Fog attenuation penalty analysis in terrestrial optical wireless communication-modified duo-binary return-to-zero system with various receiver pointing errors

In metropolitan communication infrastructures a revolutionary technique is emerge known as terrestrial optical wireless communication (OWC), which makes a high-rise building connection is possible. Even with this solution, there are many other problems like the influence of haze and fog in the propagation channel which obstruct and scatter OWC propagation light and consequently led to a big attenuation, due to propagate in temporal, angular and spatial of the light signal. Not to mention the minimum visibility that discourages the implementation of the pointing errors (PE) and tracking system. This present work aims to analyze the interrelation between multiple scattering (dense fog, heavy fog, light fog, heavy haze and light haze) and receiver PE under modified duo-binary return-to-zero (MDRZ) system. We found that PE caused by beam swag is the main controlling factor and industriously minimize the link margin, signal-to-noise ratio (SNR), and raise the bit error rate (BER) when there is an increasing the turbulence strength and the track length. We recommended to guarantee transmitter– receiver alignment by installing a variable field of view (FOV) receiver (a tracking system) to overcome the scattering impact of the fog that make render urban laser communication effective in the presence of PE.

Micro-climatic study and trend analysis of fog characteristics at IGI airport New Delhi using hourly data (1981-2005)

Indira Gandhi International (IGI) airport, New Delhi where near about 675 flights on an averagedepart and arrive daily, is highly susceptible to dense fog occurrences during the winter season. In the present paper, anattempt has been made for development of an intensity based fog climatological information system for December andJanuary based on hourly visibility data of 25-years (1981-2005) recorded at IGI airport. Variations and trends if any werealso analyzed along with their extreme years and dates of occurrences. Data since 1964 were also used to find climaticjumps in the trend which includes various higher visibilities of no fog conditions. Besides various vital fog climatologicalinformation generated through the present study for use in aviation, the most important finding is the alarming increasingtrend of the dense fog (< 200m) occurrences in both the months up to as high as 10-20 times from 1960s in contrast tounusual drastic reduction of higher visibility hours to as low as one thirtieth to one fiftieth of hours which were observedin 1960s. Thus, finally making IGI airport, a unique airport in the world which hardly experiences good visibilityconditions (>5000m) in both the months. By considering the unexpected huge annual growth of 30% in both air trafficand passengers that India including IGI has presently been experiencing against the global average of 6%, such visibilitytrend also confirms that present flight disruptions and passengers sufferings in winter will be aggravated more severely indays to come unless CAT-III ILS implemented fully. Finally, we have computed further number of consecutive hours,spell periodicity, most favorable climatological timing of fog onset and fog dispersal based on various intensities for usein aviation and fog forecasting.

Unusual long & short spell of fog conditions over Delhi and northern plains of India during December-January, 2009-2010

Sheet of fog is a common scenario during December-January months, which not only occurs in northern India but also in Bangladesh and Pakistan. Maximum fog frequency is noticed in Delhi and adjoining areas. This also affected the maximum temperature during January 1969-88, it varied between 20.6-21.5° C and during 2005 it was 18.9° C and 19.03° C during 2010. Formation of fog and its sustainability mainly depends upon surface wind, relative humidity, minimum temperature and persistency. Maximum dense fog was 285, 190 and 176 hours in 1998-99, 2002-03 and in 2009-10 respectively. During the month of January 2010 there were 5 western disturbances which enhanced the moisture over northern India, surface wind speed remained around 5 kt or less. Inversion in lower levels and freezing level has also been taken into consideration. No significant relation was found between fog and freezing level. However, inversion layer played an important role in formation of fog. Visible satellite imageries have also been taken into consideration to monitor fog over vast area of northern India, Bangladesh and Pakistan.

Vehicular Visible Light Positioning Using Receiver Diversity with Machine Learning

This paper proposes a 2-D vehicular visible light positioning (VLP) system using existing streetlights and diversity receivers. Due to the linear arrangement of streetlights, traditional positioning techniques based on triangulation or similar algorithms fail. Thus, in this work, we propose a spatial and angular diversity receiver with machine learning (ML) techniques for VLP. It is shown that a multi-layer neural network (NN) with the proposed receiver scheme outperforms other ML algorithms and can offer high accuracy with root mean square (RMS) error of 0.22 m and 0.14 m during the day and night time, respectively. Furthermore, the NN shows robustness in VLP across different weather conditions and road scenarios. The results show that only dense fog deteriorates the performance of the system due to reduced visibility across the road.

Hybrid MDM-PDM Based Ro-FSO System for Broadband Services by Incorporating Donut Modes Under Diverse Weather Conditions

High-speed data demand in sensitive locations has prompted new wireless technologies to grow in areas like hospitals for bio-sensor data transmission between doctors and patients. However, interference of electromagnetic spectrum or highly sensitive medical equipment in such locations can prevent radio waves which can further compromise the health of patients. Radio over Free Space Optics (Ro-FSO) can fulfil high-speed data demand in such locations without any such interference. However, the Ro-FSO performance is highly influenced by different adverse weather conditions, particularly haze and rainfall, which further cause attenuation in the transmission path of Ro-FSO systems. These atmospheric turbulences mainly affect the transmission link range of Ro-FSO systems. In this work, Ro-FSO system is designed by incorporating hybrid mode division multiplexing (MDM) and polarization division multiplexing (PDM) schemes to deliver four independent channels, each carrying 10 Gbps data upconverted to 40 GHz radio signal, over 3.4 km free space optical link operating under clear weather conditions. In addition to this, the proposed Ro-FSO link is subjected to different weather conditions, particularly partially hazy/rainy and dense fog/very rainy. The reported results indicate the achievement of acceptable bit error rate (BER≈10–3) for all channels up to 3400m FSO link under clear weather conditions, 1000m under partially haze/rain and 620 m under dense fog/heavy rain.

