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by dem1 » Mon Mar 06, 2017 11:15 am America/New_York
Hi,I observe a lot of invalid first bowtie (20 scanlines) in the MODIS Aqua L2 QL (NRT) products: lat/lon are set to -999 for all the bowtie or for only a part of it (one or several columns).This is the first bowtie chronologically so the last scanlines of the NetCDF file.The corresponding consolidated L2 products don't have these holes.For the day 2017-02-16 I observed 58 QL granules with this problem.Is this normal?Examples: A2017047102000.L2_LAC_OC.nc, A2017047200500.L2_LAC_OC.nc, A2017047235000.L2_LAC_OC.ncTo analyse the problem I have also compared the metadata and found this suspect: different orbit number and equator crossing: < :orbit_number = 78696 ; > :orbit_number = 78669 ; < :equatorCrossingLongitude = -108.371f ; > :equatorCrossingLongitude = -120.1655f ; < :equatorCrossingDateTime = "2017-02-16T09:45:19.550Z" ; > :equatorCrossingDateTime = "2017-02-16T09:36:13.621Z" ;Thanks in advance,Julien
Julien, The QL (quick look) products use non-optimal attitude/ephemeris data. QL products should not be used for quantitative scientific analysis. These products are only produced (as the moniker implies) as a quick look at the data. Once the definitive attitude/ephemeris data are available, the products are reprocessed.
As to whether the behavior you see is normal, well, it's not abnormal to have less than optimal data produced from less than optimal data... Now, if you notice a similar issue with the refined (i.e. non-QL) products, that would not be normal.