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instruments:mirac:mirac

Microwave Radar/Radiometer for Arctic Clouds MiRAC

Mentors: R. Gierens (radar), T. Nomokonova (radiometer)

Principle

MiRAC consists of an active and a passive remote sensing component: a 94 GHz Frequency Modulated Continuous Wave (FMCW) cloud radar (MiRAC-A) and a low-humidity profiler LHUMPRO-243-340 (MiRAC-P). MiRAC can be operated on an aircraft (nadir looking) or from the ground (zenith observations).

The cloud radar transmits saw tooth frequency chirps at 94 GHz. In this way, vertical profiles of reflectivity, Doppler velocity, Doppler spectral width are detected from 150 m to 10 km above ground. Given these measurements, information on the macrophysical (cloud boundaries, type of cloud particles) and microphysical (e.g., liquid and ice water content) properties of the detected cloud can be derived. The radar is operated in a vertically pointing mode. Additionally, the system is equipped with a passive radiometric channel at 89 GHz that is sensible to cloud liquid water. Passive and active receivers are fed by the same antenna, i.e. a perfect beam overlap is accomplished.

The LHUMPRO-243-340 is a microwave radiometer which contains a set of passive high frequency channels at 183.31 GHz (6 channels), at 243 GHz, and at 340 GHz. The measured brightness temperatures can be used to gain information on the humidity profile - in particular in conditions with low humidity as in the Arctic - and to gain information on the integrated ice water content.

Instrument

MiRAC

MiRAC (RPG) at AWIPEV on the roof of the Atmospheric Observatory. Cloud radar (left) and radiometer (right).

Data

  • If you are interested in receiving data please contact Kerstin Ebell

Current measurements:

click to enlarge

The figure shows the brightness temperature from the passive 89 GHz channel of MiRAC-A as well as radar reflectivity factor, Doppler velocity and Doppler spectral width of the MiRAC-A measurements.
Gray areas indicate no data.

History

Period Place Project
28/07/2017 - 08/10/2018 AWIPEV Ny-Ålesund, Svalbard (AC)3
05/2017 - 07/2017 Polar 5, ACLOUD campaign, Svalbard (AC)3

Specifications MiRAC-A (94 GHz FMCW cloud radar)

Parameter Specification Remark
Frequency 94 GHz ± 100 MHz corresponds to wavelength of 3.19 mm; adjustable by software between 92.3 and 95.7 GHz
IF Range 350 kHz to 3 MHz
Transmitter Power ~ 2 W solid state amplifier
Antenna gain 51.6 dB
Beam Width 0.48° FWHM
Polarisation V
System Noise Figure 3 dB
Dynamic Range -54 dBZe to +20 DBZe at 1km height, -45 dBZe to +20 dBZe at 3 km height, -36 dBZe to +20 dBZe at 10 km height
Ranging 50 m to 18 km
Calibration Transmitter power monitoring, Receiver Dicke switch (for radar and DD channels), Hot/Cold absolute receiver calibration Accuracy 0.4 dB
A/D Sampling Rate 8.2 MHz
Profile Sampling Rate 0.2 s to 30 s
Vertical Resolution 1 m to 100 m (user selectable)
Doppler Resolution ± 1.5 cm/s
Doppler Range ± 18 m/s max.
Chirp Variations 4 typical 10 possible, re-programmable
Passive Channels 89 GHz
Data Products Reflectivity, Doppler-velocity, Spectral Width, Higher Moments, Doppler Spectra, LWC profiles
Data Formats proprietary binary, netCDF (conformity with CF convention), ASCII (only moment profiles)
Rain / Snow Mitigation System Super blower for rec. / transm. radome (2000 m³/h each) Optional heater modules (2 kW to 4 kW)
Weight Radar main body: 100 kg, Table: 130 kg, Air conductors: 25 kg
Power Consumption 220 V AC, 50-60 Hz, Radar: 400 W, Blowers: 1000 W
Manufacturer RPG

Specifications MiRAC-P (LHUMPRO-243-340)

Parameter Specification
Frequencies / GHz 183.31 GHz (6 double side-band channels: 183.31±0.6; ±1.5; ±2.5; ±3.5; ±5.0; ±7.5 GHz), 243 GHz, 340 GHz
Channel band-widths / MHz 200 MHz @ 183 GHz, 4 GHz @ 243 and 340 GHz
Optical Resolution (HPBW) HPBW 1.3°
Radiometric Resolution < 0.2 K RMS typical @183 and 243 GHz, < 0.4 K RMS typical @ 340 GHz (@1 s integration time)
Temporal Resolution 1 to 2 seconds
Absolute brightness temperature accuracy ±0.5 K
Radiometric range 0-800 K
Side-lobe level < -40dBz @183 GHz, < -50dBz @243 and 340 GHz
Absolute calibration with internal ambient & external cold load
Internal calibration gain: with internal noise standard, gain + system noise: ambient temperature target + noise standard, abs. cal. of humidity profiler: sky tipping calibration
Size 63 × 36 × 90 cm³
Power Consumption < 120 Watts average, 350 Watts peak for warming-up (without dew blower heater), blower: 130 Watts max.
Weight 60 kg (without dew blower)
Manufacturer RPG
instruments/mirac/mirac.txt · Last modified: 2018/10/11 10:04 by kerstin