Efficient Low-Cost Weather Radar
Søren Overgaard, Danish Meteorological Institute, Lyngbyvej 100, DK-2100 København Ø,
Denmark. so@dmi.dk
The weather radar is called LAWR, Local Area Weather Radar. The system uses a commercial
marine X-band radar, manufactured by FURUNO, Japan. This kind of radar is produced in much
greater quantities than dedicated weather radars, and the price is therefore very low. In a double PC
the fast DOS-based first part, which controls the radar and is the signal processor, shares a disk with
a Windows 2000™ other half, which is the GUI for the system and handles the communications.
The system is located beside the antenna/transmitter/receiver unit, built into a 19’’ rack, half high.
A connection to the system through the INTERNET is suitable, but also other means of
communication are possible. The main parameters of the system are stated below:
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Radar type:
Output power:
Range:
Pixel size:
Image frequency:
Output levels:
X-band radar (941030 MHz)
25 kW
30-60 km
500 x 500 m or 250 x 250 m (option)
5 minutes
8 bit
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Antenna type:
Beam width (H):
Beam width (V):
Rotation speed:
Weight:
8 ft. Slotted wave guide array
0.95
20 (fixed antenna) ± 10 °
24 rpm.
42 kg
A system can be delivered off the shelf
without
mounting
tower
and
other
infrastructure for 47.000 USD.
The picture to the left shows the installation of
the LAWR at Odense in Denmark. The
weather radar is mounted on a 25 m high
tower. The tower is simply a high mast, thus
reducing the cost of establishing the radar site.
The antenna/trans-mitter/receiver unit is
visible on the top of the mast.
The figure below shows an example of data
from the LAWR. The image shows the island
of Fuen in Denmark, the circle representing a
distance of 60 km with the radar placed at the
centre. The colour scale to the right indicates
low to high rainfall intensity. The data can be presented locally as shown here, or may be
transmitted via the network as a GIF formatted image including an underlying map, or as a
raster image in various formats.
Figure 1
The weather radar can be calibrated against a high resolution rain gauge. The calibration is done in
order to establish a relation between the counts of the A/D-converter and the measured rainfall in 5
minutes, the highest possible updating frequency of the system. In the example below, the rain
gauge is placed app. 12 km from the radar site.
When the calibration of the LAWR is compared with the calibration of the Danish RØMØ weather
radar (Ericsson type, named ERE), the LAWR shows a pleasant almost linear relation between the
binary counts of the video signal and the resulting rainfall intensity, as shown in figures 2 and 3.
The sensitivity of the system can be changed.
Figure 2
Precipitation
50
mm/h
40
ERE
LAWR
30
20
10
0
0
100
200
300
counts
Figure 3
The image below shows data from the Danish RØMØ weather radar from 9 October 2001. The area
covered by the LAWR at Odense is shown in the square within this image.
The small image is the corresponding image from the LAWR. Note that the covering area is a circle
contained within the square.
Data from the radar are intended to be used as an element in sewer system control systems. The
resolution can be as low as 250 x 250 m, which is better than most other weather radar systems. The
low price as well as the availability of spare parts nearly all over the world make the LAWR
suitable for use in the third world. Likewise, the low price makes it feasible to establish a network
of LAWRs covering an area of the same size as the area covered by conventional weather radars.