4 down, 50 to go; an update on harbor surveys in the united states
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4 down, 50 to go; an update on harbor surveys in the United States. Dr. Gregory Johnson, Ruslan Shalaev, Christian Oates, Alion Science & Technology Capt. Richard Hartnett, PhD, US Coast Guard Academy Dr. Peter Swaszek, University of Rhode Island. ILA 36 – Orlando Florida - PowerPoint PPT PresentationTRANSCRIPT
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ILA 36 Orlando Florida16-17 October 2007Dr. Gregory Johnson, Ruslan Shalaev, Christian Oates, Alion Science & TechnologyCapt. Richard Hartnett, PhD, US Coast Guard AcademyDr. Peter Swaszek, University of Rhode Island
ILA 36 - Orlando, FL
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RequirementsAccuracy, availability, integrity, continuity Accuracy RequirementsAviation: NPA RNP 0.3 (309 meters)Maritime: HEA (8-20 meters)LimitationsSpatial and temporal variations in TOA observed by the receiver and presented to the position solution algorithm
10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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ASF corrected TOAsTo remove spatial component:Use published grid, interpolate between grid pointsIssues include grid density, regions of interest, and grid creation
To remove temporal component:Local monitor receiver, broadcast offsets over LDCIssues include correlation distance, monitor averaging, multiple monitor interpolation10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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Spatial ASF GridsHarbor Survey MethodologyConverting to a gridRequired grid densityPerformance examplesTemporal CorrectionsLDC architecture for live broadcast of differential correctionsPrototype eLoran ReceiverSample navigation performance10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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Identify the HEA area and generate sail plans that will cover all of the areas of interesttypically a 200m spacingTracks must be planned on inside and outside edges of channelsin general the area of interest needs to be over-bounded.Conduct field testStatic monitor somewhere in the harbor area (harbor monitor) Perform data collection mapping throughout the harbor; measure ASFs and GPS position10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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Convert the measured ASFs to relative ASFs by subtracting the reference site ASF for the corresponding times of the vessel ASF measurements.This eliminates any temporal variations (due to daily, seasonal, weather, or system timing effects) from the measurements. Create spatial ASF grid from tracks of relative ASFsProcedure developed and refined over a series of harbor surveysNew LondonNew YorkNorfolkBoston10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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Continuous vessel tracks in upper harborStatic locations in upper harborVesselVan on shore10/17/2007ILA 36 - Orlando, FL*
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10/17/2007ILA 36 - Orlando, FL*Vessel collected data at 25 static locations in the harborHeld station next to buoy, pier, etc.Van collected data at 19 static locations around the harbor
ILA 36 - Orlando, FL
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Different VesselContinuous Track in lower harborRepeat Upper harbor12 static locations10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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10/17/2007ILA 36 - Orlando, FL*8/22 magenta8/23 green8/24 - blue
ILA 36 - Orlando, FL
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USCG AUX Vessel MystOct 2006Nov 2006Test VanMar 2006Other vesselsMar, Apr 2006
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ILA 36 - Orlando, FL
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ILA 36 - Orlando, FL*10/17/2007
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ILA 36 - Orlando, FL
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Chesapeake Bay approach channel into Norfolk Harbor10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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ILA 36 - Orlando, FL
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Continuous tracks inner harbor, main channels, and entrance approach area10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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ILA 36 - Orlando, FL
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10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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ASFs/TOAs processed to remove receiver filtering and velocity vector toward towers (and time lag)Precise track computed using L1/L2 GPS data post-processed with GrafNav s/w using CORS reference stationsASFs recalculated using precise track position and unfiltered TOAsRelative ASFs calculated (ASFboat ASFref)10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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- Method for converting tracks to a grid- Required grid density- Performance examples
