Geodetic Monitoring of the Ionosphere

Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München Geodetic Monitoring of the Ionosphere Michael Schmidt Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM), Munich, Germany, email: mg.schmidt@tum.de Outline 1. General introduction into ionosphere modelling in geodesy 2. Ionosphere research at DGFI-TUM including applications 3. Outlook, open and future issues

Structure of the Atmosphere Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 2

Space weather Space weather means today an own, very up-to-date and interdisciplinary field of research. It describes physical processes in space caused by the Sun s radiation of energy and also induced by the radiation of energy from other cosmic sources. The manifestations of space weather are multiple, e.g. variations of the Earth magnetic field, polar lights in the northern and southern hemisphere, variations of the upper atmosphere with the compartments ionosphere and thermosphere (due to coupling processes), solar wind, i.e. the permanent emission of electrons and photons, interplanetary magnetic field, electric currents. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 3

Space weather Space weather means today an own, very up-to-date and interdisciplinary field of research. It describes physical processes in space caused by the Sun s radiation of energy and also induced by the radiation of energy from other cosmic sources. The manifestations of space weather are multiple, e.g. variations of the Earth magnetic field, polar lights in the northern and southern hemisphere, variations of the upper atmosphere with the compartments ionosphere and thermosphere (due to coupling processes), solar wind, i.e. the permanent emission of electrons and photons, interplanetary magnetic field, electric currents. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 4

Observations The solar surface and solar atmosphere is observed in near-real time to detect active regions that may become the source of large events, e.g. the STEREO satellites. Solar winds, geomagnetic storms, etc. are observed by the ACE and the follow-up mission DSCOVR. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 5

Observations GNSS The solar surface and solar atmosphere is observed in near-real time to detect active regions that may become the source of large events, e.g. the STEREO satellites. Solar winds, geomagnetic storms, etc. are observed by the ACE and the follow-up mission DSCOVR. Where is geodesy coming into play? The space-geodetic techniques provide information about the state of the ionosphere. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 6

GNSS Where is geodesy coming into play? The space-geodetic techniques provide information about the state of the ionosphere. Geodesy has a long history and large experience in developing and using sophisticated analysis techniques and modelling approaches. Conclusion: Geodesy has to occupy the topic space weather research (monitoring)! As a consequence we installed the Focus Area: Geodetic space weather research into the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG). Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 7

Focus Area 4: Geodetic Space Weather Research Chair: Michael Schmidt Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM), Munich, Germany, email: mg.schmidt@tum.de Co-chair: Klaus Börger German Space Situational Awareness Centre, GSSAC, Uedem, Germany Accepted at the GGOS Coordinating Board Meeting in Vienna, April 22, 2017 Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 8

Outline What is currently done in Geodesy? Modelling (3-D) the Vertical Total Electron Content (VTEC): various observation techniques are used (mostly satellite-based) pre-processing: mapping of STEC into the vertical (mapping function causes a degradation) different modelling approaches are applied (mathematical, empirical, physical) products (VTEC maps and other derived quantities such as ROTI) are provided to the community, i.e. to the user for both scientific and commercial applications. Modelling (4-D) the Electron Density (N e ): various observation techniques are used (mostly satellite-based, in particular radio occultation measurements) pre-processing: no mapping function necessary highest flexibility, e.g. input quantity for physics-based modelling approaches (e.g. for ionosphere-thermosphere coupling processes) hardly products available, in particular for commercial applications, but also for sciences. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 9

What is currently done in Geodesy? Vertical Total Electron Content VTEC λ, φ, t as the integral of the electron density along the height. 3-D VTEC maps, here animated between for 5 consecutive days Electron density N e λ, φ, h, t as a function of longitude, latitude, height and time 4-D N e representation of height layers between 100 km and 900 km for a fixed time 14:00 UT Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 10

Space-based observation techniques Altimetry: Jason-2, Jason-3 Radio occultation missions: F-3/C (in future: F-7/C2) GNSS: GPS, GLONASS, DORIS (DGXX receivers on board): Jason-2, SARAL, HY-2A, Jason-3, Cryosat-2, Sentinel-3A STEC = Slant Total Electron Content VTEC = Vertical Total Electron Content N e = Electron density Dual-frequency systems Geometry-free linear combination yields STEC along the ray propagation path between transmitter and receiver GNSS sites DORIS ground beacons Further observation techniques such as VLBI, Langmuir probe measurements on Swarm, ) Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 11

Modelling approaches Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 12

Global VTEC products The official IGS combined VTEC product is a weighted combination of the GIMs from the 4 IGS Ionosphere Associate Analysis Centers (IAACs) contributing since 1999, namely the Center for Orbit Determination in Europe (CODE): SH approach, Universitat Politècnica de Catalunya (UPC): Voxel approach, European Space Operations Center of the European Space Agency (ESOC/ESA), Jet Propulsion Laboratory (JPL). New contributors are the Canadian Geodetic Survey of Natural Resources Canada (NRCAN), the Chinese Academy of Sciences (CAS) and the Wuhan University (WHU). The product is provided as VTEC grids in IONEX format with a temporal resolution of 2 hours and a spatial resolution of 5 2.5 in longitude and latitude SH coefficients up to degree 15. It is based on GNSS, i.e. only GPS and GLONASS observations are considered. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 13

