 500 km of height in electron density estimation % of profiles present an extrapolation relative error with VCET less than 20%, in front of the best performed classical Chapman model (based on the constant topside scale height dependence on VTEC and F2 electron density peak), which provides less than 15% of profiles present a relative error below 20%. (More details in Hernández-Pajares et al., Electron density extrapolation above F2 peak by the linear Vary-Chapman model supporting new GNSS-LEO occultation missions, in preparation for JGR Space Physics) 25

26 References Cappellari, J.O, C.E. Velez and A.J. Fuchs, 1976, Mathematical Theory of the Goddard Trajectory Determination System, Goddard Space Flight Center, X , Greenbelt, MD, U.S.A., April 1976, Section 7.6.2, Ionosphere Models, pp Chapman, S. (1931), The absorption and dissociative or ionizing effect of monochromatic radiation in an atmosphere on a rotating Earth, Proc. Phys. Soc., 43, Feltens, J. (1998). Chapman profile approach for 3-D global TEC representation. IGS Presentation, in. Hernández-Pajares et al., Electron density extrapolation above F2 peak by the linear Vary-Chapman model supporting new GNSS-LEO occultation missions, in preparation for JGR Space Physics. Nsumei, P. A., B. Reinisch, X. Huang, and D. Bilitza (2012), New Vary-Chap profile of the topside ionosphere electron density distribution for use with the IRI model and the GIRO real time data, Radio Sci., 47, RS0L16, doi: /2012rs Olivares-Pulido, G., M. Hernández-Pajares, A. Aragón-Angel, and A. Garcia-Rigo (2016), A linear scale height Chapman model supported by GNSS occultation measurements, J. Geophys. Res. Space Physics, 121, doi: /2016ja )

27 Backup slides

28 Separability concept 28

29 Electron density from Radio Occultation data A GPS receiver on board a LEO satellite allows atmosphere sounding with high vertical resolution. COSMIC constellation coverage is rather homogeneously distributed worldwide

30 and corresponding Electron density profile (rmf2= km => hmf2 ~ 190 km)

31 Comparison with IRI outputs IRI software ( ) yields a linear electron temperature T(h) a linear scale height with temperature H(T) 31

32 Conclusions on suitability of Vary-Chapman electron density model to represent RO data 1. The scale height data provided by GPS radio occultations from a receiver on board a LEO satellite (obtained by iterating with a local Chapman model at every point of the vertical prole provided by the GNSS satellite occultation after applying the improved Abel transform) have been fitted to height by means of an LLS method. 2. The results obtained by LLS strongly suggests that the scale height H is linearly correlated with height h in top layer of the ionosphere (from ~50 km above hmf2 up to ~400 km above hmf2). 3. In general, the scale height and its gradient show consistent dependencies on LT and latitude. 4. These results are in good agreement with Vary-Chap models with linear scale height. 5. A prospective physical explanation for the linear scale height might be the imbalance between the heating and cooling scale times of the ionospheric plasma (e.g. Su et al. [2015].). 32