Publications

This paper describes the Tactical 0-2 hour Convective Weather Forecast (CWF) algorithm developed by the MIT LL for the FAA. We will address the algorithm and focus on the key scientific developments. Future directions will also be discussed.

Thousands of traffic and safety monitoring cameras are deployed or are being deployed all across the country and throughout the world. These cameras serve a wide range of uses from monitoring building access to adjusting timing cycles of traffic lights at clogged intersections. Currently, these images are typically viewed on a wall of monitors in a traffic operations or security center where observers manually monitor potentially hazardous or congested conditions and notify the appropriate authorities. However, the proliferation of camera imagery taxes the ability of the manual observer to track and respond to all incidents. In addition, the images contain a wealth of information, including visibility, precipitation type, road conditions, camera outages, etc., that often goes unreported because these variables are not always critical or go undetected. Camera deployments continue to expand and the corresponding rapid increases in both the volume and complexity of camera imagery demand that automated algorithms be developed to condense the discernable information into a form that can be easily used operationally by users. MIT Lincoln Laboratory (MIT/LL) under funding from the Federal Highway Administration (FHWA) is investigating new techniques to extract weather and road condition parameters from standard traffic camera imagery. To date, work has focused on developing an algorithm to measure atmospheric visibility and prove the algorithm concept. The initial algorithm examines the natural edges within the image (the horizon, tree lines, roadways, permanent buildings, etc) and performs a comparison of each image with a historical composite image. This comparison enables the system to determine the visibility in the direction of the sensor by detecting which edges are visible and which are not. A primary goal of the automated camera imagery feature extraction system is to ingest digital imagery with limited specific site information such as location, height, angle, and visual extent, thereby making the system easier for users to implement. There are, of course, many challenges in providing a reliable automated estimate of the visibility under all conditions (camera blockage/movement, dirt/raindrops on lens, etc) and the system attempts to compensate for these situations. This paper details the work-to-date on the visibility algorithm and defines a path for further development of the overall system.

Improved handling of severe en route and terminal convective weather has been identified by the FAA in both the Operational Evolution Plan (OEP) (FAA, 2002) and the Flight Plan for 2004-2008 (FAA, 2003) as a major thrust over the coming decade for the National Airspace System (NAS) modernization. Achieving such improved capabilities is particularly important in highly congested corridors where there is both a high density of over flights and major terminals. Delay increases during thunderstorm season have been the principal cause of the dramatic delay growth in the US aviation system. When major terminals also underlie the en route airspace, convective weather has even greater adverse impacts, especially if the convective weather occurs frequently. In response to the need to enhance both safety and capacity during adverse weather, the FAA is exploring the concept of a Corridor Integrated Weather System (CIWS). CIWS is designed to improve convective weather decision support for congested en route airspace (and the terminals that lie under that airspace) by automatically generating graphical depictions of the current severe weather situation and providing frequently updated forecasts of the future weather locations for forecast times from zero to two hours. An operational demonstration of the CIWS was conducted during the summer of 2003. This document provides a detailed description of each CIWS weather information product as it was demonstrated in 2003, including a general description of the product, what data sources are used by the product, how the product is generated from the input data, and what caveats in the technical performance apply. A discussion of how the products might be used to enhance safety and support decision-making for traffic management is also included. Detailed information on the operational benefits of the CIWS products demonstrated in 2003 is provided in a companion report (Robinson et al., 2004). Improvements made to the products for the 2004 and 2005 CIWS operational demonstrations are briefly discussed in the final chapter.

This report summarizes the results of an initial study to estimate the yearly delay reduction provided by the initial operational capability (IOC) Integrated Terminal Weather System (ITWS) at Hartsfield-Jackson Atlanta International Airport (ATL). Specific objectives of this initial study were to: (1) analyze convective weather operations at ATL to determine major causes of convective weather delay and how those might be modeled quantitatively. (2) provide estimates of the ATL ITWS delay reduction based on the "Decision/Modeling" method using questionnaires and interviews with Atlanta Terminal Radar Approach Control (TRACON) and Air Route Traffic Control Center (ARTCC) operational ITWS users. (3)assess the "reasonableness" of the model-based delay reduction estimates by comparing those savings with estimates of the actual weather-related arrival delays at ATL. In addition, the reasonableness of model-based delay reduction estimates was assessed by determining the average delay savings per ATL flight during times when adverse convective weather is within the coverage of the ATL ITWS. (4)conduct an exploratory study confirming the ATL ITWS delay savings by comparing Aviation System Performance Metrics (ASPM) database delays pre- and post-ITWS at ATL. (5) assess the accuracy of the "downstream" delay model employed in this study by analyzing ASPM data from a major US airline, and (6) make recommendations for follow-on studies of the ITWS delay reduction at Atlanta and other IOC ITWS facilities. [not complete]

