The Return of True Color to Geostationary Satellites: Transitioning from Polar, to Himawari, to GOES-R

In 1967, at the dawn of the satellite era, the Advanced Technology Satellite 3 (ATS-3) provided the first full-disk color images of Earth in its full Blue Marble splendor. Through its depiction of sapphire blue oceans, golden deserts, and emerald green forestlands beneath swirling white clouds, true color communicates information a way that is uniquely and intuitively connected to human visual perception. After ATS-3, single-band (gray-scale) visible imagery became the standard of geostationary satellites. While satisfying the basic user requirements of daytime imagery, the absence of true color capability (which requires channels in the red, green and blue portions of the visible-light spectrum) has left a notable void, filled only in part by intermittent snapshots available from a handful of polar-orbiting systems. Nearly half a century later, with the launch in 2014 of Japan's Himawari-8, there is once again a geostationary sensor (the Advanced Himawari Imager, or AHI) containing the notional spectral bands required for true color. However, AHI's green band centered at 0.51 μm is not aligned with peak vegetation reflectance signature near 0.55 μm, and mineral-rich soil absorption is enhanced. As a result, vegetation appears too brown and deserts appear too red in comparison to legacy true color imagery. We have developed a technique to mitigate these issues by blending a small amount of spectral information from a reflective-infrared band at 0.86 μm (vegetation, or ‘veggie' band) to form a ‘hybrid green' band. True color imagery based on the hybrid band is on par with that of the optimal 0.55 μm band (using MODIS and VIIRS as a benchmark)—providing the expected appearance in forested and desert regions while not impacting clouds and ocean color features. The hybrid method offers a stopgap solution adaptable to future satellites on the European, Korean program that will carry a similar band. In addition, we have developed a technique for synthesizing the ‘hybrid green' band as a correlative function of the blue, red, and veggie bands. The technique mitigates the omission of a native green band on GOES-R's Advanced Baseline Imager (ABI). Preliminary results of true color imagery based on the synthetic green band for selected scenes will be presented using AHI as a test bed. The work forms a basis for the kind of imagery that will be displayed prominently as flagship public relations material for the various programs