# Simrad angular position calculations

Angular positions in Simrad data files are stored as integers with units *phase steps*. These are interpreted as follows for each of the supported series of echosounder.

## Ex500

In relavent systems, the angles, represented by a pair of integers *i* (called phase steps), are stored as a 16-bit (two bytes) word. The most significant byte is the alongship (minor axis) angle. The least significant byte is the athwartship (major axis) angle.

The first bit of each *i* stores the sign, with 0 positive and 1 negative. The last 7 bits store the magnitude, in the range -127 to +127.

There are 64 phase steps in 180 degrees, such that

e = i × 180/64

Where:

e = electrical angle (degrees)

i = echosounder angle (phase steps)

The alongship and/or athwartship angle is defined as the mechanical angle, and is given as:

m = (e/sensitivity) - offset

Where:

m = mechanical angle (degrees)

e = electrical angle (degrees)

sensitivity = the value displayed on the Calibration page of the Variable Properties dialog box.

offset = the value for MajorAxisAngleOffset/MinorAxisAngleOffset displayed on the Calibration page of the Variable Properties dialog box.

## Ex60

The angles, represented by a pair of integers *i* (phase steps), are stored as a 16-bit (two bytes) word. The most significant byte is the alongship (minor axis) angle. The least significant byte is the athwartship (major axis) angle.

Each byte is interpreted as a *signed 2's complement* integer in the range -128 to +128.

There are 128 phase steps in 180 degrees, such that

e = i × 180/128

Where:

e = electrical angle (degrees)

i = signed integer (phase steps)

The alongship and/or athwartship angle is defined as the mechanical angle, and is given as:

m = (e/sensitivity) - offset

Where:

m = mechanical angle (degrees)

e = electrical angle (degrees)

sensitivity = the value read from the data file (visible under **File** on the Details dialog box).

offset = the value for MajorAxisAngleOffset/MinorAxisAngleOffset displayed on the Calibration page of the Variable Properties dialog box.

## EK80

Echoview reads angle data and calculates the electrical angle (e), then uses the equation for mechanical angle (m) to calculate angular position values for the angular position variable.

The mechanical angle is calculated as:

m = (e/sensitivity) - offset

Where:

m = mechanical angle (degrees)

Simrad electrical angle calculations use Simrad beam geometry. The mechanical angles are handled as

MajorAxis3dBBeamAngleandMinorAxis3dBBeamAngleand displayed on the Calibration page of the Variable Properties dialog box.e = electrical angle (degrees), calculated from complex or angle values read from the data file.

The Simrad EK80 BeamType and transducer/transceiver type determine the equations required to calculate the electrical angle. Recorded angle data types include Complex and Angle; they are processed differently. Special scaling requirements are used for split beam transducers with three sectors. The handling for electrical angle calculations is discussed in the manual '

Simrad EK80 Wide band scientific echo sounder Interface Specifications Release 2.0.0'.sensitivity = the value read from the data file (visible under

Fileon the Details dialog box).

MajorAxisAngleSensitivityorMinorAxisAngleSensitivityare displayed on the Calibration page of the Variable Properties dialog box.offset = the value for MajorAxisAngleOffset/MinorAxisAngleOffset displayed on the Calibration page of the Variable Properties dialog box.

#### See also

Simrad echosounders data files

Raw variables derived from Simrad data files

Simrad EK500 configuration

Simrad EK60 configuration