GOCE and Antarctica Rene Forsberg DTU Space Denmark

GOCE and Antarctica Rene Forsberg DTU Space, Denmark Credit: Planetary visions/CPOM/ESA Cryo. Sat

Antarctica – why is GOCE useful? A poorly mapped continent – 13. 8 million km 2, 6 x Greenland, 2 x Europe 98% ice covered, Ice up to 4. 5 km thick, E Antarctica stable, W and Peninsula loosing mass • GOCE objective: gravity to map subglacial terrain and underlying geological features • Antarctica last remaining void of gravity field data on the planet. . GOCE give a coherent picture Antarctic Peninsula East Antarctica West Pine Island gletscher

Antarctica and GOCE (2) • Antarctica gravity field has global implications – gravity pertubates satellite orbits: - Environment and polar monitoring satellites such as ESA Cryo. Sat and the upcoming Copernicus constellation degraded without knowledge of accurate polar gravity • Complete coverage of global gravity a century-old ”holy grail” of geodesy - determination of the ”geoid” requires knowledge of global gravity • GOCE satellite detection of high-resolution gravity change due to melt of large glaciers GOCE has provided a first coherent detailed view of the Antarctic gravity field – High resolution and accuracy => Useful data for geophysics and glaciology The current global standard model of the gravity field: EGM 2008 (US NGA): Red show areas: void of data, other colours show gravity data availability at varying quality levels

Antarctica gravity field from GOCE Latest GOCE gravity map (Release 5) of Antarctica – major structures can clearly be traced … a first C G A – Lake Vostok (largest sub-ice lake) B – Aurora Basin (thick sediment layers) C – Recovery ice stream valley and lake D – Trans-Antarctic Mountains E – Pine Island Glacier sub-ice valley G – Gamburtsev sub-ice mountain D Antarctic sub-ice terrain compiled from airborne radar measurements A E B Unit: m. Gal ~ 1 g (millionth of g) BEDMAP 2 - H. Pritchard, British Antarctic Survey

BEDMAP 2 seen from West – many regions need data H. Pritchard , BAS / NASA visualization

Existing gravity in Antarctica and GOCE Expensive field operations in last decade … airborne gravity filling in major voids as part of integrated geophysics projects (US, Russia, Germany, UK, … gravity low priority usually) SCAR Antarctic Geoid Project Ant. GP. . complement ADGRAV, BEDMAP Current Ant. GG project gravity coverage (M. Scheinert, TU Dresden) Some recent data: ICEGRAV (blue), ICECAP (green), ICEBRIDGE (grey)

NASA Ice. Bridge Orion-P 3 and DC 8 (operating from S America / Mc. Murdo) DTU Space/IAA/NGA ICEGRAV (Antarctic bases – Troll / Marambio)

Airborne gravity and GOCE – ICEGRAV 2011+13 (DTU-NPI-BAS cooperation) Troll (N) Halley (UK) Belgano(Arg) FD 83 (Rus. ) Error estimate: ~3 m. Gal from cross-over analysis Difference to GOCE: ~ 1 m. Gal bias, 22 m. Gal rms - Confirms good quality of airborne survey (and GOCE) -

Recovery Lakes 2013 survey: Ops from Halley, Belgrano and FD 83 / Troll camp support

Gravity and sub-ice terrain – DML Gravity free-air (m. Gal) Bedrock elevation (blue: below sea level)

Using gravity for ice stream bed elevation (example of 2 -D gravity inversion when ice radar fails). U Texas/ D Young radar Radar gap North South

Some ”surprising” GOCE results … heatflow link … ESA Dome-C SMOS/GOCE campaign Jan 2013 (AWI, Germany / DTU-Space) GOCE and airborne gravity correlates with TB radiometer data from the SMOS satellite. . due to correlation of gravity with ice thickness and heat flow insulation by overlaying ice? SMOS absolute temperature (TB, K) Gravity from GOCE and airborne data (m. Gal) Dome-C area size 500 x 500 km; Macelloni et al (in prep. )

ESA Dome-C SMOS/GOCE campaign – validation of GOCE gradients (H. Yildiz, Tscherning, Forsberg) [least-squares collocation upward continuation] Dome-C airborne gravity (overlaid on GOCE) GOCE gradient field at satellite altitude (colour scale – 80 to 80 m. E except Tyz) Validation on 5 ”good” gradients ~ 0. 02 E r. m. s. (ESA Dome-C report)

Some surprising GOCE results (2) … GOCE measures climate-related gravity changes; mass loss of individual glaciers in W Antarctica resolved for the first time GRACE trend 2003 -11 (mm w. eq. ) GOCE mass loss 2009 -13 Baumann et al, Geophysical Research Letters, 2014

GOCE Antarctica - the Polar Gap • GOCE has left gap south of 83 S due to satellite orbit. . GOCE data not global • Arctic gap covered (Arc. GP) • Southern gap no terrestrial data (only GRACE) • Airborne gravity can deliver the missing data Polar gap problem Difference in geoid from the two official R 5 GOCE models Arctic gravity field from airborne, surface and submarine data (Arc. GP compilation)

ESA-NSF International effort 2015/16 ”Pole. Gap” BAS / DTU Space / Columbia Univ. Lines coordinated with NASA-Ice. Bridge => Truly global ”final” GOCE gravity field Current planning: US NSF C-130 aircraft operating from Mc. Murdo BAS-DTU team operating from remote camps Fuel provided at US South Pole Station Primary funding: ESA + NSF (tbc) FD 83 field camp Thiel Mts camp Mc. Murdo ESA NSF Twin-Otter @ fuel cache (Ice. Grav-2013) NSF US C-130 @ south pole station

Conclusions - GOCE data in Antarctica has covered large ”white spot” regions - Useful data for geophysics, glaciology and climate change - South pole gap to be covered by airborne gravity 2015/16. . tbc