SYN1deg cloud locations/timing
Posted: Wed Oct 12, 2022 1:19 pm America/New_York
Hello,
I've noticed the SYN1deg-hourly RSR values do not always match where I (naively) expect high values to be for a given hourbox based on where reflective clouds are visible in a geostationary image. I expect hourbox-averaged geostionary radiances to align well when downscaled into the 1x1 degree equal-area gridboxes in the domain of each geostationary satellite. In one scene I'm looking at under the GOES-16 domain for example the Syn1deg-hourly RSR values appear to be time-shifted earlier in time than what an equally weighted average of the GOES-16 radiances in the hourbox would suggest (that is, following the cloud motion backwards-in-time by eye can predict where the mismatched high-RSR values will appear compared with the averaged GOES-16 radiances that show reflective clouds).
I'm under the impression there may be two causes for this:
1) some of the cloud locations are derived from low-earth orbit sensors, which may be overpassing at a different time than the 30-minute mark in the hourbox.
2) RSR may not be an equal-time-weighted average in the hourbox (I am suspicious because of this sentence in the Data Quality summary for Edition4A: "The corresponding
midpoint is 0.5 GMT, except for SW fluxes, where the integrated cosine of the solar zenith
angle is considered the midpoint of the hour box in order to facilitate the hour box averaging
as described in the previous bullet.")
In case #1, is there metadata provided in the HDF files that indicates which gridboxes are informed by low-earth-orbit sensors and which are informed by geostationary radiances? If not, do you have any recommendations on the easiest way to calculate this?
In case #2, can anyone please clarify this sentence for me? Does it mean that the geostationary radiances used as input for the RSR calculation are time-weighted when they are averaged in the hourbox, via the cos of SZA? If not then what does it mean?
And finally, if there's other possible explanations for high-RSR pixels to be shifted by a gridbox (or two) compared with the geostationary radiances, please let me know.
Thanks for any help,
-Kevin
I've noticed the SYN1deg-hourly RSR values do not always match where I (naively) expect high values to be for a given hourbox based on where reflective clouds are visible in a geostationary image. I expect hourbox-averaged geostionary radiances to align well when downscaled into the 1x1 degree equal-area gridboxes in the domain of each geostationary satellite. In one scene I'm looking at under the GOES-16 domain for example the Syn1deg-hourly RSR values appear to be time-shifted earlier in time than what an equally weighted average of the GOES-16 radiances in the hourbox would suggest (that is, following the cloud motion backwards-in-time by eye can predict where the mismatched high-RSR values will appear compared with the averaged GOES-16 radiances that show reflective clouds).
I'm under the impression there may be two causes for this:
1) some of the cloud locations are derived from low-earth orbit sensors, which may be overpassing at a different time than the 30-minute mark in the hourbox.
2) RSR may not be an equal-time-weighted average in the hourbox (I am suspicious because of this sentence in the Data Quality summary for Edition4A: "The corresponding
midpoint is 0.5 GMT, except for SW fluxes, where the integrated cosine of the solar zenith
angle is considered the midpoint of the hour box in order to facilitate the hour box averaging
as described in the previous bullet.")
In case #1, is there metadata provided in the HDF files that indicates which gridboxes are informed by low-earth-orbit sensors and which are informed by geostationary radiances? If not, do you have any recommendations on the easiest way to calculate this?
In case #2, can anyone please clarify this sentence for me? Does it mean that the geostationary radiances used as input for the RSR calculation are time-weighted when they are averaged in the hourbox, via the cos of SZA? If not then what does it mean?
And finally, if there's other possible explanations for high-RSR pixels to be shifted by a gridbox (or two) compared with the geostationary radiances, please let me know.
Thanks for any help,
-Kevin