Publications
Impacts of WSR-88D SAILS and MRLE VCP options on severe weather warning performance
July 31, 2024
Project Report
Published in:
MIT Lincoln Laboratory Report NOAA-36
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Summary
The impacts of supplemental adaptive intra-volume low-level scan (SAILS) and mid-volume rescan of low-level elevations (MRLE) usage on the Weather Surveillance Radar 1988-Doppler (WSR-88D) with respect to severe weather warning performance were evaluated. This is an update and expansion of an earlier study by Cho et al. (2022). Statistical methods applied to historical data from 2014–2022 yielded the following major results. Severe thunderstorm (SVR) warning performance metrics are shown in the figure below, where the vertical bars represent 95% confidence intervals and the numbers at the bottom correspond to the sample sizes. The results are divided according to the scanning option that is estimated to have been used at the time the decision to issue (or not issue) a warning was made. The first point to note is that probability of detection (POD), false alarm ratio (FAR), and mean lead time (MLT) improvements were associated with the usage of supplemental adaptive intra-volume low-level scan (SAILS or MRLE) in a statistically meaningful manner. As for the different sub-modes of SAILS, the multiple elevation scan option (MESO), i.e., SAILSx2 and SAILSx3, appeared to give more benefit than SAILSx1. However, the fact that the fastest base-scan update rates provided by SAILSx3 hardly yielded more benefit than SAILSx2 may indicate that the slowdown in volume scan update rates counteracted the more frequent base scans when going from SAILSx2 to SAILSx3. For POD and FAR, MRLE+4 significantly outperformed MESO-SAILS, which may also indicate that more frequent updates of elevations angle scans higher than the lowest tilt are needed by forecasters to make accurate SVR warning decisions.
Summary
The impacts of supplemental adaptive intra-volume low-level scan (SAILS) and mid-volume rescan of low-level elevations (MRLE) usage on the Weather Surveillance Radar 1988-Doppler (WSR-88D) with respect to severe weather warning performance were evaluated. This is an update and expansion of an earlier study by Cho et al. (2022). Statistical methods...
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Covariance estimation with scanning arrays: FY23 RF Systems Technical Investment Program
December 21, 2023
Project Report
Published in:
MIT Lincoln Laboratory Report TIP-194
Summary
Analog arrays with steerable beams can be capable of angle estimation and sometimes even adaptive beamforming based on power measurements taken at the outputs of multiple beam dwells. In the interesting case of a reflectarray, where beams are formed using a large collection of programmable, passive phase shifters, it is possible to use multiple dwells to estimate signal correlations among the phase shifters. These correlations form an estimated covariance matrix at the phase centers of the shifters. Adaptive beamforming and geolocation can be based on this covariance matrix. Various methods for estimating full-rank and approximately rank-deficient covariance matrices using power measurements from multiple dwells are introduced and evaluated. In some cases, the performance of an estimator can be shown to be optimal in the sense of achieving Cramer-Rao bounds for the estimated covariance parameters.
Summary
Analog arrays with steerable beams can be capable of angle estimation and sometimes even adaptive beamforming based on power measurements taken at the outputs of multiple beam dwells. In the interesting case of a reflectarray, where beams are formed using a large collection of programmable, passive phase shifters, it is...
