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<div class="cbp-l-inline-title">Illustrations of GeoColor Image</div>
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<h3 class="cbp-l-inline-title">I. Characteristics</h3>
<p>During the day, GeoColor images mainly reflect solar shortwave radiation, which is influenced by factors such as solar angle, surface reflectivity, and aerosols. As a result, different surface features and atmospheric conditions present different colors, resembling what the naked eye would see. For example, oceans or lakes appear blue, and changes in algae concentrations can produce various shades. Land areas can be brown or green, depending on vegetation type, with variations from light to dark green in vegetated areas, while exposed mountains and valleys show yellow-brown or dark brown. High-altitude regions or urban areas may display shades of gray.
At night, GeoColor images may display low-level clouds or fog areas in pink, while higher clouds are shown in white, allowing easy identification of weather phenomena that could affect navigation and aviation safety. In areas transitioning between day and night, a gradient is applied based on the solar zenith angle, and the cloud images gradually shift between daytime and nighttime signals
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<p>At night, GeoColor images may display low-level clouds or fog areas in pink, while higher clouds are shown in white, allowing easy identification of weather phenomena that could affect navigation and aviation safety. In areas transitioning between day and night, a gradient is applied based on the solar zenith angle, and the cloud images gradually shift between daytime and nighttime signals.</p>
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<h3 class="cbp-l-inline-title">II. Principle</h3>
<p>GeoColor images are synthesized using observation data from Himawari geostationary satellite, including red light (0.64 µm), green light (0.51 µm), blue light (0.47 µm), near-infrared (0.86 µm), infrared channel 1 (10.4 µm), and infrared channel 4 (3.9 µm).</p>
<p>(1) During the day, solar light passing through Earth's atmosphere undergoes Rayleigh Scattering with air molecules, causing GeoColor images to appear blurry. After atmospheric correction, the images synthesized from red, green, blue, and near-infrared channels become clearer and closer to what the naked eye would see, as shown in Figure 1.</p>
<p>(2) At night, infrared channel 1 is used to provide cloud distribution over Earth's surface, while infrared channel 4 is used to detect low clouds and fog, as shown in Figure 2.</p>
<p>(3) In areas transitioning between day and night, visible shortwave and infrared longwave data are blended based on the solar zenith angle, as shown in Figure 3.</p>
<p>(4) The 6S (Second Simulation of the Satellite Signal in the Solar Spectrum) radiative transfer model is used for more accurate atmospheric correction, reducing the occurrence of reddish-brown clouds in transition areas, as shown in Figure 4.</p>
<p>(5) The projection for GeoColor images over the Taiwan region, East Asia region, and worldwide views is now consistent with other cloud image projections, as shown in Figures 5, 6, and 7.</p>
<h3 class="cbp-l-inline-title">III. Applications</h3>
<p>GeoColor images are better at distinguishing special phenomena such as dust storms and volcanic ash compared to visible or infrared images. For instance, Figure 8a shows a strong dust storm in Mongolia on March 21, 2023, where dust is seen being carried eastward by westerly winds. Another example, shown in Figure 8b, depicts the eruption of Mount Ruang in Indonesia on April 30, 2024, where brown volcanic ash spreads through the atmosphere surrounding the volcano. Additionally, the intense eruption triggered strong convection.</p>
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<img src="/V8/assets/img/satellite/TrueColor_1.jpg" alt="Fig. 1. True Color Image" class="img-responsive">
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Fig. 1.<br>The worldwide GeoColor images after atmospheric correction are products provided on the official website.
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<img src="/V8/assets/img/satellite/TrueColor_2.jpg" alt="Fig. 2. True Color Image" class="img-responsive">
<p>Fig. 2.<br>By adding data from the infrared channel 4 (3.9 µm), potential areas of low clouds or fog within the yellow-framed regions can be identified, appearing in coral red. Meanwhile, higher cloud tops over the eastern sea area are still displayed in shades of gray and white.
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<img src="/V8/assets/img/satellite/TrueColor_3_E.jpg" alt="Fig. 3. True Color Image" class="img-responsive">
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Fig. 3.<br>Illustration of different processing methods for images that span both daytime and nighttime areas.
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<img src="/V8/assets/img/satellite/TrueColor_4_E.jpg" alt="Fig. 4. True Color Image" class="img-responsive">
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Fig. 4.<br>Improving the handling of low clouds or cloud edges in transition areas between day and night with the Satpy package, reducing the occurrence of reddish-brown clouds, as shown within the orange circle in the image.
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<img src="/V8/assets/img/satellite/TrueColor_5.jpg" alt="Fig. 5. True Color Image" class="img-responsive">
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Fig. 5.<br>Ensuring the projection settings of the Taiwan GeoColor images are consistent with other Taiwan cloud images (visible, color, enhanced, and gray scale).
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<img src="/V8/assets/img/satellite/TrueColor_6.jpg" alt="Fig. 6. True Color Image" class="img-responsive">
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Fig. 6.<br>Ensuring the projection settings of the East Asia GeoColor images are consistent with other East Asia cloud images (visible, color, enhanced, and gray scale).
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<img src="/V8/assets/img/satellite/TrueColor_7.jpg" alt="Fig. 7. True Color Image" class="img-responsive">
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Fig. 7.<br>Ensuring the projection settings of the worldwide GeoColor images are consistent with other worldwide cloud images (visible, color, enhanced, and gray scale).
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<img src="/V8/assets/img/satellite/TrueColor_8a.jpg" alt="True Color Image" class="img-responsive">
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Fig. 8a.<br>The GeoColor image of the East Asia region at 12:00 PM on March 21, 2023, clearly shows a dust storm occurring in Mongolia, as indicated by the red frame in the image.
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<img src="/V8/assets/img/satellite/TrueColor_8b.jpg" alt="True Color Image" class="img-responsive">
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Fig. 8b.<br>On April 30, 2024, the eruption of Indonesia's Mount Ruang shows a clear contrast between the brown volcanic ash and the surrounding white clouds. The red circle highlights strong convection caused by the intensive volcanic eruption.
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