Read the measurement

The Advanced Himawari Imager has sixteen spectral bands. Visible bands measure reflected sunlight; thermal infrared observations measure emitted radiation. A band is a selected wavelength range, not a separate photograph taken by a human eye. Choosing a band changes which physical information contributes to the resulting image.

For an original thought experiment, put two identical surfaces in different illumination: one in sunlight, the other at night. Their ordinary visible images can look very different even if their temperatures are similar. The lack of reflected sunlight is not evidence that the nighttime surface, or the clouds above it, has vanished.

The Himawari-9 full-disc image shown here combines observations into a color display and includes color correction. An RGB composite can assign different measured bands to red, green and blue display channels. Other products apply different transformations, so a familiar-looking color does not by itself identify the exact measurement or processing recipe.

Keep the product description with the image. Ask which satellite and instrument supplied the data, when the observation occurred, and whether colors were combined, corrected or assigned to a scale. A caption that calls every product a raw photograph discards information the reader needs to interpret it.

Infrared observations can reveal cold high clouds, including both storm clouds and cirrus. A cold-looking cloud top therefore does not establish heavy rain at the ground. Visible brightness and infrared temperature information answer different questions, and neither is a direct substitute for every surface measurement.

Suppose two cloud systems have similarly cold tops in an original comparison, but a rain gauge beneath one records much more water. That difference is a reason to combine evidence, not to alter the gauge record until it matches an image. The image describes a measured radiative signal; estimating surface rainfall requires additional interpretation and validation.