Physical and Space Geodesy - The Earth's Gravity Field - Roland Pail PDF

Physical and Space Geodesy – The Earth’s gravity field Roland Pail Chair of Astronomical and Physical Geodesy IGG – Physical and Space Geodesy | Roland Pail Who am I ?  Since 2010 full profes...

Physical and Space Geodesy – The Earth’s gravity field Roland Pail Chair of Astronomical and Physical Geodesy IGG – Physical and Space Geodesy | Roland Pail Who am I ?  Since 2010 full professor and head of Chair of Astronomical and Physical Geodesy at TUM  Before: 2002–2009 Assistant Professor at Graz University of Technology (TUG) Education:  Study of Geophysics 1991–1995  PhD (Dr. techn.), grade: “sub auspiciis praesidentis”, TUG, 1999 Functions:  2013-2014 and 2016-2019 Vice-Dean of Department Civil, Geo and Environmental Engineering (CGE), TUM  2014-2016 Dean of CGE, TUM  2020-2021 Vice-Dean of Department of Aerospace and Geodesy  Currently: Vice Department Head ASG  2015-2019 President of Commission 2 “Gravity Field” of IAG (International Association of Geodesy)  Since 2010: Board Member of Research Group Satellite Geodesy (FGS)  Since 2022: Member of the Bavarian Academy of Sciences (BAdW)  Programme Director of Study Programme ESPACE IGG – Physical and Space Geodesy | Roland Pail 2 The 3 pillars of modern geodesy IGG – Physical and Space Geodesy | Roland Pail 3 Geodetic observing systems Remote Sensing GPS VLBI DORIS Altimetry SLR Ice altimetry Gravity field IGG – Physical and Space Geodesy | Roland Pail 4 Processes in Earth system & geodetic observation Geometry & kinematics - Positions - Deformation - Sea level Rotation - Orientation - Angular rate Gravity field - static - time-variable IGG – Physical and Space Geodesy | Roland Pail 5 Temporal gravity: Sustained observation of mass transport from space CHAMP (GFZ, 2000-2010) GRACE (NASA/DLR, 2002-2017) GRACE-FO (NASA/GFZ, 2018-???) GOCE (ESA, 2009-2013) NGGM/MAGIC (GRACE-I) / Sentinel Gravity field observations are a unique measurement technique to observe and monitor mass and mass transport in the Earth‘s system. Water will be one of the most critical and geopolitically most important resources of the future. Sustained gravity field observation from space contributes significantly to a number of Essential Climate Variables (ECVs) as defined by GCOS. IGG – Physical and Space Geodesy | Roland Pail 6 Contributions of mass change monitoring to Essential Climate Variables (ECVs) Domain GCOS Essential Climate Variables Currents Surface: Air temperature, wind speed and direction, water vapour, pressure, precipitation, surface radiation budget. Atmospheric Upper-air: Temperature, wind speed and direction, water vapour, cloud Ice mass loss (over land, sea properties, Earth radiation budget (including solar irradiance). and ice) Composition: Carbon dioxide, methane, and other long-lived greenhouse Sea level rise gases, Ozone and aerosol, supported by their precursors. Currents Surface: Sea-surface temperature, sea-surface salinity, sea level, sea Earthquakes state, sea ice, surface current, ocean colour, Carbon dioxide Oceanic partial pressure, ocean acidity, phytoplankton. Sub-surface: Temperature, salinity, current, nutrients, Carbon dioxide Droughts partial pressure, ocean acidity, Oxygen, tracers. River discharge, water use, groundwater, lakes, snow cover, glaciers and ice caps, ice sheets, permafrost, albedo, land cover (including vegetation type), Terrestrial fraction of absorbed photosynthetically active radiation (FAPAR), leaf area index (LAI), above-ground biomass, soil carbon, fire disturbance, soil moisture. terrestrial water storage Water use Red: high impact Blue: medium impact Green: small impact IGG – Physical and Space Geodesy | Roland Pail 7 Contents How can we observe the Earth‘s gravity field (from space) ? 1. Basics: Earth gravity field (static, time-variable) 2. Observation techniques What did we achieve in 2 decades of gravity observation from space ? Past and current satellite gravity missions and applications 3. GRACE / GRACE-Follow On 4. GOCE What are the plans for the future ? 5. Science requirements and mission proposals 6. MAGIC: Mass-change And Geoscience International Constellation IGG – Physical and Space Geodesy | Roland Pail 8 How can we observe the Earth‘s gravity field? 1. Basics: Earth gravity field (static, time-variable) 2. Observation techniques IGG – Physical and Space Geodesy | Roland Pail 9 1. Mass and gravity Gravity change Mass change IGG – Physical and Space Geodesy | Roland Pail 10 1. Signals in the static gravity field mGal Gebirge Tiefseegräben Subduktionszonen Mittelozeanische Rücken IGG – Physical and Space Geodesy | Roland Pail 1. Signals in the static gravity field … patterns of global ocean circulation cm/s Agulhas Kuroshio ACC Golfstrom IGG – Physical and Space Geodesy | Roland Pail 1. Temporal gravity field water decrease Colli (2017) water increase IGG – Physical and Space Geodesy | Roland Pail 13 1. Mass and gravity Earth as sphere Mountains Ground water changes Skyscraper 100 10-2 10-3 10-4 10-5 10-6 10-7 Irregular mass distrib. Tides Flattening in Earth‘s interior IGG – Physical and Space Geodesy | Roland Pail 14 2. Gravity observing techniques (1)  Terrestrial data bases  Altimetric gravity  Heterogeneous data distribution  Indirect method to derive gravity from  Heterogeneous accuracy Mean Sea surface with MDT corrections  Contains also high-frequency signal  Covers oceans (problem: coastal areas)  Contains also high-frequency signal IGG – Physical and Space Geodesy | Roland Pail 15 2. Gravity observing techniques (2)  Gravity satellites Gravity from: satellite orbits satellite orbit differences acceleration differences (direct gravity functional) SLR CHAMP GRACE / GRACE-FO GOCE IGG – Physical and Space Geodesy | Roland Pail 16 2. Satellite-to-satellite Tracking (SST) in high-low mode SST high-low Key observables: GPS satellites GPS orbits SST - hl  ai  V  Vi We want to derive a physical xi quantity (mass/gravity) from a geometrical quantity (orbit 3-D accelerometer perturbation): not direct functional of gravity potential highly non-linear K 7.2 IGG – Physical and Space Geodesy | Roland Pail 17 2. Satellite-to-satellite Tracking (SST) in high-low mode IGG – Physical and Space Geodesy | Roland Pail 18 2. GRACE measurement principle SST low-low Key observables: GPS satellites Inter-satellite ranging GPS orbits SST - hl Vi(2)  Vi(1) Vi  x(j2)  x(j1) x j SST - ll  We want to derive a physical  a  (1) V  Vi(1) (1) a  (2) V  Vi(2) (2) quantity (mass/gravity) from a xi i i x i geometrical quantity (inter- satellite distance [change]): not direct functional of gravity potential highly non-linear IGG – Physical and Space Geodesy | Roland Pail 19 2. GRACE measurement principle Courtesy: D. Schütze (AEI Hannover) IGG – Physical and Space Geodesy | Roland Pail 20 2. Satellite Gravity Gradiometry Satellite Gravity Gradiometry Key observables: GPS-Satelliten Gravity gradients GPS orbits SST - hl Vi(2 )  Vi(1) 2 V SGG lim   Vij direct functional of gravity x j 0 x (2 )  x (1) x i x j j j potential (second order derivative) linear observation equation K 7.2 IGG – Physical and Space Geodesy | Roland Pail 21 2. Satellite Gravity Gradiometry IGG – Physical and Space Geodesy | Roland Pail 22 2. Mission performances Wavelength  [km] Signal GRIM1 (1976) CHAMP GRACE GRIM5c (1999) GOCE GRACE (monthly) Time variations IGG – Physical and Space Geodesy | Roland Pail 23 2. Static vs. time-variable gravity field GOCE GRACE/ GRACE-FO Static gravity field Temporal gravity variations  Spatial resolution >70 km  Long-wavelength  Globally homogeneous  Weekly to monthly accuracy IGG – Physical and Space Geodesy | Roland Pail 24  Past and current satellite gravity missions and applications 3. Gravity Recovery and Climate Experiment (GRACE) & GRACE-Follow