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  • Report No. DOT/FAA/RD-95/5

    Project Report

    ATC-275

    Lincoln Laboratory MASSACHUSETTS INSTITUTE OF TECHNOLOGY

    LEXINGTON, MASSACHUSETTS

    29 July 2002

    S.W. Troxel

    Prepared for the Federal Aviation Administration.

    Document is available to the public through the National Technical Information Service,

    Springfi eld, Virginia 22161.

    Gust Front Update Algorithm for the Weather Systems Processor (WSP)

  • This document is disseminated under the sponsorship of the Department of Trans- portation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof.

  • 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

    4. Title and Subtitle 5. Report Date

    6. Performing Organization Code

    7. Author(s) 8. Performing Organization Report No.

    9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

    11. Contract or Grant No.

    12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered

    14. Sponsoring Agency Code

    15. Supplementary Notes

    16. Abstract

    17. Key Words 18. Distribution Statement

    19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

    TECHNICAL REPORT STANDARD TITLE PAGE

    FORM DOT F 1700.7 (8-72) Reproduction of completed page authorized

    Seth W. Troxel

    MIT Lincoln Laboratory 244 Wood Street Lexington, MA 02420-9108

    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.

    ATC-275

    F19628-00-C-0002

    This document is available to the public through the National Technical Information Service, Springfi eld, VA 22161.

    Unclassifi ed

    ATC-275

    Gust Front Update Algorithm for the Weather Systems Processor (WSP)

    Unclassifi ed 32

    29 July 2002

    Project Report

    Department of Transportation Federal Aviation Administration 800 Independence Ave., S.W. Washington, D.C. 20591

    The Gust Front Update algorithm (GFUP) is part of the gust front product generation chain for the ASR-9 Weather Systems Processor (WSP). GFUP processes gust front detection and position prediction data output by the Machine Intelligent Gust Front Algorithm (MIGFA), and uses an internal timer to schedule generation of updated current and 10- and 20-minute gust front predictions at 1-minute intervals. By substituting appropriate interval gust front forecast data from MIGFA, the locations of gust fronts shown on the user display are updated at a rate that is faster than the radar base data processed by MIGFA. Prior to output, the updated curve position data are smoothed by GFUP using a tangent-spline interpolation algorithm.

    This document provides a general overview and high level description of the GFUP algorithm.

  • ABSTRACT

    The Gust Front Update algorithm (GFUP) is part of the gust front product generation chain for the ASR-9 Weather Systems Processor (WSP). GFUP processes gust front detection and position prediction data output by the Machine Intelligent Gust Front Algorithm (MIGFA), and uses an internal timer to schedule generation of updated current and 10- and 20-minute gust front predictions at 1-minute intervals. By substituting appropriate interval gust front forecast data from MIGFA, the locations of gust fronts shown on the user display are updated at a rate that is faster than the radar base data processed by MIGFA. Prior to output, the updated curve position data are smoothed by GFUP using a tangent-spline interpolation algorithm.

    This document provides a general overview and high level description of the GFUP algorithm.

    ... 111

  • TABLE OF CONTENTS

    1.

    2.

    Abstract List of Illustrations

    INTRODUCTION

    1.1 Algorithm Product Description 1.2 Conceptual Overview 1.3 Information Environment

    HIGH LEVEL ALGORITHM DESCRIPTION 2.1 Algorithm Identification and Purpose 2.2 Algorithm Data

    APPENDIX A. PARAMETER TABLE FOR GUST FRONT UPDATE (GFUP)

    GLOSSARY

    REFEmNCES

    Page

    iii vii

    3

    3 14

    21

    23

    25

    V

  • I

  • LIST OF ILLUSTRATIONS

    Figure No.

    1 External interface data flow diagram for the GFUF' algorithm.

    2 GFUP algorithm functional flow diagram.

    3 Data flow diagram for the GFW-UpdateLocations function showing mapping of the data fiom a single GF in an input GF-MAP (gf-map) into a corresponding GF in the output G F - W (updated-fine_gf-mp).

