Small Airport Surveillance Sensor (SASS) Matthew J. Rebholz 27 October 2015 Sponsor: Matthew Royston, ANG-C52, Surveillance Branch (Andras Kovacs, Manager) Distribution Statement A. Approved for public release; distribution is unlimited. This work is sponsored by the Federal Aviation Administration under Air Force Contract #FA8721-05-C-0002. Opinions, interpretations, recommendations and conclusions are those of the author and are not necessarily endorsed by the United States Government.
Outline Overview System Design Initial Data Collections Summary Small Airport Surveillance Sensor- 2
Motivation Surveillance gaps exist at many small airports Serious Runway Incursions by Airspace Class (2013) FAA Aviation Safety Information Analysis and Sharing (ASIAS) System Runway incursions remain a serious issue at small airports Visual surveillance can be impaired by decreased visibility, weather, and terrain One-In-One-Out procedures during IMC impacts airport capacity Low cost secondary surveillance solutions needed to fill surveillance gaps for small airports Small Airport Surveillance Sensor- 3
Small Airport Surveillance Sensor (SASS) Architecture Provides secondary surveillance of airport surface and nearby airspace Actively interrogates surface ATCRBS & airborne non-ads-b aircraft Receives & validates ADS-B position from 1090ES Remote Unit can be at airport, TRACON, ARTCC or remote facility Small Airport Surveillance Sensor- 4
SASS Fills Unique Role Target Airports GA airports with Class D airspace towers 370 potential airports Non-towered airports with substantial traffic 30 with 100,000+ operations per year Key Benefits Potential to fill surveillance not covered by FAA radars or ADS-B ADS-B mandate applies to Class B & C and above 10,000 Potential to integrate SASS with runway incursion safety logic Small footprint that can be located on airport property or deployed as a mobile system for special events SASS provides low-cost surveillance capability to either augment, or provide standalone, cooperative airport surface and terminal area airborne surveillance Small Airport Surveillance Sensor- 5
Outline Overview System Design Initial Data Collections Summary Small Airport Surveillance Sensor- 6
Preliminary SASS Requirements (Secondary Surveillance) Minimum Coverage Area 1 Position Error (1 σ) Surface Surveillance 10,000 ft long 2,000 ft wide 30 ft Range Position Error (1 σ) 2 Range Resolution 3 Airborne Surveillance 20 nm 0.2 nm 60 ft References: 1. Low Cost Ground Surveillance System (LCGS) Specification. 2. Required Surveillance Performance Accuracy to Support 3-Mile and 5-Mile Separation in the National Airspace System, S.D. Thompson et al, MIT Lincoln Laboratory Project Report ATC-323, November 2006. 3. Mode S Sensor Specification, FAA-E-2716, Federal Aviation Administration, 1985 Small Airport Surveillance Sensor- 7
Surveillance Methodology hyperbola SASS 1 SASS 2 Passive: Surface Surveillance of Mode S Squitters Azimuth measurements from both SASS units define two lines of position, θ 1 and θ 2 Time difference of arrival (TDOA) defines hyperbola (derived from t Rx1 and t Rx2 ) Geolocation is a least-squares solution that provides best fit to measurements Active: Surface/Airborne Surveillance of ATCRBS/Mode S Interrogations Azimuth measurement from one sensor defines one line of position, θ 1 Time of arrival (TOA) from interrogation and reply, t interr, provides range Intersection of both lines defines position Small Airport Surveillance Sensor- 8