Further developments At the IGS 2012 workshop in Olsztyn (23.7 27.7.2012) the IGS ionosphere working group members recommended to provide high resolution IGS combined GIMs. It was agreed on providing VTEC maps with a temporal resolution of 15 min and a spatial resolution of 1 1 in longitude and latitude. A global data set with a spatial resolution of 1 1 corresponds to a series expansion in SHs up to degree 180, i.e. a spatial resolution of around 110 km along the equator. At DGFI-TUM we calculate near real-time VTEC maps from hourly input data including parameter estimation procedures driven by Kalman filtering within the project: OPTIMAP ( Operational Tool for Ionospheric Mapping And Prediction ). Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 14

OPTIMAP process flowchart Parallelized processes Python based C++ Altimetry pre-processing GNSS pre-processing DORIS pre-processing LEO pre-processing Database (HDF) Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 15

GNSS data distribution GPS GLONASS Distribution of ionospheric pierce points (IPP = intersection point of the signal ray path with the single-layer model in a certain altitude) based on the hourly observation batch of February 11, 2016, 12:00 UT - 13:00 UT. The figures show exemplarily the spatial resolution of GPS and GLONASS during the time interval of 1 hour. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 16

VTEC Altimetry pre-processing Seconds of Day Jason-2 hourly batch as observed on January 3, 2014 between 21:00 and 22:00 UT Left: original VTEC measurements (red), median filtered (blue), Measurements over water surfaces along satellite track Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 17

Radio occultation (IRO) pre-processing Dual-frequency signal tracking of IRO events (signal elevation in LEO < 0 ) Retrieval of electron density profiles below the LEO orbit F-3/C orbit altitude ( 800 km) Global distribution of electron density profiles observed by the six F-3/C satellites on 2015/01/01 Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 18

DORIS pre-processing DORIS biased STEC observations through a pass of the satellite observed on January 1, 2015. We are currently using the DORIS data to the satellites Jason-2, SARAL and HY-2A; in near future we will also incorporate data from Jason-3, Cryosat-2 and Sentinel-3A. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 19

Overall data distribution The figure shows the data distribution of the different space geodetic observation techniques on July 23, 2016. Terrestrial GPS and GLONASS observations provide a high-resolution coverage of continental regions. The additional techniques, i.e. DORIS, satellite altimetry and radio occultation cannot repair the problem of data gaps, but reduce it significantly. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 20

OPTIMAP process flowchart Parallelized processes Python based C++ Altimetry pre-processing GNSS pre-processing DORIS pre-processing LEO pre-processing Sun observations pre-processing analytical stochastic Database (HDF) Modeling IONEX Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 21

1. Application: Space weather event at St. Patrick storm days DOY 75 DOY 77 DOY 76 = March 17, 2015 DOY 78 Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 22

1. Application: Space weather event at St. Patrick storm days At day 76, i.e. March 17, 2015, a peak of the regional hourly mean VTEC variations over the indicated area is clearly visible. Conclusion: The VTEC signal can clearly reflect space weather events. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 23

2. Application: Comparisons of DGFI s solution with IGS final products Conclusion: VTEC products in near real-time using a sequential (e.g. Kalman) filter will play an important role in the near future, since they are comparable with the final products. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 24

3. Application: Regional real-time VTEC map One goal of modern geodetic ionosphere monitoring is to develop global ionospheric real-time products with a highprecision ionospheric information based on data adaptive modelling approaches. GPS The terrestrial GNSS observations provide high-resolution information for specific continental regions, e.g., Europe, North America or Japan. In such areas the global ionosphere model for VTEC can be densified to a regional ionosphere model. Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 25

3. Application: Regional real-time VTEC map NRT data download t time download of near real-time (NRT) raw GNSS-data NRT data pre-processing pre-processing of near real-time GNSS-data global VTEC modelling global VTEC modelling with KF forecasted model forecasting of the global VTEC model RT data download download of real-time raw GNSS-data RT data pre-processing pre-processing of real-time GNSS-data regional model regional VTEC modelling with KF Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 26

3. Application: Regional real-time VTEC map Forecasting of the regional part of the global model VTEC reg ( RT low res.) VTEC glob (NRT, low res.) VTEC reg (RT, high res.) ΔVTEC reg (RT, high res.) Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 27

Outline Outlook, open and future issues In precise satellite orbit determination (POD) the thermospheric drag plays a key role. It is mainly depending on the neutral density, which is coupled to the electron density of the ionosphere. Thus, the thermospheric density also reflects space weather activity. Selected open issues: Choice and incorporation of appropriate Sun observations, e.g. the solar wind, into the geodetic parameter estimation models Choice of the estimation and the prediction model for space weather monitoring and alerts Handling of coupling processes, for instance, between ionosphere and thermosphere by physics-based models such as TIEGCM: Choice of drivers: global indices such as Kp and F10.7 versus the magnetic field and the electron density Choice of data assimilation technique, Impact of climate change on the upper atmosphere, i.e. ionosphere and thermosphere. Measurable effects? Measurable with geodetic techniques? Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München 28