Low/Negative SST values in tropical region

[cassandra21]

Hello everyone,

I recently came across something that caught my attention as I wasn't really expecting it.

I have been using MODIS-Aqua satellite images to study surface and near-surface ocean dynamics in Cape Verde.
So far, I have been using mostly monthly data, but now that I have some in situ data, I decided to download some daily images to see what the sensor was recording for the study area and compare that with the collected data. It was then that I noticed that some of the SST images (1km resolution, SST and SST4 products) showed very low values (e.g. 5ºC) for the region, where the average is usually between 21ºC and 28ºC, depending on the month. Later, some of the images showed pixels with negative values (e.g. -4ºC).

Can this be related to the effect of wind or to cloud interference?

Have other people reported this?

Thank you so much

[OB.DAACx - SeanBailey]

Check the flags. If the SST seems unreasonably low, it is likely a cloud. The data are not masked at L2, only flagged. When binnng SST, the code selects qual_sst of 2 or greater (keeping the highest quality data for the bin). If the qual_sst is a 3 for the pixels you find low SST, that means it's a cloud.

Sean