Geolocation Process Remote Unit Calibration Sensor A Model Parameters Sensor B Model Parameters SASS Sensor A AOA Surface AOA Surface SASS Sensor B Test Data: I/Q Samples TDOA Surface Test Data: I/Q Samples Maximum Likelihood Geolocation Estimate AOA = Angle of Arrival TDOA = Time Difference of Arrival Small Airport Surveillance Sensor- 9
Modeled Surface Surveillance Error (ft) (Hanscom Field in Bedford, MA) Model Assumptions Range error: 10 (1 σ) Azimuth error: 0.4 (1 σ) SASS Sensor SASS Sensor 30 position error or less over entire surface movement area Small Airport Surveillance Sensor- 10
Airborne Surveillance Predictions 40 30 Detection Range Secondary Surveillance Radar Range Equation 0.5 0.4 Cross-Range Accuracy Cross-Range accuracy assuming azimuth accuracy = 0.4º SNR [db] 20 10 Successful detection at 20 nm SNR Detection Threshold 0 0 10 20 30 40 50 60 Cross-range [nm] 0.3 0.2 0.1 Cross-range Accuracy Requirement Meets cross-range accuracy requirement 0 0 10 20 30 40 50 60 Range [nm] Range [nm] Can successfully detect at 20 nm Assuming azimuth accuracy = 0.4º from surface model requirement, we can achieve 0.14 cross-range accuracy at 20 nm (within 0.2 nm airborne requirement) Small Airport Surveillance Sensor- 11
Range Requirements 20 Timing Error 15 10 Gps0: Mean = 2.5 ns, Var = 7.2 ns Gps1: Mean = 2.4 ns, Var = 6.9 ns Difference: Mean = 0.7 ns, Var = 0.6 ns Est. PPS Error [ns] 5 0-5 -10-15 19.4 19.6 19.8 20 20.2 20.4 20.6 20.8 GPS Time - Hours in the Day - Note: 1 ns timing error 1 ft range error SASS meets range requirements (10 for surface and 60 for airborne) Small Airport Surveillance Sensor- 12
SASS Array Design Criteria Minimize Maximum Mainlobe Beamwidth Azimuthal or direction finding (DF) error proportional to mainlobe beamwidth Minimize Maximum Sidelobe Smaller sidelobes reduce signal ambiguities Beam Pattern: Polar Coordinates Design Optimization Technique Use Monte Carlo techniques to do sampled search of array configurations Choose array configuration which minimizes performance metric Loss [db] Performance metric defined as width of worst-case mainlobe with specified maximum sidelobe Degrees Beam Pattern: Rectangular Coordinates Small Airport Surveillance Sensor- 13
SASS Prototype Array Design 0.8 Array Layout 0.6 0.4 Meters 0.2 0-0.2 Antenna Elements (Monopoles) -0.4-0.6 Ground Plane -0.8-0.8-0.6-0.4-0.2 0 0.2 0.4 0.6 0.8 Meters Small enough for transport and able to be mounted on mobile antenna tower 5 x 5 ground plane No moving parts, minimize material cost 8 elements Small Airport Surveillance Sensor- 14
Modeled SASS Array Response Y [m] 0.5 1 0 Symmetric Array Mainlobe Characteristics - Max MB = 8º - Azimuth accuracy = 0.16º Assuming 50:1 beamsplit Y [m] 0.5 1 0 SASS Array Mainlobe Characteristics - Max MB = 11º - Azimuth accuracy = 0.22º Assuming 50:1 beamsplit -0.5-1 -1 0 1 X [m] Sidelobe Characteristics - Max SL = -0.2 db Modeled Array Beam Patterns Narrow mainlobe -0.5-1 -1 0 1-150 X [m] Sidelobe Characteristics - Max SL = -2.5 db Modeled Array Beam Patterns Narrow mainlobe db 0-1 Angle [degrees] High sidelobes -2-100 -3-9 150-10 -150-100 -50 0 50 100 150 Steering Angle [degrees] Steering Angle [degrees] -50 0 50 100 Low sidelobes SASS meets 0.4º azimuth requirements and lower sidelobes help reject false target detections Angle [degrees] -4-5 -6-7 -8 Small Airport Surveillance Sensor- 15
