radars pointing rivers water surface velocity & bed profiling

Radars Pointing Radars Pointing RiversRivers

Water Surface Velocity Water Surface Velocity &&

Bed Profiling Bed Profiling

OUTLOOKOUTLOOK Following monitoring practice in ocean and

atmosphere river monitoring moves toward remote sensing practices

USGS has put forth a team (Hydro 21) for remote, non-contact, river monitoring to replace the over 7,000 stream gages

Remote sensing might revolutionize the current multi-task (discharge – velocity – depth - slope) river monitoring practice

Intensive and extensive developments needed to overcome practical implementation

MEASUREMENT CANDIDATESMEASUREMENT CANDIDATESWave-based techniques: electromagnetic radiation

and sound (magnetic and pressure waves): radars, image velocimetry, sonars

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

http://www.geocities.com/kbachhuber2000/ems.html

RADARSRADARS

Most extensive tested so far for riverine environment

Wavelenghts from microwaves to radio waves Doppler (coherent) or non-Doppler systems Various configurations Measurement objectives:

– free-surface velocities– bathymetry– stage

OPERATING PRINCIPLEOPERATING PRINCIPLEVelocity: Bragg scattering

Issues:- what represents v?- how to relate v to velocity

in the water column?- how to get the proper free-

surface wavelength (only one detected for a given radar wavelength)

v

f'f

v = fd / (2 cos ), (f d = f-f')

v : water velocity: wave lengthfd : Doppler frequency

KOWACO

OPERATING PRINCIPLEOPERATING PRINCIPLEConfigurations: Monostatic (same antenna for emission

and reception)- Scanning strategy- Assumptions:

- Velocity constant over spot- Streamwise direction known

OPERATING PRINCIPLEOPERATING PRINCIPLEConfigurations: Bistatic (distinct antennas)

RADARS: PROs & CONsRADARS: PROs & CONs

PROs CONs Analytical support Directional velocity measurement Independent of lighting Local (point) measurement Visual output Signal (not intuitive) as output See issues Measurements F(λ, Λ, geometry) Cost

OPERATING PRINCIPLEOPERATING PRINCIPLEGround Penetrating Radar (GPR)

for Bathymetry: reflection of pulsed high-frequency electromagnetic waves

Issues:- Site specific f(surface and

subsurface permittivity)- Performance f(speed of sound in

the measured media, reflectivity, depth of investigation, resolution, interferences, calibration)

http://fate.clu-in.org/gpr.asp?techtypeid=41

GP RADARS: PROs & GP RADARS: PROs & CONsCONs

PROs CONs Analytical basis Complex signal processing Unique for such measurements See issues Visual output Cost

SELECTED RADAR SELECTED RADAR CONFIGURATIONS & CONFIGURATIONS & MEASUREMENTSMEASUREMENTS

Microwave Water Surface Current Meter (KOWACO) UHF RiverSonde Radar (CODAR) Ground Penetrating Radars (MALA GeoScience AB) Flo-Dar (Marsh-McBirney Inc.) DEMO

Microwave Water Surface Current Microwave Water Surface Current Meter Meter (MWSCM-KOWACO)(MWSCM-KOWACO)

MWSCM SPECIFICATIONSMWSCM SPECIFICATIONS Detection Method : Microwave, Doppler effect Frequency : 10 GHz Measurement Range : 0.5~10m/s Measurement Angle :

– Vertical : 20 ~ 45°– Horizontal : 0 ~ 10°

Weight– Antenna : 4.9Kg, Signal processor : 4.2Kg

MWSCM VERIFICATIONMWSCM VERIFICATION

Korea Institute of Construction Technology

0 1 2 3 4 5Carridge velocity (m/s)

0

1

2

3

4

5

Mea

sure

d ve

loci

ty (m

/s)

Velocity Comparison

Vertical angle : 20 deg.

Vertical angle : 30 deg.

Vertical angle : 40 deg.

Vertical angle : 45 deg.

MWSCM MEASUREMENTSMWSCM MEASUREMENTSDaechung Dam

0

1

2

3

4

Velo

city

(m/s

)

0 40 80 120 160 200Distance (m)

20

30

Elev

atio

n (m

)

Taechung Dam

2433 m^3/s(EL. 31.40M)

1960 m^3/s(EL. 30.90M)

1593 m^3/s(EL. 30.24M)

999 m^3/s(EL. 29.42M)

Transmitter

Receiver

RIVERSONDE RADARRIVERSONDE RADAR

Barrick et al. (2003)

GPR GPR USGS Measurements with MALA GPR

Haeni et al. (2003)

DEMODEMOFLO-DAR FLO-DAR (Marsh-McBirney (Marsh-McBirney Inc.)Inc.)Doppler 24 GHz radar

http://www.marsh-mcbirney.com/classes/flo-dar_technology/

Instrument control: FFT of the Doppler shift

Output: channel discharge

DEMODEMOFLO-DAR FLO-DAR (Marsh-McBirney (Marsh-McBirney Inc.)Inc.)

VALIDATIONVALIDATIONFLO-DAR FLO-DAR (Marsh-McBirney (Marsh-McBirney Inc.)Inc.)

1. Best measurements: continuous foam layer (errors up to 10 %)

2. Good results: floating particles (2-3 mm diameter)

3. Poor results: controlled waves (errors up to 40%)

4. Not reliable: natural free surface waviness and lower than 0.5 m/s

Fo a m

So a p Bub b le r

Bub b le s

Fa nFLO -DAR

LDV

Liq uidLSPIV

24c m 79c m

10c m1c m

16.7c m