This paper investigates methods for quantifying convective weather delay reduction benefits for weather/ATM systems and recommends approaches for future assessments. This topic is particularly important at this time because: 1. Convective weather delays continue to be a dominant factor in the overall National Airspace System (NAS) delays, and 2. Benefits quantification and NAS performance assessment have become very important in an era of significant government and airline budget constraints for civil aviation investments. Quantifying convective weather delay benefits for ATM systems has proven to be quite difficult since the delays arise from complicated, highly variable, poorly understood interactions between convective weather and a very complex aviation system. In this paper, we consider key aspects of convective weather disruptions of the aviation system, how the weather severity can be characterized, and discuss practical experience with benefits quantification by a variety of approaches. The paper concludes with recommendations for a methodology to be used in future convective weather delay reduction quantification studies.

Multiple pulse repetition interval (multi-PRI) transmission is part of an adaptive signal transmission and processing algorithm being developed to aggressively combat range-velocity ambiguity in weather radars. In the past, operational use of multi-PRI pulse trains has been hampered due to the difficulty in clutter filtering. This paper presents finite impulse response clutter filter designs for multi-PRI signals with excellent magnitude and phase responses. These filters provide strong suppression for use on low-elevation scans and yield low biases of velocity estimates so that accurate velocity dealiasing is possible. Specifically, the filters are designed for use in the Terminal Doppler Weather Radar (TDWR) and are shown to meet base data bias requirements equivalent to the Federal Aviation Administration's specifications for the current TDWR clutter filters. Also an adaptive filter selection algorithm is proposed that bases its decision on clutter power estimated during an initial long-PRI surveillance scan. Simulations show that this adaptive algorithm yields satisfactory biases for reflectivity, velocity, and spectral width. Implementation of such a scheme would enable automatic elimination of anomalous propagation signals and constant adjustment to evolving ground clutter conditions, an improvement over the current TDWR clutter filtering system.

The majority of research into the wake vortex hazard has concentrated on the in-trail encounter scenario for arrivals. At LaGuardia Airport, wake vortex spacings are applied to arrivals on runway 22 following a heavy departure on the intersecting runway 31, resulting in delay and increased workload for controllers. Previous analysis of this problem led to a recommendation for a measurement campaign to collect data on the behavior of wake vortices generated by departing heavy aircraft. In April of 2004, MIT Lincoln Laboratory deployed its wake vortex lidar system to measure such wakes at LaGuardia. Additionally, wind speed and turbulence data were collected with the hope of correlating wake behavior with the local atmospheric conditions. Analysis of the lidar data indicates that the system was able to acquire and track vortices from departures, a task not proven prior to this deployment. Further, vortices were seen to transport toward the threshold of runway 22, verifying an assumption based on analysis of the winds that wake transport is not a solution in this case. The quantity and type of data collected were insufficient to formulate a clear relationship between atmospheric turbulence and vortex decay. However, it may be possible to develop such a model by exploiting the data gathered during previous lidar deployments.

The Terminal Doppler Weather Radar (TDWR) radar data acquisition (RDA) subsystem is being replaced as part of a broader FAA program to improve the supportability of the system. An engineering prototype RDA has been developed with a scalable, open-systems hardware platform. With the dramatically increased computing power and more flexible transmitter control, modern signal processing algorithms can be implemented to improve the quality of the base data. Nation-wide, the most serious data quality challenge is range-velocity (RV) ambiguity. In a previous study (Cho et al., 2003) we showed that multiple pulse repetition interval (PRI) and constant-PRI phase-code processing have complementary strengths with respect to range-fold protection, and pro-posed an adaptive waveform and processing selection scheme on a radial-by-radial basis. Here we describe the scheme and give more details about the clutter filtering and velocity dealiasing algorithms to be used on the two types of signals.

