Mechita Schmidt-Aursch (AWI)

Ernst Flüh (GEOMAR) Michael Schnabel (BGR)

Arne Schwenk (K.U.M.)

German OBS pools: current status and ongoing developments

Introduction

OBS community in Germany:

Approx. 180 OBS in four instrument pools:

- Federal Institute for Geosciences and

Natural Resources (BGR) in Hannover

- Helmholtz Centre for Ocean Research

Kiel (GEOMAR)

- Alfred Wegener Institute, Helmholtz Centre

for Polar and Marine Research (AWI) in

Bremerhaven

- University of Hamburg (currently reorganising)

One commercial manufacturer: K.U.M. Umwelt- und Meerestechnik in Kiel

Several external users, mainly universities, e.g. Bochum, Kiel, Leipzig, Münster,

Munich, Potsdam

German OBS-Pools: BGR

Federal Institute for Geosciences and Natural Resources (BGR):

Since the mid-90s: 8 ocean bottom hydrophones (OBH)

- Syntactic foam

- SEND recorder

- Hydrophone only

- 6000 m maximum depth

Since 2008/2009: 13 K.U.M. LOBSTER OBS

- Syntactic foam

- SEND recorder, 1 new K.U.M. 6D6

- 4.5 Hz seismometer

- 6000 m maximum depth

→ Mainly used for wide-angle seismics

→ Mainly intended for own use, also used in joint projects

German OBS-Pools: GEOMAR

Helmholtz Centre for Ocean Research Kiel (GEOMAR):

Long tradition in developing ocean bottom instruments

Since the early 90s: 25 OBH

Today: 80 K.U.M. / self-made OBS

- Syntactic foam

- SEND and new GEOMAR recorder

- 4.5 Hz seismometer,

- 4 Güralp CMG-40T (60 sec)

- Other sensors: differential pressure, absolute pressure, tilt,

temperature, methan concentration, electromagnetics

- 6000 m / 8000 m (10 units) maximum depth

First generation OBS

German OBS-Pools: GEOMAR

Helmholtz Centre for Ocean Research Kiel (GEOMAR):

→ Syntactic foam and titanium only: robust and corrosion-free

→ Equally used for wide-angle seismics and long-term deployments

→ Mainly intended for own use, external use is common

Second generation OBS Third generation OBS

German OBS-Pools: AWI

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI):

Since the early 90s: 5 OBH

Since 2005/2006: 80 K.U.M. LOBSTER OBS

- Syntactic foam

- SEND recorder

- Güralp CMG-40T seismometer (60 sec)

- 6000 m / 7300 m

(12 units) max. depth

- Piggy-back experiments

(e.g. occupancy of

deep-sea fauna)

possible

(V. Schlindwein)

German OBS-Pools: AWI

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI):

Since 2015: step-by-step replacement of CMG-40T by Trillium Compact (120 s)

- CMG-40T: low power consumption (120 mW), was 2005 the only available OBS

compact seismometer, but fragile gimbal system and high self-noise for T > 10 s

- Nanometrics Trillium Compact: higher power consumption (180 mW), robust

levelling system, low self-noise for T > 10 s

Since 2016: step-by-step replacement of SEND recorder by K.U.M. 6D6 recorder

→ Marine part of “German instrument

pool for amphibian seismology

(DEPAS)“ with 80 OBS and

100 mobile onshore stations

→ Mainly intended for external use,

own use common

German OBS projects

Recent experiments: GEOMAR: Mid-Atlantic Ridge, wide-angle seismics

AWI: Chatham Rise, wide-angle seismics

GFZ Potsdam: Ireland, long-term deployment

Ongoing deployments:

GEOMAR: Chile, Marmara Sea, Alboran Sea, Mount Etna, long-term deployments

University of Potsdam: Lesser Antilles, long-term deployment

AWI: Ross Sea, Knipovich Ridge, long-term deployments

Upcoming projects:

