Project Report ATC-259 A Description of the Interfaces between the Weather Systems Processor (WSP) and the Airport Surveillance Radar (ASR-9) J.J. Saia M.L. Stone M.E. Weber 16 June 1997 Lincoln Laboratory MASSACHUSETTS INSTITUTE OF TECHNOLOGY LEXINGTON, MASSACHUSETTS Prepared for the Federal Aviation Administration, Washington, D.C.
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TECHNICAL REPORT STANDARD TITLEPAGE 2. GovernmentAccessionNo. 1. Report No. 3. Recipient’sCatalogNo. ATC-259 5. Report Date 4. Title and Subtitle 16June1997 A Description of the Interfaces between the Weather Systems Processor (WSP) and the Airport SurveiRance Radar (ASR-9) 6. PerformingOrganizationCode 8. PerformingOrganizationReportNo. 7. Author(s) John J. Saia, Melvin L. Stone, Mark E. Weber ATC-259 10. Work Unit No. (TRAIS) 9.
ABSTRACT The Weather Systems Processor (WSP) is an enhancement for the Federal Aviation Administration’s (FAA) current generation Airport Surveillance Radars (ASR-9) that provides fully automated detection of microburst and gust front wind shearphenomena,estimatesof storm cell movement and extrapolated future position, and lo- and 20-minute predictions of the future position of gust fronts.
TABLE OF CONTENTS * Section Abstract List of Illustrations List of Tables 1.O INTRODUCTION 2.0 PERTINENT ASR-9 FEATURES 2.1 ASR-9 Overview 2.2 Antenna Feed Array 2.3 Radar Shelter Equipment 2.4 Six-Level Weather Processor 3.0 WEATHER SYSTEMS PROCESSOR OVERVIEW 3.1 Radar Data Acquisition 3.2 Radar Data Processor 3.3 Display Function 3.4 Remote Monitoring System 4.0 THE WSP RADAR DATA ACQUISITION FUNCTION 4.1 Microwave Signal Acquisition 4.1.
TABLE OF CONTENTS (Continued) , Section 4.3 Control Functions 4.3.1 On-Line Channel Selection 4.3.2 Target Channel Low Beam Selection 4.3.3 ASR-9 Weather Channel Beam Switch 4.3.4 WSP Receiver Input Control (SP3T) 4.3.5 Timing and Control of Alternate Beam Switching 4.3.6 Microwave “Preselector” Filter 4.3.7 RF Receive Chain Output 4.3.8 Sensitivity Time Control Attenuator 4.3.9 Six-Level Data Output Selection 4.3.10 “Off-line” or “Fault” Condition 4.4 Radar Data Processor(RDP) Input Synchronization 5.
LIST OF ILLUSTRATIONS Page Figure 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. A-l. Supervisor’s graphical situation display and local controller’s ribbon display. Antenna and high- and low-beam patterns. ASR-9 feed array assembly (lOAl). ASR-9 four-bay assembly, including the overheadarray of microwave components for both channels. ASR-9 Six Level Weather Channel waveguide components,shown in their installed positions. ASR-9 weather receiver/SCIP. ASR-9 and WSP High Level Block Diagram.
2.0 PERTINENT ASR-9 FEATURES This section describes the architecture of the ASR-9 with emphasis on features pertinent to integration of the WSP. The WSP functions, while often analogous to those of the ASR-9, will be largely freestanding to facilitate integration, testing, and use with other coherent, highpowered radars with a suitable two-beam antennapattern and a dual-polarization feed. 2.
antenna feed horns. A “two-level” weather function embedded within the ASR-9’s target processorprovides backup to this preferred six-level weather channel. 50 *50 ANTENNA GAIN FREQUENCY = 2800 MHz LOW BEAM E-PORT HIGH BEAM E-PORT LOW BEAM H-PORT HIGH BEAM H-PORT 45 40 S/N 1081 34.1 dB 33.6 ciB 33.7 dB 32.
2.2 Antenna Feed Array Figure 3 is a detail of the ASR-9 feed horn assembly. Shown are the high and low beam feeds, associatedpolarizing sections and the input/output ports that are connected via waveguide or coaxial paths to the transmitter and receiver sub-systemswithin the radar shelter. As noted, circular polarization may be employed to reduce the magnitude of precipitation echoes in the target channel.
