Velocity measurement
The measurement of the flow velocity depends on the mounting position of the SQ sensor and the water flow conditions at the site. These conditions are defined by the settings under Velocity and Tech. velocity (v)
Viewing direction
The viewing direction of the SQ sensor in relation to the flow direction of the river, either upstream or downstream.
Possible flow directions
The setting to define if the river only flows in one direction or if two flow directions can occur, e.g. under tidal influence (see also Flow velocity).
Measurement duration
The duration of a single measurement. During this time the velocity radar signal is recorded and the radar spectrum is calculated. Generally, a measurement duration of 30 s is recommended. For very calm rivers a longer measurement duration should be selected.
Minimum velocity
The minimum expected velocity. No lower velocities are considered.
Maximum velocity
The maximum expected velocity. The velocity measurement is optimized for this setting. Usually a value of 5 m/s is adequate.
Meas. spot optimization
The expected velocity distribution in the measurement spot. The more irregular the distribution, the wider the selected spectral band width used for the velocity measurement.
For the first measurements at a new site the option standard is recommended. Later on, the measurement may be optimized by selecting another option.
Measurement type
The velocity measurement can either be performed continuously in one block, or in a sequence of five consecutive blocks with breaks in between. The sequenced method is more representative but slow-er. By default the selection should be set to continuous.
Criteria for invalid measurements and their handling
Velocity measurements can be defined as invalid by the criteria quality (SNR) and opposite direction content (Stop, min. quality (SNR) to Stop, replace value). These criteria and the handling of invalid measurements are controlled with these settings. Please refer to Tech. velocity (v) for details.
Inclination measurement
As described in Flow velocity each velocity measurement has to be corrected for sensor inclination. If the SQ sensor is mounted stably it is sufficient to measure the installation angle with the first measurement after a sensor restart. If the sensor can move it is recommended to perform an inclination measurement with each velocity measurement.
View spectral distribution
With this function the SQ radar sensor is switched into spectrum mode and the spectra are recorded by the SQ-Commander and displayed in the Measurement tab. Please refer to Radar spectrum for more details on velocity radar spectra.