A study to improve night time fog detection in the Indo-Gangetic Basin using satellite data and to investigate the connection to aerosols

Abstract

Fog is a socio-economically important weather hazard in the Indo-Gangetic Basin, Northern India, disrupting public life and incurring massive economic loss because of delays in road, rail and air traffic every winter (December-January). Accurate detection of the spatial extent of fog and forecasting of its persistence and dispersion are critical in minimizing this economic loss. In the present study, a satellite based bi-spectral brightness temperature difference (BTD) technique has been applied to detect night time fog over this region during the fog episodes of 2010-2011. The method, validated against ground-based observations from four urban centres (Amritsar, New Delhi, Lucknow and Varanasi), yields 83.9% accuracy in detecting fog for a total 393 satellite overpasses using the operational 2.5°C BTD threshold. The accuracy further increases to 88.3% with a reduction in the BTD threshold to 1.5°C. A minimum fog droplet number concentration of 3.23 cm-3 is required to degrade visibility below 1 km in the presence of aerosols at 95% RH in the Indo-Gangetic Basin. The results emphasize the need to improve treatment of aerosols in order to improve forecasting of fog occurrence in this region.