Update Frequency - We update the Cloud Free SST charts daily. NASA processes the data each day for the previous day, so the charts will always be one day behind.
Understanding the data - The Cloud Free Blended SST data is derived from a combination of data from different sources. Some of the data sources include satellite Microwave data with a resolution of 25km., GOES (Geostationary Environmental Satellite) data with a resolution of 6km., along with MODIS and AVHRR data with a resolution of 1.1km. The microwave data is not affected by cloud cover, but as you can see is very low resolution. The MODIS and AVHRR data are the highest resolution, this is the data that we use for our standard SST and Chlorophyll charts. This data is blocked by cloud cover, as our subscribers are all too aware. The goal is that by combining the cloud free microwave data with higher resolution data from other source, a reasonably accurate estimate of the SST's can be produced on a daily basis.
Realize the Limitations - At first glance this may sound like the answer to all of our problems with cloud cover, but it's not. This is just another tool to give us some information during the cloudy periods, but it is important to recognise the limitations. The microwave sst data is the only data that actually works through the clouds. This is the lowest resolution, 25k data. 25km resolution means that there is one temperature value for an area 25km by 25km, that's over 600 square kilometers of water. While this is fine for getting the big picture, it's not going to show you the smaller edges that we look for, and the actual location of the breaks shown can be off by 10 miles or more. When we do get more clearing, the "Blended SST" data will incorporate more accurate data from the higher resolution satellite sources. During these periods the overall image accuracy should be better. Incorporating the higher res data definitely improves on this, but it might also show some "edges" that are actually due to the blending of the data, instead of the actual water. When we have reasonably clear skies, you will almost always get more accurate data from our standard SST and Chlorophyll charts. But, when the clouds take over this should be a useful alternative to at least have a rough picture of what's happening out there.
We're still in the development stage with this data. We'll be adding more references and contours to many of the regions over the next few weeks. As we see how the images come out we may change the boundaries of some regions. As always, we welcome your feedback and suggestions.