Fleet Survey Team scans Djiboutian beach

Photo By Master Sgt. Joey Swafford | Petty Officer 3rd Class Michael Bronowich of Navy's Fleet Survey Team attaches a...... read more read more

Photo By Master Sgt. Joey Swafford | Petty Officer 3rd Class Michael Bronowich of Navy's Fleet Survey Team attaches a stabilizing fin to a side-scan SONAR during a coastline survey in the Gulf of Aden. The side-scan SONAR is used to take acoustic video of the ocean floor to search for obstructions and hazards in preparation of a beach assault exercise by a Marine Expeditionary Unit.  see less | View Image Page

CAMP LEMONNIER, DJIBOUTI

05.22.2009

Story by Chief Petty Officer James Drake 

Combined Joint Task Force - Horn of Africa

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CAMP LEMONIER, Djibouti -- A crew of four people arrived here this week from the remote and swampy Stennis Space Center in Mississippi to capture, interpret and chart sonar images of part of the Djiboutian coast. The Sailors are performing a beach survey on behalf of a Marine Expeditionary Unit which would like to safely conduct an assault exercise on the beach.

"It's what my division, the Expeditionary Survey Division of the Fleet Survey Team, specializes in — very shallow water," said Chief Petty Officer Michael Duke, a chief aerographer's mate and native of Splendora, Texas, who is a qualified Level 2 military hydrographer and the assistant hydrographer for this mission.

What the FST crew is doing is called bottom mapping. The useful end result of their work is known as bathymetry; literally the sonar and visual survey mapping of objects under the surface of the water in the vicinity of the oceanic surf zone. The things they're looking for don't usually appear on maps without being put there by a small crew like this one.

Hydrography is an essential component of planning for any amphibious landing, according to Duke, and the FST is responsible for the wet side of the beach. Beach Master Unit crews, usually in the form of detachments accompanying shipboard MEUs, share the responsibility on the dry side.

"In simple terms, the Beach Masters go and conduct a survey of the beach from the land side, with a view to managing the landing of amphibious forces. They have a limited ability to do hydrographic work," said Royal Navy Lt. Michael Redmayne, the hydrographer-in-charge and leader of the four-person, Stennis-based FST and part of the U.S. Navy's Personnel Exchange Program. "[BMUs] can do two or three survey lines, if they have a boat available. The benefit of them to us is that they provide us with a really good picture of the feet-dry part of the beach."

"Offshore charts are compiled from various sources. Deep-water charts of the wide ocean are compiled using data from different surveys, and are suitable for high-seas navigation. In environments where the beaches change because of waves, coastal charts may not be as accurate for as long," Redmayne said.

"A lot of the world continues to be unsurveyed — or was surveyed by explorers in the 'Age of Sail.' In those areas with a lack of more modern information, that data is still shown on navigation charts. The data that we just acquired may or may not make it to a chart, but that is the decision of the National Hydrographic Office. On many charts still in use today, there are soundings gathered by Captain James Cook," said Redmayne. "He gathered a great deal of data [prior to his death in the South Pacific in 1779]."

The navigation ability of the ships ferrying the MEU is primarily assisted by those pre-existing charts, but the Naval Oceanographic Office has several other elements within its structure. "NAVO, our next echelon -- which operates T-AGS survey ships -- is one of two elements which chart deeper water. The T-AGS ships are medium-sized, white survey vessels that do deep-water survey work," Duke said.

"We have two main survey divisions within FST. The first, the larger one, is Boat Division. Those guys do shallow water surveys; five-meter contours on out to in excess of 100 meters, depending on mission and equipment," Duke said. "The second division, ours, is the Expeditionary Survey Division. We specialize in the VSW environment, meaning very shallow water. We are also in the high-energy environment, the surf zone. We are capable of operating off of rigid or inflatable boats, but we generally use personal watercraft (PWCs are usually craft like Wave Runners and Jet Skis) which facilitates being able to work in a riverine or, primarily, the surf environment. Our bread-and-butter work are beaches; surveys in support of amphibious landings."

"Beach Masters are interested primarily in the terrain of the beach. What we do is fulfill the bits that they can't do of the underwater terrain offshore," Redmayne said. "Their primary mission is to determine whether a beach is suitable with a view to running the beach during an amphibious landing."

