Impacts of spacecraft events and calibration on Himawari-8 Images
- Degradation of image navigation accuracy
- AHI's automatic sun avoidance function for the spring and autumn eclipse periods
- Stray light
- Image quality degradation due to lunar interference
Degradation of image navigation accuracy
Image navigation accuracy in Himawari-8/AHI regional observation data may be degraded during maneuvers and unloading. Full Disk and regional observation conducted immediately after maneuvers may also have the same issue. Figure 1 shows band 3 Japan Area observation conducted just before and during the unloading. Information on maneuvers and unloading is provided in Himawari Standard Data (HSD) Basic information block 1.
AHI's automatic sun avoidance function for the spring and autumn eclipse periods
Around midnight during the spring and autumn eclipse periods, sunlight can enter the AHI sensor when the sun and the earth occasionally lie in an approximate line with the satellite. To avoid this, the AHI has a function by which part of the observation area can be automatically skipped based on prediction of the sun's position and potential problem areas (Figure 2).
The skipped area is filled with missing values from HSD Data block 12. HSD Basic information block 1 also contains solar eclipse flag.
Each observation were automatically skipped based on solar interference prediction.
Stray light (a term given to reflected or diffused sunlight entering the sensor) can be seen in AHI images when the sun and the earth occasionally lie in an approximate line with the satellite during the spring and autumn eclipse periods. Figure 3 shows full-disk images captured at midnight during the spring eclipse. Stray light can be seen in bands 1 to 9.
Image quality degradation due to lunar interference
Anomalous radiometric calibration can occur with certain positional relations among the earth, the satellite and the moon. This results in a degradation of image quality (as seen with the horizontal stripes in Figure 4). Information on lunar interference is provided in HSD Basic information block 1.
AHI detector sensitivity differences can cause horizontal stripes (Figure 5).