Overview

In the past, MTSAT data was broadcast in multiple formats, including High Resolution Imager Data (HiRID), which was terminated in March/April 2008. It is currently broadcast in High Rate Information Transmission (HRIT), the format covered in this chapter.

The MTSAT satellite provides one visible image channel and four IR channels. In the HRIT format, the data rate is 3.5 Mb/second and spatial resolution at the sub-satellite point is 1 km for the visible channel and 4 km for the IR channels.

For each channel, the transmitted image data is divided into multiple separate files, called image segment files. Full Earth images consist of ten image segment files per channel, and single hemisphere images consist of five image segment files per channel. A full Earth MTSAT visible channel image is 11,000 lines by 11,000 elements, so a complete visible image consists of ten image segment files, each containing 1,100 lines by 11,000 elements. Similarly, a full Earth MTSAT IR channel image is 2,750 lines by 2,750 elements, so a complete IR image consists of ten image segment files, each 275 lines by 2,750 elements. See Figure 1 for a graphic depicting a full Earth visible or IR image and its ten segment files.

The data contained in an image segment file can be fully determined by the file name alone. The naming convention is:

ffffppppccccYYYYMMDDhhmmnnnn

Where:

ffff

is the file type (IMG_ for image data, OVL_ for map overlay)

pppp

is the projection (DK01 for full disk, DK02 for Northern Hemisphere, DK03 for Southern Hemisphere, SF01 for Small Frame image)

cccc

is the spectral channel (VIS_, IR1_, IR2_, IR3_, or IR4_, which correspond to McIDAS band numbers 1, 2, 3, 4 and 5, respectively)

YYYYMMDD

is the observation date (YYYY=year, MM=month, DD=day)

hhmm

is the observation time (hh=hour, mm=minute)

nnnn

is the image segment file number (_001 to _010)

For example, the file IMG_DK01IR1_200612312332_001 is image segment data file #1 of a full Earth disk image for infrared channel 1, observed at 23:32 UTC on 31 December 2006. Note: If the file type is OVL_, the file name consists of only the file type, the projection, and a three-character spectral channel (e.g., OVL_DK01_VIS or OVL_DK02_IR_).

Figure 1. Full Earth Image and HRIT Segment Files (from JMA HRIT Mission Specific Implementation, Issue 1.2 [pdf])

An ASCII text file named MANAM is also extracted from the transmitted data. The file, which is short for "Manual Amendment", contains the current operational plan for the satellite. The file can be consulted for the regular transmission schedule, and for changes/anomalies due to maneuvers, eclipses, etc.

The MANAM file is written to the same directory as image data, and is purged on the same schedule. Each time a new MANAM file is received (typically twice daily), a backup copy with the naming format MANAM_YYYYMMDDhhmm (where YYYYMMDDhhmm is the received date and time) is created. This ensures that the file named MANAM has the most recent information, and that backup files (with the date and time in their name) are also available.

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ffff	is the file type (IMG_ for image data, OVL_ for map overlay)
pppp	is the projection (DK01 for full disk, DK02 for Northern Hemisphere, DK03 for Southern Hemisphere, SF01 for Small Frame image)
cccc	is the spectral channel (VIS_, IR1_, IR2_, IR3_, or IR4_, which correspond to McIDAS band numbers 1, 2, 3, 4 and 5, respectively)
YYYYMMDD	is the observation date (YYYY=year, MM=month, DD=day)
hhmm	is the observation time (hh=hour, mm=minute)
nnnn	is the image segment file number (_001 to _010)