ILA 36 - Orlando, FL
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Overdetermined least squares estimation method akin to an inverse interpolation (ION GNSS 2006)10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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Recall standard linear interpolation: Given a function at grid points, we can interpolate a general F(x, y) by
with
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ILA 36 - Orlando, FL
Xj,Yk
Xj+1,Yk
Xj,Yk+1
Xj+1,Yk+1
X,Y
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Turn the equations around:
a, b, and F(x, y) are knownso each data point yields a linear equation in 4 unknownssolve large set of simultaneous linear equations to get grids10/17/2007ILA 36 - Orlando, FL*
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- LDC Architecture- Typical Spatial Correlation10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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10/17/2007ILA 36 - Orlando, FL*Seasonal Monitor SitesSeasonal Monitor SitesSeasonal Monitor SitesSeasonal Monitor SitesSeasonal Monitor SitesSeasonal Monitor ServerwxTxmtr grab ASF values from current SM data file Convert to offsets from reference value write in LDC format to file ftp file to server at LSULSUFTP ServerLoran TransmitterLoran TransmitterLoran TransmitterLoran TransmitterLDCLoran and GPS data at 1min intervalsArchived data
ILA 36 - Orlando, FL
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Each message is 45 bits and takes 24 symbols to transmit at 1 symbol/groupAt 8970 takes 2.15sec/msgTime: 5 every 64 messages or ~ every 27.5secASF data repeats every 2.3 min10/17/2007ILA 36 - Orlando, FL*Mon-6Msg-0Mon-6Msg-1Mon-6Msg-2Mon-6Msg-3Mon-6Msg-4Mon-6Msg-5Mon-4Msg-0Mon-4Msg-1Mon-4Msg-2Mon-4Msg-3Mon-4Msg-4Mon-4Msg-5TimeAlm.Mon-0Msg-0Mon-0Msg-1Mon-0Msg-2Mon-0Msg-3Mon-0Msg-4Mon-0Msg-5Mon-0Msg-0Mon-0Msg-1Mon-0Msg-2Mon-0Msg-3Mon-0Msg-4Mon-0Msg-5TimeAlm.Mon-3Msg-0Mon-3Msg-1Mon-3Msg-2Mon-3Msg-3Mon-3Msg-4Mon-3Msg-5TimeAlm.Mon-8Msg-0Mon-8Msg-1Mon-8Msg-2Mon-8Msg-3Mon-8Msg-4Mon-8Msg-5Mon-5Msg-0Mon-5Msg-1Mon-5Msg-2Mon-5Msg-3Mon-5Msg-4Mon-5Msg-5TimeAlm.Mon-9Msg-0Mon-9Msg-1Mon-9Msg-2Mon-9Msg-3Mon-9Msg-4Mon-9Msg-5Mon-1Msg-0Mon-1Msg-1Mon-1Msg-2Mon-1Msg-3Mon-1Msg-4Mon-1Msg-5TimeAlm.repeats
ILA 36 - Orlando, FL
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- Prototype receiver- Sample performance10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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10/17/2007ILA 36 - Orlando, FL*USCGA DDC Receiver TOAs demodulated LDC symbols real-time ASFs (for comparison)Matlab Script Lookup ASF grid value RS decode LDC symbols, Interpret transmitted data Apply transmitted temporal correction and reference station value Calculate position solutionOutput position as NMEA stringTransview Display Display position tracks of eLoran, Loran, and GPS systemsSatMate Receiver Loran positionNovAtel Receiver GPS position
ILA 36 - Orlando, FL
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10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
- Spatial ASF GridsNoise in the ASF measurements gets averaged out by the grid creation process500m grid spacing is typically sufficientSmaller spacing only if dictated by physical size of HEASmaller sizes just chase the noise in the measurementsHarbor Survey procedure has been established and provenTemporal ASFCorrect temporal value is critical to meeting HEA accuracyCurrently under investigation:Frequency (and filtering) of corrections Monitor site spacingEnd-state distribution architectureeLoran ReceiverIn areas where geometry / signal strength are poor, receiver performance becomes critical
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Alion New London TeamChristian OatesRuslan ShalaevMark WigginsKen DykstraUSCG AuxiliaryCaptain and crew of Launch #5 (New York)Captain and crew of Myst (New London)Captain and crew of Halcyon Lace (Norfolk)Captain and crew of Three Js (Boston)USCG Loran Support UnitCDR Chris NicholsLT Chris Dufresne10/17/2007ILA 36 - Orlando, FL*
ILA 36 - Orlando, FL
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[email protected]@[email protected]
ILA 36 - Orlando, FL
*Subbullets:GPS is vulnerable to intentional and unintentional jammingLoran provides an independent backup***In this paper we will describe a complete mapping of the Thames River, New London harbor, and approaches and the development of the ASF spatial grid using the inverse interpolation technique that we discussed in ION GNSS 2006. This real world data will also be used to examine the required grid density. This grid will be supplied to a user receiver for a demonstration of eLoran. In addition, differential corrections from a reference station at the Coast Guard Academy will be broadcast live from Seneca. This paper will discuss the development of the proof-of-concept eLoran receiver used to navigate the harbor in real-time with sub-20m accuracy using Loran TOAs, the ASF grid, and demodulated differential corrections.************- SM architecture and equipment discussed at ILA******