But as is demonstrated all too well by the recent collision between USS San Francisco -- a Los Angeles-class fast-attack SSN -- and an uncharted underwater mountain near the Federated States of Micronesia island chain, the world’s oceans still hold serious hazards for those who go down to, and into, the sea in ships. Media discussions in recent days, based in part on information released by the U.S. Navy plus interviews with oceanographers and former submariners, point to holes in the accuracy of available nautical charts as a major factor regarding San Francisco’s accident. According to various open sources, other collisions or near-collisions between nuclear submarines and uncharted seafloor topography have occurred in the past.

In this essay, I would like to describe how filling certain gaps, in budgets and in communication cultures, might help prevent or at least reduce problems of this type in the future. I state here that such gaps demand attention because resources are available which might have aided San Francisco to avoid her deadly mishap altogether -- and these resources are being dangerously underutilized. So just what are these resources?

Two distinct methods exist, and have been proven reliable, for efficiently mapping swaths of seafloor terrain without compromising a naval submarine’s stealth. Both involve measuring, in very different ways, the local effects of gravity.

Satellite Altimetry: To get started on this interesting topic, first think of Earth idealized, notionally, as a sphere that’s slightly fattened near the equator and flat near the poles. This “oblate spheroid” defines a basis for further discussion among cartographers. Terrain features of the actual Earth become bumps and slabs and ripples and cracks of different heights and depths, relative to this spheroid used as a standard of reference. Got that, more or less? Let’s proceed.

Specially designed satellites, in orbit for several decades, are able to measure the real height of the ocean’s surface at different locations to a precision as fine as an inch. The measurements are done using radar pulses aimed at the water from above. “Real height” means data carefully adjusted for distortions from a multitude of natural phenomena, including variations in the behavior of the ionosphere, the atmospheric humidity along the to-and-fro path of the radar pulse, currents and tides, and constantly changing wave crests and troughs. Compared to the idealized spheroid, advanced computer models construct a three dimensional map of the stable real-height ocean surface -- and that surface, as it happens, is by no means smooth and featureless.

Gravity is an attractive force between masses. Because rock is much more dense that water -- more mass per unit of volume -- seamounts (undersea mountains) exert an extra gravity pull on the ocean around them, compared to an area of ocean where the bottom is uniformly flat. Since water is incompressible, that pull causes the local ocean to pile up over the seamount by as much as tens of meters. For the same reason, a deep trench or fissure produces a weak spot in gravity’s pull, and water is drawn away to either side, creating a dip in real height of the ocean’s surface miles above the seam in the floor. Scientists have proven that features, on a map of the ocean bottom-terrain created via satellite altimetry, coincide very accurately with known features in seafloor topography mapped by conventional depth-sounding sonar. Each point on the map grid must be overflown by satellites several times -- which because of orbital mechanics can take a year or more -- and the data are then combined mathematically to obtain the best results. The process is therefore neither quick nor cheap, but it’s much quicker and cheaper than trying to cover the ocean using research ships -- the National Geophysical Data Center estimates that doing the latter thoroughly would take a century!

To summarize, through satellite altimetry it’s possible to produce what’s called “pseudo-bathymetry” -- a nautical chart of the ocean’s depths derived solely by surveillance from outer space, on which a typical seamount would stand out clearly. Agencies involved in this work include NASA, NOAA (the National Oceanic and Atmospheric Administration), and the U.S. military. Satellites used in these efforts have included the pioneering Geos-3 launched in the 1970s, Geosat in the 1980s, the European Space Agency’s ERS-1 and ERS-2 from the mid-1990s, and the U.S. Navy’s GFO since 2000. Portions of the mapping results, and details of ongoing studies, remain classified. However, one may conjecture, as I do, that some of this data might have prevented San Francisco from hitting the seamount.

