Monitoring of Aerosol Patterns along the River Valleys of Nepal using MODIS Visible Channels

Research Team: Julien Brun, Prabhakar Shrestha and Ana P. Barros

Project description:

MODIS satellite images show that the Himalayas act as a barrier for the aerosols being transported from the Indian Gangetic Plains (IGP). This accumulation of aerosols during the pre-monsoon season not only affects the radiation budget, but can also have a profound impact on the evolution of orographically induced clouds and the local hydrological cycle.

 

The coarse spatial resolution (10km*10km to reduce signal noise ratio) of MODIS aerosol products cannot resolve the effects of local terrain in the spatial organization of the aerosol plumes, which is critical for the study of aerosol-cloud rainfall interactions in this region. However, high resolution images from MODIS visible channels have the ability to show the organization of the aerosol plumes in the Plains that penetrate along north-south river valleys from the IGP to the Tibetan Plateau. The developed methodology aims to use MODIS visible channels to monitor the time-space evolution of aerosol intrusions in the Himalayas by applying object oriented classification algorithms and GIS techniques on the MODIS visible channels to extract the aerosols extent evolution along seasons during the MODIS era (2000 - 2009). This 3-D spatial information of aerosol extent at high spatial resolution could be used in numerous applications ranging from designing of field campaigns, aerosol transport modeling, and environmental health-impact studies.

Image
 nepal_patterns.jpg

This figure displays the elevation extracted for each external object with the shaded relief of the area as background overlaid by contour lines every 500m. These first results show that the haze elevation and intrusion length varie from valley to valley, likely reflecting the wind patterns and terrain complexity. As expected, the farther into the mountain range, the higher the haze ceiling (up to 4,000 m) as the valley bottom elevation is increasing along the river valley." title="This figure displays the elevation extracted for each external object with the shaded relief of the area as background overlaid by contour lines every 500m. These first results show that the haze elevation and intrusion length varie from valley to valley, likely reflecting the wind patterns and terrain complexity. As expected, the farther into the mountain range, the higher the haze ceiling (up to 4,000 m) as the valley bottom elevation is increasing along the river valley.