Cloud cover, cloud liquid water and cloud attenuation at Ka and V bands over equatorial climate

Cloud cover statistics and their diurnal variation have been obtained from in situ and satellite measurements for three equatorial locations. Cloud liquid water content, 0 °C isotherm height and cloud attenuation have also been obtained from radiosonde measurement using the so-called Salonen model at Kuala Lumpur (Malaysia). The results show a strong seasonal variation of cloud cover and cloud liquid water content on the two monsoon seasons. The Liquid Water Content (LWC) obtained from radiosonde and the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) is higher during the Northeast Monsoon season, which corresponds to the period of higher percentage cloud cover and high rainfall accumulation. The International Telecommunication Union—Region (ITU-R) model underestimates the cumulative distribution of LWC values at the present station. The relationship of the cloud attenuation, derived from the profiles of liquid water density and temperature within the cloud, shows an underestimate by the data obtained from the ITU-R model. The cloud attenuation at Kuala Lumpur is somewhat underestimated by the ITU-R model up to about 1.2 dB at Ka (30 GHz) and 3.4 dB at V (50 GHz) bands. The results of the specific attenuation can be used for the estimation of cloud attenuation at microwave and millimetre wave over earth-space paths. The present data are important for planning and design of satellite communications at Ka and V bands on the Earth–space path in the equatorial region

Some preliminary results of the fine structure profiles of radio refractivity near the surface at Ota, Southwest Nigeria

Some preliminary results are presented of the fine structure profiles of surface radio refractivity, Ns, over Ota, Southwest Nigeria (6° 42'N, 3° 14'E) computed from in-situ, one minute interval measurements of surface pressure, temperature and relative humidity. A wireless Davis Vantage Pro2 Weather Station instrument installed at the Department of Physics, Covenant University, Ota in April 2012, was used to obtain the measured variables. Hourly, daily and monthly average values of surface water vapour density, dry, wet and total radio refractivity were obtained for the months of April 2012 to March 2013. The distance to the radio horizon for a given transmitter height may be deduced from the observation that Ns is well correlated with the gradient of refractivity over the first kilometer above ground. Refractivity gradients utilized for the work were those obtained in a previous work for Oshodi, a meteorological weather station near the coast and close to Ota

Cloud attenuation studies of the six major climatic zones of Africa for Ka and V satellite system design

Cloud cover statistics, cloud base and top height, cloud temperature, frequency of precipitation, freezing height, total cloud liquid water content (TCLWC) and cloud attenuation data have been obtained for the six major climatic zones of Africa. The present results reveal a strong positive correlation between the monthly distribution of low cloud cover, cloud top height, cloud temperature, and frequency of precipitation in the six zones. The cumulative distribution of the TCLWC derived from radiosonde measurement in each climatic zone shows a departure from the TCLWC recommended by the ITU Study Group 3 data, with an exceedance percentage difference of 32% to 90% occurring 0.01% to 10% of the time. The underestimation of the TCLWC is greatest in the tropical rain forest. A comparison of the cloud attenuation cumulative distribution in the Ka and V bands reveals that the International Telecommunication Union – Region (ITU-R) is an intergovernmental organization that develops rain model based on collected data around the world. This model underestimates the cloud attenuation in all of the six climatic zones by 2.0 dB and 4.7 dB for the arid Sahara desert, 1.3 dB and 3.0 dB in semi-arid North Africa, 1.3 dB and 1.5 dB in savannah North Africa, 2.0 dB and 3.6 dB in the tropical rain forest, 1.3 dB and 2.9 dB in savannah South Africa and 0.9 dB and 2.6 dB in semi-arid South Africa, respectively, at 30 and 50 GHz. Overall, the cloud attenuation in the tropical rain-forest zone is very high because of the high annual total cloud cover(98%), high annual frequency of precipitation (4.5), low annual clear sky amount (8%), high cloud depth (10,937 m), high 0°C isotherm height (4.7 km), high TCLWC (4.0 kg/m2 at 0.01%) and low seasonal cloud base height (356 m)

Usporedba modela intenziteta oborine za područja s ekvatorijalnom klimom u jugoistočnoj Aziji

