Showing papers by "Animesh Maitra published in 2009"

Cloud Liquid Water Content and Cloud Attenuation Studies with Radiosonde Data at a Tropical Location

Abstract: The profile of cloud liquid water density and the total liquid water content (LWC) are obtained from the radiosonde data using the Salonen model at Kolkata, India, a tropical location. The cumulative distribution LWC shows a departure from the ITU-R model at this location, exhibiting a significantly enhanced occurrence during the monsoon months. The cloud attenuation, derived by integrating the profile of specific attenuation obtained from the radiosonde data, is related to LWC at different frequencies in the range 10-100 GHz. A comparison indicates that the cloud attenuation at frequencies below 50 GHz is somewhat overestimated by the ITU-R model generated values and significantly underestimated by the ITU-R model at frequencies above 70 GHz at the present location.

Rain Depolarization Measurements on Low Margin Ku-Band Satellite Signal at a Tropical Location

Abstract: The phenomenon of depolarization of a Ku-band satellite signal caused by rain has been studied with a simple experimental system in which the attenuation of the copolar component and the enhancement of the cross-polar component signal have been measured at a tropical location. The degradation of cross-polarization discrimination (XPD) due to rain over the Earth space path has been obtained from these measurements and compared to that estimated from the ITU-R model, indicating the characteristic feature of a tropical location.

Joint statistics of rain rate and event duration for a tropical location in India

Abstract: The optimum microwave link design requires the knowledge of rain rate distribution as well as of the duration statistics of the rain events. The rain rates measurements at Ahmedabad, a tropical location in India, are analysed and models for various event parameters are developed using three years of continuous measurements. The average number of cases with at least 1 min event duration shows an exponential dependence on the rainfall rate with a correlation coefficient of 0.93. Also, the average durations for different rainfall rates are found to follow a power law with a correlation coefficient of 0.97. It is found that the average duration more effectively represent the event duration at higher rain rates. The results are compared with those obtained for the temperate and other tropical locations to indicate the distinctiveness of the studied parameters over the location. It has been observed that although the tropical locations show similar qualitative features, the characteristics of the Indian region show quantitative difference from other tropical regions.

Classification of convective and stratiform types of rain and their characteristics features at a tropical location

Abstract: The effect of rain attenuation in high frequency signals need proper understanding of the variation of drop size distribution (DSD) separately in convective and stratiform rain due to different characteristics. This paper presents the analysis of variation of vertical rain rate profile for these two types from micro rain radar observations as well as the variation of DSD at ground using Disdrometer, of an event observed over Ahmedabad. The bright band signature in vertical rain rate profile is used for rain classification as well as the rain classification based on ground based DSD model is also attempted. The results highlight a rain classification scheme based on lognormal DSD parameter. It is also found that large drops size is more in convective cases associated with high rain rate. It is also observed that for lower rain rates, convective cases have smaller number of bigger drops than stratiform types of rain of same rain intensity. The information will be of importance for classification for rain and rain attenuation study.

Comparison of TRMM estimated rainfall with ground truth over Calcutta

Abstract: The precipitation radar(PR) onboard Tropical Rain Monitoring Mission( TRMM) estimates rainfall from space covering vast geographical area. It is necessary to compare such estimates with ground truth. In this paper PR estimated rain has been compared with that obtained from India Meteorological Department( IMD) and also disdrometer over Calcutta. PR estimated rainfall statistics have been presented along with IMD derived rainfall statistics. Regression relationships of rainfall have been derived as a function of surface temperature (DBT) and surface dew point temperature (DPT). Also rainfall phenomena have been studied as a signature of EL-NINO and LA-NINA occurrence.

Observations of rain drop size distribution and rain attenuation of a satellite signal at a tropical location

Abstract: Measurement of rain drop size distribution (DSD) along with rain attenuation have been carried out at Kolkata (22.65°N, 88.45°E), India, a tropical location since 2004. On analyzing the rain event, it has been noted that the distribution of the larger drops have been found to dominate the growing phase of the event in comparison to the later part for identical rain rates. At the same time, the analysis of monthly variation of rain DSD spectrum shows that the number density of larger drops are greater for the pre-monsoon months in comparison to the monsoon period for similar rain rates. The seasonal variation of rain attenuation at Ku-band indicates the larger attenuation values in the pre-monsoon months than in the monsoon period for identical rain rates during the years, 2005–2007. This is basically due to the convective nature of the rainfall, accompanying thunderstorm that occur mostly in the pre-monsoon period. The convective process increases the rain height, which in turn results in high attenuation values in the pre-monsoon months of the year.

Development of channel model to predict rain rate and attenuation for FMT applications

Abstract: A new model is presented to predict rain rate serially during a rain event at a tropical location. The model is based on the Gaussian distribution of the conditional occurrence of rain rate with a particular value of the rain rate occurring before. The mean and standard deviation of the distribution are modeled with the measured data. The rain rate at a particular time instant is predicted from the knowledge of previous samples. The predictor has tested well with a mean error within 10% for rain rates above 20 mm/hr for 10 sec time interval. The same technique is also successfully applied to predict time series of rain attenuation. The practical application of channel predictor is also shown in this paper for FMT simulation.