And it turns out, according to a civilian geophysicist interviewed in the New York Times on 15 January, that there is indeed some indication of a seamount at the crash site in radar altimetry obtained in the mid-1980s. The data, though, was described as having a large margin of error and being too vague. I would not presume to disagree with this caveat. I would say that, at a minimum, there ought to have been a notation on the San Francisco’s charts, last updated in 1989, to the effect of “Here there be possible uncharted seamounts” -- and there wasn’t. Furthermore, given progress since the mid-’80s in so many aspects of aerospace and radar engineering, downlink baud rates, and supercomputer speeds, data obtained much more recently (by GFO?) might show the location of that seamount with no ambiguity. My conjecture -- which is only that -- as stated above still holds.

Gravimetric Gradiometry: The topography of the ocean floor can be mapped by an entirely separate approach that also relies on local variations in the force of gravity, caused by the same density difference between water and rock (and mud and silt) that satellite altimetry uses. This technique measures local three-dimensional gravity fields directly, and in real-time. The raw data is obtained by one or more sets of accelerometers on small rotating platforms, a mobile set-up emplaced amid or over the area that needs to be mapped. This data is fed into complicated mathematical models that work backwards to calculate the unique configuration of nearby terrain that would produce the gravity fields actually measured. This terrain map is then rendered for viewing by the user as a 3-D see-through image on a video display screen. To watch a gravimeter demonstrated for the first time is impressive, as I can testify myself. It seems like science fiction, but it’s real, and in fact has become routine.

The method, civilianized after the Cold War, is a valuable tool in commercial mining and oil and natural gas exploration: In one mode it can identify deeply buried geological formations without the need to take core samples -- or conduct much cruder mapping via seismic echo-sounding with explosives set off at ground level. In this context, airborne versions of the gravimeter systematically overfly areas of interest to search for untapped mineral wealth and find new fossil-fuel energy reserves.

Public information from around 1999 indicated that a next-generation gravimeter installed on a nuclear sub could at that time clearly “see” underwater terrain out to about thirty miles, and at close range had a resolution -- sharpness -- of under ten meters. (Improvements in these specs since then seem likely). The hardware and software available in ‘99 refreshed the imagery several times per minute while the submarine moved with no limitations as to her depth, course, and speed. Because gravity reaches through solid rock, the 3-D gravimeter display can also see through solid rock -- it’s possible to known in advance about one seamount that’s hidden behind another from the submarine’s perspective. It’s also possible to detect the legs of off-shore drilling rigs, and gain warning of the presence of unmarked shipwrecks. Metal, like rock, is much denser than water, grist for the mill of the gravimetric gradiometer.

One big advantage of this approach is that it’s completely passive -- it generates no signature that might compromise the submarine’s stealth. (The Navy originally developed the technology in secret, for SSBN strategic-missile deterrent subs to be able to obtain precision navigation fixes while remaining totally covert.) In applications for the rather different mission roles of SSN fast-attacks, the system isn’t dependent on any stored data or charts, or even on the wildest guess about the sub’s location, to develop a very good picture of the topography surrounding the vessel. You merely switch it on, and voila. Unlike active and passive sonars, it can’t be spoofed or decoyed, its performance isn’t degraded by the distracting sounds a submarine makes itself when it goes very fast, and the system is completely immune to outside loud noises (grinding ice caps, exploding torpedoes) that can “blue out” sonar hydrophones.

One disadvantage of the gravimeter is that its algorithms are unable to track moving objects -- such as other nuclear submarines whose reactor compartments, with their massive shielding, thick containment-vessel walls, and super-dense uranium core(s), make for a substantial discontinuity in micro-scale gravity fields. So a nuclear sub had better not sit still, hovering, when being hunted by another sub equipped with a gravimeter. This raises interesting questions about offensive and defensive tactics, particularly under ice, which are beyond the scope of this essay. Ditto for antisubmarine weapon homing sensors in an era of ever-increasing miniaturization. (The unjammable multi-use technology, by the way, can also identify sub-soil voids -- empty chambers -- with very low false-positive and false-negative rates. It thus might even some day be mounted in recon drones and cruise missiles: to locate, map, target, and destroy enemy cave hideouts and deep hardened bunkers with ultra-high confidence in success on the first try, and with the least possible collateral damage.)

