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 CANDIDATES
Wave-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 PRINCIPLE
Velocity: 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 PRINCIPLE
Configurations: Monostatic (same antenna for emission and reception)
- Scanning strategy- Assumptions:
- Velocity constant over spot- Streamwise direction known
OPERATING PRINCIPLEOPERATING PRINCIPLE
Configurations: 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 PRINCIPLE
Ground 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
Me
asu
red
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 MEASUREMENTS
Daechung 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 pBub b le r
Bub b le s
Fa nFLO -DAR
LDV
Liq uid
LSPIV24c m
79c m
10c m1c m
16.7c m