Project Report ATC-288 The Beacon Target Detector (BTD) Algorithms Deployed in the ASR-9 Processor Augmentation Card (9-PAC) G. R. Elkin J. L. Gertz 5 September 2000 Lincoln Laboratory MASSACHUSETTS INSTITUTE OF TECHNOLOGY LEXINGTON, MASSACHUSETTS Prepared for the Federal Aviation Administration, Washington, D.C. 20591 This document is available to the public through the National Technical Information Service, Springfield, VA 22161 This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. TECHNICALREPORT STANDARD TITLE PAGE 1. Report No. 2. GovernmentAccession No. 3. Recipients Catalog No. ATC-288 4. Title and Subtitle 5. Report Date The Beacon Target Detector (BTD) Algorithms Deployed in the ASR-9 5 September 2000 Processor Augmentation Card (9-PAC) 6. Performing OrganizationCode 7. Author(s) 8. Performing OrganizationReport No. G.R. EIkin and J.L. Gertz ATC-288 9. Performing OrganizationName and Address IO. Work Unit No. (TRAIS) MIT Lincoln Laboratory 244 Wood Street 11. Contractor Grant No. Lexiugton, MA 02420-9108 2. SponsoringAgency Name and Address 13. Type of Report and Period Covered Department of Transportation ATClAugust 2000 Federal Aviation Administration Systems Research and Development Service 14. SponsoringAgency Code Washington, DC 20591 5. SupplementaryNotes This report is based on studies performed at Lincoln Laboratory, a center for research operated by Massachusetts Institute of Technology, under Air Force Contract F19628-00-C-0002. 6. Abstract This project report describes the Beacon Target Detector (BTD) algorithms implemented in the ASR-9 Processor Augmentation Card (9-PAC). The BTD function combines replies that arise from the same aircraft to form beacon targets, and sends these beacon targets to the 9-PAC merge process where they are combined with primary radar targets. The 9-PAC BTD algorithm was designed to solve two problems with the ASR-9 Array Signal Processor (ASP) BTD: identifying and removing false beacon targets due to reflections, and preventing merging or splitting of targets due to reply overlap and garble. The BTD reflection processing algorithm marks each beacon target as either real or false, and provides this information to the 9-PAC merge process. Discrete Mode 3/A reflection false targets are identified when duplicate code reports satisfying stringent conditions are located. In order to find non- discrete Mode 3/A code reflection false targets, the BTD builds an automated, dynamic reflector databasebased on the geography of real and false targets with discrete Mode 3/A codes. This report supersedesan earlier report (ATC-220) which described the 9-PAC BTD algorithms prior to the operational field testing effort conducted by the FAA in 1995 and 1996. Nationwide deployment of 9-PAC on production hardware was approved in April 1999. To date, more than 60 installations have been performed, and hardware has been procured to update all 134 ASR-9s in the National Airspace System. 7. Key Words 18. Distribution Statement This document is available to the public through the National Technical Information Service, Springileld, VA 22161. 9. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 2% FORM DOT F 1700.7 (8-72) Reproduction. of completed page authorized EXECUTIVE SUMMARY Since 1990, the Airport Surveillance Radar-9 (ASR-9) has been installed and commissioned at more than 130 airports in the United States. The ASR-9 provides aircraft detection and false alarm performance that is superior to that of earlier generations of airport surveillance radars. The ASR-9 uses two types of surveillance to monitor aircraft activity. In primary or skin surveillance, the radar transmits a pulse of electromagnetic energy that is reflected by the metal components of an aircraft. Secondary, or beacon, surveillance uses a second antenna mounted on top of the ASR-9 primary antenna to interrogate a transponder device located on board all commercial and most general aviation aircraft. The transponder E reply is contains identification code or altitude. The ASR-9 is designedto operate as a standaloneradar or in conjunction with the Mode S secondary radar system. The Mode S system provides more advanced beacon surveillance. The standalonebeacon surveillance is the subject of this report and is referred to as the interim beacon interrogator (IBI) mode. After the first several ASR-9 systems were placed on-line, operational problems were cited by air traffic controllers, both with the primary and the beacon radar surveillance functions. The beaconproblems, which are the focus -of this report, were as follows: . false beacon target reports resulting from signal reflections caused by buildings and other reflective surfacesnear airports; and . missing or extra beacon target reports, or reports with inaccurate azimuth measurements (particularly on approach to parallel runways), resulting from interference between overlapping reply pulses from multiple aircraft in the main beam of the antenna. In 1992, Lincoln Laboratory proposed a replacement of the surveillance data processing elements in the ASR-9, the so-called Array Signal Processor (ASP), with a Processor Augmentation Card (9-PAC). The increased processing and memory capacity of the 9-PAC made it possible to solve the surveillance problems listed above by implementing sophisticated algorithms in software. This report describesthe 9-PAC Beacon Target Detector (BTD) algorithms, which were developed to solve the beacon reflection and interference problems cited above. The BTD receives beacon reply data from ASR-9 beacon reply processing hardware, combines replies that arise from the same aircraft to form beacon target reports, and outputs these target reports to the 9-PAC Merge process,where they are combined with primary radar reports. While the ASP BTD makes no attempt to remove false target reports caused by reflections, the 9-PAC BTD has a Dynamic Reflector False Target Algorithm (DRFTA). DRFTA determines the location and geometric characteristics of reflecting surfaces through analysis of target report data, and stores this information in a dynamic reflector database. The reflector databaseis then used to identify false targets. The dynamic databasehandles reflections caused by moving reflectors, such as ships and airplanes, and requires no hand entered inputs when new buildings are constructednear an airport. ..- 111 The 9-PAC BTD reduces the reply interference problems by using knowledge of track history to correct corrupted reply code and altitude data. The ASP BTD had to assign each beacon reply to a target at its time of reception, but the 9-PAC BTD postponestarget formation decisions until all replies in an area have been received, and then processesthe group in batch mode when all information is available. This results in a reduction in missed target reports, merging replies from two aircraft into one target report, or splitting the replies from one aircraft into two target reports. Data analysis during field testing of the algorithms described in this report has demonstratedmore than an order of magnitude improvement in the beacon false target rate of the ASR-9. False target rates of 4 reports per antenna scan have been reduced to less than 1 false target in 5 antenna scans. Nationwide deployment of these algorithms on production 9-PAC hardware was approved by the FAA in April, 1999. To date, more than 60 installations have been performed, and hardware has been procured to update all 134 ASR-9’s in the National Airspace System (NAS). iv ACKNOWLEDGMENTS The authors wish to acknowledge the contributions of several people without whom the algorithms described in this paper would never have found their way into the ASR-9. Ed Hall and Jim Pieronek designed and built the 9-PAC prototype boards, and Robert Callahan supervised the repair of boards that broke during field testing. Oliver Newell provided the considerable benefits of his experiencein real-time software techniques,and he also wrote the 9- PAC operating system software and much more. Jenifer Evans developed the 9-PAC Radar/Beacon Target Merge algorithm. Walter Heath wrote the flash card file system software used to store reflector maps and monitor the system tests, and offered advice about debugging real-time embedded software on numerous occasions. Tammy Parsons and Paul Harrell of Northrop Grumman performed an independent validation and verification effort prior to field testing. Bill Goodchild of the FAA directed the field acceptancetesting effort at Philadelphia, Los Angeles, Dallas/Fort Worth, and Oakland airports, and worked in the trenches with the authors in analyzing recorded data. Marc Edwards and Edward Paule at the FAA Technical Center (AOS-270) modified the ASR-9 software to work with 9-PAC. Wesley Johnson supported the Albuquerque field site testing effort. Robert Grappel patiently reviewed this report. c TABLEOFCONTENTS ... Executive Summary ...........................................................................................................................................................111 Ackn owledgments............................................................................................................................................................... List of Illustrations .............................................................................................................................................................xi