Sensitivity analysis of infrasound based source verification

Sensitivity analysis of infrasound based source verification:
influences of atmospheric conditions and surface orography
Christoph Pilger, Florian Streicher, Sabine Wüst and Michael Bittner
Deutsches Zentrum für Luft- und Raumfahrt (DLR), Deutsches Fernerkundungsdatenzentrum (DFD)
82234 Oberpfaffenhofen, Germany - Contact: [email protected]
Abstract
Infrasound propagation influenced by atmospheric conditions
The detection and verification of natural or anthropogenic signatures
using the infrasound technique is based on propagation modeling
Infrasound propagation influenced by surface orography
(2a)
(1a)
between source and receiver. Atmospheric background conditions as
well as orography significantly influence the propagation path of
infrasound signals and may therefore permit or prohibit signal
detection.
Infrasound propagation modeling is performed at the German
Aerospace Center (DLR) using the improved 3d ray-tracing model
(1b)
HARPA/DLR. Case studies of infrasound propagation are presented
(2b)
with respect to different atmospheric temperature and wind fields
using climatological, weather forecast and satellite data. Furthermore,
influences of reflection by uneven surface orography on infrasound
propagation are described using advanced German Aerospace
DEUTSCHES FERNERKUNDUNGSDATENZENTRUM
Center (DLR) terrain models.
(1c)
…
A sensitivity analysis of atmospheric/orographic influences on
infrasound propagation will be presented quantifying the differences in
propagation paths and emphasizing the importance for source
verification.
Modeling
2009) performs acoustic ray-tracing for infrasound propagation
calculations.
HARPA/DLR
regards
(2d)
(2c)
The HARPA/DLR model (see Jones et al., 1986; Pilger and Bittner,
atmospheric
background
conditions in 4-dimensionally (3 spatial, 1 temporal) varying
Fig. 1: HARPA/DLR infrasound propagation modeling showing different atmospheric background implementations (for Jan 27, 2010,
Oberpfaffenhofen (48.08°N,11.27°E) in west-east directions): (1a) temperature and wind profiles based on climatology (HWM07 /
MSIS00) only, (1b) enhanced temperature profile through merging of climatological and satellite data (temperature between 15 and 105
km are from TIMED/SABER satellite). (1c) enhanced background profile through merging of climatological and numerical weather
forecast data (temperature and winds between 0 and 50 km are from ECMWF reanalysis data). Absorption from 0 to 62 dB is color-coded.
temperature and wind profiles by a combination of climatological,
Discussion
satellite and numerical weather forecast data. Data sets used
therefore are the NRL-MSISE-00 temperature and HWM-07 wind
image by NASA MODIS
Figure 1 shows the influence of atmospheric background
Figure 2 shows the influence of surface orography
modeling on infrasound propagation. While the pure
on infrasound propagation. While reflections from a
climatological modeling is the only realization of
flat terrain conserve the pattern of wave fronts, the
atmospheric
altitude,
reflection from a realistic/rough surface (as e.g. the
HARPA/DLR furthermore provides the opportunity to regard surface
temperature and wind can be described below 100 km in
Alpine ridge in this example) leads to variable and
orography to give a realistic estimation of the reflection angles of
a more realistic way by satellite data and numerical
erratic
sound rays over actual terrain. Data of the DLR SRTM (Shuttle Radar
weather
reflection
Topography Mission) terrain model are used for a first study, they can
behavior occur due to the different background models:
occurrence of further returns to the surface:
The distance for first eastward stratospheric returns e.g.
Sound rays returning to the surface for the second
varies from 190 km (climatology) to 175 km (satellite) to
time change from 560 km (flat terrain) to >600 km
The use of numerical weather forecast data complemented by satellite observations (e.g. TIMED/SABER
130 km (weather forecast). The turning heights for
(rough terrain) and a huge amount of rays is guided
temperature profiles, but also further temperature and wind measurements for the middle atmosphere) and the
thermospheric rays varies from 120 km (climatology) to
into the thermosphere without return when reflected
implementation of terrain models (e.g. SRTM orography, but also improved satellite-based elevation models
100 km (satellite data). The overall propagation pattern
by rough terrain instead of flat one. The regular
as e.g. by TerraSAR-X) could help to increase the potential of infrasound detection and source verification.
significantly varies when using enhanced atmospheric
non-orography propagation pattern considerably
It is thereby suggested to include satellite-based remote sensing for atmospheric background conditions and
background realizations.
varies when affected by irregular terrain.
surface orography in the source verification framework of e.g. infrasound propagation modeling.
climatology,
ECMWF
TIMED/SABER
numerical
weather
satellite
forecast
temperature
profiles
profiles
for
wind
and
and
temperature.
be further improved in resolution by using the DLR TerraSAR-X
(Radar Satellite) Elevation Digital Surface Model.
References:
Jones, R. M., Riley, J. P., and Georges, T. M. (1986). HARPA: A versatile three-dimensional
Hamiltonian ray-tracing program for acoustic waves in the atmosphere above irregular terrain.
Technical report, NOAA.
Pilger, C. and Bittner, M. (2009). Infrasound from tropospheric sources: Impact on mesopause
temperature? Journal of Atmospheric and Solar-Terrestrial Physics 71, 816–822.
conditions
forecast.
above
Differences
100
in
the
km
propagation
ray
reflections
angles
and
strongly modifying
the
thereby
and
distance
Fig. 2: HARPA/DLR infrasound propagation modeling over flat and realistic terrain (for Jul 19, 2010, from (50.10°N, 10.58°E) in southern
direction): (2a) orography based on flat terrain only regarding earth curvature. (2b) orography based on realistic terrain using the SRTM
terrain model for a north-south cross-section of the Alpine ridge. (2c) detail of the terrain cross-section and infrasound ray reflections due
to this orography. (2d) area of the cross-section (following the 10.58 longitude) in the German/Austrian/Italian Alps region.
Conclusions
The modeling of infrasound propagation for the detection and source verification of CTBT-relevant signatures
strongly depends on the best available representation of atmospheric and orographic background conditions.
Vortrag > Autor > Dokumentname > 09.11.2005