Heath & Erik,
In Reply #31 of this thread, the graphic you show depicting the Nauticos search area is actually the search area from the Waitt search.
There have been to date four deep-water searches for the Electra, conducted in the general vicinity of Howland Island: (1) Dana Timmer in 1998 (or it might have been 1999), (2) Nauticos in 2002, (3) Nauticos + Waitt in 2006, and (4) Waitt in 2009. The first three of those searches used towed systems. Only Waitt 2009 used autonomous underwater vehicles (AUV's), 2 REMUS-6000 vehicles ("6000" refers to the maximum operating depth of the vehicles, 6000 meters), built by Hydroid, a commercial spin-off from Woods Hole Oceanographic Institute (WHOI) which has developed over many years the very successful family of REMUS AUV's. Hydroid was purchased by Kongsberg Marine several years ago. Waitt owns the two REMUS-6000 AUV's but has WHOI/Hydroid operate them; Waitt does not have the in-house expertise or experience to operate these vehicles.
Only Waitt has made public any of its data, including the area searched. Nauticos has not made is data public and presumably will not do so unless and until it finds the Electra.
The waters around Howland Island approach 18,000 feet deep. In the deep-ocean search business, 20,000 feet -- which is approximately 6000 m -- is called "full-ocean depth". Twenty-thousand feet to the deepest point in the oceans (approximately 36,000 feet at the bottom of the Marianas Trench) is called "ultimate ocean depth". For comparison, the TITANIC lies at about 12,000 feet deep.
Getting to 12,000 feet or 18,000 feet is no easy feat. There are literally only a handful of systems in the world, towed and AUV, which can reach full-ocean depth. And there is an even smaller handful of companies in the world which own and operate these complex systems. A significant part of the cost of hiring one of these companies and one of these systems (again, towed or AUV) is the cost of the group of technicians which operates and maintains the system. A key part of this group is own or more individuals with expertise in analyzing and interpreting side-scan sonar data. Side-scan imagery sometimes looks a lot like a photograph, and there are some similar principles involved in the two different imaging schemes; but side-scan is really a different beast which requires specialized training, skills, and experience to accurately interprete it. "Reading" a side-scan image often is not easy, it's not like looking at a photograph.
Towed systems are the older technology, but they are not that much less complex overall compared to a full-ocean depth AUV. The cost for "hiring" a towed system is probably about the same as the cost for an AUV system with similar capabilities. Towed or AUV, each has its own set of unique advantages and disadvantages compared to the other system. The deep-ocean search business is slowly moving toward AUV's, but towed systems will likely be around for quite some time yet. The number of full-ocean depth AUV's available to the "private" or commercial sector (i.e AUV's outside of the navies of the world and outside of basically government-owned/operated oceanographic institutions) is tiny. Basically there are the two Waitt REMUS-6000 vehicles, there is one REMUS-6000 which I think is owned and operated by a French oceanographic institute, and there is one or two Hugin AUV's built, owned, and operated by Kongsberg Marine. That's it as far as I know for full-ocean depth AUV's in the private sector.
The deep-water oil and natural gas industry drives the demand for AUV's. So far this industry has had no need to operate much below 12,000 or 15,000 feet. This is why there are so few full-ocean depth AUV's available in the commercial world.
Any of these full-ocean depth systems, towed or AUV, has a side-scan sonar very much capable of detecting Earhart's Electra (again, assuming the side-scan data the system collects is analyzed and interpreted by a side-scan expert), if it does happen to lie on the ocean floor somewhere near Howland Island.
Traditionally, side-scan sonar systems have been very expensive (even systems which don't have to operate anywhere near full-ocean depth). This is because underwater search has always been a niche industry with a small number of users, and because the equipment has been high-tech. The large research and development costs associated with these systems, coupled with relatively few commercial customers interested in buying them, has made the per unit cost of a side-scan system very high.
The situation has been changing in the last few years. Sport and commercial fisherman (as well as small government interests such as underwater search and rescue teams, have always been interested in having a side-scan sonar capability but couldn't afford it. With the advances electronics and the general decreasing costs of electronic components, the manufacturers of marine electronics have started making side-scan sonars units which are within the price range of the recreational boater/fisherman. I know Humminbird and Lowrance now are selling such systems. These are hull-mounted systems designed to be used in very shallow water. I don't know what these units cost, but I would guess they sell for around $5000 per unit. If you're interested, you might want to check out the Humminbird 1198c SI or the Lowrance HDS 10.