Detection of fog using brightness temperature difference: theoretical aspects
Student name: Ms Garima Sachdeva
Guide: Dr Anu Rani Sharma
Year of completion: 2015
Host Organisation: Center for Atmospheric Science, Indian Institute of Technology Delhi
Supervisor (Host Organisation): Dr Sagnik Dey
Abstract: Fog is a complex atmospheric phenomenon which limits the visibility to less than 1km .It is a boundary layer phenomenon whose formation is usually influenced by surface conditions. It has a huge impact over the socio-economic life due to disruption in daily life and transportation due to low visibility. The main aim of this study is to observe the optical properties of fog at various wavelengths and different droplet size- large drop (30-1300μm) and small drop (0.2μm-50μm). In the study the relationship between concentrations of droplets of different size with respect to visibility is observed. A satellite based bi-spectral brightness temperature difference (BTD) technique has been used for fog detection at 50 and 60 degree solar zenith angles over Delhi, Lucknow , Amritsar and Varanasi regions. The negative value 0f -2 kelvin for brightness temperature difference for visibility above 700 meters is observed in theoretical calculations. In the Study the validation of the theoretical calculation with ground observation data and satellite datasets is done over December month of 2012.
KEY WORDS: Fog, Brightness temperature difference, Bi-Spectral, Radiative Transfer Model, Visibility.
