[Acoustics] High number of bad ensembles

[Pedro Moreira]

Hello,

I wonder if any one you have experienced ADCP river discharge measurements with exaggerated number of single ping bad ensembles (40% and even 60% of total ensembles) and identified the cause. 

Amazon basin is a challenge for river measurements with doppler effect based equipments. Madeira river has a high sediment concentration ( > 2.000 ppm) and mooving bottom at Porto Velho site. The measuments were made by ANA (Brazilian National Agency) and HIBAM (Hydrology of Amazon Basin) with a 300 and 600 kHz WorkHorse Monitor ADCP, Winriver wizard commands, maximum depth = 35 meters and averaged discharge between 23.000 and 31.000 m3/s . 
Even though range is improved by higher sediment concentration some colleagues think over mooving bottom as a probable cause. Others believe in bed rugosity and/or bed fractured rocks. No problem with bad bins (between 0 and 1%).
As a test, I suggested to field personnel to use once the user command WB1, trying to cross the bottom material obstacle. RD Instruments expert command description says that: sets profiling mode bandwidth (sampling rate).  Smaller bandwidths allow the ADCP to profile farther, but the standard deviation is increased by as much as 2.5 times., even knowing that 300 and 600 kHz maximum ranges are 60 and 130 meters, respctively. Standard deviation could be reduced increasing the depht cell size, averaging ensembles ou using multi pings ensembles. No improvment was achieved.

If requested I can upload raw and configuration files to a FTP folder for analysis.

Thank you,

Pedro Moreira
CPRM - Brazilian Geologic Service
Hydrology Departament
Rio de Janeiro - Brasil
55 21 2546-0352
 
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