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BMEWS Scintillation Environment at Clear AFS: A DoD/OSA Phase I Study P. K. Rastogi S. N. Hunt C. M. Sorrentino March 1997 MITRE Organization: D710 Revision Mar 4, 1998

BMEWS Scintillation Environment at the Clear AFS : 

BMEWS Scintillation Environment at the Clear AFS MITRE study for DoD/OSA Phase I February 1998 Model the effects of ionospheric scintillations on critical functions of Ballistic Missile Early Warning System (BMEWS) at Clear for different space-weather scenarios using state-of-the-art modeling programs Analysis overview Models Radar simulation and modeling program TD/SAT Scintillation modeling program WBMOD Analysis approach combines TD/SAT and WBMOD Scenarios Space-Weather: Sunspot number, Kp index, Epoch Radar: Threat trajectory and target type Analysis, Results and Discussion

Analysis Overview: Models Radar Simulation Program TD/SAT: 

Analysis Overview: Models Radar Simulation Program TD/SAT Test Driver/Software Algorithm Testbed (TD/SAT) High-fidelity end-to-end radar simulation and modeling program developed by XonTech Evolved from Integrated Radar Algorithm Simulator (IRAS) Four major system components Test Driver (TD) SAT Signal Processor (SP) SAT Data Processor (DP) TD/SAT Displays Includes limited ionospheric amplitude and phase scintillation modeling capability “Dial-in” fixed scintillation level along the trajectory Residual Position and Velocity Errors (RPE and RVE)

Analysis Overview: Models Discussion of Position and Velocity Errors: 

Analysis Overview: Models Discussion of Position and Velocity Errors Unlike a real radar, the true target trajectory and velocity are modeled and available in TD/SAT for comparison with radar-estimated target position and velocity Residual Position Error (RPE) Residual Velocity Error (RVE) Radar-estimated position and velocity estimates (using a Kalman filter for tracking) have associated covariance uncertainties Covariance Position Uncertainty (CPU) Covariance Velocity Uncertainty (CVU) Tracker-derived CPU and CVU are robust and small, though not always true. These are not discussed here. TD/SAT derived RPU and RVE are initially very large but become smaller after a few minutes as the target is tracked

Analysis Overview: Models Scintillation Modeling Program WBMOD: 

Analysis Overview: Models Scintillation Modeling Program WBMOD Robust statistical-climatological model (not predictive) of ionospheric intensity and phase scintillations based on Statistical phase-screen model Extensive one-way satellite-beacon observations Developed over the last two decades at Phillips Laboratory and Northwest Research Associates Models percentile levels of intensity scintillation index S4 (ratio of r.m.s. and average intensities) and r.m.s. phase scintillation index sf for a given epoch and space-weather scenarios (SSN, Kp, precipitation boundary or default) User specified uplink-downlink correlation (assumed 1) and required phase-coherence time (assumed 0 second) Current version includes updated high-latitude scintillation climatology and a user-specified trajectory

Analysis Overview: Models Combining TD/SAT and WBMOD: 

Analysis Overview: Models Combining TD/SAT and WBMOD

Analysis Overview: Space-Weather Scenarios: 

Analysis Overview: Space-Weather Scenarios Smoothed Sunspot Number (SSN) Low 15 Medium 80 High 160 Global geomagnetic index Kp Quiet 1.5 (almost 2-) Moderate 3 Disturbed 7 Auroral electron-precipitation boundary Using internal model in WBMOD based on Kp index Epoch: Mid-winter (January 15) and 0200 local time at Clear for peak scintillation activity

Analysis Overview: Radar Scenario in TD/SAT: 

Analysis Overview: Radar Scenario in TD/SAT Target Trajectory Imeni-Gastelo (51.2°N, 66.1°E) to Hawaii (21.5°N, 158°W) Minimum energy path with optimum burnout Radar Site: Clear AFS (64.29°N, 149.19°W) Radar Targets Detection and tracking requires a 10 dB SNR threshold Realistic targets exhibit large SNR variation due to precession and tumbling. RCS of a re-entry vehicle (RV) is too small, but a tank has acceptable RCS. A calibration sphere with flat 1 m2 RCS is also used. Scintillations SNR along the trajectory in the absence of scintillations TD/SAT internal scintillation model used for S4=0.5

Radar Analysis Using Combined TD/SAT and WBMOD Models: 

Radar Analysis Using Combined TD/SAT and WBMOD Models WBMOD and space-weather inputs are used externally to modify SNR in accordance with two-way intensity scintillations modeled along the target trajectory Modified SNR, Residual Position Error (RPE) and Residual Velocity Error (RVE) are examined along the target trajectory for a set of space-weather scenarios Sample realizations using WBMOD-TD/SAT are discussed WBMOD two-way intensity modulation vs. SSN & Kp SNR and RCS for a tank under extreme SSN and Kp RPE and RVE in tracking a tank/sphere for extreme SSN and Kp values SSN and Kp dependence of RPE for the tank in the initial part (300 sec) of the trajectory Results are indicative but not statistically significant

Radar Analysis Using Combined TD/SAT and WBMOD Models: Two-Way Intensity Modulation: 

Radar Analysis Using Combined TD/SAT and WBMOD Models: Two-Way Intensity Modulation 160 80 15 1.5 3 7 Kp SSN

Radar Analysis Using Combined TD/SAT and WBMOD Models: SNR Input to Tracker: 

Radar Analysis Using Combined TD/SAT and WBMOD Models: SNR Input to Tracker

Radar Analysis Using Combined TD/SAT and WBMOD Models: RCS After Detection: 

