Geography Reference
In-Depth Information
data using a t-test. The test indicated that for all stations the differences
between the calculated and measured values were random. The MR method
gave plausible results, so it was chosen to interpolate the meteorological data
to be used as input for the forecasting models.
2.3. Spatial Precipitation Data
16 radar stations are run by the German meteorological service to record
precipitation all over Germany. These stations do not measure the amount of
precipitation at ground level but the signal reflected from the rain drops in the
atmosphere. These measurements at first only allowed calculation of an un-
specific ‗precipitation intensity', a shortcoming. With the system RADOLAN
intensity is now calibrated online with data from a comprehensive network of
ombrometers, using complex mathematic algorithms. As a result the amount of
precipitation can be provided in a spatial resolution of 1 km² (Bartels, 2006).
These calibrated amounts of precipitation based on radar measured rainfall
intensities are referred to as ―radar data‖ in the following. The validation of
precipitation data took place in intensely used agricultural areas, joining the
radar grid with stations of the meteorological network. In this way, it was
possible to relate each station to a grid cell.
The radar derived precipitation at the station's grid cell and the actually
measured data formed the basis for the statistical verification. Since rain
events differ throughout the year, two representative months (May and August
2007) were selected to analyse uniform rainfalls in spring as well as convecti-
ve rainfall events in summer. This resulted in a validation dataset of 1488
hours for each MS.
Table 1. Validation of data on temperature and relative humidity;
deviation between calculated values and measured data with MR
temperature [°C]
relative humidity [%]
year
2003
2004
2005
2006
2003
2004
2005
2006
CoD
96%
96%
99%
98%
94%
96%
95%
92%
mean dev.
0.0
0.0
0.0
0.1
0.3
0.1
0.1
-0.6
maximum
4.4
4.1
4.3
4.7
19.6
32.6
21.6
21.2
minimum
-3.8
-4.5
-4.5
-4.1
-18.9
-21.9
-22.8
-22.8
t-test
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n.s.
n = 92160 hours, n.s. = not significant.
