1. By: LT ‘Chuck’ Williams
Correcting Wind Speeds
for vessel movement
By:
LT ‘Chuck’ Williams
Note: All Decimal Days are for 21 July, 2006.

2. Brief Outline Position Variability UDAS COG UDAS SOG
How are True Winds calculated?
Heading input from GPS vs. True Winds
Results / Conclusions
Further Studies
Data Collection

3. GPS Position(s)
First we will look at Positions based on a number of instruments that UDAS records
Visually they are very close.
Next zoom in to get a closer visual idea.

4. Variability This Course is over approximately 2.6 hours of data.
The reason for using 2.6 hours was difficulties in ingesting the abundance of Raw Data
MAtLab did not like the ‘$’ and would not ingest the data properly
MS Excel would only do the first 2.6 hours
Note a period of relative low variability
This period will be shown in the next slide to correspond to the period when the ship was moving (~10 kts)
The periods that we were on station had high course variability
and unfortunately were the periods that I focused on
The variabilities in speed were less pronounced
At low speeds (near DIW)
At higher speeds

5. Where does UDAS get COG ?
UDAS Follows True Course

6. How accurate is UDAS Course?

7. How accurate is UDAS Speed (kts)?
Speed (applying various filters and running means to raw GPS data) was always lower than the Raw data.
Difference was < 1 kt  minimal impact

8. Heading vs. True Wind
I took most of my project looking at COURSE and Speed. Towards the end of my project I discovered that another line of code from GPS gave heading
If you take and subtract the Relative winds from the True Winds, what should be left is the Ships heading
But is this so?

9. Results / Conclusions
Positions for all instruments were fairly accurate
When measured directly from GPS:
There are always variations in Ships Speed
These variations increase dramatically at low speeds
There are always variations in Ships Course
There are minimal variations in the heading
When measured directly from UDAS:
Speed (applying various filters and running means to raw GPS data) was always lower than the Raw data.
Difference was < 1 kt  minimal impact
Seems to use a ~60 second running mean, then extracts every 36th Second.
36 seconds is the time to complete one loop of data collection
UDAS COG Follows True Course
GPS Heading and UDAS Gyro very similar

10. Further Studies If study is repeated
Have ship do ONE or more circles
Have someone look into the MatLab Signal Browser
Can more correctly remove ship’s movement (pitch / roll)
Etc