Geodetic Hazard Monitoring

Topic Leader: Dr. Tilo Schöne

With the devastating tsunami in Indonesia in 2004, or later in 2010 with severe earthquakes in Haiti and Chile insufficiencies in global geodetic Earth observation and hazard monitoring and the need for improved impact prediction and early warning were clearly demonstrated. Section 1.2 contributes with it’s expertise in sea level and GNSS measurements to the tsunami warning system in Indonesia, in Oman, and more generally, to systems around the Indian Ocean.

Section 1.2 operates a large network of tide gauges around the Indian Ocean. Most stations are GNSS-controlled gauges. This network contributes to various Indian Ocean Tsunami Early Warning Systems (e.g., the Indonesian InaTEWS) and is part of our sea level monitoring system. Beside the early warning aspect, the gauges are used as ground control for satellite radar altimetry and contribute to the IGS TIGA Project. At each gauge a suite of individual tide gauge sensors are sampling and analyzing the water level for tsunamis and provide this information to international users. The connected GNSS ensures the monitoring of long-term or rapid height changes, providing a reliable height control. In addition, all data is used for our climate monitoring activities as well.

Based on early experience in the development of GPS-equipped near-shore buoys for radar altimetry calibration and river buoys for flood monitoring, this technology has meanwhile been extended to sense the sea surface heights with high-precision differential GNSS for sites of up to 80nm off-shore. With today’s processing capabilities, this technology is able to detect tsunami waves down to 5cm amplitude, which is sufficient for the expected large tsunamis off Sumatra. The ruggedized buoys had been operated as part of the Indonesian Tsunami Early Warning System (InaTEWS) in water depths up to 6000m.

A third contribution is the GNSS displacement detection system (Ground Tracking System). This software system operated as part of InaTEWS detects and estimates earthquake-related ground movements using GNSS data from various locations over wider areas. Data input is obtained either real-time or on request from GNSS stations (stand-alone stations, remotely operated multi-parameter stations (ROMPS)). The individual station coordinates (North, East, Up) are precisely and continuously estimated with low latencies (e.g., less than 5 minutes), using a network of reference stations and an automatic near real-time data processing system. Information on co-seismic displacements provides important information to recognize the mechanism of an earthquake and thus of the earthquake’s potential to generate a tsunami.

Also an important research field is the contribution of Section 1.2 for the establishment and operation of a hydrometeorological network in Central Asia (CAWA) and the contribution to GFZ’s Global Change Observatory at Glaciers in Central Asia (GCO-CA). Based on the long-term experience of our Section in designing and operating remotely operated multi-parameter stations (ROMPS), we provide technological and scientific expertise to Central Asia. Since many years Central Asia is suffering from the short-falling of fresh water for living and irrigation. In 2008 the Berlin Process of the German Foreign Ministry addressed this issue asking for the establishment of a hydrological monitoring system in this region. Our monitoring system is providing the necessary ground-based data (GNSS, meteorological parameters, snow parameters, discharge systems), which are either used in climate models or are used to validate time variable gravity fields (hydrological cycle) or radar altimetry of CryoSat (Glacier mass and volume balances).

Sea Level rise is of great concern, both on the global as well as on regional scales. While the global average rise (within the 66° latitude band) is around 3mm/year, local rates can be much higher due to, e.g., human-induced land subsidence (coastal compaction, oil and natural gas extraction, fresh water supply). We continuously analyze and improve data from past and current radar altimetry missions to estimate sea level parameters, like global sea level change, basin scale sea level variability in the North Atlantic, and provide validation of GRACE ocean dealiasing products. The focus of our section is harmonization and inter-calibration of radar altimetry missions and orbit determination based on most recent gravity field models. This work is supported by our contribution to TIGA and by the operation of GNSS-controlled tide gauges around the Indian Ocean.

As part of our regional sea level hazard monitoring activities we are operating two GNSS-controlled tide gauges in Indonesia (Semarang, Jakarta). Semarang is experiencing subsidence of up to 10mm/year caused by soil compaction and fresh water extraction. Jakarta is subsiding at a slightly lower rate. However, large parts of Jakarta are below mean sea level. Frequent torrential rain causes flooding of those areas, impacting the infrastructure and causing health problems. For this research field we are contribution to GGOS Theme 3.

The most important projects of Topic 4 are:  

• High-frequency sea level from altimetry for the validation of GRACE ocean dealiasing products
• Basin scale sea level variability in the North Atlantic (REKLIM)
• GPS analyses at tide gauges (TIGA)
• Automatic near real-time processing of GPS-data
• GPS-controlled Tide Gauges
• Operation of a Hydrometeorological Network in Central Asia

Our geodetic monitoring infrastructure contributes to IAG and GGOS activities and provides the basis to assess long-term, short-term and rapid changes of various Earth Parameters.