Monday, July 09, 2007

Adding Search and Rescue Capabilities (part I): Using Hyperspectral and Multispectral Cameras to Search for Non-Evading Targets

In the search for the Tenacious, I mentioned the possibility of using Hyperspectral or multispectral cameras on-board current satellites to see if there was a way to locate it. The big challenge resides in the resolution. Most of these cameras have a coarser resolution than, say, either the Tenacious or any medium sailing boat (i.e. one pixel is more than the size of the boat). Hence the generic expectation is that one cannot locate a boat using these. These cameras are also mostly used for other purposes such as environmental studies and the access is rightfully restricted to a small circle of experts. Because of that there is a large amount of convincing to do in order to have access to that imagery. The underlying reasoning as to why we could, in effect, discriminate between something that is interesting and something that is not, can be put in two categories:
  • the boat and its wake span a large part of the pixel and using a few bands, one can see a large difference between a man made object and the sea. In other words, the underlying scene is very sparse and one in effect detect very rapidly interesting artifacts. This a little bit like superresolution.
  • In some cameras like Hyperion on EO-1 or Meris (Envisat) there are 250 spectral channels. Even if the spatial resolution is coarse, we are bound to see something different when using 250 bands (as opposed to the traditional three color bands) especially against a very uniform background (sea). Techniques such as the ones developed by Mauro Maggioni and Ronald Coifman should be evaluated for that purpose.

Recall that the idea is to produce a map of what is potentially interesting, not an exact match of where that target is. A second step dealing with data fusion is responsible for eliminating the false positives given information from other sensors. With the help of Lawrence Ong, Sorin Popescu and I showed that you could see boats with Landsat 7. This is new but falls into the first category highlighted above. The second category has not been investigated as far as I know: Maybe it should. There are three categories of targets/signatures that should be investigated:

  • During the Tenacious search, a false positive was detected in the form of a sighting of a green dye. These dye are generally part of "distress kits" and used whenever a boat want to make it clear it has problem. While it was a false positive for other reasons, I had a discussion with the EO-1 folks (at JPL and Goddard) who mentioned that maybe producing ground truth data with green dye and Hyperion could probably lead to having a similar capability than the one we currently have for detecting volcanoes. In other words, produce a calibration formula to be fed to EO-1 so that in the future, its autonomous detection capability can provide data to the ground that this green dye has been detected over a specific area. Since one can schedule imagery on EO-1 and figure out Envisat data gathering cycle, this could be done as a small private endeavor.
  • Another signature of interest is that of the boat as produced on the camera. If it is a boat or a plane, it is very likely that these have been imaged before by the same camera over the same harbour or airport at some other time. But for the latter, a signature is not really that important per se. A large signal over background noise on some channels should be enough to find that boat/plane. In the case of the plane, the signature may be interesting as the background is generally cluttered.
  • In order to verify the ability to find current boats at sea, one could try to locate the boats currently involved in much advertized journeys or races. One could find out from the current stock of envisat and eo-1 photos whether boats like the Schooner Anne can be located. That boat is part of a 1000 days at sea journey. They have a map of their location day after day. The boat is a schooner (or about 120 feet large).

Another item that would have sped up the search is the ability to query simultaneously different databases on the availability of hyperspectral or multispectral images from different platforms. Either USGS or the ESA platforms are very nice, but making it into one search would have been a nice time saver. I am also pretty sure that there are other Earth Observation platforms from Asia (India in particular) that could have been used, provided I knew about them. Yet I cannot find anywhere on the web a catalog of civilian hyperspectral or multispectral imagers on current satellites.

Finally, let us recall that doing this can help us locate hard cases like the Tenacious but it may also help us in a totally different endeavor. As one can see from the extraordinary effort of the Coast Guards for the Tenacious, one boat can consume a large amount of man power. Let us imagine a case where you have to do the tracking of 8000 targets lost at sea.

In the search for Cessna N2700Q, the Civil Air Patrol tried the new ARCHER system without success on that search. And it looks like this is not happening only for this search as some people are doubting its capability for Search and Rescue Operations.
As indicated by Bradley,

CAP forum posts indicate ARCHER
requires a very narrow search area to be of much use. Our problem is that we're not sure where this Cessna pilot went after he dropped
below radar (N34° 48' 7" , W111° 56' 52").
This is the same problem that arises for EO-1, the swath of interest is generally very narrow compared to the size of the problem. We should probably think of a way of integrating Compressed Sensing into current hyperspectral imagery to increase the field of view. Let us recall that one of the reason this would be interesting is that these systems are there to point out major differences from the background, they are not there to produce very nice imagery.

If any of those items are of interest to you please contact me. I am particularly interested in people (from Asia, Europe or the U.S.) that can have direct access to this type of imagery so we can test some of what is said in this entry.

[ Si vous pensez que ce sujet est important et qu'il doit etre etudie, je serais tres heureux de pouvoir vous aider. N'hesitez pas a me contacter ]

1 comment:

ctwardy said...

I don't have access to satellite imagery, but I do know search theory and Bayesian AI. I would like to work on this, and I'm more than happy to help chase grants etc.