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WSR-88D microburst detection performance evaluation
November 28, 2023
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-455
Summary
An empirical study of Weather Surveillance Radar 1988-Doppler (WSR-88D) microburst detection performance is conducted using Integrated Terminal Weather System (ITWS) microburst detections as reference. Data from 14 airport regions during 181 independent time periods spanning the years 2015–2022 are utilized for the evaluation. Results show that the detection and false alarm probabilities depend on event range from the WSR-88D. ITWS-level detection (~95%) and false alarm (~5%) probabilities are achieved for 0 to 20 km range, while at 20 to 30 km range, detection (~80%) and false alarm (~5%) rates meeting or exceeding Weather Systems Processor (WSP) microburst detection (≥80%) and false alarm (≤15%) probability requirements are observed. Beyond ~30 km from the radar, the WSR-88D microburst detection performance falls to operationally unacceptable levels. Timing analysis indicates that, on average, WSR-88D microburst detections lag ITWS microburst detections with a median value on the order of 30 s. The detection time difference distribution shows a normal symmetric form around zero with a thin tail extending in the positive lag direction, implying that the thin tail is responsible for the positive median lag time. The lag distribution tail is shown to be shortened, and the median lag time reduced to ~10 s, if the WSR-88D's slower base scan update modes are eliminated. The study shows that the WSR-88D (and its future replacement) could generate operationally useful microburst alerts for airports that are located close enough (less than ~20 km) to the radar. The long detection lag times for a small fraction of cases that are associated with WSR-88D scan strategies that have long base (lowest elevation angle) scan update periods is an issue that may need to be addressed if the current system is to be considered for operational air traffic control purposes. Also, the unavailability of output data from the first eight range gates (2 km) should be addressed for a future replacement radar by adding a minimum observation range requirement comparable to the Terminal Doppler Weather Radar's (TDWR; 0.5 km) to the follow-on radar program requirements.
Summary
An empirical study of Weather Surveillance Radar 1988-Doppler (WSR-88D) microburst detection performance is conducted using Integrated Terminal Weather System (ITWS) microburst detections as reference. Data from 14 airport regions during 181 independent time periods spanning the years 2015–2022 are utilized for the evaluation. Results show that the detection and false...
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Radio frequency interference censoring scheme for Canadian Weather Radar
July 12, 2023
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-454
Summary
An automated scheme is developed for the upgraded S-band polarimetric Canadian weather radars to detect and censor radio frequency interference from wireless communication devices. The suite of algorithms employed in this scheme effectively identifies and edits out interference-contaminated reflectivity data, while preserving data dominated by weather signals. This scheme was implemented in the NextGen Weather Processor test reference system for continuous real-time testing, and is expected to be incorporated into the new Canadian Aviation Weather Systems.
Summary
An automated scheme is developed for the upgraded S-band polarimetric Canadian weather radars to detect and censor radio frequency interference from wireless communication devices. The suite of algorithms employed in this scheme effectively identifies and edits out interference-contaminated reflectivity data, while preserving data dominated by weather signals. This scheme was...
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A deep learning-based velocity dealiasing algorithm derived from the WSR-88D open radar product generator
July 1, 2023
Journal Article
Published in:
Artificial Intelligence for the Earth Systems, Vol. 2, Issue 3, July 2023.
Summary
Radial velocity estimates provided by Doppler weather radar are critical measurements used by operational forecasters for the detection and monitoring of life-impacting storms. The sampling methods used to produce these measurements are inherently susceptible to aliasing, which produces ambiguous velocity values in regions with high winds and needs to be corrected using a velocity dealiasing algorithm (VDA). In the United States, the Weather Surveillance Radar-1988 Doppler (WSR-88D) Open Radar Product Generator (ORPG) is a processing environment that provides a world-class VDA; however, this algorithm is complex and can be difficult to port to other radar systems outside the WSR-88D network. In this work, a deep neural network (DNN) is used to emulate the two-dimensional WSR-88D ORPG dealiasing algorithm. It is shown that a DNN, specifically a customized U-Net, is highly effective for building VDAs that are accurate, fast, and portable to multiple radar types. To train the DNN model, a large dataset is generated containing aligned samples of folded and dealiased velocity pairs. This dataset contains samples collected from WSR-88D Level-II and Level-III archives and uses the ORPG dealiasing algorithm output as a source of truth. Using this dataset, a U-Net is trained to produce the number of folds at each point of a velocity image. Several performance metrics are presented using WSR-88D data. The algorithm is also applied to other non-WSR-88D radar systems to demonstrate portability to other hardware/software interfaces. A discussion of the broad applicability of this method is presented, including how other Level-III algorithms may benefit from this approach.
