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ILA 36 Orlando Florida 16-17 October 2007 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 Slide 2 Requirements Accuracy, availability, integrity, continuity Accuracy Requirements Aviation: NPA RNP 0.3 (309 meters) Maritime: HEA (8-20 meters) Limitations Spatial and temporal variations in TOA observed by the receiver and presented to the position solution algorithm 10/17/2007ILA 36 - Orlando, FL2 Slide 3 ASF corrected TOAs To remove spatial component: Use published grid, interpolate between grid points Issues include grid density, regions of interest, and grid creation To remove temporal component: Local monitor receiver, broadcast offsets over LDC Issues include correlation distance, monitor averaging, multiple monitor interpolation 10/17/2007ILA 36 - Orlando, FL3 Slide 4 Spatial ASF Grids Harbor Survey Methodology Converting to a grid Required grid density Performance examples Temporal Corrections LDC architecture for live broadcast of differential corrections Prototype eLoran Receiver Sample navigation performance 10/17/2007ILA 36 - Orlando, FL4 Slide 5 Identify the HEA area and generate sail plans that will cover all of the areas of interest typically a 200m spacing Tracks must be planned on inside and outside edges of channels in general the area of interest needs to be over-bounded. Conduct field test Static monitor somewhere in the harbor area (harbor monitor) Perform data collection mapping throughout the harbor; measure ASFs and GPS position 10/17/2007ILA 36 - Orlando, FL5 Slide 6 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 ASFs Procedure developed and refined over a series of harbor surveys New London New York Norfolk Boston 10/17/2007ILA 36 - Orlando, FL6 Slide 7 Continuous vessel tracks in upper harbor Static locations in upper harbor Vessel Van on shore 10/17/2007ILA 36 - Orlando, FL7 Slide 8 10/17/2007ILA 36 - Orlando, FL8 Slide 9 10/17/2007ILA 36 - Orlando, FL9 Slide 10 10/17/2007ILA 36 - Orlando, FL10 Slide 11 10/17/2007ILA 36 - Orlando, FL11 Vessel collected data at 25 static locations in the harbor Held station next to buoy, pier, etc. Van collected data at 19 static locations around the harbor Slide 12 Different Vessel Continuous Track in lower harbor Repeat Upper harbor 12 static locations 10/17/2007ILA 36 - Orlando, FL12 Slide 13 10/17/2007ILA 36 - Orlando, FL13 Slide 14 10/17/2007ILA 36 - Orlando, FL14 8/22 magenta 8/23 green 8/24 - blue Slide 15 10/17/2007ILA 36 - Orlando, FL15 Slide 16 USCG AUX Vessel Myst Oct 2006 Nov 2006 Test Van Mar 2006 Other vessels Mar, Apr 2006 10/17/2007ILA 36 - Orlando, FL16 Slide 17 ILA 36 - Orlando, FL17 10/ 17/ 200 7 Slide 18 ILA 36 - Orlando, FL18 Slide 19 Chesapeake Bay approach channel into Norfolk Harbor 10/17/2007ILA 36 - Orlando, FL19 Slide 20 10/17/2007ILA 36 - Orlando, FL20 Slide 21 10/17/2007ILA 36 - Orlando, FL21 Slide 22 10/17/2007ILA 36 - Orlando, FL22 Slide 23 Continuous tracks inner harbor, main channels, and entrance approach area 10/17/2007ILA 36 - Orlando, FL23 Slide 24 10/17/2007ILA 36 - Orlando, FL24 Slide 25 10/17/2007ILA 36 - Orlando, FL25 Slide 26 10/17/2007ILA 36 - Orlando, FL26 Slide 27 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 stations ASFs recalculated using precise track position and unfiltered TOAs Relative ASFs calculated (ASF boat ASF ref ) 10/17/2007ILA 36 - Orlando, FL27 Slide 28 - Method for converting tracks to a grid - Required grid density - Performance examples Slide 29 Overdetermined least