Detection of Fog Using Derived Dual Channel Difference of MODIS Data Dr. Devendra Singh ,Director

1. Detection of Fog Using Derived Dual Channel Difference of MODIS Data Dr. Devendra Singh ,Director Satellite Meteorology Division,India Meteorological Department, New Delhi-110003, INDIA • Importance of fog detection • Aviation industry: • One diversion of Aircraft from airport causes rescheduling of over many flights and crew, great expense and • passenger inconvenience. • Meteorology • One of the most significant problems for forecasters • NWP, assimilation and data advances enable progress • Why the Need for Combined Channel Products? • Poor thermal or visible contrast between feature of interest and background • Fog, aerosols (volcanic ash) • Complex set of conditions • Icing • Remote sensing main means of detection • Trace gases (SO2, ozone, water vapor) • Stretching of Intensity Ranges • The range of interest for the MODIS channels varies, depending on: • the phenomenon of interest (high clouds, low clouds, surface features,fog, dust, smoke ) • the season (winter, summer) • the time of the day (day / night / twilight) Methodology :The method of detecting fog at day and night time using the infrared images of different wavelengths uses the property of emissivity of the infrared radiation. At about 11µm the opaque cloud composing of water droplets has an emissivity of almost one, but at about 3.9µm, they have the values of emissivity of about 0.8-0.9. Therefore, the measured brightness temperature from satellite data is significantly different. The significant difference in these two brightness temperatures has been exploited for the detection of fog A blanket of fog over parts of Pakistan on November 27, 2004, created poor visibility and led to several traffic-related deaths. This image from the Moderate Resolution Imaging Spectroradiometer (MODIS)on NASA’s Terrasatellite that morning shows the foggy area in the center and left-center of the scene. The fog sits over the fertile region through which rivers draining out of the Himalaya Mountains (upper right) flow southward into the Indus River. A grayish layer of haze also hangs over the area. By the time the MODIS sensor on the Aqua satellite captured an image of this area in the afternoon,the fog had partially receded. Image courtesy the MODIS Rapid Response Team, NASA-GSFC Fog stretched over northern India on December 17, 2004, and mixed with a river of haze that flowed west and south across Bangladesh and over the Bay of Bengal. According to news reports from the area, over the weekend of December 18 and 19, the foggy, smoggy conditions caused numerous deadly accidents in the Indian states of Bihar, Haryana, and Uttar Pradesh. All forms of transportation were delayed throughout the weekend, including air, train, and road traffic. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Stretching of Intensity Ranges- Example Fog at Day - Stretching of Intensity Ranges- Example Fog at Day - Total Range = -40 K / +1 K Stretched Range = -15 K / 0 K MODIS, 27 November 2004, 05:40 UTC, Diff. IR11.0 – IR3.97 Total Range = -40 K / +1 K Stretched Range = -15 K / 0 K MODIS, 17 December 2004, 05:15 UTC, Diff. IR11.0 – IR3.97 Stretching of Intensity Ranges- Example Fog at Night - Stretching of Intensity Ranges- Example Fog at Night - Total Range = -7.0 K / +18 K Stretched Range = -5.7 K / 6.1 K MODIS, 31 December 2003, 20:30 UTC, Diff. IR3.97 – IR11.0 Total Range = -6.0 K / +4.5 K Stretched Range = -4.5 K / +4.1 K MODIS, 1 January 2005, 20:30 UTC, Diff. IR3.97 – IR11.0 • Summary • Many hazards can be detected with multi-channel combinations. Without them detection of hazards are impossible. • In the past few years, the combined channel applications have progressed from simple 2-band to multi-band products. • Future spacecraft will allow expanded capabilities due to better spectral and spatial resolution. Acknowledgement: I am thankful to Mr. Rink, Thomas, SSEC, University of Wisconsin for his kind assistance in MODIS data processing. International EOS/NPP Direct Readout Meeting, Benevento Italy, 3-6 October 2005