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

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

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.

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

Where does UDAS get COG ? UDAS Follows True Course

How accurate is UDAS Course?

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

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?

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

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