2.3 Radar Shelter Equipment Figure 4 depicts the ASR-9’s four-bay assembly consisting of redundant (“A” and “B” channel) transmitter and receiver/processor cabinets, the Remote Monitoring System (RMS) cabinet and the Six-Level Weather/Surveillance Communication Interface Processor(SCIP). The four-bay assembly is housed in an environmentally controlled radar shelter building located next to the antenna tower. This shelter is typically remote from the air traffic control tower and unmanned.
ADAPTER MICROWAVE ASSY SPDT SWITCH S5 BANDPASS FILTER FL3 (Tuneable) HY3’ WEATHEl CHANNEI HYI. HY2 = CIRCULATOR HY3’= ISOLATOR AT = ATTENUATOR/LOAD AT9, AT10 = 50 52 (Termination) CR = CRYSTAL DETECTOR DC5, DC6, DC7 = BI-DIRECTIONAL COUPLER -. - I / LOW NOISE AMP (LNA) AR3 (RW / W/G-TOkOAX TRANSITION CP5 276122-l Figure 5. ASR-9 Six Level Weather Channel waveguide components, shown in their installed positions. 2.
r- ~Tk~RE~I”EiiiSCi&~) - - - - - - - - - - - - - - 1 Figure 6. ASR-9 weather receiver/SCIP. 1 , 1 .
The ASR-9 Weather channel has a RF-IF receiver that includes a low-noise front end, a stable local oscillator, and mixer. A filtering and magnitude function is implemented in the sixlevel weather channel to handle the batches of A/D data comprised of samples from 18 pulses generated during the transit of each beam width. A six-level weather detector thresholds the processedbatch data and performs spatial and temporal smoothing.
3.0 WEATHER SYSTEMS PROCESSOR OVERVIEW The WSP is comprised of four major functional elements: the Radar Data Acquisition @DA) unit, the Radar Data Processor (RDP), the Display Function (DF) and a Remote Monitoring System (RMS) (See Figure 7). The RDA acquires radio frequency (RF), timing and reference signals from the ASR-9, as well as accomplishing various control functions describedbelow. The RDP consists of commercial off-the-shelf (COTS) processors, housed in a VME chassis.
8 polarization are active. The RDA includes a dedicated, high dynamic range receive chain that provides the primary input to the WSP’s Doppler processing algorithms. Intermediate frequency (IF) test signals generatedby the ASR-9 circuits and coupled directly into the WSP are available for use during the 4%range gate calibration interval which is programmed during the eight-pulse coherent processing interval block. The weather test signal is used for off-line calibration.
3.2 Radar Data Processor The RDP is comprised of commercial off-the-shelf single-board computers, interconnected through a VME-standard backplane. It accomplishes the entire suite of data processing operations required to convert input radar quadrature samples to images of precipitation reflectivity, Doppler velocity and spectrum width (“base data”),. and to extract user-oriented meteorological products from these.
Local Meteorological Data Display WSP Host . ---- wx Alg Ret n Signal rrocessing - . FFlMMMM PPEAAA TowerKracon G P s R 8 0 4 x O 6 C P u SSMRRR 11 , . 1 (To ASR-9) c--w-Remote Situation/ RMS Displays Figure 9. Lincoln Laboratory prototype WSP Radar Data Processor (RDP) configuration. 3.3 Display Function Y Meteorological products from the algorithms within the RDP are transmitted asynchronously to the DF via a TCP-IP Ethernet protocol.
Each DF unit consists of a Situation Display (a UNIX workstation or PC running a UNIX environment) and one or more Ribbon Displays. The latter may be dedicated alphanumeric monitors, or in some casesmay be implemented as separatevirtual windows on the SD. The DF software is again C/C++ and employs many of the graphical interface tools and drivers used in the RDP monitoring processes. 3.4 Remote Monitoring System The WSP RMS function is comprised of: 1.
