CERES 'definition of SSF instantaneous footprint information for Level 2 products

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CERES 'definition of SSF instantaneous footprint information for Level 2 products

by xwgw » Mon Apr 15, 2024 8:12 am America/New_York

CERES Level 2 product SSF, how is this instantaneous footprint information defined, is it consistent with the transit time of the satellite, for example, how many times the satellite has passed through a certain area, how many footprint information, is that right? Because I downloaded the instantaneous footprint information of Ceres Level 2 product SSF on TERRA satellite, I downloaded the data of January 31, and then checked the satellite's 110 transit times in this month, but the footprint provided by SSF has 291 footprint points, which do not correspond with the transit time, so I want to know the relationship between the transit time and footprint information.


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Re: CERES 'definition of SSF instantaneous footprint information for Level 2 products

by wfmiller » Mon Apr 22, 2024 3:47 pm America/New_York

The CERES instruments scans the Earth with a view zenith angle varying from 0 to 65 degrees on each side of the satellite when in cross track mode. There are about 86 footprints on the SSF per scan with separation growing with view zenith angle. The footprints are about 8 km apart at nadir and growing to 35 km at 65 degrees. The footprint in the next scan varies from 15 to 45 km depending if it is on the start of the scan or at the end, i.e. the scan and return is a V pattern.

It than becomes how you define transit time of the satellite and how large of an area that you have defined. Given an average of 3.5 transits per day, it appears that you are looking at an area near the pole and not requiring the transit to be overhead. Your requested area must be large enough to contain multiple footprints at least on some overpasses. However, the time of the footprints should match the transit time within a few seconds.

If the instrument is in RAPS mode than it will be crossing a point multiple times since the instrument is looking both in front and behind the satellite. Again, the times should be within 10 minutes of the transit time.

I would need more information to better understand yours concerns.

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