    4 Call tree for GFUP.

    Page

    4

    5

    6

    9

    vii

  • 1. INTRODUCTION

    1.1 ALGORITHM PRODUCT DESCRIPTION

    GFUP is used in the generation of the gust front products. It interprets the output of the Machine Intelligent Gust Front Algorithm (MIGFA), containing gust front locations and estimates of f h r e locations along with associated wind shear information, to provide the following:

    1. Smoothed symbolic representations of current gust front locations and associated 10- and 20- minute forecast gust front locations.

    2. The estimated-time-to-impact (ETI) for the gust front that will first enter a pre-determined gust front impact zone surrounding the airport.

    Since sensor measurements that supply input data to MIGFA do not provide the desired update rate for gust front outputs and MIGFA outputs require additional spatial smoothing, GFUP utilizes an internal timer together with forecast gust fiont location information supplied by MIGFA to produce smoothed output at the desired (faster) update rate.

    1.2 CONCEPTUAL OVERVIEW

    For each gust front detection, MIGFA [l J [2] [3] provides associated gust front location forecasts with the desired temporal resolution (via its list of 1-minute interval position forecast data) to allow GFUP to update the gust front positions at the required update rate. To do this, GFUP utilizes an internal timer as a scheduler. When the timer reaches the next update interval, GFUP computes the total elapsed time (this includes any processing latency from MIGFA itself as well as the time since the last update) and selects the appropriate forecast curves to represent the “new” current and forecast locations of each gust front.

    Gust front outputs provided by MIGFA can sometimes contain irregular or jagged curves that are meteorologically unrealistic, as well as being too irregular from a human factors viewpoint, to directly serve as symbolic representations of gust fronts on the user display. It is desirable to produce a smoother approximation of the MIGFA output for the end user. In addition, complications can arise when gust fronts collide or split. MIGFA can occasionally misinterpret the situation and produce a single set of curve points having a sharp bend at the juncture between the two fronts. Most conventional curve fitting algorithms would have difficulty negotiating such a sharp bend. In fact, the sharp bend represents a natural break point that should not be fitted. The curve should be broken into two segments and smoothing should be applied to the two segments separately. GFUP employs a tangent-spline smoothing procedure that is designed to provide an approximating curve for a collection of curve points that have been declared to belong to a gust front. The final product of the tangent-spline procedure is a continuously differentiable spline that approximates the curve points. If it is not possible to create a

    1

  • single curve that provides a good fit of the points, then the final gust front representation may be comprised of two or more tangent-spline segments. Since the curve smoothing can be computationally intensive, it is applied only to those curve points that have been selected to comprise the updated current and 10- and 20-minute forecast locations.

    Finally, to satisfy airport planning requirements, GFUP computes the estimatled-time-to-impact (ETI) for the nearest (in time) gust front in the updated gust front map. By first testing all current gust front locations to see if they intersect the predefined Gust Front Impact Zone, and then expanding the search by 1-minute forecast increments, GFUP is able to quickly report the least amount of time until a gust front will intersect the impact zone.

    1.3 INFORMATION ENVIRONMENT

    13.1 Meteorological Information

    Gust front detection and forecast data from the output of the gust front detection algorithm (MIGFA_gustfronts) are the only information required by GFUP.

    1.3.2 Adaptation Parameters

    The algorithm processing depends on certain adaptation parameters. It is assumed that the values of these parameters will be made available whenevk they are needed for processing. A complete listing of these parameters is provided in 2.3.3.

    2

  • 2. HIGH LEVEL ALGORITHM DESCRIPTION

    2.1 ALGORITHM IDENTIFICATION AND PURPOSE

    2.1.1 Algorithm Identifier

    The algorithm identifier is GFUP.

    2.1.2 Algorithm Description

    Overview

    GFUP is a gust front post-processing algorithm that performs three principal tasks:

    1. Create a map of gust front locations and associated 10- and 20-minute forecast locations upon amval of

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