Radiometric Measurements of Clear and Cloudy Sky Brightness Temperatures at C-, Ku-, and Ka-band of Frequencies
Arakelyan, Artashes; Hambaryan, Astghik; Vardan, Hambaryan; Arakelyan, Arsen
ECOSERV Remote Observation Centre Co.Ltd., ARMENIA

Hail and shower cause great and severe damage to agriculture and human properties. To reduce material damage in size it is necessary to have many stations of anti-hail protection equipped by hail clouds detector-classifiers. Usually, for hail detection powerful Weather Doppler radar is used, operating at short centimeter or millimeter band of waves. These radars cost several hundred thousand USD, have serious disadvantages and cannot solve the problem totally. Therefore a reason is appeared to develop and to produce new kind of detector-identifiers, which will cost cheaper and have additional advantages.
Clouds brightness temperature is a function of many parameters, in which air and particles temperature, fraction type (water or ice) and particles size are the principal variables. The changes of clouds radio brightness temperatures, related with the changes of dielectric properties of particles and their temperatures, depend on frequencies and polarizations of observation. Therefore, by synergetic application of data of multi-frequency and multi-polarization microwave radiometric observations it is possible to detect and to recognize type of the clouds, its water content and the stage of transformation of water vapour and drops of water to hail (to ice). Radiometric observation may not miss the stage of transformation of water vapour and drops of water to hail, because water and ice dielectric constants are very differ and such formations' brightness temperatures will sufficiently vary one from the other. So, for precise and high probable detection and classification of hail clouds, for real time scale recording of hailing time, for upcoming hail storm's start time prediction, for retrieval of hail-stones' probable sizes, for assessment of expected quantity of hail precipitation it is necessary to develop multi-frequency and multi-polarization microwave radiometric system to carry out clear sky and clouds sustainable monitoring. Before that, it is necessary to specify appropriate frequencies and polarization for solution of hail clouds detection, classification and precipitation parameters and quantities assessment by multi-frequency and multi-polarization microwave radiometric system.
In this paper the results of multi-frequency (at 5.6GHz, 15GHz and 37GHZ) and polarization measurements of clear air and clouds brightness (antenna) temperatures are presented, measured under various observation angles. The results have been obtained during the measurements carried out in Armenia from the measuring complex built under the framework of ISTC Projects A-872 and A-1524. The measurements were carried out at vertical and horizontal polarizations, under various angles of sensing by C-, Ku-, and Ka-band combined scatterometric-radiometric systems (ArtAr-5.6, ArtAr-15, and ArtAr-37) developed and built by ECOSERV Remote Observation Centre Co.Ltd. under the framework of the above Projects.
In the paper structural and operational features of the utilized system and the whole measuring complex will be considered and discussed as well. The main technical characteristics of utilized ArtAr-5.6, ArtAr-15, and ArtAr-37 systemsí radiometers are presented below.
ArtAr-5.6
Central frequency - 37GHz Parabolic antenna with a beamwidth - 5.20 Radiometer receivers bandwidth - ~0.5GHz Radiometer Channel's sensitivity at 1s - ~0.1K
ArtAr-15
Central frequency - 37GHz Parabolic antenna with a beamwidth - 5.60 Radiometer receivers bandwidth - ~0.5GHz Radiometer Channel's sensitivity at 1s - ~0.2K
ArtAr-15
Central frequency - 37GHz Horn antenna with a beamwidth - 70 Radiometer receivers bandwidth - ~1GHz Radiometer Channel's sensitivity at 1s - ~0.3K