In this paper, we summarize contemporary approaches to quantifying convective weather delay reduction benefits. We outline a program to develop a significantly improved capability that can be used to assess benefits of specific systems. This program may potentially accomplish weather impact normalization for studies of National Airspace System (NAS) performance in handling convective weather. Benefits quantification and NAS performance assessment have become very important topics for the aviation weather community. In an era of significant federal government and airline budget austerity for civil aviation investments, it is essential to quantitatively demonstrate delay reduction benefits of improved weather decision support systems. Major FAA initiatives stress the importance of quantitative system performance metrics that are related to aviation weather. For example, the new FAA Air Traffic Organization (ATO) and the FAA Flight Plan 2004-08 both have quantitative performance metrics that are closely related to reducing convective weather delays. The Flight Plan metrics include: "Improving the percentage of all flights arriving within 15 minutes of schedule at the 35 OEP airports by 7%, as measured from the FY2000-02 baseline, through FY08," and "Maintaining average en route travel times among the eight major metropolitan areas." The ATO metrics include the percentage of on time gate arrivals and the fraction of departures that are delayed greater than 40 minutes. However, these metrics currently do not account for the differences in convective weather severity and changes in the NAS. The dramatic increase in convective season delays in 2004 (Figure 1) due to a combination of severe weather, increases in overall demand, and specific airport issues has demonstrated that one needs to consider these other factors. Approaches to delay reduction quantification that were viewed as successful and valid several years ago are no longer considered to be adequate by either by the FAA investment analysis branch or by the Office of Management and Budget (OMB). The paper proceeds as follows. We first discuss at some length the mechanisms by which convective weather delay occurs in the NAS and highlight challenges in delay reduction assessment. We consider this to be very important since one needs to understand how the system operates if one is to design an effective, accurate performance assessment system. We then consider benefits quantification based on feedback from experienced users of a system. Feedback on "average" benefits from a system at the end of a test period was used to generate delay reduction estimates for the Integrated Terminal Weather System (ITWS) and the Weather and Radar Processor (WARP). This end-of-season interview approach was not viable in highly congested en route airspace. Hence, a new approach was developed for Corridor Integrated Weather System (CIWS) benefits assessment that uses real time observations of product usage during convective weather events coupled with in depth analysis of specific cases. Next, we discuss the problems that arise when one attempts to quantify delay reduction benefits by comparing flight delays before and after the Integrated Terminal Weather System (ITWS) system was deployed at Atlanta Hartsfield International Airport (ATL). This seemingly simple approach has proven very difficult in practice because the convective weather events in the different time periods are virtually never identical and because other aspects of the NAS may also have changed (e.g., user demand, fleet mix, and other systems that impact convective weather delays). It has become clear that one needs a quantitative model for the NAS that would permit adjustment of measured delay data to account at least for the differences in convective weather and changes in user demand (i.e., flight scheduling). The paper concludes with recommendations for measuring near term benefits of various classes of convective weather decision support systems.

Major airlines and FAA Traffic Flow Managers alike would prefer to plan their flight routes around convective weather and thereby avoid the tactical maneuvering that results when unforecasted thunderstorms occur. Strategic planning takes place daily and 2-6 hr forecasts are utilized, but these early plans remain unaltered in only the most predictable of convective weather scenarios. More typically, the ATC System Command Center and the Air Route Traffic Control Centers together with airline dispatchers will help flights to utilize jet routes that remain available within regions of convection, or facilitate major reroutes around convection, according to the available "playbook" routes. For this tactical routing in the presence of convective weather to work, both a precise and timely shared picture of current weather is required as well as an accurate, reliable short term (0-2 hr) forecast. This is crucial to containing the system-wide and airport-specific delays that are so prevalent in the summer months (Figure 1), especially as traffic demands approach full capacity at the pacing airports. This paper describes the Tactical 0-2 hr Convective Weather Forecast (CWF) algorithm developed by the MIT Lincoln Laboratory for the FAA, principally sponsored by the Aviation Weather Research Program (AWRP). This CWF technology is currently being utilized in both the Integrated Terminal Weather System (ITWS; Wolfson et al., 2004) and the Corridor Integrated Weather System (CIWS; Evans et al., 2004) proof-of-concept demonstrations. Some of this technology is also being utilized in the National Convective Weather Forecast from the Aviation Weather Center (Megenhardt, 2004), the NCAR Autonowcaster (Saxen et al., 2004), and in various private-vendor forecast systems.