2016, BGR: Central Indian Ridge, wide-angle seismics

2017, BGR: East Greenland, wide-angle seismics

2017, AWI: Ross Sea, Sri Lanka, wide-angle seismics

2017, GEOMAR: Ligurian Sea, long-term deployment (Alp Array) (W.S. Lee)

Developments: GEOMAR data recorder

GEOMAR data recorder GEOLOG:

- ADC: 32 bit

- Clock: CSAC atomic clock

- Channels: 3 seismometer, 2 hydrophone

- Sampling rate: 50 Hz - 2000 Hz

- Power supply: 6.5 V - 32 V

- Power consumption: 280 mW - 550 mW,

230 mW standby

- Storage: 2 * 128 GB Micro SD

- Dimensions: 11 cm x 10.5 cm x 7 cm

- Weight: 385 g

→ Active seismics: 20 successful deployments since 2015

→ Long-term seismology: ongoing deployment March 2016 - 2017

Developments: K.U.M. data recorder

K.U.M. data recorder 6D6:

- ADC: 32 bit

- Clock: MCXO, accuracy 0.02 ppm, own

battery, no loss of synchronisation for years

- CSAC atomic clock available (+ 120 mW)

- Channels: up to 7, modular design

- Sampling rate: 50 Hz - 4000 Hz

- Power consumption: 125 mW, 4 µW standby

- Storage: 512 GB SDXC card (up to 2 TB)

- Dimensions: 8.2 cm x 8.2 cm x 8 cm

- Weight: 240 g

→ Active seismics: 10 successful deployments since 2015

→ Long-term seismology: ongoing deployment August 2016 - October 2017

Developments: K.U.M. OBS

K.U.M. OBS NAMMU:

- Syntactic foam and titanium frame and tubes

- 6000 m maximum deployment depth

- Compact design, half-pallet size, stackable

- Weight: 155 kg (fully mounted, without anchor)

- K.U.M. 6D6 data recorder

- Trillium Compact (120 s) seismometer

First successful deployments in 2016

(wide-angle seismics)

Developments: K.U.M. OBS

K.U.M. OBS NAMMU:

Head buoy (fixed)

Battery, seismometer data recorder

Releaser Hydrophone

Beacon, flash light

Developments: K.U.M. OBS

K.U.M. OBS NAMMU:

- 1 year deployment time, with extension 3 years

- Web interface, LAN or wireless (e.g. smartphone)

- Integrated GPS and AIS available

- External hot plug-in storage available

- Permanently synchronised: long-lasting clock battery

- Suitable for rapid response operations

1 year 3 years

Outlook

Rotational seismology (LMU Munich and AWI):

- How strong are translational measurements of a

seismometer affected by rotational components?

- Parallel recording of a seismometer (Güralp

CMG-40T, 60 s) and a 3-component fiber

optic gyroscope (Northrop Grumman

LITEF LCG-Demonstrator)

- Power consumption

of gyroscope: 28 W !

- Pilot study: 4 days

near Heligoland

- Water depth:

approx. 30 m

(Lindner et al., SRL, accepted)

Recovery buoy

Gyroscope, recorders, batteries

Seismometer

Releaser

Outlook

Rotational seismology:

- High noise due to shallow water

- High correlation (cc up to 0.94)

between rotations and horizontal

translations

- Tilt correction of seismometer data:

clear noise reduction (up to 11 dB)

between 5 s and 13 s

→ Horizontal translational components

are severely contaminated by rotations

between 5 s and 13 s

→ We can correct this!

(If we have enough batteries....)

(Lindner et al., SRL, accepted)

Summary

OBS pools in Germany: - Approx. 180 instruments in four pools (Hannover, Kiel, Bremerhaven, Hamburg)

- Many external users, especially universities

- One commercial manufacturer

- Various designs, but syntactic foam and titanium frames are mostly used

- Seismometer: 4.5 Hz, Güralp CMG-40T (60 s), Trillium Compact (120 s)

Developments:

- New GEOMAR and K.U.M. data recorders

- New K.U.M. OBS

(W.S. Lee)