WERA Ocean Radar Capability of Real -Time Tsunami Detection · radar system with beamforming in...

member of and

WERA Ocean Radar Capability of

Real-Time Tsunami Detection

Dr. Anna Dzvonkovskaya

Helzel Messtechnik GmbH

Kaltenkirchen, GERMANY

e-mail: dzvonkovskaya@helzel.com

Worldwide WERA® HF Ocean Radar Installations

Permanent WERA Installation

Temporary WERA Installation

Planned WERA Installation

Sultanate of Oman: National Multi-Hazard Early

Warning System (NMHEWS), March 2015

Ocean Networks Canada, British Columbia, March 2016

University of Concepcion, Chile, April 2016

HF Ocean Radar Remote-Sensing Basics:

Resonant Backscatter from Ocean Waves

WERA® (Wellen Radar) is a shore-based radar remote sensing system

operating at 5…50 MHz and using the over-the-horizon radar

technology to monitor ocean surface currents, waves and wind

direction. A vertically polarised electromagnetic wave is coupled to the

conductive salty ocean water and follows the curvature of the earth.

The rough ocean surface

interacts with the radio wave

and due to the Bragg Effect

back-scattered signals can

be detected at ranges of

more than 200 km

The back-scattered radar signal will be Doppler shifted with a

specific frequency offset given by the velocity of the gravity wave

that is responsible for the resonant Bragg scattering.

The Doppler shifted signals

are symmetrical around the

centre frequency as long as

the ocean surface does not

exist.

fcurrent fcurrent

0πλg

Doppler Shift

at no Radial

Current

An ocean surface current

simultaneously shifts the

Bragg peaks in frequency.

Radar Spectrum

A Doppler frequency shift is

converted to radial surface

velocity.

Radial Surface Current Velocity on a Grid

Multi-Purpose Remote Sensing by HF Radar

Operating

continuously 24/7

without human operators

WERA Radar System

Information update

every 33 sec Online Data

Simultaneous

multi-purpose

spectrum analysis Signal Processing

Surveillance Coastal

Oceanography TSUNAMI

The WERA software reads a series of coherent files

with 128 samples each and combines them to form

sub-spectra. There is a special routine that controls this

process. Once the coherent series of files is interrupted,

the process to combine files is restarted repeatedly.

For current measurements, the sub-spectra (yellow)

are averaged until the user defined sample number is

covered (e. g. 1024 samples) to form the gridded

spectra file (green) for currents. These files are written

at time increments.

For wave measurements, the sub-spectra (yellow) are

averaged until the user defined sample number is

covered (e. g. 2048 samples) to form the gridded

spectra file (red) for waves. These files are written at

time increments.

128 samples

1024 samples

2048 samples

For Ship Tracking and Tsunami Detection a defined

sample number of 512 samples is needed.

512 samples

WERA Permanent Acquisition Processing Software

Tsunami

Detection

Currents

128 samples

WERA Permanent Acquisition Processing Software

.TSU.SPEC

NTSU_STEP

.TSU.SPEC

The unique, parallel and phase conserving signal processing of

the WERA system allows software beamforming to provide data

from entire range within short integration time:

Features of the Unique System Concept

2 min in 30-sec steps for ship tracking / disaster warning

5 min for surface current mapping

20 min for wave data on a grid

WERA Parallel Implementation of

Ship Tracking and Oceanography

WERA Positions

AIS Positions +

HF Radar System Concept for Tsunami Monitoring:

Necessary Criteria to Support Tsunami Detection and

Information to TEWS

• to plan an effective ocean radar installation.

Known bottom topography

• to allow time for issuing and transmitting a tsunami alert

Ocean shelf extension

• to resolve the tsunami current signatures at different directions a phased-array radar system with beamforming in real-time

Good spatial resolution of radar mapping

• to detect the rapidly changing surface velocity with periods of several minutes a phased-array radar system with beamforming in real-time (direction-finding compact ocean radar systems lacks of fast measurement mode)

High temporal resolution of radar data

• a radar system should be equipped with an additional UPS unit (possible power outage)

Uninterrupted power supply unit

• the transmission link between a radar site and a central server of TEWS should be stable and independent of local communication networks (possible network failure)

Transmission link

Short integration time and fast update data rate

The software beamforming for directivity in real-time

Coherent intergration time 133 sec

Radial velocity resolution 0.14 m/s

Coherent intergration time 532 sec

Radial velocity resolution 0.04 m/s

Tsunami Detection: a Time-Sensitive Application!

