Impacts of spacecraft events and calibration on Himawari-8 Images

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.


Figure 1: Band 3 Japan Area observation started at 02:37:30 UTC (left, before unloading) and 02:40:00 UTC (right, during unloading) on 5 August 2015

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.


Figure 2
Each observation were automatically skipped based on solar interference prediction.
Band 13 Full Disk observation started at 15:20 UTC on 1 April 2015.
Band 13 Full Disk observation started at 14:10 UTC on 12 October 2016.

Band 13 Japan Area observation started at 14:30 UTC on 11 April 2015.
Band 13 target area observation started at 14:50 UTC on 14 April 2016.

Band 13 Full Disk observation started at 14:10 UTC on 13 October 2018.

Stray light

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.


Figure 3
True-color imagery from band 1, 2 and 3 observations started at 14:30 UTC on 13 April 2015. Stray light is seen in the north-western part of the images.

Band 13 Japan Area observation started at 14:30 UTC on 11 April 2015.
Band 13 target area observation started at 14:50 UTC on 14 April 2016.

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.

Figure 4: Band 11 Full Disk observation started at 19:00UTC on 22 June 2015

Striping

AHI detector sensitivity differences can cause horizontal stripes (Figure 5).

Figure 5: Band 2 Full Disk observation started at 04:00 UTC on 23 June 2015