squares estimation method akin to an inverse interpolation (ION GNSS 2006) 10/17/2007ILA 36 - Orlando, FL29 Slide 30 Recall standard linear interpolation: Given a function at grid points, we can interpolate a general F(x, y) by with 10/17/2007ILA 36 - Orlando, FL30 a b Slide 31 Turn the equations around: a, b, and F(x, y) are known so each data point yields a linear equation in 4 unknowns solve large set of simultaneous linear equations to get grids 10/17/2007ILA 36 - Orlando, FL31 Slide 32 10/17/2007ILA 36 - Orlando, FL32 Slide 33 10/17/2007ILA 36 - Orlando, FL33 Slide 34 10/17/2007ILA 36 - Orlando, FL34 Slide 35 10/17/2007ILA 36 - Orlando, FL35 Slide 36 10/17/2007ILA 36 - Orlando, FL36 Slide 37 10/17/2007ILA 36 - Orlando, FL37 Slide 38 10/17/2007ILA 36 - Orlando, FL38 Slide 39 10/17/2007ILA 36 - Orlando, FL39 Slide 40 10/17/2007ILA 36 - Orlando, FL40 Slide 41 10/17/2007ILA 36 - Orlando, FL41 Slide 42 10/17/2007ILA 36 - Orlando, FL42 Slide 43 - LDC Architecture - Typical Spatial Correlation 10/17/2007ILA 36 - Orlando, FL43 Slide 44 10/17/2007ILA 36 - Orlando, FL44 Seasonal Monitor Sites Seasonal 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 LSU LSU FTP Server Loran Transmitter LDC Loran and GPS data at 1min intervals Archived data Slide 45 Each message is 45 bits and takes 24 symbols to transmit at 1 symbol/group At 8970 takes 2.15sec/msg Time: 5 every 64 messages or ~ every 27.5sec ASF data repeats every 2.3 min 10/17/2007ILA 36 - Orlando, FL45 Mon-6 Msg-0 Mon-6 Msg-1 Mon-6 Msg-2 Mon-6 Msg-3 Mon-6 Msg-4 Mon-6 Msg-5 Mon-4 Msg-0 Mon-4 Msg-1 Mon-4 Msg-2 Mon-4 Msg-3 Mon-4 Msg-4 Mon-4 Msg-5 TimeAlm. Mon-0 Msg-0 Mon-0 Msg-1 Mon-0 Msg-2 Mon-0 Msg-3 Mon-0 Msg-4 Mon-0 Msg-5 Mon-0 Msg-0 Mon-0 Msg-1 Mon-0 Msg-2 Mon-0 Msg-3 Mon-0 Msg-4 Mon-0 Msg-5 TimeAlm. Mon-3 Msg-0 Mon-3 Msg-1 Mon-3 Msg-2 Mon-3 Msg-3 Mon-3 Msg-4 Mon-3 Msg-5 TimeAlm. Mon-8 Msg-0 Mon-8 Msg-1 Mon-8 Msg-2 Mon-8 Msg-3 Mon-8 Msg-4 Mon-8 Msg-5 Mon-5 Msg-0 Mon-5 Msg-1 Mon-5 Msg-2 Mon-5 Msg-3 Mon-5 Msg-4 Mon-5 Msg-5 TimeAlm. Mon-9 Msg-0 Mon-9 Msg-1 Mon-9 Msg-2 Mon-9 Msg-3 Mon-9 Msg-4 Mon-9 Msg-5 Mon-1 Msg-0 Mon-1 Msg-1 Mon-1 Msg-2 Mon-1 Msg-3 Mon-1 Msg-4 Mon-1 Msg-5 TimeAlm. repeats Slide 46 - Prototype receiver - Sample performance 10/17/2007ILA 36 - Orlando, FL46 Slide 47 10/17/2007ILA 36 - Orlando, FL47 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 solution Output position as NMEA string Transview Display Display position tracks of eLoran, Loran, and GPS systems SatMate Receiver Loran position NovAtel Receiver GPS position Slide 48 10/17/2007ILA 36 - Orlando, FL48 Slide 49 Spatial ASF Grids Noise in the ASF measurements gets averaged out by the grid creation process 500m grid spacing is typically sufficient Smaller spacing only if dictated by physical size of HEA Smaller sizes just chase the noise in the measurements Harbor Survey procedure has been established and proven Temporal ASF Correct temporal value is critical to meeting HEA accuracy Currently under investigation: Frequency (and filtering) of corrections Monitor site spacing End-state distribution architecture eLoran Receiver In areas where geometry / signal strength are poor, receiver performance becomes critical Slide 50 Alion New London Team Christian Oates Ruslan Shalaev Mark Wiggins Ken Dykstra USCG Auxiliary Captain 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 Unit CDR Chris Nichols LT Chris Dufresne 10/17/2007ILA 36 - Orlando, FL50 Slide 51 gwjohnson@alionscience.comswaszek@ele.uri.eduRichard.j.hartnett@uscga.edu