HTI sample data to Sv, TS and angular position

Values in sample files

HTI Sample (.smp) files that contain all calibration and settings information have the following values for each sample.

HTI Sample (.smp) files which require .cfg and .cal files to be added to a fileset, will also have the following values for each sample. Refer to HTI data files for more information.

Value

Description 

ang_UD

The electrical angle (phase difference) between the up and down halves of the split-beam transducer (see About beam geometry)

ang_LR

The electrical angle (phase difference) between the left and right halves of the split-beam transducer (see About beam geometry)

det20

The received voltage signal with 20Log(R) TVG applied and absorption (alpha) losses removed

det40_i

The in phase component of det40

det40_q

The quadrature component of det40

det40

det40 is the received voltage signal with 40Log(R) TVG applied and absorption (alpha) losses removed. Sample files created before April 2003 contain a single det40 value for each sample. Sample files created after April 2003 contain a det40_i and det40_q value for each sample. When Echoview reads a sample file containing det40_i and det40_q it combines them to calculate det40 as follows:

Calculating Sv, TS and angular position

For each sample Echoview displays in an echogram it will calculate as required:

Note: The conversions on this page are derived from the HTI Operator's Manual for the Model 241/243/244 Split Beam Digital Echosounder System (Version 1.7 1998) and through correspondence with HTI directly.

Calculation of ping time

The ping time is stored in the .smp file in the ping header. Where the a ping has the same time as the previous ping, Echoview will ignore the recorded ping time and recalculate the ping time by adding the relevant period interval (stored in the .cfg file or .smp file) to the time of previous ping (in the file).

Calculation of sample range

The range of the sample is calculated as follows:

fs = 12 kHz - the known sampling frequency

Ts =  c / fs  - the sample thickness in meters (where c is sound speed and is read from the .cfg file or the .smp file)

Range = Ts x ( i - 0.5 ) where i is the number of the sample within the ping starting from 1

Calculation of Sv, TS and angular position

Sv, TS and angular position are calculated according to:

Sv = 20log(det20) - SL - RG - G20 - TVG - Xcorrection - 10log(πcBτe) + Cal

TS = 20log(det40) - SL - RG - G40 - TVG + Cal

minor axis angle = ang_UD / αV

major axis angle = ang_LR / αH

Where:

Cal = The CalibrationOffset entered on the Calibration page of the Variable Properties dialog box in Echoview (default = 0)
SL = Source_Level_n where Transmit_Power = Transmit_Power_n
Xcorrection = 20log(Xcollection/Xcalibration)
τe = τ if Chirp_bandwidth = 0
  = 0.72 ms if Chirp_bandwidth = 2.5 kHz
  = 0.36 ms if Chirp_bandwidth = 5.0 kHz
  = 0.18 ms if Chirp_bandwidth = 10.0 kHz

and whenever required, Echoview reads from the relevant .cfg and .cal files or directly from .smp files containing calibration and settings data:

Symbol

Name

Units

File

Section

 

Chirp_BandWidth

kHz

.cfg

[Sequence_s SamplePeriod_p Settings]

 

Period_Interval  

s

.cfg

[Sequence_s SamplePeriod_p Settings]

τ

Pulse_Width  

s

.cfg

[Sequence_s SamplePeriod_p Settings]

RG

Receiver_Gain  

dB

.cfg

[Sequence_s SamplePeriod_p Settings]

c

Speed_sound   

m/s

.cfg

[Sequence_s SamplePeriod_p Settings]

 

Transmit_Power

dB re 1W

.cfg

[Sequence_s SamplePeriod_p Settings]

Xcollection

Tvg_Crossover  

m

.cfg

[Sequence_s SamplePeriod_p Settings]

TVG

Tvg_Gain

-

.cfg

[Sequence_s SamplePeriod_p Settings]

B

Beam_Pattern_Factor

-

.cal

[Beam Dimension Values]

αH

Horizontal

-

.cal

[Ratio Values]

αV

Vertical

-

.cal

[Ratio Values]

SL

Source_Level_n   

dB

.cal

[Source Level Values]

G20

Log_20

dB

.cal

[Through System Gain]

G40

Log_40

dB

.cal

[Through System Gain]

Xcalibration

Tvg_Crossover

m

.cal

[Through System Gain]

 

Transmit_Power_n

dB re 1W

.cal

[Transmit Power Settings]

Notes:

See also

HTI data files

Raw variables derived from HTI data files