Summary
Radial velocity estimates provided by Doppler weather radar are critical measurements used by operational forecasters for the detection and monitoring of life-impacting storms. The sampling methods used to produce these measurements are inherently susceptible to aliasing, which produces ambiguous velocity values in regions with high winds and needs to be...
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Visibility estimation through image analytics
June 20, 2023
Project Report
Published in:
MIT Lincoln Laboratory Report ATC-453
Summary
MIT Lincoln Laboratory (MIT LL) has developed an algorithm, known as the Visibility Estimation through Image Analytics Algorithm (VEIA), that ingests camera imagery collected by the FAA Weather Cameras Program Office (WeatherCams) and estimates the meteorological visibility in statute miles. The algorithm uses the presence of edges in the imagery and the strength of those edges to provide an estimation of the meteorological visibility within the scene. The algorithm also combines the estimates from multiple camera images into one estimate for a site or location using information about the agreement between camera estimates and the position of the Sun relative to each camera's view. The final output for a site is a prevailing visibility estimate in statute miles that can be easily compared to existing automated surface observation systems (ASOS) and/or human-observed visibility. This report includes thorough discussion of the VEIA background, development methodology, and transition process to the WeatherCams office operational platform (Sections 2–4). A detailed software description with flow diagrams is also provided in Section 5. Section 6 provides a brief overview of future research and development related to the VEIA algorithm.
Summary
MIT Lincoln Laboratory (MIT LL) has developed an algorithm, known as the Visibility Estimation through Image Analytics Algorithm (VEIA), that ingests camera imagery collected by the FAA Weather Cameras Program Office (WeatherCams) and estimates the meteorological visibility in statute miles. The algorithm uses the presence of edges in the imagery...
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Extended polarimetric observations of chaff using the WSR-88D weather radar network
June 20, 2023
Journal Article
Published in:
IEEE Transactions on Radar Systems, vol. 1, pp. 181-192, 2023.
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Summary
Military chaff is a metallic, fibrous radar countermeasure that is released by aircraft and rockets for diversion and masking of targets. It is often released across the United States for training purposes, and, due to its resonant cut lengths, is often observed on the S-band Weather Surveillance Radar–1988 Doppler (WSR-88D) network. Efforts to identify and characterize chaff and other non-meteorological targets algorithmically require a statistical understanding of the targets. Previous studies of chaff characteristics have provided important information that has proven to be useful for algorithmic development. However, recent changes to the WSR-88D processing suite have allowed for a vastly extended range of differential reflectivity, a prime topic of previous studies on chaff using weather radar. Motivated by these changes, a new dataset of 2.8 million range gates of chaff from 267 cases across the United States is analyzed. With a better spatiotemporal representation of cases compared to previous studies, new analyses of height dependence, as well as changes in statistics by volume coverage pattern are examined, along with an investigation of the new "full" range of differential reflectivity. A discussion of how these findings are being used in WSR-88D algorithm development is presented, specifically with a focus on machine learning and separation of different target types.
Summary
Military chaff is a metallic, fibrous radar countermeasure that is released by aircraft and rockets for diversion and masking of targets. It is often released across the United States for training purposes, and, due to its resonant cut lengths, is often observed on the S-band Weather Surveillance Radar–1988 Doppler (WSR-88D)...
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Poisoning network flow classifiers [e-print]
June 2, 2023
Journal Article
Published in:
arXiv:2306.01655v1 [cs.CR]
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Summary
As machine learning (ML) classifiers increasingly oversee the automated monitoring of network traffic, studying their resilience against adversarial attacks becomes critical. This paper focuses on poisoning attacks, specifically backdoor attacks, against network traffic flow classifiers. We investigate the challenging scenario of clean-label poisoning where the adversary's capabilities are constrained to tampering only with the training data - without the ability to arbitrarily modify the training labels or any other component of the training process. We describe a trigger crafting strategy that leverages model interpretability techniques to generate trigger patterns that are effective even at very low poisoning rates. Finally, we design novel strategies to generate stealthy triggers, including an approach based on generative Bayesian network models, with the goal of minimizing the conspicuousness of the trigger, and thus making detection of an ongoing poisoning campaign more challenging. Our findings provide significant insights into the feasibility of poisoning attacks on network traffic classifiers used in multiple scenarios, including detecting malicious communication and application classification.
