衛星雲圖

The primary instrument aboard Himawari 8, the Advanced Himawari Imager (AHI), is a 16 channel multispectral imager to capture visible light and infrared images of the Asia-Pacific region. This new instrument enables use of the true-color imagery from the geostationary orbit. True to its name, true color combines appropriately scaled red(0.64µm)-, green(0.51µm)-, and blue(0.47µm)-band reflectance values to form imagery that approximates the response of normal human vision. As Rayleigh scattering efficiency is considerably more notice-able for shorter wavelengths, true-color imagery will take on a milky blue appearance, particularly near the horizon where the viewing path through the atmosphere is long.

真實色彩衛星影像雲圖圖例

After the Rayleigh correction is performed at each band in order to correct for the effects of Rayleigh scattering, the result is an image that is significantly more crisp and clear, and less milky, than without the correction. Thus, atmospheric features such as clouds, dust storms, volcanic ash, and smoke/pollution are distinguishable in true color. The figure shows a dust storm event on May 3, 2017.

沙塵暴影像修正後圖例

The Geocolor algorithm is applied to the imagery at nighttime. It turns out that a difference between two infrared channels (3.9 and 10.8um) provide an ability to identify these low-clouds/fog layers because of differences in scattering properties between the two channels. White colors are high level ice clouds, red colors represent lower level liquid water cloud and city lights (static) are shown in yellow.

夜間影像圖圖例