ads-b in a radar environment
TRANSCRIPT
ADS-B in a radar
environment
Greg Dunstone
Surveillance Program Lead,
Airservices Australia
Reduced radar investment
Radar + ADS-B instead of Two radars
Reduced maintenance Australia expects to
decommission 4 radars in 2017 (ADS-B instead)
ADS-B IN
Situational awareness Update rate Accuracy
Airport & Surface
A-SMGCS PRM
Why ADS-B in a radar
environment?
Better Coverage Fill coverage holes at low cost Extend beyond limits of radar PRF Access to sites unavailable to radar Often better detection than radar
Higher Update rate
½ second update possible Detection of manoeuvres
• Eg Turn onto final STCA performance PRM function?
Better Accuracy
Higher accuracy Accuracy independent of range
Better Velocity vector Determined in aircraft (instead of noisy
radar positions) Lower latency, higher accuracy Better safety net performance
Surveillance performance
benefits of ADS-B
Heading noise
Radar System Track Heading Variation from Mean
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
0 50 100 150 200
Radar System Track Update Number
De
gre
es
ADS-B System Track Heading - Variation from Mean
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
0 50 100 150 200
ADS-B System Track Update Number
De
gre
es
ADS_B RADAR
“As a radar” Asterix Cat 48 Acceptable, Not desirable
o Does not maximise performance
ADS-B processing Tracking with 24 bit code Identity (Flight ID, 24 bit code, ModeA
if available) Radar alignment
o NO ADS-B alignment o Radar alignment is critical (as it is for
radar-radar alignment) Fusion with radar
o Mosaic system / Priority system o Treat as a radar o Kalman filter integration (Best)
Taking care of quality factors
NIC,NAC,NUC,SIL etc
Taking care of failure modes GPS dependence Changeover transponder procedures Get flight ID right “on ground”
ATM Integration with radar
Position: Integrity A containment radius of <1 NM and the likelihood of the position error exceeding containment radius of 1e – 5 This can be represented by either: a) Navigation Integrity Category >= 5 and Surveillance Integrity Limit = 2 (or better) & Navigation Accuracy Category >= 6 Or b) Navigation Uncertainty Category >= 5 or better;
ICAO Circular 326 : Terminal area
} The requirement is met by HPL < 1 nautical mile & accuracy < 0.3 Nm
Circular 326 Representation for DO260 and DO260A/B (NUC=5 requires HPL<0.5 Nm And very conservatively implies accuracy < 0.3 NM )
Minimum Requirements for 3 NM Separation Service
(Accuracy < 0.3 Nm) (Integrity as below)
This can be represented by either: a) Navigation Integrity Category >= 5 and Surveillance Integrity Limit = 2 & Navigation Accuracy Category >= 6 Or b) Navigation Uncertainty Category = 4 or better;
Australian position
Minimum Requirement 3 NM
Requires HPL<1 NM As per Circular 326
Australia uses Circular 326 note and Safety case to argue that NUC=4 is acceptable for DO260. (NUC=4 requires HPL<1 NM and means accuracy < 0.3 NM) Note.– For the provision of separation services to aircraft equipped with DO260 avionics, a State may select lower encoded values for NUC in relation to accuracy and integrity when it is demonstrated by safety assessment that the 95 percentile accuracy, and containment radius values, identified in Table C-1 will continue to be met.
}
CASA accepts that
If DO260 NUC <=4 (HPL< 1 Nm) implies that Accuracy (95%) < 0.3 mile
Safety case considered the following
issues : • Range of Applicability of performance comparison
with radar • Airservices Australia captured empirical data • Analysis of rare cases, when there are less than 5
satellites in view • The reference radar which allows inaccurate
outlier samples 5% of the time with errors up to 5 times the core accuracy (95%) value
• Availability of GNSS Performance to Support ADS-B” by Matt Harris, Tim Murphy from Boeing Commercial Airplanes presented at the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) .
More stringent integrity requirement More ADS-B outages NUC=5 outages do occur
If the required quality factors are too
stringent
When GPS geometry is poor • Integrity value will drop • Low integrity ADS-B data will be discarded
by the system o Loss of ADS-B service
When GPS receiver has poor reception
• Integrity value will drop • Low integrity ADS-B data will be discarded
by the system o Loss of ADS-B service
Safety is compromised
IF the required quality factors are too lax
Safety is compromised
Why this is important ?
HPL Requirement
2NM (NUC3)
1NM (NUC4)
0.5 NM (NUC5)
Transitions
to Inadequate
NUC/NIC
This can be represented by either: a) Navigation Integrity Category = 4 (or better) and Surveillance Integrity Limit = 2 (or better) Or b) Navigation Uncertainty Category = 3 or better;
Australian position
Minimum Requirement Enroute 5 NM separation
Requires HPL<2 Nm As per Circular 326
Whilst the case of NUC=3 has been accepted for Enroute, Australia uses NUC=4 because we do not see outages at NUC=4
}
ADS-B is as good or better than a Terminal area radar ADS-B can be used alone or together with radars in enroute or TMA to • Improve surveillance performance • Reduce cost • Support ADS-B IN applications
ANSPs and regulators need to determine the appropriate and required ADS-B quality factors
Conclusion
