CospasCospas--Sarsat Sarsat --Satellite SAR ... Location katz.pdf · Daniel Katz © Mobit Telecom...

Daniel Katz © Mobit Telecom Ltd. 11

SAR SAR –– LocationLocation

Founded in 1982 by Canada, France, Russia, USA

43 countries and organizations participate (2010)

Instrumental in the Instrumental in the rescue of >rescue of >3030,,000 000 liveslives

No end user fees

Israel is not a member but uses C/S – ships, yachts, airplanes

CospasCospas--Sarsat Sarsat -- Satellite SAR SystemSatellite SAR System



Provide accurate, timely, and reliable distress alert and location data to help SAR authorities assist persons in distress

Mission of C/S



System Structure

77 Ground stations (LUTs) receive, process and forward satellite downlinks.

Radio beacons: EPIRBs - ships, ELTs - airplanes, PLBs – personal.

Satellites - relay distress signals to ground stations.

30 Mission Control Centers (MCCs) distribute alerts to RCCs, SPOCs or

other MCCs.

Rescue Coordination Centers (RCCs), ~1 per country, coordinate the actual

SAR activity.



GEOLUT & LEOLUT at ITMCC



Radio beacons

EPIRBs (Emergency Position Indicating Radio Beacons) – for maritime use.

ELTs (Emergency Locator Transmitters) – for aircraft.

PLBs (Personal Locator Beacons) - for personal use.



Wrist Worn PLB – SAT406 (by Mobit)

Ensuring availability when the unexpected occurs



SAR Satellite Constellations

SATs Coverage Availability Latency Accuracy Method

LEOSAR 6 Full ~ every 1h Up to ~1h ~1500m Doppler

GEOSAR 5 70°S-70°N Always Immediate ~125m* GPS

MEOSARMEOSAR >>7575 FullFull AlwaysAlways 2 2 secsec ~~150150mm InverseInverse--GPSGPS



LEOSAR Location – Satellite Based Location Born

Sputnik - October 4, 1957At a known location (Johns Hopkins Applied Physics Lab - APL)

measuring Doppler shift of Sputnik’s radio signals → Sputnik’s orbit determined.

Frank McClure (APL chairman) suggested that: knowing the satellite's position and

measuring the Doppler shift, → determine location of a receiver on Earth.



LEOSAR Location – Method: Doppler Effect

∆f/f= Vrel*cos(A1)/C (for stationary beacon Vrel = Vsat)



Convergence towards the true position

Convergence towards the mirror position

LEOSAR Location – Frequency & Satellite Ground Track

At TCA (Time of Closest Approach) A1=90° and ∆f=0



Fc

FmF

T

Doppler curve

Fr

• Assume distance [d] from beacon to satellite track

• Generate frequency vs. time curve

• Calculate SQRT [ Σni=1( Fr

i – Fci)2 /n]

• Iterate [d] until the above square root is small enough

LEOSAR Location – Numeric Process



12

2B

1B2A1A

LEOSAR Location – Solving Ambiguity



LEOSAR Location – weakness

Small footprint x 6 satellites → Temporal Availability ~1h

Small footprint → Latency (store & forward over the ocean)

Doppler → Depends on Freq. accuracy → Location Accuracy → ~1500m

∆f/f= V*cos(A1)/C



GEOSAR Location – Geo Sats + GPS Era

GEOSAR Satellite(s)Navigation

Satellites (GPS)

Ground Station Beacon reports GPS position

GEOSAR Satellites + GPS = Worldwide Coverage



GEOSAR Location – weakness

Stationary Satellites → No Doppler → Dependent on GPS

Short Message → Location report resolution limited to 4” Lat/Lon → ~125m

Far satellites → Lower SNR

GPS orbit inclination 55º → Lower coverage at NZ

No service by the Poles

Far satellites → Lower SNR



MEOSAR Location – Following the GPS



MEOSAR Location – weakness (?)

Trilateration Ranging → DSSS transmission → CDMA

Limited BW DSSS → Limited Accuracy → ~150m

1-G (LEOSAR/GEOSAR) Signal BW = 3Khz

2-G (MEOSAR) Signal BW = 60KHz



Standard Beacon Transmission Time



Mobit’s method to Communicate Extra Data

CospasCospas--Sarsat Sarsat --Satellite SAR ... Location katz.pdf · Daniel Katz © Mobit Telecom...

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