On 4. Gravity field and steady-state Ocean Circulation Explorer (GOCE) IGG – Physical and Space Geodesy | Roland Pail 25 3. GRACE GRACE / GRACE-FO Gravity Recovery And Climate Experiment IGG – Physical and Space Geodesy | Roland Pail 26 3. GRACE mission parameters & payload Mission parameters Launch: 17 March 2002 (Plesetsk) Orbit inclination: i = 89° Initial orbit altitude: 485 km; decreasing Measurement period: until 2017 Distance measurement between satellites with K-band microwave link: - accuracy: ~m 2 satellite platforms/busses - distance between satellites: ca. 200 km Key payload K-Band Microwave Ranging System (KBR) SuperStar Accelerometer GPS BlackJack Receiver Laser-Retroreflektor Star trackers Coarse Earth and Sun sensor Ultra-stable oscillator K-band ranging system CoM trim assembly IGG – Physical and Space Geodesy | Roland Pail 27 3. GRACE Follow-On Launch: 22 May 2018 Mission period: 5 years (nominal), 10 years (target) Funded by NASA, co-funded by Germany Based on heritage of GRACE, several technological improvements Laser interferometer (~10 nm) in parallel to microwave system as demonstrator IGG – Physical and Space Geodesy | Roland Pail 28 3. GRACE and GRACE-Follow On GRACE/GRACE-FO have been observing since 2002 A map of water storage every month GRACE GRACE-FO IGG – Physical and Space Geodesy | Roland Pail 3. GRACE and GRACE-Follow On GRACE/GRACE-FO have been observing since 2002 GRACE 2004-04 less water more water A map of water storage every month GRACE GRACE-FO IGG – Physical and Space Geodesy | Roland Pail 3. Water balance equation P  R  ET = S P … Precipitation R … Run-off ET … Evapotranspiration S … Storage change Gravity field satellites are the only observation technique  to measure directly the right-hand side of the water balance equation (storage change)  that is sensitive to ground water IGG – Physical and Space Geodesy | Roland Pail 31 3. Global (water) mass redistribution water decrease Colli (2017) water increase IGG – Physical and Space Geodesy | Roland Pail 32 3. Global hydrology: long-term trends Long-term trends Middle East North-China California Nord-India NW-Australia water decrease water increase IGG – Physical and Space Geodesy | Roland Pail 33 3. Hydrology in North India Monitoring of loss of non-renewable freshwater reservoirs from space Tiwari et al. (1999) EWH IGG – Physical and Space Geodesy | Roland Pail 34 3. Climate-induced trends [Rodell et al. 2019] IGG – Physical and Space Geodesy | Roland Pail 35 3. Drought in california IGG – Physical and Space Geodesy | Roland Pail 36 3. Drought in Central Europe (2015) September 2014 September 2015 September 2014 September 2015 IGG – Physical and Space Geodesy | Roland Pail 37 3. Drought in Europe (2022) Soil moisture index: end of July 2022 IGG – Physical and Space Geodesy | Roland Pail 38 3. Temporal gravity: long-term trends Long-term trend Greenland Alaska Antarctica water decreasing water increasing 39 IGG – Physical and Space Geodesy | Roland Pail 39 3. Ice mass variation: Greenland 40 IGG – Physical and Space Geodesy | Roland Pail 40 3. Ice mass variation: Antarctica 41 IGG – Physical and Space Geodesy | Roland Pail 41 3. IMBIE-2: Ice mass balance for Antarctica West Antarctica 1992 – 2001: 53  29 Gt/yr 2010 – 2015: 159  26 Gt/yr East Antarctica 25 years average: 5  46 Gt/yr [Shepherd et al. 2018] IGG – Physical and Space Geodesy | Roland Pail 42 3. Ice mass balance: glacier systems [Wouters et al. 2019] IGG – Physical and Space Geodesy | Roland Pail 43 3. Cumulative mass change & sea level contribution: Antarctica c: NASA/JPL Rule of thumb: 360 Gt/year  1 mm/year global sea level rise IGG – Physical and Space Geodesy | Roland Pail 44 3. Sea level change Cryosphere (ice masses) Hydrology Solar irradiation MASS VOLUME Sea level IGG – Physical and Space Geodesy | Roland Pail 3. Global sea level rise [Annual period reduced] Total sea level ~3 