Determination of sky status by ground based radiometric data analysis

Manabendra Maiti,Salil Kumar Biswas,Ayan Pradhan,Kausik Bhattacharyya,Judhajit Sanyal,Md Anoarul Islam

doi:10.17485/ijst/v14i27.447

Abstract

Objectives: To predict meteorological phenomena such as rain events from sky status during rainy and non-rainy periods. Methods: The method used here is based on brightness temperature ratio measurement at two different frequencies, namely 23.8 GHz and 30 GHz respectively, using ground based dual frequency radiometric data. The ratios of brightness temperature readings obtained by the dual-frequency radiometer at the two above mentioned frequencies are calculated for each simultaneously-taken pair of measurements. Data obtained by the authors for the year 2009 at Cachoeira Paulista in Brazil has been used for analysis. Findings: The major results obtained from the analysis of data collected over a continuous period of seven months are used to construct corresponding histograms and cumulative count graphs of brightness temperature ratios. The histograms and graphs clearly show three peak values that could be interpreted as thresholds between clear sky, cloudy sky and rainy sky conditions respectively. Novelty: The study implements detection of rain events from sky status during rainy and non-rainy periods using peak brightness temperature values obtained from graphs generated using the observation data. The outlined technique can therefore be used to clearly determine sky conditions and accurately predict rain phenomena. The ratio of brightness temperatures at the two frequencies is a unique parameter which is critical to the successful estimation of rain from sky status. The results agree well with multi-channel radiometric data obtained by other researchers at lower frequencies. Keywords: sky status; microwave; millimeter wave; dual frequency radiometer; brightness temperature; rainfall

Highlights

To meet the growing needs of higher data rates for present day communications and multimedia systems, use of electromagnetic spectrum above 10 GHz in microwave and millimeter wave region is an obvious solution. The signals in this frequency range get impaired by rain that causes serious attenuation especially in tropical and equatorial countries that are characterized by heavy rainfall
Sky status is important for designing fade margins for satellite communication systems
Advantages in the use of the sky status indicator for optimal functioning of satellite communication systems are in the easy software implementation of the measurement and sky status determination algorithm and in the online system performance monitoring capability so that dynamic fade mitigation techniques could be designed and systems set up, to contrast possible degradation of a satellite propagation channel due to scattering processes arising from rain

Summary

Introduction

To meet the growing needs of higher data rates for present day communications and multimedia systems, use of electromagnetic spectrum above 10 GHz in microwave and millimeter wave region is an obvious solution. A ground based microwave radiometer [1,2] has proved its utility to monitor the atmosphere up to 10 Km continuously by measuring very low level microwave radiation at some specific frequency channels in the microwave bands dominated by atmospheric water vapor, cloud liquid water and molecular oxygen emissions. Geophysical observables such as the total amount of water vapor (PWV), the non-precipitating cloud liquid content (LWC) and rain are have frequently been used to develop models [3,4]. Brightness temperatures (Tb’s) measured at the ground level, within the frequency range of 20-30 GHz under rainy conditions are not appropriate to retrieve the above mentioned quantities [6]

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Conclusion