Session VII b Navigation Systems Using an “Accuracy Statement”

The GPS Must be a Marine Grade GPS, the one used for driving is not appropriate Turn it on at least 3 minutes prior to taking a reading, so it can acquire the required minimum of 4 satellites. If your GPS reports HDOP, say so in the accuracy statement, else EPE is assumed. HDOP = Horizontal Displacement of Position (Represents Quality) EPE = Estimated Position Error (Possible number of feet off) 2

This is the standard “Accuracy Statement” 1.A Garmin GPS 76 GPS with WAAS enabled, operating in 3D Differential was used to fix the aid. On-scene EPE was 7.0 feet. Pre-underway accuracy was checked with another GPS. 2.A Hummingbird Wide 100 echo sounder was used to take the depth. Pre-underway accuracy was checked at the dock with a hand-held echo sounder. Correction for the transducer is 0.8 feet. The on- scene Substation was Neponset River on Boston. 3.The reported fix and depth were taken approximately 3 feet from the aid. 3

Some contents of the “Accuracy Statement” are fixed Manufacturer’s name and model numbers of all the electronic measuring equipment being used. Special GPS features that measure quality. A digital record of the equipment being used is established. The next slide shows this data. 4

ACCURACY STATEMENT: 1.A Garmin GPS 76 GPS with WAAS enabled, operating in 3D was used to fix the aid. On-scene EPE was 7.0 feet. Pre-underway accuracy was checked with another GPS. 2.A Hummingbird Wide 100 echo sounder was used to take the depth. Pre-underway accuracy was checked at the dock with a hand-held echo sounder. Correction for the transducer is 0.8 feet. The on-scene Substation was Neponset River on Boston. 3.The reported fix and depth were taken approximately 13 feet from the aid. 5

Pre-underway Check Review of Measuring Equipment Step 1 – The GPS is checked. Step 2 – The Echo Sounder is checked. The next slide shows how you validated the accuracy of your electronic measuring equipment before getting underway. 6

ACCURACY STATEMENT: A Garmin GPS 76 GPS with WAAS enabled, operating in 3D Differential was used to fix the aid. On-scene EPE was 7.0 feet. Pre-underway accuracy was checked with another GPS. A Hummingbird Wide 100 echo sounder was used to take the depth. Pre-underway accuracy was checked at the dock with a hand-held echo sounder. Correction for the transducer is 0.8 feet. The on-scene Substation was Neponset River on Boston. The reported fix and depth were taken approximately 13 feet from the aid. 7

Equipment Accuracy checks when on scene at the aid GPS quality checks: –Record the 3D – needs 4 or more satellites. –Record the EPE – should be under 20 feet, or –Record the HDOP – should be between 1 and 2 Echo Sounder quality checks: –Sanity check for accuracy. –Record the H.O.T. – Height of Tide. –Record the Substation used. Distance off PATON. –Record on the Accuracy Statement. The next slide demonstrates this data. 8

ACCURACY STATEMENT: A Garmin GPS 76 GPS with WAAS enabled, operating in 3D was used to fix the aid. On-scene EPE was 7.0 feet. Pre-underway accuracy was checked with another GPS. A Hummingbird Wide 100 echo sounder was used to take the depth. Pre-underway accuracy was checked at the dock with a hand-held echo sounder. Correction for the transducer is 0.8 feet. The on-scene Substation was Neponset River on Boston. The reported fix and depth were taken approximately 13 feet from the aid. 9

Four Easy Steps Step 1. Maintain a copy of an “ Accuracy Statement ” on your computer’s desktop, updated with the fixed features of your GPS and Echo Sounder. Usually, this data doesn’t change unless you change OPFACs. Step 2. Update with your pre-underway data checks. Normally, this data stays the same for the PATONs being verified during the same patrol. Step 3. Update with your on-scene data checks. This data is recorded for a specific PATON. Step 4. Copy and paste the “ Accuracy Statement ” to your “ 7054 AV Verification Report.” 10

7054 Verification Report Copy the “Accuracy Statement” from your desktop and paste it to your “7054 AV Verification Report.” A special field is provided for this purpose. 11