mm/year Altimetry Total rate: 3.2 mm/year Mass effect ~2 mm/year GRACE GRACE Thermosteric effect ~1 mm/year ARGO IGG – Physical and Space Geodesy | Roland Pail 46 4. GOCE GOCE Gravity field and steady-state Ocean Circulation Explorer IGG – Physical and Space Geodesy | Roland Pail 47 4. Satellite gravity gradiometry IGG – Physical and Space Geodesy | Roland Pail 48 4. GOCE mission parameters Mission parameters Launch: 17 March 2009 (Plesetsk) Orbit inclination: i = 96.5° (sunsynchronous) Orbit altitude: 254.9 km 225 km Mission period: 2009 - 2013 Innovations Gradiometer (first-time ever) DFAC (Drag-Free & Attitude Control) extremely low altitude IGG – Physical and Space Geodesy | Roland Pail 49 4. GOCE Payload Magneto-torquers Star tracker Gradiometer GPS receiver Ion propulsion module IGG – Physical and Space Geodesy | Roland Pail 50 4. GOCE mission profile 1. GOCE End End gravity model Nominal Extended Start GOCE Launch Mission Mission MOP Swan-song 2009 2010 2011 2012 2013 17/03/09 10/2009 06/2010 04/2011 12/2012 IGG – Physical and Space Geodesy | Roland Pail 51 4. Orbit lowering Step-wise lowering of orbit altitude higher sensitivity for details of Earth’s gravity field Courtesy: ESA IGG – Physical and Space Geodesy | Roland Pail 52 4. Atmosphere density and air drag Courtesy: ESA Lower altitude higher atmospheric density (drag) Drag compensation (DFAC) in real-time during whole mission K 7.6 IGG – Physical and Space Geodesy | Roland Pail 53 4. GOCE de-orbiting Fuel consumption of Xe gas for ion thrusters (in total: ~41 kg) Courtesy: ESA IGG – Physical and Space Geodesy | Roland Pail 54 4. GOCE de-orbiting The very last days of GOCE … IGG – Physical and Space Geodesy | Roland Pail 55 4. GOCE de-orbiting: re-entry predictions 11-11-2013, 0:16 UTC IGG – Physical and Space Geodesy | Roland Pail 56 4. GOCE de-orbiting: the last view on GOCE c: Bill Chater F 16-46 IGG – Physical and Space Geodesy | Roland Pail 57 4. GOCE de-orbiting: detail information F 16-47 IGG – Physical and Space Geodesy | Roland Pail 58 4. GOCE gravity modelling GOCE gravity modelling IGG – Physical and Space Geodesy | Roland Pail 59 4. GOCE HPF GOCE High-Level Processing Facility (HPF) UCPH AIUB: Astronomical Institute University Bern CNES: Centre Nationale d‘Etudes SRON Spatiale, GRGS, Toulouse FAE/A&S: Faculty of Aerospace Engineering, TU Delft FAE/A&S GFZ: GeoForschungsZentrum GFZ Potsdam IAPG: Institute of Astronomical and Physical Geodesy, TU Munich ITG IAPG ITG: Institute of Geodesy and Geoinformation, Univ. Bonn POLIMI: Politecnico di Milano AIUB SRON: Netherlands Institute for Space Research TUG TUG: Institute of Navigation and Satellite Geodesy, TU Graz UCPH: Department of Geophysics, CNES University Copenhagen POLIMI IGG – Physical and Space Geodesy | Roland Pail 60 4. GOCE gravity modelling n 1 n R   n max GM V (r , ,  )  R    n0  r  P m0 nm (cos  )  C nm cos( m  )  S nm sin( m  ) Satellite observations gravity field parameters Satellite orbit Spherical harmonic coefficients V  ai  x i Gradiometry 2V Vij  x ix j IGG – Physical and Space Geodesy | Roland Pail 61 4. Mean Dynamic Ocean Topography ALTIMETRY H=h-N GEOID Mean Sea Surface: (time-averaged) geometric surface of the ocean Geoid: physical reference surface of the „ideal“ ocean (only gravity-driven) Mean dynamic topography (MDT): Deviation of the real ocean surface from the „ideal“ one IGG – Physical and Space Geodesy | Roland Pail 62 4. Ocean current velocities derived from GOCE and satellite altimetry cm/s Agulhas Current Kuroshio Current ACC Gulf Stream IGG – Physical and Space Geodesy | Roland Pail 63  What are the plans for the future ? 