[Acoustics] RE: Acoustics Digest, Vol 29, Issue 3

[Randy Marsden]

Pedro,

Please send the data and configuration files to RD Instruments field
service for analysis. You can put them in the incoming folder at
"ftp.rdinstruments.com" and send an email to rdifs at rdinstruments.com .

Randy Marsden
Water Resources Applications Scientist
Teledyne RD Instruments
 
Ph: 858-693-1178
email: rmarsden at rdinstruments.com


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Today's Topics:

   1. High number of bad ensembles (Pedro Moreira)


----------------------------------------------------------------------

Message: 1
Date: Thu, 8 Dec 2005 18:25:08 -0200
From: "Pedro Moreira" <pneto at rj.cprm.gov.br>
Subject: [Acoustics] High number of bad ensembles
To: <Acoustics at simon.er.usgs.gov>
Cc: Newton de Oliveira Carvalho <newtonoc at openlink.com.br>,
	"naziano.filizola" <naziano.filizola at ig.com.br>
Message-ID: <002301c5fc35$7bea3520$cf10000a at pedro>
Content-Type: text/plain; charset="iso-8859-1"

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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