"We have a good working relationship with the BMUs, and generally our requirement comes from them," Redmayne said. "It depends on the mission; sometimes they have a specific requirement, and other times, it's as simple as saying 'We want a chart of the area. Give us hydrography and look for objects'."

"We didn't bring much," Duke said, regarding this deployment to the Horn of Africa. "We have the capability to rove a beach, using high-end global positioning system device to chart out the land-sea interface; that can then be used to geo-rectify readily available satellite imagery. That term, geo-rectify, means to attach GPS coordinates to imagery, so that we may use specialized software to overlay our bathymetry onto imagery that otherwise probably wouldn't reveal any sub-surface features."

Duke said his ESD is typically on-site, or at least in theater, for two weeks. The Boat Division of NAVO is generally on site from one to three months to collect sufficient data to update nautical charts. "The work that we can get done on the personal watercraft in that 10-meter-and-under depth is typically high-speed, low-drag -- and only slightly less accurate."

"When we leave, we'll have been here for eight days, and spent three on the water. The five days on land were setting up the equipment, and then after the survey, processing the large amounts of data that we gathered," said Redmayne. "We processed our sounding and sonar data here on Camp Lemonier. We got some space from the [Meteorological and Oceanographic] folks, and produced a field chart and beach report."

"A tactical chart is a hydrographic chart that has not been ratified by a national hydrographic office, and therefore is for guidance rather than approved for navigation. It's not a legal document, but in areas of the world where there is little or no data, it becomes very useful to the war-fighter," Redmayne explained. "We have a standard set of equipment to conduct the majority of requested beach surveys. This (Djiboutian) beach shelved off rapidly. We were not required to survey as far out to sea as is often the case when conducting surveys with a more shallow gradient."

Duke explained that units which employ the ESD are not generally concerned with highly detailed, long-term charting, or with the historical or future trends of a piece of coastline. Instead, his customers are looking to use current knowledge about a beach long enough to run it over with troops, trucks and amphibious assault craft.

"We are predominantly single-mission support, whereas Boat Division's product would typically be submitted for inclusion into official nautical charts," said Duke. "The strengths between the two divisions would be that 'Boat' is more detailed and precise, where we have a faster turnaround and are more in tune with the Navy and Marine Corps' amphibious community."

"By mapping the characteristics of the beach, the customer is able to see the slope angle — the gradient — of the beach," Duke said. "We also add GPS coordinates while imaging aids to navigation — obstructions, hazards and so on. For example, we make notes about what landmarks actually look like from a particular angle and embed those notes into the chart."

"If, for example, a radio tower should appear at so many degrees from your approach, we can add metadata to the chart that shows the tower and what it should look like if the customer is in the right place and on course," Duke said. "It depends on what's available -- how many of those items are available, or are essential to the mission -- dictates what we insert. If there is nothing available there but jungle, we would only be able to supply a stitched panorama image of the beach."

Duke said the one of the first operational needs of this kind of surf-zone charting information dates back almost 66 years, to the island-hopping campaign in the Pacific during World War II.

"The landing at Tarawa was one of the first times when hydrography, or rather the absence of bathymetry, played a major role. You can look up some of the problems; coral atolls caused trouble for the landing craft, they would either hang-up on the reefs, presenting a defenseless mortar target, or would simply breach the hull. The troops would then disembark their craft and step right off the coral shelves with all their gear into deeper water. ... Our nation lost a lot of good troops that day," Duke said.

"Back then, hydrographic surveys were done with a lead-weighted line marked with depths. Positions were taken using a sextant, Duke said. "[The work] was very slow, not very accurate and very labor and time-intensive. It basically kept evolving after that. During World War II, Underwater Demolition Team 'Frogmen' conducted those kinds of surveys," said Duke. "They went in with only their shorts and a knife, smeared with blue-colored grease for camouflage. I recommend reading a book called "Naked Warriors," which details the war efforts of UDT Sailors."

The tangible benefit of their underwater charting to an amphibious force hasn't changed in the six intervening decades since Tarawa, according to Duke, but he said the tools of the trade have. The technology that the ESD brought -- and which Duke described as limited by its size and expeditionary nature -- includes some commercially available sonar and some 'down-home ingenuity.'