5. Science requirements and mission proposals 6. MAGIC: Mass-change And Geoscience International Constellation IGG – Physical and Space Geodesy | Roland Pail 5. Consolidated Science and User Needs Users’ priorities … Extension of observation time series → separation of natural and anthropogenic forcing Improved spatial resolution Improved temporal resolution → operational applications … expressed in numbers Target. Significant leap forward Significantly increased spatial and temporal resolution New applications (science, societal benefit) IGG – Physical and Space Geodesy | Roland Pail 65 5. „Science for society“ User needs Needs for service applications: High temporal resolution (daily) Short latencies (max. a few days) IGG – Physical and Space Geodesy | Roland Pail 66 5. Future mission concepts: potential for improvements 1. New/improved measurement technologies Improved inter-satellite ranging: KBR vs. LRI Improved technologies of accelerometry/gradiometry High-precision optical clocks Improved thruster technologies; AOCS 2. Satellite formations Improved spatial and temporal resolution due to formation flights in a certain constellation Reduction of temporal aliasing effects 3. Processing & combination with complementary geophysical models De-aliasing by means of improved spatial-temporal parameterization Improved separation of signals due to complementary information Integrate models of the complex system Earth IGG – Physical and Space Geodesy | Roland Pail 67 5. Future missions: cooperation ESA+NASA Science and User Needs NASA/ESA Interagency Gravity Mission proposals Science Working Group e-.motion2 (ESA EE9; double pair) MOBILE (ESA EE10; high- low tracking) NASA/ESA joint activities NASA Mass Change Designated Observable (MCDO) study ESA Next-Generation Gravity Mission (NGGM) study, MAGIC Phase A IGG – Physical and Space Geodesy | Roland Pail 68 6. Mass-change And Geoscience International Constellation (MAGIC) Currents Ice mass loss Sea level rise Currents Earthquakes Droughts Water use IGG – Physical and Space Geodesy | Roland Pail 69 6. Mass-change And Geoscience International Constellation (MAGIC) Joint ESA/NASA Mission Requirement Document (MRD) MRD is basic document for:  2 parallel ESA industry Phase A studies  MAGIC science study (TUM [lead], GFZ, TU Delft, CNES) IGG – Physical and Space Geodesy | Roland Pail 70 6. Best performing constellation Which constellation performs best ? In-line single-pair Pendulum single-pair MARVEL 3 sats. Bender double-pair 71 IGG – Physical and Space Geodesy | Roland Pail 6. Satellite formations: Pendulum IGG – Physical and Space Geodesy | Roland Pail 72 6. Satellite formations: Bender double-pair IGG – Physical and Space Geodesy | Roland Pail 73 6. MAGIC Science study (ESA) MAGIC/Science Constellations: ID Satellite pair 1 Satellite pair 2 Single-pair (with various assumptions on Alt. [km] Incl. [deg] Alt. [km] Incl. [deg] instrumentation [ACC, ISL]) – reference scenario HH 463 89 432 70 Single-pair pendulum with varying opening angle HL 492 89 344 71.5 Bender double pair LL 376 89 344 70 Bender double pair with one or two pairs in pendulum Further key parameters: Goals: Satellite altitude Narrow down the trade space Inter-satellite distance in interaction with parallel system Phase A studies Retrieval periods Identification of optimum set-up regarding science return, technical feasibility, and costs IGG – Physical and Space Geodesy | Roland Pail 74 6. Numerical closed-loop simulations IGG – Physical and Space Geodesy | Roland Pail 75 6. Simulation results: full-noise (31-day solutions) G … GRACE type noise: ACC ~ 10-10 m/s2/Hz N … NGGM noise: ACC ~ 10-11 m/s2/Hz [m] EWH N IGG – Physical and Space Geodesy | Roland Pail 76 6. Simulation results: full-noise (31-day solutions) MAGIC/Science In-line pair (G) Pendulum pair 30° (G) Bender double-pair (G, N) Bender double-p. low orbits IGG – Physical and Space Geodesy | Roland Pail 77 6. Full-scale simulation results main conclusions MAGIC/Science Bender pairs outperform single-pair concepts (in-line & pendulum) by far No added value by flying a pendulum pair as part of a Bender-type constellation Rather low inclination of second