[Acoustics] Edge estimation errors for Tethered Boat deployments

["Rainville,François [CIS-WSB]"]

Edge estimation errors have likely been discussed in the past but I would like feedback for this as it relates to tethered boat deployment techniques. Also I would love to receive ideas on other methods being developed by operators to measure their edge distances from bridges.

Background:
As is known, the ADCP software uses verctors to calculate flow within the measured section while edges are computed using scalar values. Therefore, whatever the path we take with the ADCP, the measured area of flow will be corrected for any angle. However, the Q values at the edges then depend on how the distance to shore is measured.

Problem: 
If I cross a bridge diagonal to a river with a tethered boat, should not my estimate for the shore distance be perpendicular to the shore?  This is a concern because of techniques being adopted to estimate edge distances for tethered boats on bridges. A sighting perpendicular to the bridge to measure the distance between the last ensemble to the shore is sometimes used. This provides a cross section length in ways similar to what was done when Current Meters were used at similar sites. But in this case, my edge distances are then longer than if measured perpendicular to shore (like when measuring with ADCP from a boat). I might thus create a bias due to the deployment method employed. And this will be particularly important for smaller streams where edges may represent a greater percentage of the flow.  I am also curious about how angled current near the shore will end up being factored in properly for the edge mmt...

*- Can anyone confirm my concerns?
*- Did anyone look at the influence of edges on the total error for tethered boat deployments?  
*- What are the methods being adopted by other operators to measure edge distances from bridges?


Thanks

Francois Rainville