"On this assignment, we're using a single-beam Ceeducer sonar, which is commercially available, and a seven-meter rigid-hulled, inflatable boat we borrowed from the Combined Joint Task Force-Horn of Africa's EOD detachment (Explosive Ordnance Disposal Mobile Unit 3, Platoon 342 is part of the CJTF-HOA team)," said Duke. "We're also using a 'pole kit' which mounts our gear to pretty much whatever platform we can get our hands on. We can bolt it onto any small vessel, and we have a slightly smaller version we can bolt onto almost any personal watercraft. We call it a 'boat-of-opportunity kit,' or BOO. This kit was manufactured by our very own Aerographer's Mate 2nd Class (SW) Durwin Wallace."

Wallace, 27, is from Jacksonville, Fla. He is the lead data collection specialist on this mission, but his primary responsibilities are setup and operation of the ESD's gear and equipment. "He's the EST's ad hoc mechanic, too. He does mechanical work on our gear and pole kits," said Duke.

"Wallace is one of those rare individuals that, as managers, we hope to have throughout our time in the Navy. He fixes gear, engineers solutions, leads and trains the junior Sailors, and is a natural surveyor," said Duke. "He also has one of those 24/7 amicable attitudes that people just feel comfortable being around. We would have irreconcilable delays if it were not for him being on-scene."

"We're also using side-scan sonar," said Duke. "We brought with us an EdgeTech 4125-D, a commercially available towed unit. We're using the RHIB as a platform for that also. Both can operate at the same time because they're on different frequencies. We have a good, high-end GPS unit as well."

"The main challenge with this particular beach (in Djibouti) is the presence of large rocks and coral heads that present a danger to landing craft," said Redmayne. "This survey has actually gone very, very well. The logistics support that we got from Camp Lemonier, the METOC office and the EOD chaps has all been really great. That help enabled us to complete the survey and produce the product for delivery to the customers on time."

Duke said his command is split into even thirds between civilians, officers and enlisted service members. "In my division, we're all military. We're very small. Our manning is 11 people. We typically deploy in three- to four-man teams," Duke said. "We're expeditionary in nature, so we don't travel with all of our gear — just what we absolutely need. We advertise the capability of deploying in less than 72 hours. We found out late on a Thursday morning that this deployment to Africa was happening, and we were en route by Friday afternoon. We were gone in less than 30 hours."

The crew of four have several skill sets each, according to Duke. Just like Wallace, Aerographer's Mate Petty Officer 3rd Class Michael Bronowich, an aerographer's mate and 21-year-old Sailor from Secaucus, N.J., is performing double-duty on this mission. He's assigned as a survey technician, but he's also piloting watercraft.

"Bronowich did an individual augmentee tour up in Camp Bucca, Iraq, this past year," said Duke. "We're fortunate to have gotten him back this past December. He's a Sailor with a big heart, a thirst for knowledge and he's a natural pilot on the PWCs. There are two positions on the personal watercraft; a pilot and a data recorder. Bronowich is quickly becoming a stand-out survey tech. This was a 'learning' trip for him, and -- although he is new to the division -- he quickly learned gear setup. By the second day, he was already setting up and operating the gear independently. Back [at Stennis], he performs as the divisional training petty officer as well as inventory control, and is one of only three certified Navy swim-test evaluators in southern Mississippi."

The survey team's ability to put people into the surf zone and verify findings ties it all back together for the team's leadership. In addition to the GPS' electronic findings, Duke said, they are able to say with confidence that they've put human eyeballs on what they found under the surface of the waves.

"It is a fundamental theory of surveying that the survey measurement should be at least one order more accurate than the equipment being used to navigate based on the findings. In comparison to what we're using, the navigational GPS being used by the guys on the landing craft is fine for their purposes — but not accurate enough for ours," Redmayne said. "My error budget — the way we quantify how accurate our soundings are — is in the order of 0.3 meters horizontally and 0.8 meters vertically. That volume is about the same as the three-dimensional space occupied by an ice-chest."

"It is the responsibility of the mariner to navigate by the most safe means possible and if the work that Fleet Survey Team performs can aid the mariner, then we have achieved our mission," Redmayne said.