reflect_loss_rayleigh Class Reference
[Ocean Boundaries]

Collaboration diagram for reflect_loss_rayleigh:
Collaboration graph
[legend]

Detailed Description

Models bottom loss from a flat fluid-solid interface.

Includes the effects of both compression and shear waves in the bottom. This model is only used for bottom reflection. Note that the Rayleigh model is frequency independent because all of the frequency terms cancel out.

The effect of attenuation is incorporated into the model as a complex component of the sound speed:

\[ c_w = c_{rw} \]

\[ c_b = c_{rb}-i \frac{ \alpha_b c_{rb}^2 }{ \omega } \]

\[ \alpha_b = \frac{ \alpha_{\lambda b} }{ \lambda_b 20 \log{e} } \]

where:

The effect of absorption on the in-water sound speed is assumed to be negligible.

The complex reflection coefficient is modeled as a combination of the acoustic impedances for compressional and shear waves. The effect of shear on the in-water impedance is assumed to be negligible.

\[ Z_{pn} = \frac{ \rho_n c_n }{ cos(\theta_{pn}) } \]

\[ Z_{sb} = \frac{ \rho_b c_{sb} }{ cos(\theta_{sb}) } \]

\[ Z_w = Z_{pw} \]

\[ Z_b = Z_{pb} sin^2(2\theta_{sn}) + Z_{sb} cos^2(2\theta_{sn}) \]

\[ R = \frac{ Z_b - Z_w }{ Z_b + Z_w } \]

where:

The angles between the ray and surface normal in each medium is computed using Snell's Law:

\[ \frac{sin(\theta_w)}{c_w} = \frac{sin(\theta_{pb})}{c_{pb}} = \frac{sin(\theta_{sb})}{c_{sb}} \]

Note that the sin() and cos() terms in this derivation have been inverted from the reference to take into account the difference between grazing angle and angle to the surface normal.

References:
F.B. Jensen, W.A. Kuperman, M.B. Porter, H. Schmidt, "Computational Ocean Acoustics", pp. 35-49.

Member Enumeration Documentation

Bottom types supported by table lookup feature.

Enumerator:
CLAY 
SILT 
SAND 
GRAVEL 
MORAINE 
CHALK 
LIMESTONE 
BASALT 

Constructor & Destructor Documentation

Initialize model with a generic bottom type.

Initialize model with impedance mis-match factors.

Uses an internal lookup table to convert into impedance mis-match factors.

Parameters:
type Generic bottom for table lookup of impedance mis-match factors.
reflect_loss_rayleigh ( size_t  type  ) 

Initialize model with a generic bottom type as integer representation.

Initialize model with impedance mis-match factors.

Uses an internal lookup table to convert into impedance mis-match factors.

Parameters:
type Integer representation of generic bottom type.
reflect_loss_rayleigh ( double  density,
double  speed,
double  att_bottom = 0.0,
double  speed_shear = 0.0,
double  att_shear = 0.0 
)

Initialize model with impedance mis-match factors.

Defined in terms of ratios to match commonly used databases.

Parameters:
density Ratio of bottom density to water density Water density is assumed to be 1000 kg/m^3.
speed Ratio of compressional sound speed in the bottom to the sound speed in water. The sound speed in water is assumed to be 1500 m/s.
att_bottom Compressional wave attenuation in bottom (dB/wavelength). No attenuation if this is zero.
speed_shear Ratio of shear wave sound speed in the bottom to the sound speed in water.
att_shear Shear wave attenuation in bottom (dB/wavelength).

Member Function Documentation

complex< double > impedance ( double  density,
double  speed,
double  attenuation,
double  angle,
complex< double > *  cosA,
bool  shear 
) [private]

Computes the impedance for compression or shear waves with attenuation.

Compute impedance for compression or shear waves with attenuation.

Includes the Snell's Law computation of transmitted angle.

Parameters:
density Ratio of bottom density to water density Water density is assumed to be 1000 kg/m^3.
speed Ratio of compressional sound speed in the bottom to the sound speed in water. The sound speed in water is assumed to be 1500 m/s.
attenuation Compressional wave attenuation in bottom (dB/wavelength). No attenuation if this is zero.
angle Reflection angle relative to the normal (radians).
cosA Returns the cosine of the transmitted angle computed using Snell's Law.
shear Treat impendance for shear instances as special cases.
void reflect_loss ( const wposition1 location,
const seq_vector frequencies,
double  angle,
vector< double > *  amplitude,
vector< double > *  phase = NULL 
) [virtual]

Computes the broadband reflection loss and phase change for a single location.

Computes the broadband reflection loss and phase change.

Parameters:
location Location at which to compute attenuation.
frequencies Frequencies over which to compute loss. (Hz)
angle Reflection angle relative to the normal (radians).
amplitude Change in ray strength in dB (output).
phase Change in ray phase in radians (output). Phase change not computed if this is NULL.

Implements reflect_loss_model.


Member Data Documentation

const double _att_bottom [private]

Compressional wave attenuation in bottom (nepers/wavelength).

const double _att_shear [private]

Shear wave attenuation in bottom (nepers/wavelength).

const double _density_bottom [private]

Bottom density (kg/m^3).

const double _density_water [private]

Density of water (kg/m^3).

const double _speed_bottom [private]

Compressional speed of sound in bottom (m/s).

const double _speed_shear [private]

Shear speed of sound in bottom (m/s).

const double _speed_water [private]

Speed of sound in water (m/s).

Bottom types lookup table.


Generated on 4 May 2015 for USML by  doxygen 1.6.1