pair (~70°) is paramount for de- N aliasing capability of constellation Temporal aliasing errors are currently dominant error source. An improved accelerometer (~10-11) has most impact in a double pair constellations (due to improved de-aliasing capabilities) Flying in lower altitudes improves the performance regarding shorter-wavelength (and thus spatial resolution) significantly altitude is the main performance driver Only double-pair concepts can meet the MRD requirements regarding temporal resolution (short-term solutions) IGG – Physical and Space Geodesy | Roland Pail 78 Status NGGM & MAGIC Pair 1: GRACE-C NASA/DLR Scheduled launch: Dec. 2028 Polar orbit, ca. 500 km altitude, decaying (drifting orbit) Continuation of GRACE/GRACE-FO time series Pair 2: NGGM ESA: Confirmation of phase B1 at ESA EO Programme Board Scheduled launch: Dec. 2032 (goal: overlap with GRACE-C of at least 4 years) Inclined orbit (70°), constant altitude of 396 km, homogeneous ground track Improved spatial and temporal resolution, higher accuracy Short latencies -> (pre-)operational service applications in the frame of Copernicus (droughts, floods, water management) IGG – Physical and Space Geodesy | Roland Pail MAGIC improvements Significantly improved accuracy, spatial and temporal resolution Products with short latency operational service applications (droughts, floods, water management, …) Single pair Double pair IGG – Physical and Space Geodesy | Roland Pail 80 Quantum gravimetry Quantum gravimetry for future Earth observation from space (QUANTGRAV) DLR project: investigation of future perspective of quantum/hybrid sensors for gravity field determination Quantum Space Gravimetry for monitoring Earth’s Mass Transport Processes (QSG4EMT) ESA project: Extended constellations and new missions scenarios involving quantum/hybrid accelerometers Cold Atom Rubidium Interferometer in Orbit for Quantum Accelerometry – Pathfinder Mission Preparation (CARIOQA) EU project: Development of instrumentation and design of a quantum gravimetry pathfinder mission IGG – Physical and Space Geodesy | Roland Pail 81 CubeSats gravity field missions Compromise between: 6-hourly gravity fields:  Improved temporal resolution of multi-satellite networks 1 polar pair + 4 polar pairs +  Reduced measurement accuracy due to miniaturized payload 1 inclined pair 4 inclined pairs Cube-satellite networks for geodetic Earth observation on the example of gravity field retrieval (CubeGrav) DFG project: mission/constellations design and performance analysis of cube-sat network Dynamic Optical Ranging & Timing – In Motion (DORT-IM) BMBF project (start-up): development of a miniaturized dynamic optical inter-satellite ranging system IGG – Physical and Space Geodesy | Roland Pail 82 Take-home messages There are strong user needs for future gravity missions with higher spatial and temporal resolution. Especially operation service applications request high temporal resolution and short latencies. Mission concepts to meet the ambitious science and user requirements exist. Currently, a NASA/ESA inter-agency cooperation strives towards the realization of a future gravity mission constellation MAGIC and will go into Phase B in autumn 2023. IGG – Physical and Space Geodesy | Roland Pail 83 Announcement: elective module “Gravity and mass transport monitoring from space – technologies and applications” Summer semester (6th semester B.Sc. Aerospace) Contents Motivation: Earth gravity field, mass transport processes in the Earth system & climate- related signals (2) Techniques for observing the gravity field from space, orbit dynamics, gradiometry (2) Main sensors & support payload Missions: CHAMP, GRACE, GOCE (3) Gravity field modelling (4) Potential theory and spherical harmonics (2) Complementary data types, combined modelling (1) Dependence on altitude, inclination IGG – Physical and Space Geodesy | Roland Pail 84