SASS Signal Processing Chain Antenna (x8) Timing Amplifier Receiver (x8) Digital Signal Processor Item Unit Cost Total Antenna (x8) - Monopole $100 $800 Amplifier - 8-Channel Amplifier $2000 $2000 Receiver (x8) - Ettus N210 Universal Software Defined Radio (USRP) $2200 $17,600 Timing - Trimble Thunderbolt E GPS Receiver $1000 $1000 Timing - Ettus OctoClock-G 8-Channel Clock Distributor $1600 $1600 Digital Signal Processor - Thinkmate Server $10,000 $10,000 $33,000 Simple processing chain and COTS equipment lead to low cost system Small Airport Surveillance Sensor- 16
SASS Sensor Prototype Hardware Cost: $33,000 Power Consumption: ~1200W Dimension: ~2 W x 3 H (~14U) Ettus OctoClock-G Extra OctoClock-Gs and USRPs for future 1030 MHz processing Ettus N210 USRPs Processing Server and Storage RAID Antenna Array Small Airport Surveillance Sensor- 17
Outline Overview System Design Initial Data Collections Summary Small Airport Surveillance Sensor- 18
Hanscom Field Data Collection ADS-B equipped aircraft SASS Sensor Test vehicle with DGPS & transponder Transponder DGPS Test Vehicle SASS Sensor Remote Unit Truth sources: DGPS, Lincoln Mode S radar (MODSEF), ADS-B equipped targets of opportunity & video cameras MODSEF (1.3 nm away) Small Airport Surveillance Sensor- 19
Hanscom Field Data Collection Phased Array SASS Sensor SASS Sensor Remote Unit Phased Array Cameras DGPS Base Station Small Airport Surveillance Sensor- 20
Flight Facility Tower Cab View of airfield to North from Flight Facility tower cab Master Processing CPU Situation Display Camera Display Used to simulate Hanscom (BED) tower Situation & video displays placed in front of Hut window Video cameras installed for surveillance verification Similar view from Hanscom Tower nearby Small Airport Surveillance Sensor- 21
Initial Field Experiment Position Error at Hanscom Field - - - Truth from DGPS Feet 90 Achieved Accuracy Mean Error: 22.7 ft Standard Deviation: 17.2 ft RMS Error: 28.5 ft 60 30 80 60 40 20 Histogram of Position Errors 0 0 0 50 100 150 200 250 Position Error [ft] Preliminary results are within expected accuracy predicted by model Expect improved performance with the addition of a track filter and additional calibration data Small Airport Surveillance Sensor- 22
Small Airport Surveillance Sensor- 23 Aircraft Target of Opportunity
Outline Overview System Design Initial Data Collections Summary Small Airport Surveillance Sensor- 24
Future Work Q1 FY16 Real-time passive geolocation demo Finalize USRP real-time interface Obtain real-time processing rates Implement single SASS sensor geolocation Q2 FY16 Add 1030 MHz processing for active geolocation Detection and demodulation Interrogation/reply association Examine airborne surveillance performance Q3 and Q4 FY16 Field demonstration with passive and active surveillance Small Airport Surveillance Sensor- 25
Summary SASS provides low-cost secondary surveillance for small airports Accurate surface surveillance (30ft) and airborne surveillance out to 20nm Key benefits Improved controller traffic situation awareness Support for automated runway incursion alerting Key design features Highly accurate, low-cost phased array Low cost COTS signal processing equipment State-of-the-art digital signal processing leveraged from DoD work Low power and small footprint can support mobile applications Small Airport Surveillance Sensor- 26
Acknowledgements FAA NextGen Surveillance Branch (ANG-C52) Andras Kovacs, Matthew Royston, Amit Choudhri, & Rachel Groggel MIT Lincoln Laboratory SASS Team Swaroop Appadwedula, Steve Campbell, Skip Copeland, Bob Downing, Derek Espinola, Joe Finnivan, Gary Hatke, James Keefe, Jamie Pelagatti, Tom Reardon, Matt Rebholz, Gregg Shoults, Mike Spitalere & Loren Wood Small Airport Surveillance Sensor- 27