I have been using the WorldView web application to identify clear sky days to download MODIS images. However there are some instances where I see a clear day image, then download the MOD09 product and there is a stripe of no data across my area of interest.
I understand that areas can be missed due to the orbit the satellite is on, but why am I seeing a clear image on the WorldView but not in the MOD09 product for the same day? Not the same image??
Take for example the 22nd June 2015 shown on worldview here. A bit of cloud around but I can see the snow pack on the NSW snowy mountains. Then when I download the MOD09 product from here (I need to merge two tiles H29 V12 and H30 V12 for my area) I get a big stripe of no data through my area of interest shown in the image below.
How do they come up with an image in worldview? It doesn't appear to be the Aqua image (as far as I can tell anyway), is there another tool which would be better for previewing an area before downloading the MOD09 product?
Since using the new preview method I mention in the comments below I still see issues like this here (South Eastern Australia is missing coverage), and it happens periodically some day fine and others not but always that section.
What's causing this?
Is there another resource I could use to get the MOD09 product for this area?
I got in touch with someone at the MODIS LDOPE facility and they were kind enough to help me understand why this is happening.
Here is there response below:
World view uses local time while mapping the observation data. Our browse uses the GMT which is the reference time used to identify granule acquisition time. Except for that beginning or ending portion of the day you will see that all the orbits are in place in both global images. Our global browse images are for science quality assessment and is more in line with the orbit map shown at this url http://www.ssec.wisc.edu/datacenter/terra/GLOBAL2015_07_05_186.gif">as shown here. So I was basically looking in the wrong days folder when it come to downloading the hdf file on their server.
You should not use WorldView as a preview application for the reasons mentioned above. Instead you should be using the MODIS Browse website (you may need to scroll down to see the images). Another handy tool is this website which allows you to see the orbit tracks.
Hope this helps someone else.