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Concept Study and Designs of Radar Sensors for Maritime Surveillance and Near-Field Tsunami Early Warning

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GITEWS

Concept Study and Designs of Radar Sensors for Maritime

Surveillance and Near-Field Tsunami Early Warning

Dr. Thomas Börner

, Michele Galletti, Dr. Nicolas Marquart

Microwaves and Radar Institute (HR)

German Aerospace Center (DLR)

(2)

Tsunami Early-Warning: Far-field and Near-field

NEAR-FIELD TSUNAMI

< 30 min

First warning to be issued

within 5

min

from the quake!

Temporal Coverage: 24/7, for

immediate response.

Spatial Coverage: dictated by plate

tectonics.

Tsunamigenic areas of the Indian Ocean

Makran Subduction Zone

Sunda trench

FAR-FIELD TSUNAMI

> 30 min

Tsunami can happen anytime but

trans-oceanic propagation can take hours!

Far-field Tsunami Early-Warning is

operational and effective.

Under near-field tsunami threat in the world ocean:

Indonesia, Makran Subduction zone (Iran, Pakistan),

Japan, Mediterranean countries, Cascadia,

(3)

d = 40 m

d = 4000 m

= 150 km

= 15 km

a = 0.7 m

a = 5 m

Deep Ocean

Coastal Area

U = 0.08 m/s

U = 2.5 m/s

Tsunamis are easier to detect in coastal areas

Tsunami Scale

(4)

The WERA system (

W

av

E RA

dar) is a shore-based HF radar to monitor ocean surface currents, waves and wind

direction. The system is manufactured by Helzel GmbH. The vertically polarised radiated wave couples to the

conductive ocean surface and propagates as a surface wave with a maximum range of about 200 km and a field

of view of about 120°. Radar performance depends on site geometry, system configuration and environmental

conditions.

There is a trade-off between Doppler resolution and Integration time.

(5)

HF Radar Range and Integration Times

30s (@ 5 MHz)

15s (@ 10 MHz)

100 cm/s

1min (@ 5 MHz)

30s (@ 10 MHz)

50 cm/s

2min30s (@ 5 MHz)

1min 15s (@ 10 MHz)

20 cm/s

5min (@ 5 MHz)

2min 30s (@ 10 MHz)

10 cm/s

10min (@ 5 MHz)

5min (@ 10 MHz)

5 cm/s

T

min

V

radial

60

30

100

15

200

8

Range [km]

Frequency [MHz]

(6)

Possible

Configuration

(Banda Aceh)

(7)

Tsunami Signatures for Air-/Spaceborne Radar

Wave height

altimetry

Orbital velocities

Doppler

Internal waves

radar cross section (RCS)

Tsunami shadows

RCS

Godin, O. A. (2004), Air-sea interaction and feasibility of tsunami detection in the open ocean, J. Geophys. Res., 109.

(8)

First civilian SAR satellite: SEASAT (1978)

2300 kg

Weight

25 m x 25 m

Resolution

100 km

Swath Width

10,74 m x

2,16 m

Antenna

Size

~ 23°

Incident Angle

19 MHz

Bandwidth

~780 km

Altitude

0,235 m

Wavelength

June 26, 1978

Launch

Crucial disadvantages:

not geostationary

poor revisit times

(days/weeks)

(9)

Geosynchronous satellite at ~20 km

(500 km to horizon)

Unmanned, Untethered

Persistence: 1 year on station

Develop long term clutter maps

Learn normal patterns

1 min for attitude change

Stationary

Improved Doppler precision

Continuous Coverage

Airship Size: >50m diameter, 150m length

Accommodate large aperture

Limited payload prime power and weight

No stowing, launch or deployment

required

Easy to maintain

Near Space Platforms:

Stationary Stratospheric Airships for 24/7 coverage

(10)

NESTRAD (NEar-Space Tsunami RADar): System Design

45°

Max. scan angle (elevation)

-15 dB

Side lobe level

60°

Max. scan angle (azimuth)

51 dBi

Antenna Gain

30 m

2

Antenna Aperture

3 dB

Noise Figure

3 dB

Path Loss

VV

Polarization

5 GHz

Frequency

10×3 m

2

phased array

Antenna

Sy

stem

Sy

stem

AntennaAntenna

(11)

100% FMCW

Duty Cycle

150 MHz

Bandwidth

800 Hz

PRF

1.25 ms

Pulse Width

100 W

Peak Power

13 dB

SNR

87°

Incidence angle

-30 dB

Backscatter cross section

2000 m

Azimuth resolution

1 m

Range resolution

Waveform Parameters

Far range

100 % FMCW

Duty Cycle

150 MHz

Bandwidth

2 kHz

PRF

0.5 ms

Pulse Width

1 W

Peak Power

40 dB

SNR

20°

Incidence angle

-20 dB

Backscatter cross section

100 m

Azimuth resolution

3 m

Range resolution

Waveform Parameters

Near range

Far range resolution: 2

×

0.5 km

Near range resolution: 100 × 100 m

We can resolve tsunami shadows: tens

×

thousands of kms !

(12)

NESTRAD: Waveform Design (Doppler Mode)

N = 1000

(dwell-time=1s)

Τ

c

= 10 ms

PRT = 1ms

1

1

1

SNR

n





exp

2

2

c

t

t

t

n

1

2

2

1

N

s

cm

PRT

V

2

.

5

/

2

1

2

s

cm

PRT

V

1

,

07

/

2

1

2

SNR = 10 dB

SNR =

20 dB

(13)

RC

S

500 km

NESTRAD concept

NESTRAD

D

o

p

p

ler

Altimetry

21 km

RCS

-mode

spacial coverage:

approx

. 1000 km

(14)
(15)

Resolution @ 150 MHz

Bandwidth and 10 m

antenna length:

5 m azimuth

1 m range

NESTRAD additional modes: SAR and InSAR

NESTRAD

NESTRAD

(16)

NESTRAD additional modes: ATI (along-track interf.)

NESTRAD

Antenna devided in along-track direction

moving target identication or motion

detection (e.g. ocean currents, ships

and traffic monitoring)!

Min. resolvable radial target velocities:

v

min

= v

P

/(2L) = 0.025 m/s = 0.09 km/h

(17)

Real Road Traffic near Chiemsee on 16. July 2007

(18)

NESTRAD additional modes: bistatic geometries

increase of power

(forward scattering)

NESTRAD II

NESTRAD I

bistatic / specular scattering

(increase of coherence)

additional / complementary

information

(19)

What could be done …

Seldom do Tsunami happen!

NESTRAD must be conceived as a

multi-purpose sensor

serving e.g.

Tsunami detection

Sea state monitoring

Ship tracking (traffic, piracy, etc.)

Reconnaissance and surveillance

Weather monitoring

Hurricane monitoring

Volcano monitoring

Flood monitoring

Traffic monitoring

Platform:

can carry

multiple sensors

(radar, GNSS, optical, infrared, etc.)

References

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