MTSAT-1R Band 5 Anomaly Apparent ghosting in CCD imager Warmer scenes introduce cold bias to adjacent block of pixels. Prepared by Chris Schmidt ([email protected]),

MTSAT-1R Band 5 Anomaly

Apparent ghosting in CCD imagerWarmer scenes introduce cold bias to adjacent block of pixels.

Prepared by Chris Schmidt ([email protected]), UW-Madison/SSEC/CIMSS, 18 Sept 2009. MTSAT-1R data from SSEC Datacenter, imagery and measurements from McIDAS-X. V2.0

MTSAT-1R instrument basics

• MTSAT-1R was a replacement for a very GOES-like MTSAT-1 which was lost at launch.

• Imager (JAMI) built by Raytheon, allegedly a GOES-R demo unit.

• Uses a CCD array scanning in adjacent blocks.• Image is built from the blocks, imager footprint for IR is a

square or rectangle at least 32 samples wide (at 2 km resolution).

• Data is remapped onboard to 4 km resolution (for IR).

MTSAT-1R: 14:30 UTC on 2009259 (local night)“Ghost” of hurricane eye is zero radiance (reads as very cold BT/bright white, the same as space reads for MTSAT-1R). Offset from real eye by 16 pixels. Also, there is a vertical displacement of 1-2 pixels. Horizontal offset corresponds to block spacing.

RAW counts around ghost are ~1015. Top of scale (which is coldest!) is 1023.

MTSAT-1R: 15:30 UTC on 2009259 (local night)Just like 14:30 UTC, “Ghost” of hurricane eye is zero radiance (reads as very cold BT, the same as space reads). Offset from real eye by 16 pixels. Also, there is a vertical displacement of 1-2 pixels.

MTSAT-1R: 4:30 UTC on 2009259 (local day)The ghost is there during the day, but does not cause 0 radiance. It cools the pixels slightly (and increases the RAW counts by approximately 12). Offsets are the same.

Original Enhanced

Visible

MTSAT-1R: 17:30 UTC on 2009259 (local night)“Ghost” of warm area between clouds, offset from source by 16 pixels. Also, there is a vertical displacement of 1-2 pixels.

MTSAT-1R: 14:30 UTC on 2009259 (local night)Values where radiance is zero (BRIT=255 in McIDAS) are changed to black. Not all BRIT=255 are ghosts, some are just very cold. Other ghosts are visible.

Sloped scan pattern is somewhat evident on this image.

MTSAT-1R: 14:30 UTC on 28 Oct 2008 (local night, heavily enhanced)Angled scan pattern of MTSAT-1R is easier to see. Lines converge off in space to the right. Yellow line shows the slope. Note it changes from north to south!

Summary• Ghosts are present day and night.• Are most noticeable when a warm scene is to the immediate left of a

cold scene (sensor moves from left to right).• Likely impacts ALL of the radiances from the instrument (before any

calibration or other processing is applied), just often not visible – but might explain the large number of 0 radiance pixels over clouds.

• Seen best at night because cooling by ghost increases the RAW counts by at least 12, causing cold cloudtops to hit the top of the RAW scale for MTSAT-1R (1023, corresponding Brightness Temperature of 131.99 K, which is meaningless).

• Clouds with white pixels are very common on MTSAT-1R data, this anomaly may have been present since launch. Or it has developed (or worsened) as the sensor has aged.

• Instrument cross-talk was a problem with the instrument in the past, this ghosting could be a form of cross-talk.