A proposal of a self-checking quantitative echo sounder

                                   Masahiko Furusawa

                              Tokyo University of Fisheries
                        4-5-7 Kounan, Minato Tokyo, 108 Japan
                             E-mail:frsw@tokyo-u-fish.ac.jp

     There are some  important problems, which cannot  be easily resolved,  in   the 
acoustic estimation method of fish abundance:  limitation in single echo measurements 
(fish  number in  sampling  volume  must be  small),  transducer motion  error,  fish 
avoidance  effect  to surveying  vessel,  target    strength (TS)  variability  by  fish 
behavior and  swim-bladder condition, and so  on.  Most important  point is that  we 
could not  easily notice the deterioration  in measured results by  these problems and 
have a possibility to accept the results without checking the reliability.  
     One  solution for  such  problems  is comparisons  of  the results  obtained  by 
several  methods as  different  as  possible.   The  comparisons  will provide  useful 
information for checking the reliability of the measurements.
     Therefore, we propose a method or a quantitative echo sounder which enable us 
to  compare  results  from   several  processings:  1)  dual  beam  echo   integration 
(comparison  between  narrow   beam  and  wide  beam,  2)   multi-frequency  echo 
integration,  3)  split-beam  echo  counting    with  different  sampling  volumes,  4) 
split-beam TS measurement with different cutoff angles, 5) comparison of distribution 
density  obtained by  echo counting  and echo  integration, 6)  TS measurements  by 
split-beam principle and by division  of SV by  echo-count.  Some of these  methods 
have already been established and sometimes used in post processings.  Our proposal 
is that   some of these functions  should be included in  online process of a  sounder 
and the results compared, for example difference  in measured TS's, should be output 
as an indicator of reliability of the measurement.
     We discuss  on the problems,  each elementary method,  and how to  install the 
methods in a sounder.