b"Expert Advice:Acoustic ProfilersUnderstanding Blanking andScreening DistanceIsaacJonesSonTek, Product Segment ManagerScreeningBlankingIn the world of discharge measurementparticularly with acoustic instrumentsthere's a lot of specialized vocabulary, which can be confusing. Two terms we frequently hear confused, sometimes even by experienced users, are blanking distance and screening distance.Figure 1Blanking and screening distances illustrated in cross-sectional view. The user cannot change the blanking distance. Still, the screening distance Both terms refer to the region immediately adjacentcan be increased past the blanking distance to exclude disturbances.to an Acoustic Doppler Profiler (ADCP), from which no velocity data is included in the final discharge calculation. Yet, each has a distinct meaning andShore EdgeShore Edge justifies clarification.Estimate Top Estimate Estimate Starting with a brief primer on the underlying principles and physics, ADCPs use what are called monostatic transducers for measuring waterMeasured Areavelocity. A monostatic transducer both transmits and receives acoustic pulses. When the acoustic pulse is transmitted, it's reflected off tiny particles in the water, and that reflected pulse is recorded. Bottom EstimateFor the transducer to accurately receive and register the return pulse (critical for measuring velocity),Figure 2Cross-sectional view of the measured and unmeasured areas of an ADCP transect. The depth of the top unmeasured portion is defined by the the transducer must come to a complete rest (stoptransducer depth plus blanking distance OR the screening distance (referenced ringing) after transmitting the measurement pulse.to the water surface) if input.62 MISSION: WATER"