Vaisala IRIS - Velocity Correction Algorithm: INU Example

Cruising oshore at ~10 km (6.2 mi) and observe fixed ground targets while collecting IRIS
data. You may want to use a sector scan for this at low elevation. Verify the following:
• The real time color display should show ground targets at zero velocity.
• The Rays utility should show targets at zero velocity.
• PPI velocity products with a fine resolution velocity scale can be constructed to verify
the velocity correction.
If the corrected velocity of ground targets is not 0, you must isolate the problem. If the
antenna is properly stabilized, it is likely that both the INU (or Gyro system) and the antenna
controller are functioning properly. Therefore, the error is most likely due to alignment:
• The INU or Gyro system vertical and the antenna vertical must be co-aligned.
• The INU or Gyro system azimuths must be co-aligned.
• The moment arms must be properly measured.
The INU or Gyro/Antenna alignment can be checked with the sun tracking feature of the
Antenna utility. The moment arm measurement can be checked dynamically.
B.1.6.1 Dynamic Adjustment of Moment Arms
Measuring moment arms or extracting them from the ship's drawing can be dicult. The
athwartship component of the moment arm is usually the easiest measure and, in most
cases, the antenna is centered across the ship. This leaves the vertical and the for/aft
moments.
You can check these moments dynamically by observing ground targets in special ship or
antenna configurations.
1. Isolate the vertical component of the moment arm by scanning over the beam of the
ship while looking at on-shore clutter targets.
In this case, the velocity correction is dominated by the roll of the ship and the vertical
moment arm. The athwartship position error of the antenna moment arm has the same
eect. In this configuration, adjust the vertical moment arm in Antsetup until the
observed velocity of ground targets is 0. The ship must be rolling during this test.
2. Point the antenna fore or aft to observe clutter targets.
Adjust the fore/aft component of the moment arm to remove any remaining velocity
error. The ship must be pitching during this test.
B.1.7
Velocity Correction Algorithm: INU Example
1. V
R
= V
R
− V
R sℎip
2. V
R sℎip
= x ⋅ y
A
⋅
3. y
A
= y
I
⋅
+ A
⋅
−1
Δy′
AI
4.
y′ =
SpeedEast
SpeedNortℎ
Speed Up
as measured by tℎe INU
5.
Δy
AI
= antenna position
forward
port
over
tℎe INU position
IRIS Product and Display User Guide M211319EN-H
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