b"Water SurfaceTransducer Depth TransducerScreeningBlanking DistanceDistance Distance that corresponds to electronics and transducer recovery time (after ping)Side Lobe(lower sound intensity)ProfiledMain Beam Area(higher sound intensity)Side Lobe(lower sound intensity)Area of side lobe interferenceFigure 3Simplified illustration showing the sound propagation from a single transducer and the unmeasured areas in cross-section.The blanking distance is the region directlyEven if input before the measurement, this setting adjacent to the ADCP where no measurementcan be changed, post-measurement, to include all of velocity is made, dictated by the physics andvelocity cells measured. The ADCP will measure electronics, and cannot be changed by the user. and record velocity cells from the first cell past the Note that this is a function of the ADCPs transducerblanking distance to the maximum depth.construction, acoustic frequency, speed of sound in water, and firmware programming. A primary use for the screening distance parameter is boat-mounted applications, where the setting can The screening distance is a user-adjustable input tobe used to filter out the flow disturbance from the exclude velocity cells measured by an ADCP from aboat's hull. For example, consider a measurement discharge calculation. It is measured from the wateron the Amazon River made using a RiverSurveyor surface and needs to be greater than the defaultM9 mounted over the side of a ferry boat with a unmeasured distance equal to the transducer depthdraft of 1m. The transducer depth was 0.25m. The + blanking distance (Figure 3). The purpose ofscreening distance parameter was used to exclude the screening distance is to exclude any measuredvelocity cells affected by flow disturbance generated velocities near the ADCP where there is knownby the boat's hull.or suspected flow disturbanceand therefore not representative of the naturally occurring waterAnother common example is the USGS default velocity in the channel.screening distance of transducer depth + 0.52ft for the RiverSurveyor M9. They have implemented this One important clarification is that the blankingas standard practice for using the M9 after research distance is referenced from the face of the verticalshowed that the M9 3MHz transducers in pulse acoustic beam (the lowest point on the instrumentcoherent mode register flow disturbance created by housing). In contrast, the screening distancethe M9 housing. This default screening distance is an is referenced from the water surface. It is alsoautomatic option upon installing RiverSurveyor Live.important to emphasize that the screening distance can be input before or input/adjusted after a measurement in post-processing. Changing thisHave questions about blanking or setting does not affect the raw velocity cell datascreening distance? We have answers. measured by the ADCP. Contact us at Support@SonTek.com!Whos Minding the Planet? 63"