The ALOMAR-Wind-Radar - ALWIN

On October 12th, 1998 a new VHF-radar was taken into operation at Andenes/Norway (69.17°N; 16.01°E) for investigations of the dynamics and structure of the tropo-, strato-, and mesosphere. Height profiles of the 3-D wind vector and of the radar reflectivity can continuously and unattended be derived by the Spaced-Antenna (SA) and Doppler-Beam-Swinging (DBS) method (Latteck et al., 1999).

The system is composed of four essential units. The completely transistorized transmitter of the company ATRAD consists of six units each with 6 kW transmitting power. The signals of each unit are transferred through a passive transmitting-receiving-switch  to the antenna steering unit thus allowing an automatic operation of the transmitting/receiving antenna system in SA- and DBS-mode.

Technical Parameters

Frequency

53,5 MHz

Peak power

36 kW

Mean power

1,8 kW (bei 5% Duty Cycle)

3dB beamwidth

Pulse length

1 ... 50 µs

Pulse repetition frequency

< 50 kHz

Height ranges

(0,4) 1 ... 18 km (65 ... 95 km)

Height resolution

150 m, 300 m, 600 m, 1000 m

Time resolution

~ 1 min

Transmitted signal

Einzelimpuls, Komplementärkodes, Barkerkodes

Pulse shape

Rechteck, Gauß, modifizierter Gauß (für max. Leistung)

The transmitting/receiving antenna consists of 144 four-element-Yagi antennas grouped in quadratic subsystems of four antennas each and arranged in a 6x6 matrix. The distance between the individual antennas is λ/√2. The antennas are aligned by an angle of 45°concerning the North-South-axis thus ensuring that an identical antenna characteristic can be used in DBS-mode for zonal (East-West) and meridional (North-South) direction. In case of the SA-mode the antenna field for reception is subdivided in 6 individual fields consisting of 6 subsystems each. These 6 individual fields can be connected with maximum 6 receiving channels. In DBS-mode it is possible to swing the antenna beam in three zenith angles (7°, 14°, 21°) in the four directions North, South, East, and West. Such steering is made by a phase delayed feeding of the six antenna rows or columns in transmission case and in case of reception by a software supported post-beam steering (PBS).

The receiving system consists of 6 channels where the signals are pre-processed into their quadrature components. The following analysis of the row data can be carried out online or as post process at the integrated host PC or at every other internet connected computer. A comprehensive software for the configuration and operational steering of the measuring experiments as well as for the diagnosis of the hardware permits a comfortable local and remote access to the system.

By use of single and coded pulses in a combined mode continuous wind profiles from 1 to 18 km can be estimated. I principle also measurements are possible within the boundary layer above 400 m by use of a modified SA-method.

In the mesosphere the ALWIN-VHF-Radar is mainly used for investigations of mesospheric radar echoes at polar latitudes in summer (PMSE) and in winter (PMWE).

Since 2003 the ALWIN-VHF-Radar has the additional possibility to make investigations during selected measuring campaigns at ionisation traces caused by invading meteoroids using a separate transmitting antenna and spatial separated receiving antennas. From the echo amplitude, the radial velocity and the life time of such echoes the wind field between about 80 and 110 km as well as the temperature at about 87 km can be estimated.

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