Developing a long-term high-resolution winter fog climatology over south Asia using satellite observations from 2002 to 2020

The vast Indo-Gangetic Plains (IGP) south of the Himalaya are subject to dense fog every year during winter months (December-January), severely disrupting rail, air and public transport of millions of people living in northern India, Pakistan, Nepal and Bangladesh. Air pollution combined with high moisture availability in the shallow boundary layer, are important factors affecting the persistence and widespread nature of fog over the IGP. Despite the environmental significance and impacts on the public at-large, an in depth understanding of the long-term spatial-temporal distribution of the south Asian fog, is presently not available in the literature. We utilize infrared remote sensing techniques to develop a high-resolution (≈1 km x 1 km) fog detection climatology over the past two decades (2002 – 2020), using Aqua/MODIS satellite observations. A dynamic brightness temperature difference threshold (involving 3.96 μm and 11.03 μm bands) for nighttime fog detection is constructed based on systematic radiative transfer simulations involving cloud effective radius, cloud top height, cloud optical depth and satellite viewing geometry. Our satellite-based fog detection is consistent with theoretical simulations of fog characterization and is also found to be well-correlated with near-surface visibility observations of dense fog (r = 0.87, p-value << 0.01). We also provide satellite-derived nighttime estimates of fog/low-cloud effective radius which is in general agreement with the operational daytime MODIS cloud data product and limited in situ observations. In terms of fog frequency, the IGP is relatively uniformly covered by widespread fog occurrences with the largest frequency found in the low-lying Terai region, bordering India and Nepal, which is also consistently observed in our daytime fog detection results over the last two decades. Additionally, the interannual variations in fog occurrences track closely with that of relative humidity in the IGP, which is associated with shallow boundary layer conditions during winter-time favoring the formation and persistence of fog. Overall, these long-term satellite-derived results present new high-resolution data and insights into the dense and often intense winter fog occurrences which routinely engulf the entire stretch of the Indo-Gangetic Plains and cause significant degradation to ground visibility in one of the world’s most densely populated regions.

Application of Ground based Microwave Radiometer in Aviation Weather Forecasting in Indian Air Force

Time and intensity specific very short-term forecasting or nowcasting is the biggest challenge faced by an Aviation Meteorologist. Ground-based Microwave Radiometer (MWR) has been used for nowcasting convective activity and it was established that there is a good comparison between thermodynamic parameters derived from MWR and GPS radiosonde observations, indicating that MWR observations can be used to develop techniques for nowcasting severe convective activity. In this study, efforts have been made to bring out the efficacy of MWR in nowcasting thunderstorms and fog. Firstly, the observations of MWR located at Palam, New Delhi, India have been compared with the nearest radiosonde (RS) data to ascertain the variation in respective profiles. Large differences were found in Relative Humidity (RH) whereas temperatures from MWR were found to be close to RS observed temperature upto 3.5 Km. Subsequently, the scattered plots and correlation coefficient of thermodynamic indices / parameters indicated that most of the parameters are either not correlated or have moderate correlation only for 1200 UTC profiles. The superepoch technique of lagged composite for various thermodynamic indices / parameters to obtain a combined picture of all the thunderstorm and dense fog cases on the time series could not determine any pattern to predict thunderstorm and dense fog with lead time of 2-4 hours. MWR profile for a case of occurrence of thunderstorm was analyzed. No significant variation was observed in most of the indices (as calculated from MWR observed parameters) prior to the occurrence of thunderstorm. RH at freezing level and between 950 and 700 hPa levels were the only parameters which increased four hours prior to the occurrence.

A Fog Climatology at Abu Dhabi International Airport

Fog has a significant effect on aviation and road transport networks around the world. The International Airport in Abu Dhabi, United Arab Emirates, experiences dense fog during winter months that affect operations at the airport. We describe the fog climatology at the airport using 36 years of aviation routine weather reports (METAR), an important long-term data source, and report on the number of fog days per year, the seasonal cycle, the diurnal cycle, and the duration of fog events. Fog days per year vary from 8 to 51, with a mean of ~23.91 days (standard deviation of 9.83). Events are most frequent from September until March, with December and January being the most active months. November, unexpectedly, has a low number of fog days, which appears to be due to a decrease in aerosol loading in the atmosphere. The most fog days experienced in one month is 13 (March 2004). Fog occurs any time from 1900 to 1100 local time, and the frequency increases as night progresses, peaking around sunrise. Fog events most frequently last 1 h or less. Events of 9 h or more were recorded in January and December, with the longest event lasting 16 h. Events are strongly dependent on the land–sea breeze and seldom form when the wind is blowing from the Arabian Gulf. The thickness of the nocturnal inversion layer increases up to about 500 m AGL on fog days as compared with 273 m AGL on clear-sky days. This study is the first to use the 36-yr dataset to characterize fog climatology at Abu Dhabi Airport.