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 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:
For each sample Echoview displays in an echogram it will calculate as required:
the ping time
the sample range, and
the sample value(s) (Sv, TS or minor and major axis angles).
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.
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).
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
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
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: