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.TH PATH 1 "Ultrasonics Lab"
.SH NAME
path - Generate Multipath Data
.SH SYNOPSIS
.B path [options]
.SH DESCRIPTION
This program generates 
projection data for
an ellipse.
The transducer is considered to have
a non-zero width and the two outermost
rays are used to approximate the multipath signal
that might be received experimentally.
No calculation is made of any effects due
to refraction.
Either the attenuation or the time of flight 
of the simulated received signals can be estimated.
All physical parameters of the experiment
(ellipse size, transducer size, etc.)
can be set from the command line.
.PP
This program operates in two distinct modes.
The first mode is used to generate
attenuated versions of the water path
signal.  
This is specified with the 
.B -g
option.
This data is later used as input to this program when calculating
the received signal in TOF mode.
.PP
In the second mode of operation
the received waveforms are calculated
and either the estimate of the TOF
or the attenuation is written into a file.
A file containing attenuated versions
of the water path signal is used to
estimate the time of flight.
See the
.B -g
option.
.PP
Projection data can be generated for either
Time-of-Flight or Attenuation tomography.
This is specified with the 
.B -t
and the
.B -a
flags.
The default is to calculate attenuation data.
.PP
There are many options.
.PP
.B File Options
.TP 10
.B if=water
In the generate mode this file contains
the time domain representation
of the ultrasound pulse that will be used for later calculations.
This binary waveform will be attenuated and written out
(see the 
.B gf 
and the
.B -g
options.)
The default is the file
.B  water.
.TP
.B gf=tof
The file contains the output from the generate mode
and is used as the input of the TOF estimation mode.
This file contains attenuated (frequency dependent)
versions of the water path signal.
The default file is
.B tof
.TP
.B of=for003.dat
In the estimation mode this file will contain the
estimated projection data.
If this argument is not specified then
the data is placed into 
.B for003.dat.
.PP
.B Mode Options
.TP 10
.B -g
specifies that attenuated versions of the water
path signal should be calculated and saved.
These waveforms can later be used as input to
this program when calculating TOF projection data.
.TP
.B -t
Generate TOF data. 
A file with attenuated versions of the
ultrasound pulse must be present 
(see the 
.B gf
option.)
.TP
.B -a
Generate attenuation data.
.TP
.B -m
Include the effect of multipath in 
the calculations.
This flag is normally turned off.
.TP
.B -d
Use spectral division to estimate attenuation coefficient.
Use of this flag also sets the
.B -a 
flag.
It is normally not set.
.TP
.B -s
causes the spectrums to be saved as they are computed
in the file
.B spectrum.
Each spectrum will be 256 floating point numbers.
Each sample of each projection will be saved.
.TP
.B -p
turns off printing of program parameters.
.PP
.B Physical Constants
.TP 10
.B a=4
is the length (in cm) of the semi-major axis of the
ellipse. 
.TP
.B b=4
is the length (in cm) of the semi-minor axis of the
ellipse.
.TP
.B width=1
is the width of the transducer in cm.
.TP
.B dis=25
is the distance between the transducers.
.TP
.B vw=1500
is the velocity of sound in water.
.TP
.B c=1550
is the velocity of sound in the object.
.PP
.B Experimental Set Up
.TP 10
.B n=50
represents the number of samples per projection.
.TP
.B k=1
gives the number of projections.
.TP
.B level=2
is an integer number representing the
threshold for TOF calculations.
This number will be dependent on the 
input waveform used.
.TP
.B dt=.01
is the sampling time in micro-seconds.
.PP
.B Attenuation Estimation Parameters
.TP 10
.B gamma=1
represents the coefficient that the frequency is raised to.
.TP
.B gammap=1
is gamma prime.
.TP
.B alpha=.05
is the slope of the frequency dependent attenuation.
.TP
.B sigma=3.0
is the standard deviation of the power spectrum.
.TP
.B b1=3 b2=10
are the lower and upper frequency bands for
the frequency division method to estimate attenuation.
.SH FILES
.TP 10
water
water path signal for signal generation.
.TP
transform
is the spectrum of the transmitted pulse.
It is used when in calculating the attenuation
coefficient.
This file is should contain 256 floating point numbers
(128 real followed by 128 imaginary.)
.TP
tof
is the default name for the TOF signals.
It is generated with the
.B -g 
option and the data is used when
calculating TOF coefficients.
.TP
for003.dat
is the default output file for either
TOF or attenuation data.
.TP
spectrum
is the name of the file where the spectrums of
the received waveforms are stored.
See the
.B -s 
option.
.SH SEE ALSO
Crawford, Carl, 
"Multipath artifacts in Ultrasonic Transmission Tomography,"
Purdue University Electrical Engineering Department Technical Report,
TR 81-43,
December 1981.
.SH DIAGNOSTICS
All IO errors are indicated.
.SH BUGS
Very little error checking.