An Investigation into the Temporal Correlation at the ASF Monitor Sites byProf. Peter Swaszek, URI/USCGADr. Gregory Johnson, AlionCapt. Richard Hartnett, USCGADr. Sherman Lo, Stanford

or

A Partial Answer to David Lasts Question on Monitor Spacing Requirements

BackgroundILA-35 (2006) Warping Time and Space: Spatial Correlation of Temporal VariationsSeasonal Monitor NetworkSites, equipment, softwareSpatial CorrelationSeveral anecdotal examplesASF FilteringReduce receiver noise effects

Prior ConclusionsThere is an obvious correlation in the ASFs of nearby sitesDepends on local topographyLand-path stations experience more variationMost extreme variations occur in winterPlacement of monitors for dLoran will be dependent upon worst-case correlationWinter in the NorthEast is the long pole

ILA-36 (today)Look at some of the available data2 new sitesSome sites collecting over almost 2 yearsMore on temporal correlation including error effectsStatistical measuresError performance

The Seasonal Monitors circa Oct. 2007

Sites Monitored at CGAUSCGA, New London CTURI, Kingston RIVolpe, Cambridge MAFAATC, Atlantic City NJOU, Athens OHStaten Island, NYGoodspeed (CT)New Haven (CT)NEW !!!

Seasonal Monitor Sites **MANY MILES

Shorter Baselines Distances*

Chart1

31.1413

41.3118

49.6281

67.2315

77.9875

103.9335

116.7221

123.1448

134.9314

138.6527

152.7312

kilometers

Sheet1

Site 1Site 2Distance (km)

CGAGSPD30.8

HVNGSPD41.4

CGAURI49.6

CGAURI49.6

CGAHVN67.2

URIGSPD77.8

URITSC103.9

URIHVN116.7

STIHVN123.1

ACYSTI134.9

CGATSC138.7

TSCGSPD152.7

STIGSPD164.2

CGASTI185.7

TSCHVN193.1

URISTI234.5

ACYHVN247.1

ACYGSPD284.9

CGAACY299.0

TSCSTI316.2

URIACY343.0

TSCACY436.7

ACYOUA660.6

OUASTI714.9

OUAHVN826.0

OUAGSPD865.9

CGAOUA893.1

URIOUA942.7

TSCOUA1002.3

Sheet2

CGA-GSPD31.1413

HVN-GSPD41.3118

CGA-URI49.6281

CGA-HVN67.2315

URI-GSPD77.9875

URI-TSC103.9335

URI-HVN116.7221

STI-HVN123.1448

ACY-STI134.9314

CGA-TSC138.6527

TSC-GSPD152.7312

STI-GSPD164.1755

CGA-STI185.7239

TSC-HVN193.136

URI-STI234.5461

ACY-HVN247.0728

ACY-GSPD284.9618

CGA-ACY298.9813

TSC-STI316.1811

URI-ACY343.0303

TSC-ACY436.6684

ACY-OUA660.5972

OUA-STI714.8881

OUA-HVN825.9639

OUA-GSPD865.7591

CGA-OUA893.1158

URI-OUA942.6819

TSC-OUA1002.339

Sheet2

Sheet3

kilometers

Purposes of Monitor NetworkAnalysis of ASF variation for aviationCenter of range studiesBounds on error

dLoran system component for HEAASF updates to LSUBroadcast out on LDC

Shermans presentation nextGregs presentation tomorrow

Whats New TodayWe have lots more data, some on shorter baselinesIncludes pre/post-TOT transition2 summers/winters for the early sitesExamine statistics versus distanceExamine position error performance of dLoran versus distance

Some ASF Data

Typical ASF Data

ASF Data from Monitor SitesHave long assumed that the ASF can be decomposed into 3 independent, additive terms:Spatial termTemporal termDirectional term for a moving antennaFor further visuals, we remove (zero out) the spatial termTemporal term forced to mean of zeroDirectional term assumed to be zero

Typical Temporal Term

Some ComparisonsSeasonal differencesSummer (June1 August 31)Winter (January 1 March 31)Two year repeatabilityCorrelation site-to-siteHighLow ASF differences

Our Winter/Summer Definition

Repeatability of ASFs 2 Years at One Site

Repeatability Zoom of Summer

Repeatability Zoom into Winter

Site-to-Site, Strong Correlation

Site-to-Site, Weaker Correlation

Differences of the ASFs

and

Statistics Whats relevant to compute?Correlation coefficient is one option

= 1 just means a linear relationshipIgnores scaling and offsetNot relevant for error analysisWill look at average differences in ASF

Measure spread of differences in ASF by standard deviation of differencesTabulate average standard deviation of differences

Focus on pairwise characteristics of close sites short baselines only

Table of Results (nanosec)

Position Error PerformanceHow far away from a monitor site are the ASFs good enough for dLoran?Measure above is unclearAnecdotal evidence from harbor testingApproach identify position error due to mismatchConsider one monitor site as a mobile receiver Use ASFs from second site in position solution

Example URI & TSC ASFsSWAP ASFs

ExampleSUMMERWINTER

Performance ResultsAverage over timeAll year, winter, summerTabulate 95% error radiiFocus on pairwise characteristics of close sites short baselines only

Best Site-to-Site PerformanceSUMMERWINTER

95% Error Radius vs Distance

Conclusions/FutureWhile ASFs are clearly correlated at nearby sites, position performance is sensitive to mismatchClose spacing seems necessary for HEAdLoran for aviation could accept wider spacing Error budget needs to also include receiver noise and spatial ASF componentsWill continue collecting and testing data Get shorter baseline data (along coastline) from PIG/LSU sitesPoint Allerton (MA)Sandy Hook (NJ)

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