4.0 THE WSP RADAR DATA ACQUISITION FUNCTION The RDA provides the system-specific interface between an existing unit (the ASR-9) and the often markedly different signal processing operations performed by the WSP. In combination with the necessity of leaving existing ASR-9 search radar performance unaltered, the following WSP processingrequirements dictate the design of the RDA. 1.
next coherent processinginterval pair to begin. This operation registersthe ASR-9 geocontrol and censoring maps with the terrain). To facilitate identification of data, each pulse repetition interval is marked with the bearing, time of day, antenna beam position, and A/B channel selection and polarization. When archived, date and time of day are recorded in the header. 9. Circular polarization signal intensity is corrected by appropriate combination of the co- and cross-polarized signals.
high-speed, single-pole, double-throw (SPDT) waveguide switch is installed in each channel (SWlOl, SW102) to extract the low-beam signal for processingin the RDA. The added switch is slaved to the existing RAG beam switch (S2, S3) so as to direct the low-beam signal to the RDA receiver when the high-beam horn is connected to the target channel receiver. The low-beam signal is connected to the target channel receiver under ASR-9 RAG control beyond the nominal 15 nmi range.
ASR-9 WAVEGUIDES LOW NOISE AMP BANDPASS UNI-DIRECTIONAL RCVR PROTECTOR NOTE: 1. CHANNEL CHANNEL CONTROL B ILLUSTRATED: A IS A MIRROR IMAGE OF B 2.
4.1.1.2 High Beam Interface In contrast to the low beam mode of acquisition, the target channel’s use of high beam signals at short range precludes their exclusive use by WSP. The target channel’s receive chain design-specifically application of up to 60 dB Sensitivity Time Control (STC) attenuation, and limited (63 dB) instantaneous dynamic range-preclude use of the target channel A/D converter output for WSP.
beam signal is processedby the WSP for all range gates for one full antenna scan; the switch then toggles so that high beam signals are processed’during the following scan. As shown in Figure 10, the WSP’s SP3T (XSW5) switch is connectedto the coaxial microwave path to select the orthogonally polarized ports for input to the WSP RF/IF receive chain in CP mode.
be used by the WSP with the addition of instantaneousautomatic gain control (IAGC) at the IF stage in order to match the A/D converter dynamic range interval to that of the front end LNA. However, 14-bit or greater signal quantization is preferred, which will require additional circuit modification. Northrop Grumman engineers are also examining a direct digitization coherent detection receiver as describedbelow. 4.1.3.1.
4.2 Timing, Reference and Digital Signal Acquisition In order to control its microwave signal acquisition circuits, drive its dedicated IF receive chain and A/D converters, and perform its base data generation functions, the WSP requires nonintrusive accessto a number of ASR-9 internal system signals.
Table 1 (Continued) WSP ASR9 Source Functional Name ?F Test Target 3enerator(s) Signal Name RF test target generator Part Name /Tie Point Part Name /Tie Point Linear “‘A”, “B”, & CP Used off-line as in ASR-9 TBD qF-IF TTG selected COHO COHOSP A3S2-J4 (COHO module) WSP Receiver & timing ,inear “A” - high or low 3eam selection BEAMONLOI +/- & BEAMONHI +/- 2A4A120: A61/A62 & A63lA64 Matrix control ,inear “B” - high or low team selection BEAMONLOI +/- & BEAMONH I +/- 5A4A120: A61/A62 & A63lA6
Table 1 (Continued) WSP ASR-9 Source Functional Name Signal Nzime Part Name nie Point Part Name flie Point Transmit Time Trigger RGPRETO- A4A122: A82 REF.: 2.3.1.1.3.3.2.2.2 Timing and control Range zero RGRO- A4A120: B75 Timing and control Interrogate INTERROGATE A4A121: 876 Ref. 2.3.1.1.3.3.2.
4.2.2 COHO The COHO is available on A352-J4 (COHOSP) at +2dBm level. 4.2.3 Azimuth Reference for the WSP The ASR-9 derives its azimuth reference from one of the two pulse generators (with one online) located on the antenna pedestal. A train of 4096 azimuth change pulses are generated per revolution of the antenna, and a reference pulse is generatedas the antennapassesnorth.
