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Charting Sardinia’s Grotta del Fico

Swiss u/w photographer and tech instructor Gatien Cosendey takes us for a dive into PHREATIC’s recent “Map the Gulf” citizen science project. Their goal? Produce a digital map of Grotta del Fico, one of the major springs located along Sardinia’s Gulf of Orosei, using MNemo devices and Ariane’s Line software. For the citizen scientist in you!

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By Gatien Cosendey. Images courtesy of G. Cosendey unless noted.

Central-eastern Sardinia’s Supramonte mountain range is one of the biggest karst areas of the island, covering a surface of about 170 km2. It is made of nearly a kilometer-thick layer of limestones and dolostones that covers a granite and schist basement and comprises more than 400 known caves, out of which only two percent contain important groundwater bodies (Cabras et al. 2008). This karst aquifer extends eastward up to the Tyrrhenian Sea and encompasses the Gulf of Orosei, whose 37 km/23 miles long shoreline makes up a succession of vertical carbonate rock cliffs reaching a height of 700 m/2,297 ft (Sanna and De Waele 2010). The main cave diving springs along the Gulf of Orosei are; Grotta del Bue Marino, Bel Torrente, Risorgenza di Cala Luna, Utopia, Euforia, Grotta del Fico and Macedonia.

Map of the Gulf of Orosei (D’Angeli et al. 2013).

Based in Cala Gonone, Phreatic is a nonprofit organization founded in 2014 by a group of explorers, researchers, and scientists who are mainly active in the Supramonte plateau and Gulf of Orosei areas. Their stated mission is to advance knowledge about groundwater resources and marine caves, and to insure their protection and conservation, with projects covering a broad spectrum of topics including environmental processes, geology, speleology, marine biology and conservation. 

We believe it’s important to raise public awareness of not only how important these fragile karst geo-ecosystems are, but also about the hazards related to these environments, such as sinkholes and flash floods. “Map the Gulf” is one of the ongoing projects from Phreatic, and it relies on citizen science to gather data and survey flooded caves of the Gulf of Orosei with the goal of making all the resulting data available to the public. 

Indeed, the available data on these cave systems is scarce outside of the dry passageways, and detailed and complete maps are missing. The latest Map the Gulf campaign started in March 2022 and focuses on Grotta del Fico. Operations are run from Base1 Sardinia, a dive center located in Cala Gonone delivering logistics for cave and wreck diving in the Gulf of Orosei (See PHREATIC).

Phreatic Exploration

Grotta del Fico, together with Bue Marino, are the two cave systems of the Gulf, which have dry passageways open to tourists in addition to underwater conduits for cave divers. Each summer more than 15,000 visitors come and admire the beauty of the speleothem formations within Grotta del Fico, accessing the cave through the main entrance located 10 m above sea level on a steep cliff. Two other entrances open underwater, one of them being used by cave divers. 

Cave exploration of Grotta del Fico started in the 1960s, and recent exploration revealed a total development of cave conduits to more than 2.5 km/8203 ft. These conduits are characterized by a main air-filled passage parallel to the coastline and a smaller mostly submerged branch running perpendicular to the coast (Sanna and De Waele 2010, D’Angeli et al. 2013).

Current map of Grotta del Fico showing both dry and flooded tunnels (D’Angeli et al. 2013). Note the question marks at the end of the submerged western end of the cave.
One of the two seawater entrances to the Grotta del Fico.
Restriction located at the start of Grotta del Fico main line.
Grotta del Fico submerged passages are often narrow and full of features.

I joined the second project session, which took place from June 19-24, 2022. I arrived one day early and teamed up with two fellow project attendees for a warm up dive in Grotta del Blue Marino It is worth explaining the logistics required to dive caves in the Gulf of Orosei—the aforementioned caves are underground rivers that spring directly into the sea, which means that the natural access to dive these caves is from the ocean.
As mentioned, the shoreline is mainly made of high cliffs; therefore, the Gulf of Orosei is only one of few locations worldwide where a rigid-hulled inflatable boat (RHIB) ride is the normal way to go cave diving. For the same reason, cave divers will experience both a halocline and a thermocline while transitioning from the warm seawater to the cool freshwater of the caves.

The line disappears behind the halocline in Blue Marino cave.
A diver is admiring a speleothem in Bue Marino cave. The halocline makes half the image look blurry.