Returning to our main theme, another disadvantage of gravimeters on naval submarines is that each system installation is very expensive. Reportedly, the Navy, the Department of Defense, and Congress -- in some combination thereof -- decided that these powerful navigational tools were too costly for continuing widespread use. Reliance for terrain avoidance, during stealthy ops where sonar pings are precluded, was to be placed instead on traditional nautical charts. Again one may conjecture that if San Francisco had had a gravimeter aboard, she’d have gotten ample warning of the uncharted seamount ahead of her, to maneuver to avoid it.

Communications, and Funding: Other news of the early 21st century -- including the final report of the 9/11 Commission, the investigation of the loss of Space Shuttle Columbia, and the end of the fruitless hunt for Saddam Hussein’s WMDs -- show that the prompt and accurate sharing of relevant and vital information between different government bodies remains an ongoing, daunting challenge. Large, diverse, and widely dispersed organizational complexes, it appears, can produce results that amount to much less than the sum of their parts. Stale satellite altimetry data existed suggesting a possible uncharted-seamount hazard along USS San Francisco’s route, but this wasn’t conveyed to the submarine. It would not be surprising to eventually find that more-modern data exists somewhere, definitively identifying the seamount with which San Francisco collided, but said data was never analyzed fully, or was never made available to authorities who establish safe transit corridors and navigation procedures for submarines.

Time and again, our politically-driven national budgeting process shows itself prone to addressing solutions to dangers too late, reactively, often closing the barn door only after the horses have bolted -- and sometimes not even then. Voters are much more willing to accept the burden of paying for fixes after the latent danger becomes an outright catastrophe, splashing across front-page headlines while saturating the audio-video media and circling the globe via Internet blogs. Such is human nature, infamously difficult to change.

But the San Francisco collision has served upon us due warning. One crewman died of his injuries, and many others were seriously hurt. How much is a human life worth, compared to the cost of providing better obstacle-avoidance aids? San Francisco suffered serious damage, and her emergency surfacing after the crash was at first rather “touch and go.” Repairs to her hull and bow sonar will be extremely expensive. If she’d hit the seamount in a slightly different place, or at a slightly different angle, she might have been lost with all hands. How much are 137 highly-trained submariners’ lives worth, collectively? The price to replace San Francisco by a new submarine would run in the billions. The ecological -- and psychological -- impacts of an American nuclear reactor sunk near populated islands are hard to reckon. The diplomatic and public-relations consequences, within the U.S. and internationally, would surely be dire. Our nation, and our national security, had a very close call, much more so than most people seem to realize or admit.

Might it not be a wise investment to selectively equip those SSNs tasked to operate in poorly charted waters with on-board gravimeters? Or are we going to behave again, institutionally, the way we did after the Space Shuttle Challenger disaster? Few lessons were learned then, they were all forgotten quickly, and another, equal disaster became inevitable -- and did occur. The same can be said about a long string of CIA failures and missteps, and about the series of increasingly brazen al Qaeda attacks against two U.S. embassies and then the destroyer USS Cole before September 11, 2001.

Our Navy is gearing up more and more for operations in shallow-water and near-shore undersea environments. Too few submarines must rush hither and yon to cover too many crisis contingencies. In such circumstances, safe undersea navigation takes on a whole new degree of importance. We mustn’t make the same team error with our thinly-stretched Silent Service that we’ve already made with manned space flight, intelligence gathering, and homeland security. Submariners, and their families, deserve better than that.

JoeBuff.Com / Joe Buff Inc. Joe Buff, President Dutchess County, New York E-Mail readermail@JoeBuff.Com