Confluence Retirement

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λb= wavelength of the water wave or Bragg wave, Gigahertz; GHz

λ = wavelength of the transmitted radar signal; GHz

θ is the incidence angle

λ = c / v


c = speed of light = 3E8 meters per second, m/s

v = frequency in hertz; Hz


K-band radar transmission frequency = 24 GHz = 24E9 Hz

Incidence angle = 45 degrees

λb = 24 GHz x 29.98 cm/GHz3E8 m/s x 100 cm/m / 24E9 Hz / (2 x sin 45 degrees) = 0 .88 cm, which represents the small-scale surface waves that serve as scatterers. A wind-drift correction algorithm was developed and applied to the Red River of the North at Grand Forks, ND (Chris Laveau). The results are illustrated in figures 10 (raw discharge) and 11 (corrected discharge for wind drift).


v = 1055 Hz x 186,000 mi/x 5,280 ft/mi/(2 x 24.150 GHz x 10Hz/1 GHz)  =  21.5 fps          Eq. 3

Some portable and fixed-mount radars (Sommer Messtechnik) produce spectra, which offer a quantitative tool that serves as a “spin test” for electromagnetic instruments and can be used to qualify the value of surface-water velocity estimate. Figures 14 through 16 offer examples of good, fair, and poor spectra that can be used to assess the quality of the measurement.



Figure 1

Handheld radar (Stalker Pro II SVR) deployed from a bridge used to measure surface-water velocities concurrently while measuring point velocities with a FlowTracker at the y-axis in a cross section.