4.2.3.1 Azimuth Change Pulse (ACP) Connection The Azimuth Change Pulse appearsat the rear of the card cage on the STU trigger amplifier (A4A221) pin 6. A more convenient location to acquire the signal is at the BNC connector on A5Jl in the top of the four-bay cabinet. The signal is an 85.3 Hertz pulse and is 0 to +15 into 75 ohms. The driver schematic for this signal can be found in ASR-9 T16310.28, figure 1l-8, page 8 of 17. 4.2.3.
4.2.6 Rejection of Range Ambiguous Weather Echoes by Microstagger An important feature of the WSP is its ability to reject second trip or range ambiguous weather echoes by taking advantage of microstagger operation implemented by the ASR-9 to eliminate range ambiguous aircraft echoes.
4.2.7.1.1 AID Data Manipulation The read-write algorithm used by the two-block, 18-pulse data structure of the ASR-9 target channel processor is transformed into a three-block, 27-pulse data analogue for the WSP. The write order distributes I and Q data for 973 range cells each pulse repetition interval. The WSP stores range-ordered data continuously. The high and low CPIs operate with two different pulse repetition frequencies to eliminate Doppler blind speed effects in the target detection.
BUI bRTsOR .-# INTERPULSE PERIODS RANGE ORDER (WRITE) Extended Coherent Processing interval (ECPI) 17,514 RANGE CELLS R ONE BAT II Cel BULK MEtl ~~RPZZ%G~GT~ BATCH ORDER (READ) Modified TI 6310.28, Figure Z-33, Page Z-147 Figure 13. Read and write order of digital samples showing both the CPIP and ECIP array.
4.3 Control Functions As described previously, the WSP RDA controls a network of microwave switches which route appropriate signals to the WSP receive chain. When on-line, the WSP must determine the appropriate positions for these switches using high speed logic devices, and generate suitable drive signals. The sequencing of signals processedby the WSP RDP is summarized in Figure 14. Special timing signals are provided for implementing the required switching of the microwave circuits and digital signals.
4.32 Target Channel Low Beam Selection Beam switches XSWlOl (“A” channel) and XSW102 (“B” channel) are controlled to provide WSP access to the active channel, co-polarized, low beam microwave signals. The control signals are slaved to the active channel RAG beam select signal so as to divert low beam data to the WSP only when it is not in use by the target channel. The waveguide is connected to the ASR-9 in the default condition. 4.3.
4.3.6 Microwave ‘Preselector” Filter Switches S5 and S6 are controlled by the WSP when on-line to select the microwave bandpassfilter (FL3 or PL4) matched to the active channel transmitter frequency. 4.3.7 RF Receive Chain Output As shown in figure 10, the RF receiving chain components of the ASR-9’s six level weather channel are sharedby the WSP. When on-line, the WSP RDA sets switch XSW107 to direct this output to the WSP’s high dynamic range II? receiver. 4.3.
2. Control of the weather channel preselector switches (S5 and S6) and STC unit is returned to the ASR-9 six-level weather channel. 3. Switch XSW107 is latched so at to provide RF receive chain output to the existing ASR-9 six-level weather channel IF receiver, digitization and processing circuits. 4. Control of the cross-polarized signal coaxial waveguide switch (10AlSl) is returned to the ASR-9. This allows for resumption of the RAG beam selection mode required by the ASR-9. six-level weather channel. 5.
Table 3 VDI-RPG Message Format WORD I Bits Bits Bits Bits 3-O: 7-4: 15-8: 18-l 6: Bit 19: Bit 20: Bit 21: Bit 22: Bit 23: Bit 24: 1, 2 Bits 30-25: Bit 31: Bit 30-O: 4 Bit 31: Bits 11-O: Bits 31-l 2: Bits 11-O: 5 Bits 31-12: Bits 30-O: 3 6 7 8 9 IDENTlilER Year Ones Year Tens Drive ID (0x01) XSW105 Status: 001 - LP, low beam; 010 - LP, high beam; loo-CP XSW103 & 104 Status A=O, B=l Channel: A=O, B=l Polarization: L=l , CP=O Scan: even=O, odd=1 XSW107 Switch Position: O=ASR-9,i =WSP STC Switch Pos
5.0 SUMMARY As discussedin this report, the required inputs to the WSP can be acquired from the ASR-9 through implementation of suitable microwave and digital signal interfaces, appropriately controlled by logic devices within the WSP. Although detailed design of this interface will be accomplished by the WSP implementation contractor, we expect that many features described herein will be preserved at least functionally.
