tetrascatt {tetrascatt}

tetrascatt

Description

This function computes the volumetric backscattering from a mesh of tetrahedrons.

Usage

tetrascatt(parameters, freq, mesh, kversor)

Arguments

parameters

a list including the parameters model, it must include

• cw: sound speed in the water in m/s

• g: g density constrast value, i.e g= rho1/rhow, where rho1 and rhow are the density values of the stcatterer and the media (sea water) respectively.

• h: h density sound speed contrast value, that is h= c1/cw where c1 is the sound speed of the stcatterer.

freq

an array of frequencies where the scattering is computed.

mesh

a list representing the mesh, it must include

• vertex: a data.frame with the vertex of the tetrahedra, each vertex has to have three coordinates.

• tetra: a data.frame containing the four index of each tetrahedra.

kversor

A three component vector that indicates the direction of the incident plane wave.

Value

List containing the frequencies, freq, and their corresponding Target Strength values, ts .

See Also

read_mesh to get this kind of list from a .mesh file.

Examples

#########################################
### Set  the Frequency range    ########
#########################################
fmin=12
fmax=400
freqs= seq(fmin,fmax, by=1)
# for tetrascatt freq unities  should be in Hz.
freq=freqs*1000
############################################################
########### Set properties of media and scatterer ######
############################################################
cw <- 1477.4 #soundspeed surrounding fluid (m/s)
rho <- 1026.8 #density surrounding fluid (kg/m^3)
g <- 1028.9/rho #density contrast
h <- 1480.3/cw #soundspeed contrast
my_parameters=list(cw=cw,g=g,h=h)

##########################################################
### Set the incident direction of the plane wave #####
##########################################################
kversor=c(1,0,0)

##########################################################
### Set the scatterer geometry #######################
##########################################################
# generates a pseudofile that has  the mesh of cube of one meter
# side
pseudofile=c("MeshVersionFormatted 2",
  "","Dimension 3","","Vertices","8","-0.5 -0.5 0.5 6 ",
   "-0.5 -0.5 -0.5 7 ","-0.5 0.5 0.5 9 ","-0.5 0.5 -0.5 11 ",
   "0.5 -0.5 0.5 16 ","0.5 -0.5 -0.5 17 ","0.5 0.5 0.5 19 ",
   "0.5 0.5 -0.5 21 ","","Edges", "12","2 1 5 ","1 3 8 ",
   "4 3 10 ","2 4 12 ","6 5 15 ","5 7 18 ","8 7 20 ","6 8 22 ",
  "2 6 25 ","1 5 26 ","4 8 29 ","3 7 30 ","","Triangles",
  "12","2 1 3 3 ","3 4 2 3 ","5 6 8 13 ","8 7 5 13 ",
  "2 6 5 23 ","5 1 2 23 ","8 4 3 27 ","3 7 8 27 ","2 4 8 31 ",
  "8 6 2 31 ","3 1 5 33 ","5 7 3 33 ","","Tetrahedra",
  "5","5 2 1 3 1 ","4 2 8 3 1 ","8 5 7 3 1 ","8 2 6 5 1 ",
  "3 2 8 5 1 ","","End","" )

# creating an empty temporary mesh file
temp_mesh_file=tempfile(fileext = ".mesh")
# loading the file with data.
writeLines(pseudofile,temp_mesh_file)


#reading the mesh
my_mesh=read_mesh( meshfile=temp_mesh_file)

# Computing the scattering
output= tetrascatt(parameters=my_parameters,freq,
                   mesh=my_mesh,kversor)

plot(output$freq,output$ts)

# unliking the teporary file.
unlink(temp_mesh_file)