Satellite imagery

The Himawari series of geostationary meteorological satellites provides constant and uniform coverage of the earth from around 35,800 km above the equator with an orbit corresponding to the period of the earth’s rotation. This allows them to perform uninterrupted observation of meteorological phenomena such as typhoons, depressions and fronts.

Types of satellite imagery

The JMA website provides satellite-derived visible, infrared, water vapor and color-enhanced imagery.

Visible imagery

Visible imagery captures sunlight reflected by clouds and land. Developed rain clouds reflect sunlight well, and thicker clouds appear whiter in visible imagery. At nighttime, visible imagery is black due to the absence of sunlight. The spatial resolution of visible imagery (Band No.3) is 500 m at the sub-satellite point.

Infrared imagery

Infrared imagery captures infrared radiation emitted from clouds, land and the atmosphere. High-altitude clouds are cold and appear white in infrared imagery, while low-altitude clouds and fog are hardly distinguishable from land. As high-altitude clouds may be either well-developed thunderclouds or clear-day cirrus, areas appearing in white are not necessarily associated with heavy rain. The spatial resolution of infrared imagery is 2 km at the sub-satellite point.

Water vapor imagery

Water vapor imagery captures 6.2-micrometer infrared radiation emitted by water vapor in the atmosphere. As atmospheric water vapor absorbs and emits such radiation, areas containing large amounts of vapor in the upper and middle troposphere appear white in this type of imagery. It shows atmospheric humidity and the atmospheric stream via a series of animated images.

Color-enhanced imagery

In addition, color-enhanced imagery is derived from the above output. This type of imagery shows cloud-top heights in rainbow-like colors superimposed onto visible imagery (daytime) and infrared imagery (nighttime). Cloud-top heights are estimated from the intensity of infrared radiation emitted from clouds. Red is used to indicate the possible presence of well-developed thunderclouds. Color-enhanced imagery is provided at Satellite Imagery (Rapid Scan).

True Color Reproduction imagery

True Color Reproduction (TCR) technology enables the display of earth images taken from space in a way that is familiar to the human eye. The imagery consists of data from three visible bands (Band 1, 2 and 3), one near-infrared band (Band 4) and one infrared band (Band 13). To reproduce colors as seen by the human eye, RGB signals observed by AHI are converted into CIE XYZ values and reconverted into RGB signals for output devices compliant with sRGB (an international standard for RGB color space) (Murata et al., 2018). In this process, as an alternative to the bi-spectral hybrid green method outlined by Miller et al. (2016), the green band is optimally adjusted using Band 2, 3 and 4. To make the imagery more vivid, atmospheric correction (Rayleigh correction, Miller et al., 2016) is also applied to AHI Bands 1-4. Software for this purpose was provided by the Cooperative Institute for Research in the Atmosphere (CIRA) established by NOAA/NESDIS and Colorado State University in United States of America.

Acknowledgement

The imagery was developed on the basis of collaboration between the JMA Meteorological Satellite Center and the NOAA/NESDIS/STAR GOES-R Algorithm Working Group imagery team. We would like to acknowledge them for the collaboration and their permission to use the software.

Reference

Miller, S., T. Schmit, C. Seaman, D. Lindsey, M. Gunshor, R. Kohrs, Y. Sumida, and D. Hillger, 2016: A Sight for Sore Eyes - The Return of True Color to Geostationary Satellites. Bull. Amer. Meteor. Soc., doi: 10.1175/BAMS-D-15-00154.1.

Murata, H., K. Saitoh, Y. Sumida, 2018: True color imagery rendering for Himawari-8 with a color reproduction approach based on the CIE XYZ color system. J. Meteor. Soc. Japan., doi: 10.2151/jmsj. 2018-049.

Terms of Use for True Color Reproduction imagery

All usage of satellite imagery provided JMA webpage is subject to the Terms of Use for the JMA website and True Color Reproduction imagery.

Observation schedule

Observation for full-disk Himawari satellite imagery is performed every 10 minutes, while observation for the Japan area and the target area is performed every 2.5 minutes. For more information, see Observation area and periodicity (* Link to MSC).

Impact of imager’s sun avoidance function

At night during the equinox season, sunlight shines directly against the Himawari satellite’s direction of view. Accordingly, some imagery may be partially missing in order to avoid the direct incidence of sunlight onto the satellite’s imager. Visible imagery is also corrected to prevent the appearance of stray sunlight in imagery. The following web page provides the information for stray sunlight: http://www.data.jma.go.jp/mscweb/en/operation8/foundation/image/image_info.html#003