Statistics of 1 minute rain rate has a major impact in the design of satellite communication systems at frequencies above 10 GHz. The effect of rain causes serious degradation of radio signals at frequencies above about 10 GHz; therefore, models for the prediction of statistics of excess path attenuation needed for the design of communication propagation paths requires a statistical description of rain-rate occurrences. In this paper, the tasks are tackled by processing 3 years rain rate data for selected sites in the equatorial region. A comparison between rain rate data set with a sampling period of 1 minute and existing rain rate prediction models is presented.Statistika minutnih intenziteta oborine ima veliki utjecaj na modeliranje satelitskih komunikacijskih sustava koji rade na frekvencijama višim od 10 GHz. Utjecaj kiše uzrokuje jaku degradaciju radio signala na frekvencijama 10 GHz i višim; stoga modeli za predviđanje prekoračenja dozvoljenog propagacijskog gušenja, koje je potrebno za izbor komunikacijskih pravaca, zahtijevaju statistički opis intenziteta oborine na tim pravcima. U ovom su radu obrađeni trogodišnji nizovi podataka s intenzitetima oborine za odabrane postaje u ekvatorijalnom području. Uspoređeni su rezultati dobiveni s nizovima podataka intenziteta oborine koji su uzorkovani s periodom jedne minute s onima dobivenima prognostičkim modelima intenziteta oborine

Atmospheric gas impact on fixed satellite communication link a study of its effects at Ku, Ka and V bands in Nigeria

The total atmospheric absorption due to Oxygen and water vapour on the earth-space path at Ku (12/14 GHz), Ka (20/30 GHz), and V (40/50 GHz) bands was evaluated for communication with Nigeria communication satellite (Nigcomsat1) on both uplink and down link at 0.01 % unavailability of an average year. The basic input climatic data used include monthly and yearly mean meteorological parameters of surface and vertical profiles of pressure, temperature, and relative humidity obtained from recent measurement from space by the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua spacecraft for the period 2002 to 2006. The International Telecommunication Union Radio Propagation Recommendation (ITU-RP 676, 2009) procedure was used for the computation of gaseous attenuation for each of the 37-stations in Nigeria. Attenuation values were obtain for both uplink and downlink frequencies, at Ku, Ka and V bands, total atmospheric absorption was determined to be between (0.11 to 0.24) dB, (0.7 to 1.1) dB and (0.82 to 3.1) dB for Ku, Ka, and V bands respectively. Contour maps showing a consistent signal absorption due to Oxygen is generally higher in the South-West region and water-vapour attenuation higher in the South-South part of Nigeria are presented

Emerging debt and equity markets: an exploratory investigation of integration using daily data

In this paper we examine integration between emerging and U.S. debt and equity markets. We first investigate price changes around significant "events," in this case changes in short-term U.S. interest rates brought about by actions of the Federal Reserve. Second, we estimate the predictability of returns using both domestic and U.S. variables. Finally, we test whether a single latent variable can explain these returns. The evidence suggests that the degree of integration varies with security types and the country of origin. However, these differences between security types become less apparent over time

Propagation Measurement on Earth-Sky Signal Effects for High Speed Train Satellite Channel in Tropical Region at Ku-Band

Recent advances in satellite communication technologies in the tropical regions have led to significant increase in the demand for services and applications that require high channel quality for mobile satellite terminals. Determination and quantification of these requirements are important to optimize service quality, particularly in the Malaysian region. Moreover, the tests on current satellite propagation models were carried out at temperate regions whose environmental characteristics are much different from those in Malaysia. This difference renders these propagation models inapplicable and irrelevant to tropical regions in general. This paper presents the link characteristics observations and performance analysis with propagation measurements done in tropical region to provide an accurate database regarding rain and power arches supply (PAs) attenuations in the tropics for mobile scenarios. Hence, an extension for improving the performance assessment and analysis of satellite/transmission has been achieved. The Malaysia propagation measurement for mobile scenario (Malaysia-PMMS) enables first-hand coarse estimation and attenuation analysis, because the attenuation resulting from rain and PAs becomes easily amenable for measurement. Parallel to that, the measured attenuation has been compared with that of the simulated output at noise floor level. The underlying analytical tool is validated by measurements specific at tropical region, for dynamic model of mobile satellite links operating at higher than 10 GHz