Vaisala IRIS - Radial Velocity Correction

Note that A
-1
is the transpose of A. Where the vectors are defined as:
x =
East
Nortℎ
Up
x′ =
Towards rigℎt
Towards bow
Towards zenitℎ
B.1.2
Radial Velocity Correction
The scalar radial velocity of the scatterers V
R
can be expressed as:
V
R
= V
R meas
− V
R sℎip
where V
R meas
is the Doppler velocity measured by the signal processor and V
R ship
is the
radial velocity correction for ship motion. The radial velocity correction is found by taking
the dot product of the antenna vector x in earth coordinates with the velocity of the
antenna in earth coordinates y
A
, as follows:
V
R sℎip
= x ⋅ y
A
⋅
The antenna vector is a unit vector pointing in the direction of the antenna which depends
on the true (earth relative) azimuth and elevation of the antenna, as follows:
x =
sin AZ cos EL
cos AZ cos EL
sin EL
AZand EL are eartℎ relative
These are known from the antenna controller. Thus, the problem is to determine the y
A
, the
velocity of the antenna.
The velocity correction used in IRIS allows for the following types of ship motion sensing:
Inertial Navigation Unit (INU)
(INU Case) The INU is typically placed close to the antenna. The INU reports pitch, roll,
and heading (and their rates of change), as well as the east, north and vertical motion
(u, v, w). In this case, the INU is used as the ship reference point.
Gyro System with GPS
(Gyro Case) The gyros report pitch, roll, and heading (and their rates of change). Mean
translational motion of the center of the ship (u, v, w) is obtained from a GPS or other
navigational system. In this case the ship center of rotation is used as the ship
reference point.
Appendix B – Radial Velocity Correction
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