MIRA-35 Cloud Radar

System Description



MIRA-35 is a Ka-band radar for detecting clouds, fog, and precipitation in the Atmosphere. It is typically operating at 35.1 GHz or a wavelength of 8.55 mm.


MIRA-36 LindenbergMIRA-36 NUIG

In its standard configuration it has a vertically pointing 1 m antenna which is mounted on an enclosed trailer or an outdoor enclosure.

It is also available with a scanning unit for making azimuth and elevation scans. In the scanning configuration the antenna and the radar electronics are mounted on a two axis positioner. 


MIRA-35 Cloud Scanner Trailer

Also a light weight configuration for airborne installation is available which fits to a 19 inch rack with a height of 14 U (including PC).


Polarization Feature

MIRA-35 transmits with one single linear polarization and receives the co-polarized and optionally the cross-polarized signal. For the cross polarized signal a separate receiver is used so that reflectivity and LDR (the ration between the reflectivity of the cross and the co channel) is provided simultaneously. The cross channel is very useful for the target classification. The radar can also be configured for Simultaneouly transmitting and receiving H- and V-polarized signals (STAR).


Transmitter

The transmitting signal is generated by a magnetron providing 30 kW pulse power at pulse durations betreen 100 ns and 400 ns. Due to the high pulse power a fine range resolution is possible without pulse compression. When operated continuously these magnetrons have a very long life time.


Receiver

The total noise figure of the receiver, including waveguide-, circulator-, and tr-switch-losses is 6.3 dB. The image band noise is rejected at each frequency conversion stage. The minimum detectable reflectivity factor is -52.4 dBZ at range = 5 km, PRF = 5 kHz, FFT size = 256, number of coherent averages = 200 (i.e. integration time = 10 s), and a pulse length of 200 ns (30 m).


Doppler Technique

As each pulse transmitted by the magnetron has a random phase the Doppler capability of MIRA-35 is realized by the "digital coherence on receiver technique": A small fraction of the transmitted signal is coupled into the receiver. From this signal the phase of the transmitted pulse, compared to the local oscillator, is measured. During the rest of the pulse cycle the phase of the transmitted pulse is subtracted from the I-Q-signal. This phase correction is performed by FPGAs after the sampled I-Q-signal was filtered and decomposed to 1000 range gates. 


Signal Processing

The complete signal processing is implemeted by FPGA.  The FFT processing and moment estimation 2*1000 range gates can be processed with or without in-coheren averagin averaging. Alternatively it is possible to save all the spectra or I-Q data on the PCs hard disk and let the PC do the processing.


Calibration

A permanent calibration system is included in the raceiver.

A fraction of the transmitted signal is coupled to a thermistor detector in order to monitor the average transmitting power (=peak power x duty cycle). The receiver calibration is derived from two alternative sources:


Software for radar operation

A GUI-interface for operating the radar and for making all setting is provided. The radar can as well be operated by scripts and and cron-jobs. The radar software is tailored for remote administration and for automatic operation. The radar software is available for windows and linux. The linux version is more suitable for remote administration. Each module of the radar electronics (transmitter, receiver, LO frequency control, scanning drive control unit) is equipped with an own microcontroller. These microcontrollers have analog and digital in- and outputs for controlling the operational mode and for providing diagnostic information in case of failures. Each hardware controller is programmed to protect the hardware instantaneously on basis of the measured data even if the radar PC is down. Once per second approximately 50 measured parameters are transmitted to the radar PC. These parameters are saved to a log file which simplifies trouble shooting. These parameters are analyzed continuously by a perl script which can be configured to send e-mail warnings to the radar operator in case any parameter exceeds the expected range.


Software for visualization

Platform independent “Data Clients” are provided for viewing the actually measured radar data. They are launched on the users PC. Then they connect to the radar PC via network to get the radar data as it is measured.

For visualizing radar data which is saved on the hard disk IDL programs are provided. These IDL programs are used by a command line interface. Therefore they can also be used for automatic generation of images. The png-images which can be found on this web-server are generated by these IDL-programs.


Software for Target separation and classification

Algorithms for separating multiple peaks from the Doppler spectra and for the classification of these peaks have been and are still developed by METEK. See the Extended Abstract “Target Separation and Classification using Cloud Radar Doppler Spectra” of our contribution to the 33rd Conference on Radar Meteorology for a description of these algorithms.


System Specifications

The following specifications represent typical settings which give an idea field of application of MIRA-36. Other specifications can be selected or provided by design. Please contact METEK if other specifications are needed for your application.


Radar Type

Mono static, pulsed, magnetron transmitter

Frequency

33–37 GHz depending on local frequency allocation. Standard: 35.5 GHz +/- 150 MHz

Peak Power

30 kW

Duty Cycle

max 1:500; typically 1:1000

Pulse Width

100, 200, and 400 ns according to

15, 30, and 60 m range resolution

Minimum Height

150 m, full sensitivity above 350 m

Maximum Height

0.5*c * (1/PRF - 8 μs), due to calibration, typically 28 km

Maximum Number of Rage Gates

2*1000 (two polarizations)

Doppler Velocity Resolution

< 0.02 m/s

Pulse repetition frequency (PRF)

2.5 – 10 kHz according to velocity un-ambiguity of 11 – 42 m/s, typically 5 kHz

FFT Length

128, 256, 512, 1024

Minimum Averaging Time

Moments of instantaneous spectra can be evaluated without skipping samples if NFFT > 128.

Receiver Type

Digital receiver.

Dynamic Range

16 bit / 125 MHz

Antenna Type

Cassegrain

Diameter of Antenna

1, 1.2, or 2 m

Antenna Beam Width (6 dB/two-way, 1.2 m Antenna)

0.5 deg. x 0.5 deg, Gain = 50.4 dBi

Noise Figure of the receiver

6.5 dB including T-R switch losses

Sensitivity at 5 km, prf=5 kHz, 200 ns, nfft=256, averaging time 10 s (200 in-coherent averages)

-52.4 dBZ (-58.4 dBZ can be achieved by using 400 ns pulses)

Dimensions excluding the antenna

19” Rack 14U + PC with 64 Bit PCI-bus for hosting the DSP-Bord

Power consumption with duty cycle of 1/1000

Radar: 600 W at 1/1000

PC 130 W

Air Conditioning 600 W

Regulated antenna heating for winter operation 800 W