ACRONYMS AND ABBREVIATIONS ACP AGC AGL AP ASR-9 ATCBI ATCT BIT BIT/FIT BNC BRITE CFAR CMT COHO COTS CP CPI CPIENO CPIP DEDS DF DRI ECPI EEPROM FAA GPS I&Q IAGC IF LED LNA LP MDS MTD NAS NIMS PLL PPI PRETO PRF PRI PRT RAG Analog to Digital Antenna Change Pulse Automatic Gain Control Above Ground Level Anomalous Propagation Azimuth ReferencePulse Airport Surveillance Radar Air Traffic Control Beacon Target Interrogator Air Traffic Control Tower Built-in Test Built-in Test/Fault-Isolation Test Bayonet Neil1
RDA RDI RDP RDT RI? RF-IF RGPRETO RMS RPG SCIP SCSI SD SP3T SPDT STALO STC STU TDWR TPG TRACON TTG VDI VME VSP WSP Radar Data Acquisition Radar Digital Interface Radar Data Processor Ribbon Display Terminal (an alphanumeric display) Radio Frequency Radio Frequency-Intermediate Frequency Range Pretrigger Remote Monitoring System Radar Product Generator Surveillance Communications Interface Processor Small Computer Systems Interface Situation Display Single-Pole, Triple-Throw Single-Pole, Double-Throw Stable
REFERENCE i31 Mark E. Weber, “ASR Weather Systems Processor (WSP) Signal Processing Algorithms,” Lexington, MA, MIT Lincoln Laboratory, Project Report ATC-255, publication pending.
APPENDIX SUPPLEMENTAL MATERIAL ON THE ASR-9 SIX-LEVEL WEATHER CHANNEL The following paragraphsprovide supplemental information on six-level weather processor functions. Where provided, the parenthetical numbers in the sub-section headings refer to the ASR-9 Technical Instruction Manual paragraphwhere the associatedfunction is described. c A.
synchronizes the antenna position pulses with range sample pulses. The function of the STU B (A4A121) is to provide an interface between the transmitter, RF/if receiver, frequency generator, weather receiver/SCIP, and the monitoring control function. The STU B receives radar mode data from the weather receiver/SCIP and usesthis data to generatecontrol signals that are output to the transmitter. It also receives buffered triggers from the RAG generator and outputs them to the transmitter.
E. A/D Interrogate Pulse Generation (2.3.1.1.1.5) The A/D pulse function is used on the ASR-9 A/D converter board of the RF-IF receiver for A/D interrogations. The PRT start triggers PRETO. RGPRETO enables the output of the interrogate signal INTERROGATE. A similar function is required for the WSP. Becauseof the need to have a fine adjustment of the INTERROGATE while maintaining its phase synchronization with the radar timing, a 10.35 MHz clock shifts the 1.
2042 . LIVE DATA LIVE DATA LIVE DATA 973 RC%: IandQ v) = 8 Q) F 8 2*48 CALIBRATION DATA CALIBRATION DATA UNUSED 0 A 48 AL +8PRTe+++ lOPRTe+9PRTe+j MODIFIED FOR WSP Bulk Memory Data Diagram TI 8810.28 (01 Dec. 90) pg 2-151 WSP bulk memory located in the Radar Data Acquisition unit. Figure A-l. Bulk memory diagram showing the 960 weather target range cells, the 13 CFAR cells used by the target channel, and the nominal 48 range cells usedfor calibration signals. H.
scheme. The image signal is effectively canceled by the hybrid arrangement and subsequent mixers. The overall gain of the RF receiver is 14 dB, plus or minus 1.4 dB. The ASR-9 amplifier has an AGC attenuator at the output of its first stagewhich is controlled by the digital processor via a D/A converter to maintain constant gain and hold the receiver output noise at a constant level.