Linear Wave Theory

Tsunami phase velocity:

Horizontal orbital velocity:

Robust Detection of Small Tsunami Surface Currents

Tsunami Detection

Thresholds based on

Linear Wave Theory

Proposed Tsunami Detection and Alerting by

WERA Ocean Radar

Alert Message to Tsunami Warning Center

Tsunami ALERT decision

Tsunami probability map

Tsunami current velocity map

Remove natural tidal currents

Ocean surface current velocity on a gridded map

Underwater Earthquake near Japan, March 2011

Region:

NEAR THE EAST COAST OF HONSHU,

Magnitude: 9.0

Time: March 11, 2011 at 05:46:23 UTC

(02:46:23 PM at epicenter)

Location: 38.322°N, 142.369°E

Depth: 32 km

Distances:

130 km E of Sendai, Honshu, Japan

178 km ENE of Fukushima, Honshu, Japan

373 km NE of TOKYO, Japan

The Japan Tsunami Propagation Time

WERA HF Radar at Rumena, Chile

Transmit power 30 W Range up to 50 km Operating frequency 22 MHz Bandwidth 500 kHz Range cell 0.3 km Linear FMCW waveform 8 receive antenna elements

Ocean Surface Current Estimation

Radial

surface current velocity:

2fv 0currentradcurr

First-Order Peaks

Doppler frequency

at no radial

current

fcurrent fcurrent fcurrent

HF Radar Spectrum Changes During Tsunami Runups

Japan Tsunami

Radial Surface Current Velocity Measured in Chile

Data from www.ioc-sealevelmonitoring.org

Residuals of Radial Surface Current Velocity Measured by WERA in Chile

Tsunami Wave Period Estimation

Comparison Between NOAA Modeled Heights and

Water Level Measured by the Tide Gauge in Lebu

By courtesy of Christopher Moore, NOAA, USA,

and Dante Figueroa, University of Concepcion, Chile

Comparison Between NOAA Modeled Velocities and

Tsunami Velocities Measured by WERA Ocean Radar

By courtesy of Christopher Moore, NOAA, USA,

and Dante Figueroa, University of Concepcion, Chile

Bathymetry at Radar Coverage

Real-Time Visualization of Tsunami Probability

Provided by WERA System

Tsunami Alert Decision Provided by WERA System

No Tsunami

Tsunami is possible

Tsunami ALERT

Ocean Networks Canada, British Columbia

since March 2016

Ocean Networks Canada, British Columbia, March 2016

Linear Receive Array with 12 elements

Transmit Array @ 13.5 MHz, 30 W, LFMCW

Ocean Networks Canada, British Columbia

since March 2016

Typhoon Songda in the Northwest Pacific Ocean

in October 2016

Oct 3, 2016

Oct 16, 2016

Oct 14, 2016

Real-Time Meteotsunami Observation on 14 October

2016 by WERA System in Canada

Meteo Buoy 46206

WERA Data

Tide Gauge Data

Real-Time Meteotsunami Observation

on 14 October 2016 by WERA System in Canada

WERA-Tofino DataViewer

http://85.214.102.219:8080/

Meteotsunami Observation on 29 May 2017 by

Tide Gauges at the North Sea

Tide Gauges

WERA (Netherlands)

WERA (Germany)

Meteotsunami Observation on 29 May 2017 by

WERA Systems at the Dutsch Coast

Conclusions

HF ocean radar systems have a unique capability to monitor the ocean

surface over the horizon.

The unique event detected on October 14, 2016, by the WERA ocean

radar system showed that the system was capable to measure and track

unusual patterns of surface current velocity starting 60 km offshore and

in real-time.

In locations where the shelf edge is extended tens of kilometers off the

coast the first appearance of tsunami waves can be monitored early

enough to issue an automatic alert.

The analysis of the available data records from nearby tide gauges and a

meteorological buoy located in the radar coverage showed that this

unusual event was caused by a sharp pressure drop during the cold

atmospheric frontal passage. The event can be potentially identified as a

type of meteotsunami.

The outstanding temporal resolution makes WERA system a perfect

component for parallel time-critical applications like tsunami warning

and vessel tracking.

WERA Ocean Radar Capability of Real -Time Tsunami Detection · radar system with beamforming in...

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