Fourth Study Conference on BALTEX Scala Cinema Gudhjem

-39-
Calibrated Surface Temperature Maps of Heterogeneous Terrain Derived
from Helipod and German Air Force Tornado Flights during LITFASS-
2003
Jens Bange, Stephan Wilken, Thomas Spieß, and Peter Zittel
Aerospace Systems, TU Braunschweig, Hermann-Blenk-Str. 23, 38108 Braunschweig - Germany. E-Mail: j.bange@tu-bs.de
1. Introduction
Complementary to the ground-based measurement systems,
the remote sensing, and the numerical models in the
LITFASS-2003 field experiment, two air-borne systems
were employed: The helicopter-borne turbulence probe
Helipod (Fig. 1; e.g. Bange and Roth 1999, Bange et al.
2002) of the Technical University of Braunschweig and
Tornado aircraft (Fig. 2) of the 51 th Recon. Sqr. of the
German Air Force.
Fig. 1: The helicopter-borne turbulence probe Helipod.
Fig. 2: A German Air Force RECCE Tornado.
The Tornado aircraft were equipped with a line-scanning
infra-red (IR) camera that provided high-contrast images of
the surface temperature variations. These images were
calibrated using absolute surface temperature measurements
performed with the Helipod. It is expected that the resulting
high-resolution temperature maps will help with the
initialization and verification of numerical models of the
atmosphere, especially with the parameterization and
initialization of Large Eddy Simulations (LES): The surface
temperature together with an estimation of the surface
roughness may offer a reasonable alternate to pre-defined
turbulent surface fluxes.
2. Experimental Set-Up and Strategy
The LITFASS experimental site is characterized by
heterogeneity on nearly every length scale (Fig. 3) which
is quite characteristic for areas within the BALTIC region.
This distinct heterogeneity makes it difficult to define
area-averaged turbulent fluxes or representative sub-scale
parameterizations for numerical models.
Fig. 3: Land-use of the experimental site in 2003.
To receive an impression of the variety of surface
temperatures of the individual surface types within the
site, Tornado aircraft photographed on several days the 20
km x 20 km area within 20 minutes. Since these images
(located in 2 km wide stripes under the airplanes flight
path) show only temperature contrasts they need to be
calibrated. To do so the Helipod performed low-level grid
flights in close temporal connection to the Tornado flights.
Since the Helipod's IR sensor was not able to do line
scans, the results were thin lines of the absolutely
measured surface temperature through the experimental
site (Fig. 4 and 5). The size of the Helipod flight mesh and
the size of the Tornado IR images were chosen in a way
that every IR images contained at least one Helipod flight
section.
Fig. 4: Helipod flight mesh and a geo-referenced IR
image provided by a Tornado flight.