INFRASOUND PROPAGATION CALCULATION TECHNIQUES USING MESOSCALE ATMOSPHERIC AND TERRAIN SPECIFICATIONS   Robert Gibson1, Douglas Drob2 and David Norris1 1BBN Technologies Arlington, VA, USA 2Naval Research Laboratory Washington, DC, USA Infrasound Technology Workshop, Tokyo, Japan November 2007

Motivation Calculation of infrasound propagation paths is necessary for event identification, phase association and source location Explaining details of infrasound propagation relies on: Propagation models that capture the fundamental physical processes Accurate characterization of the propagation medium Linkages to near-real-time atmospheric characterizations enable higher-fidelity infrasound propagation modeling Infrasound propagation at regional ranges Characterized by higher frequencies than at global ranges Effects of the boundary conditions of the propagation domain, in particular the variable terrain elevation, become increasingly important Model validation and calibration using observed events and ground truth is necessary

Recent Efforts Development of techniques for utilizing: accurate, high-resolution regional atmospheric specifications terrain elevation databases Mesoscale atmospheric models that: focus on the meteorology of a specific region account for and resolve wind and temperature phenomena relevant to regional and local infrasound propagation provide atmospheric profiles that are consistent with the variable terrain elevation in a region Investigation of realistic atmospheric and terrain specifications at a range of resolutions to determine appropriate spatial and temporal scales necessary to improve infrasound predictions at relevant frequencies and ranges

Enabling Technologies and Tools InfraMAP tool kit Infrasonic Modeling of Atmospheric Propagation (BBN) NRL-G2S Naval Research Laboratory Ground to Space Specification Numerical Weather Prediction (NWP) models Operational physics-based atmospheric models Including regional (mesoscale) models, such as: Weather Research and Forecasting Model (WRF) Collaborative effort: National Center for Atmospheric Research (NCAR); NOAA/ National Weather Service/ National Centers for Environmental Prediction (NCEP); Air Force Weather Agency; Naval Research Lab; Oklahoma Univ.; FAA, etc. Output is being integrated into G2S-mesoscale framework 1-hour intervals, 0-20 km altitude, up to 10-km resolution (with higher resolutions possible if necessary)

InfraMAP Modeling Schematic

Mesoscale Integration Techniques Framework for high-resolution regional specification Atmosphere and topography considered Incorporating synoptic and mesoscale numerical weather analyses into NRL Ground-to-Space global specification

Mesoscale Atmospheric Models Regional Numerical Weather Prediction (NWP) Physics-based synoptic models; domain is smaller than global. Assimilation of atmospheric data from many sources. Accounts for terrain and surface effects on the atmospheric dynamics. Nested grid models, interpolating and enhancing global models. Relocatable grids, user-defined dimensions and resolutions. Terrain-following sigma-coordinate system at the lower boundary. Must be merged with global specifications at higher altitudes. Available at update frequencies up to 15 minutes. Range (km) from western edge of specification domain. Example of mesoscale atmospheric wind specification for an east-west vertical cross-section of southwestern US, showing variable vertical resolution of sigma coordinate system and terrain-following grid domain.

Comparison of Wind Specifications Wind magnitude shown below over southwest US domain, ~2.5 km altitude. Global G2S, at 2.5 km altitude G2S-Mesoscale, at contour level 15, approx. 2.5 km alt.

Regional Topography Specifications Terrain elevation model used to specify the lower boundary of model domain Height (km) above mean sea level of the first (lowest) layer of a mesoscale atmospheric specification

Regional Weather Specification Meridional Wind (SW US, over White Sands, New Mexico) Horizontal axis is distance from western edge of specification domain. March 25, 2006 , 9UT

Range Dependence in Atmosphere Zonal Local/regional variations may be significant Shown are 20 zonal wind profiles at 15 km intervals (along a meridian) Green: from the WRF mesoscale weather analysis. Red: the WRF profile at the midpoint of the 300 km path. Blue: profile from global G2S, corresponding to the midpoint. Terrain elevation at grid cells shown by red dots Example shown: Midpoint location is I31KZ WRF Local G2S

Comparison of Specification Profiles

Example Mesoscale Domains

Atmosphere over Mesoscale Domain Static sound velocity (m/s) at a height 10 m above the ground/ocean surface Vertical Wind Slices (along white line segments) are shown in next slide

Examples: Wind Specification Winds (m/s), from 0-20 km, across slices of SW US domain shown in previous slide North-south vertical cross-section of the zonal (east-west) wind fields (in m/s) East-west vertical cross-section of the meridional (north-south) wind fields (in m/s)

Terrain Effect in Ray Tracing Model Hypothetical modeling scenario shown over 450 km path from source (S) to receiver (R) Topography over great circle path between source and receiver

Ray Interaction with Surface Typical eigenray solution, for stratospheric path Interaction with ground at first bounce, in detail

Propagation Example (1) Propagation paths from elevated source (left) to ground-based receiver (right) Propagation paths using global G2S Propagation paths using G2S-Mesoscale

Propagation Example (2) Propagation paths from elevated source (left) to ground-based receiver (right) Propagation paths using global G2S Propagation paths using G2S-Mesoscale

Conclusions High-resolution mesoscale grids enable propagation calculations suitable for regional events. Improved characterization of the lower regions of the atmosphere Incorporation of terrain effects on propagation Specifications of arbitrary regional domains of interest can be generated with the Weather Research and Forecasting (WRF) model using observational inputs from global scale weather models. Modeling capabilities for mesoscale atmosphere and terrain are in use. Capability developed to supplement existing global G2S specifications with high-resolution mesoscale-G2S specifications Significant progress on production of multi-day mesoscale specifications   New capabilities are being integrated within InfraMAP Ongoing analysis of ground truth infrasound events Understanding of mesoscale effects on propagation characteristics Determination of appropriate spatial length scales in atmosphere and terrain specification for propagation modeling at infrasonic frequencies of interest