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Imager (AHI)

Imaging channels

Himawari-8 and -9 will have a dedicated meteorological mission, whereas MTSAT performs both meteorological and aeronautical functions. The satellites will have a new payload called the Advanced Himawari Imager (AHI).

Table 1 shows the AHI observing bands*1. The functions and specifications are notably improved from those of the imagers on board MTSATs, and enable better nowcasting, improved numerical weather prediction accuracy and enhanced environmental monitoring. Color images will be derived by compositing three visible channels (blue: 0.47 µm; green: 0.51 µm; red: 0.64 µm).

*1 The Himawari-8/9 band corresponding to the MTSAT-1R/2 IR1 band was changed from 11.2 µm to 10.4 µm on 31 October, 2013.

Table 1.  Imager specifications.
Wave length
[µm]
Himawari-8/9 MTSAT-1R/2
Band
number
Spatial
resolution
at SSP
[km]
Central wave length
[µm]
Channel
name
Spatial
resolution
at SSP
[km]
AHI-8
(Himawari-8)
AHI-9
(Himawari-9)
0.47 1 1 0.47063 0.47059 - -
0.51 2 1 0.51000 0.50993 - -
0.64 3 0.5 0.63914 0.63972 VIS 1
0.86 4 1 0.85670 0.85668 - -
1.6 5 2 1.6101 1.6065 - -
2.3 6 2 2.2568 2.2570 - -
3.9 7 2 3.8853 3.8289 IR4 4
6.2 8 2 6.2429 6.2479 IR3 4
6.9 9 2 6.9410 6.9555 - -
7.3 10 2 7.3467 7.3437 - -
8.6 11 2 8.5926 8.5936 - -
9.6 12 2 9.6372 9.6274 - -
10.4 13 2 10.4073 10.4074 IR1 4
11.2 14 2 11.2395 11.2080 - -
12.4 15 2 12.3806 12.3648 IR2 4
13.3 16 2 13.2807 13.3107 - -
Central wavelengths of the AHIs are "Moment center wavelength" (provided by Exelis).
SSP : sub satellite point

Spectral Response Functions

The figures below show the SRFs (Spectral Response Functions) of the AHI on board Himawari-8 as of September 2013. Microsoft Excel workbooks (zip files) of the SRFs can also be downloaded from the hyperlink below.

AHI SRF (VIS, NIR) AHI SRF (IR)
Figure 1: Latest Spectral response functions of the AHI on board Himawari-8. Left: VIS and NIR, right: IR (Click figure to enlarge.)

Test results

The performance of the AHI on board Himawari-8 is evaluated in ground testing. The test results, including data on the center wavelength, bandwidth, bits, SNR, dynamic range, radiometric calibration accuracy, internal calibration target (ICT) emissivity and out-of-band response, can be accessed via the following link:


Observation area and periodicity

Himawari-8 and -9 will each carry an AHI scanning five areas: Full Disk (images of the whole Earth as seen from the satellites), the Japan Area (Regions 1 and 2), the Target Area (Region 3) and two Landmark Areas (Regions 4 and 5). While the scan ranges for Full Disk and the Japan Area will be preliminarily fixed, those of the Target Area and Landmark Areas will be flexible to enable prompt reaction to meteorological conditions. At the beginning of Himawari-8’s operation, Landmark Area data will be used only for navigation, and are not intended for use as satellite products. In the future, JMA plans to use Region 5 for observation of phenomena such as rapidly developing cumulonimbus clouds and to provide the resulting data to users. In each 10-minute period, the AHI will scan the Full Disk once, the Japan Area and Target Area four times, and the two Landmark Areas twenty times. These 10-minute divisions are basic units of an observation schedule called a timeline. In Himawari-8 and -9’s baseline observation, the timeline will be repeated every 10 minutes except in their housekeeping operation. The observation areas and frequencies are shown in Table 2, and scan images on a timeline are shown in Figure 1. The Japan Area is shown in Figure 3. The observation areas and numbers of pixels are shown in Table 3 (pixel numbers for regional observations may be changed in orbit testing after launch). The following movie shows the concept of the AHI observation sequence on a 10-minute timeline:

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AHI observation areas
Figure 2: AHI observation sequence within a 10-minute time frame (Click figure to enlarge.)

AHI observation areas
Figure 3: Coverage of the Japan Area
(Subject to slight changes based on the results of in-orbit testing after launch)

Table 2. Himawari-8 and -9 observation areas and frequencies
Observations per timeline Time cycle [min.] Observations per day
Full Disk (Fixed) 1 10 144
Japan Area (Fixed)
(Region 1 + Region 2)
4 2.5 576
Target Area (Flexible)
(Region 3)
4 2.5 576
Landmark Area (Flexible)
(Region 4)
20 0.5 2,880
Landmark Area (Flexible)
(Region 5)
20 0.5 2,880

Table 3. Himawari-8 and -9 observation areas and numbers of pixels
Observation area Band number
(see Table 1)
Spatial resolution at SSP
(sub satellite point)[km]
Numbers of pixels
East-west direction North-south direction
Full Disk 3 0.5 22,000 22,000
1,2,4 1 11,000 11,000
5-16 2 5,500 5,500
Japan Area
(Region 1 + Region 2)
3 0.5 6,000 4,800
1,2,4 1 3,000 2,400
5-16 2 1,500 1,200
Target Area
(Region 3)
3 0.5 2,000 2,000
1,2,4 1 1,000 1,000
5-16 2 500 500
Landmark Area
(Region 4)
3 0.5 2,000 1,000
1,2,4 1 1,000 500
5-16 2 500 250
Landmark Area
(Region 5)
3 0.5 2,000 1,000
1,2,4 1 1,000 500
5-16 2 500 250

Photographs (Click figure to enlarge.)

The AHI unit to be installed on the Himawari-8 satellite is under manufacture.  (Photos © ITT Exelis)

Sensor Unit Sensor Unit
Sensor unit
Cryocooler Electronics Cryocooler Electronics
Cryocooler electronics
Electronics Unit Electronics Unit
Electronics unit