Time frame of single ISCCP file

[Derek Tropf]

 I am wondering the true time frame for a single ISCCP file.

The naming convention for a file includes an hour marker after the date -- for example '1984.03.01.0600'

My initial understanding was that the data from this file spans the three hour period of 0300-0600, however there exists global variables in the same file which say the following:

:time_coverage_start = "1984-03-01T04:30:00.000Z"

:time_coverage_end = "1984-03-01T07:29:59.999Z"

These variables claim a different time frame.

Could someone help clarify this?

Thank you again for all the help.

[Ken Knapp - NOAA Federal]

Hi

The images in ISCCP are 3-hourly snapshots. The target time (in your example) is 06:00 UTC. However, the Geostationary satellites have slightly different timing for each one: GOES East usually starts 15 minutes before the hour (05:45), GOES-West starts on the hour, Meteosat and the INS positions are usually on the half hour before (05:30), etc.

The AVHRR sensor is on a polar orbiter, so it continuously records data, so the data from it does likely span 4:30 to 7:29.

Also, if a GEO image was missing, the image could be replaced by a nearby time (e.g., 17:15 instead of 17:45).

The key is that each is an instantaneous snapshot (not an average over time) when the point is viewed.

In short, the 06:00 time should be seen as an optimal observation time.

I hope this helps-

-Ken

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Ken Knapp, Ph.D.

Meteorologist,

NOAA National Centers for Environmental Information

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