Radar Analysis Using Combined TD/SAT and WBMOD Models: RCS After Detection

Radar Analysis Using Combined TD/SAT and WBMOD Models: RPE for Tank: 

Radar Analysis Using Combined TD/SAT and WBMOD Models: RPE for Tank

Radar Analysis Using Combined TD/SAT and WBMOD Models: RPE for Sphere: 

Radar Analysis Using Combined TD/SAT and WBMOD Models: RPE for Sphere

Radar Analysis Using Combined TD/SAT and WBMOD Models: RVE for Tank: 

Radar Analysis Using Combined TD/SAT and WBMOD Models: RVE for Tank

Radar Analysis Using Combined TD/SAT and WBMOD Models: RVE for Sphere: 

Radar Analysis Using Combined TD/SAT and WBMOD Models: RVE for Sphere

Analysis Results Using Combined TD/SAT and WBMOD Models: RMS RPE First 300 Seconds: 

Analysis Results Using Combined TD/SAT and WBMOD Models: RMS RPE First 300 Seconds Single Realization. No Statistical Significance. Tank

BMEWS Scintillation Environment at Clear: Summary of DoD/OSA Phase I Results: 

BMEWS Scintillation Environment at Clear: Summary of DoD/OSA Phase I Results The radar simulation program TD/SAT and the ionospheric scintillation modeling program WBMOD have been integrated for intensity scintillations and tested with large RCS targets for a diverse set of space-weather conditions. Strong ionospheric scintillations are comparable to the inherent RCS variations of the tank selected for its large RCS to circumvent the coherent-integration issues. Single realizations for the tank do not show distinct space-weather effects, e.g., the averaged residual position error is unrealistically about the same for the low-SSN low-Kp and high-SSN, high-Kp cases. For the cases examined, luck of the draw gives inconclusive results. Extreme space-weather effects are more evident in the RPE/RVE for the sphere target. Discussion of Statistical Issues and Mission Impact

BMEWS Scintillation Environment at Clear: Discussion of Statistical Issues: 

BMEWS Scintillation Environment at Clear: Discussion of Statistical Issues Behavior of RPE and RVE in single realizations for each space-weather condition should not be used to address statistical issues such as probability of false-alarm, target identification and discrimination, and their space-weather dependence. These issues will require large-scale Monte-Carlo simulations. The BMEWS system and its simulation in TD/SAT are designed to detect and track targets above a SNR threshold of ~10 dB. Inherently large RCS variations (20 dB or more) in a complex, large-RCS target mask space-weather effects. For small targets, space-weather (scintillations) effects become closely intertwined with coherent-integration and tracker performance and design issues that are also significant for the National Missile Defense (NMD) project.

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions: 

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions BMEWS and Upgraded PAVE PAWS Early Warning Radars (UEWRs) support or may support the following missions ITW/AA Integrated Tactical Warning/Attack Assessment NMD National Missile Defense SSN/SOI Space Surveillance Network/Space Object ID Following scintillation mission impact assessment is based on prior knowledge and the single WBMOD-TD/SAT realizations that need statistical validation ITW/AA Large targets are of interest (harbor smaller targets) UEWR function of detection and tracking large targets is not severely affected by adverse space weather Short time-scale accuracy bounds on RPE are marginal and may not meet ITW/AA mission objectives

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions: 

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions NMD (Clear UEWR is currently not an NMD sensor) Mission objectives include use of UEWRs to expand battle space for early detection of RVs at long range and reliable tracking at low elevation angles for timely target classification and track handover to other mission sensors Current UEWRs need a ~10 dB or ten-fold increase in the Power Aperture Product (PAP) to meet the above mission objective. This approach is too expensive. A ~10 dB signal processing gain is possible through coherent-integration (CI) over multiple pulses, but is realizable only if phase scintillations are slow and small during the integration time. Unsaturated (moderate) amplitude scintillations are associated with ~3 dB average SNR enhancement and may help in CI.

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions: 

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions NMD (contd from previous page) Scintillations impair all aspects of target classification as they affect statistical signal attributes used for classification. Scintillation have an effect similar to target fragmentation and may thus have a direct impact on Kill Probability. Research Areas CI Impact on radar-resource allocation, Tracker Design Space-Weather effects through scintillations (other effects include NMD range errors, auroral clutter)

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions: 

BMEWS Scintillation Environment at Clear: Discussion of Scintillation Impact on Missions SSN/SOI Mission objectives include satellite and missile identification (including space debris that may impact the space station and geostationary communication satellites) detection, tracking, identification and cataloguing of ~8000 known (and many unknown) space objects primary UHF sensors are FPS 85 at Eglin AFB, PARCS in North Dakota, and the Altair at Kwajalein object identification with X-band radars BMEWS and UEWRs provide routine and ad-hoc support to the SSN/SOI mission Tracking of low-elevation and deep space objects at ~20,000 km range uses CI (affected by scintillations)

BMEWS Scintillation Environment at Clear: Recommendation for future DoD/OSA effort : 

BMEWS Scintillation Environment at Clear: Recommendation for future DoD/OSA effort A software-integration of TD/SAT and WBMOD in which WBMOD replaces the internal scintillation model in TD/SAT is necessary for any future DoD/OSA effort in this area as these efforts will require extensive Monte-carlo simulations The integration and Monte-carlo simulations should preferably be coordinated with the NMD program. The following issues are under active consideration for this program: Computation intensive multiple-hypothesis tracker for improved tracking of small targets Phase-scintillations model and coherent integration for extending the radar detection and tracking capability to smaller targets (e.g. RVs) Data collection on calibration sphere targets for evaluating coherent-integration schemes

The End: 

The End