On March 11, 2011 at 5:46 UTC, (14:46 Japan local time), an 8.8 magnitude earthquake and an accompanying tsunami hit Sendai, Japan. Researchers were interested in finding satellite coverage of the region as soon as possible after this tragic event. There are several ways to acquire this information in COVE.
First, we might check to see if a particular satellite crossed over the region on that day. ALOS is a JAXA satellite designed for disaster monitoring, among other functions. Here is the view of the PALSAR instrument on ALOS on March 11.
We immediately see that ALOS did pass over Sendai on March 11th, but if we click on the swath, we find that it passed over at 00:49:30 (UTC), which is before the earthquake occurred. If we need satellite imagery of Sendai before the earthquake, this is useful, but to find satellite imagery afterwards, we will need to keep looking.
Another satellite we might consider is RADARSAT-2. Here is the view of the SAR-C instrument on RADARSAT-2 on March 11. From this view, we see that RADARSAT passed over this region at roughly 8:53 UTC, which is just under 3 hours after the earthquake struck.
For a more comprehensive list of acquisitions, we might use the Rapid Acquisition Tool. Entering the latitude and longitude of Sendai (38.268 lat, 140.870 long), we can select a number of missions and quickly get a table of all acquisitions over Sendai on March 11th.