Summary
As machine learning (ML) classifiers increasingly oversee the automated monitoring of network traffic, studying their resilience against adversarial attacks becomes critical. This paper focuses on poisoning attacks, specifically backdoor attacks, against network traffic flow classifiers. We investigate the challenging scenario of clean-label poisoning where the adversary's capabilities are constrained to...
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Improving long-text authorship verification via model selection and data tuning
May 5, 2023
Conference Paper
Published in:
Proc. 7th Joint SIGHUM Workshop on Computational Linguistics for Cultural Heritage, Social Sciences, Humanities and Literature, LaTeCH-CLfL2023, 5 May 2023, pp. 28-37.
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Summary
Authorship verification is used to link texts written by the same author without needing a model per author, making it useful for deanonymizing users spreading text with malicious intent. Recent advances in Transformer-based language models hold great promise for author verification, though short context lengths and non-diverse training regimes present challenges for their practical application. In this work, we investigate the effect of these challenges in the application of a Cross-Encoder Transformer-based author verification system under multiple conditions. We perform experiments with four Transformer backbones using differently tuned variants of fanfiction data and found that our BigBird pipeline outperformed Longformer, RoBERTa, and ELECTRA and performed competitively against the official top ranked system from the PAN evaluation. We also examined the effect of authors and fandoms not seen in training on model performance. Through this, we found fandom has the greatest influence on true trials, pairs of text written by the same author, and that a balanced training dataset in terms of class and fandom performed the most consistently.
Summary
Authorship verification is used to link texts written by the same author without needing a model per author, making it useful for deanonymizing users spreading text with malicious intent. Recent advances in Transformer-based language models hold great promise for author verification, though short context lengths and non-diverse training regimes present...
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Network performance of pLEO topologies in a high-inclination Walker Delta Satellite Constellation
March 4, 2023
Conference Paper
Published in:
IEEE Aerospace Conf. Proc., 4-11 March 2023, 188722.
Summary
Low-earth-orbit satellite constellations with hundreds to thousands of satellites are emerging as practical alternatives for providing various types of data services such as global networking and large-scale sensing. The network performance of these satellite constellations is strongly dependent on the topology of the inter-satellite links (ISLs) in such systems. This paper studies the effects of six different ISL topologies, coupled with three configurations of ground relay terminals, on path failure rate, path latency, and link transmission efficiency in an example highly-inclined Walker Delta constellation with 360 satellites. These network performance parameters are calculated in the presence of satellite failures in the constellation. Trade-offs between ISL connection density and overall performance are examined and quantified. Topologies with 4 active ISLs per satellite are shown to perform significantly better than topologies requiring fewer, especially as the average number of active ISLs per satellite becomes significantly less than three. Latencies for a topology requiring 3 active ISLs per satellite are shown to be between 15 and 60% higher than for a 4-ISL reference topology. Path availabilities for the 3-ISL topology are shown to be on the order of 30% lower for a benchmark case of 10 satellite failures. The performance of near-minimal topologies (e.g., an average of 2.2 active ISLs per satellite) is much worse. Latency reductions of 10-30% and path failure rate improvements on the order of 45% are shown to be obtainable by the inclusion of 2 to 5 strategically located ground relay stations
Summary
Low-earth-orbit satellite constellations with hundreds to thousands of satellites are emerging as practical alternatives for providing various types of data services such as global networking and large-scale sensing. The network performance of these satellite constellations is strongly dependent on the topology of the inter-satellite links (ISLs) in such systems. This...
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