The project week started with a full classroom day led by project leader, Base1 co-founder, and Global Underwater Explorers (GUE) cave Instructor Examiner, Andrea Marassich. The session included a general orientation about local geography and geology, an overview of the project, a statement of objectives, and detailed explanation of methods and procedures. As mentioned, this year’s Map The Gulf campaign is focused on surveying Grotta del Fico’s main flooded passageways.

The Digital Surveying Process

The survey process can be broken down into the following steps; First, stations are defined using numbered cookies, a.k.a. survey cookies, which are placed at each tie-off, tee, and jump arrow of the cave main line. These stations help to spatially reference the different types of data that will be subsequently acquired. The next step makes use of a MNemo device from Ariane’s line to acquire stick map data: the MNemo is clipped onto the main line, measures distances using an optical sensor while running along the line and acquires depth and azimuth angle at both the beginning and end of segments between stations. Afterwards, left-right-up-down (LRUD) distance estimates are collected at each station and written down in wetnotes and correspond to the available space for a diver to swim through the given cave section.

Both MNemo and LRUD data can be collected simultaneously by a buddy pair and will at the end of the day be loaded into Ariane’s Line software (or equivalent) in order to produce the cave stick map with polyhedral volume estimates. The resulting stick map and LRUD distances are then printed on water friendly paper, taped onto chopping boards and taken with a pencil into the cave. While one diver sketches details of the cave walls and features, his buddy records videos of the corresponding passage for further reference. This enables the divers to complete or correct the drawing outside of the cave while watching the videos with survey cookies referencing the video sequences with respect to the sketched map.
The afternoon was about a MNemo dry run with everyone practicing correct use of the device and subsequent data loading into the dedicated software. The day ended up with some of us going for a test dive from shore, the others enjoying the beach. Note that this first day was the only one to be light enough for us to have a bit of chilling time.

Andrea is drawing the Grotta del Fico stick map from memory during the briefing.
The MNemo from Arian’s Line makes cave surveying much easier and more accurate.

Teams were formed on the first day: a GUE Cave 2 (C2) team, a GUE Cave 1 (C1) team, and finally my team, the TDI “freak” team. Indeed, my buddy was diving sidemount and I was flying the Divesoft Liberty CCR, both of us being full cave divers. Previous teams had obtained MNemo stick map and LRUD data of a first segment of the cave of about 175 m during the first 2022 project week and started sketching it. Therefore, the one team would primarily focus on sketching and shooting referencing videos of this first segment, while the other teams would venture further into the cave and start surveying the next segment.

The C1 team’s plans for the week were quite straightforward. Diving on thirds of 2/3 of their total gas, their limited reach would not allow them to penetrate far into the cave. However, their skills would be precious to make use of the previously acquired stick map and LRUD data and sketch the first segment of the cave. 

Recalculating their gas after exiting the cave, they were able to perform two dives per twinset, bringing their total dive count per day to four as they were taking a second twinset on the boat. As the first segment of the cave is below 10 m/30 ft, they had plenty of time to carefully draw details of the cave map plan and profile views as well as the main cave features. Using videos shot during their dives, they were able to further refine their sketches during the data processing time at the end of each dive day.

The C1 team shares tasks. One diver sketches the cave…
…while his buddy shoots videos using a GoPro.

The other two teams took one, sometimes two, stages performing one long dive and extending the survey past the first segment. The tasks performed were, in order: drop survey cookies at all stations, data acquisition for the stick map with the MNemo, LRUD data collection, and finally sketch of cave walls and features. The mixed team also surveyed two bypasses within the first segment while the C2 team laid some new line in the far end of the first sump. In addition to the survey tasks, I also took my camera on four out of the five dives that we performed, sometimes juggling between the camera and the MNemo to fulfill all objectives. Well, to be honest, I screwed up my first MNemo measurement, which explained why I had to deal with both the MNemo and the camera on the next dive.

I would like to thank my buddy Vas for taking care of the navigation and most of the data collection, allowing me to play with my camera. We also took the time to stage a few shots on the last dive, which was pure bliss given the discipline and skill level of all my teammates. We spent a total of more than 13 hours underwater over the five project dives.

This is the Italian sign for “the MNemo is not operating as expected”.
A diver swims past survey cookie number 22.
The MNemo is run along the main line to measure distances between stations.
LRUP data is collected at each station.
Team C2 is sketching a remote segment of the cave.

Bringing Home the Data

Back from the dive, we met at the dive center and processed the newly acquired data. This was a decisive moment, where we would know whether the data collection was properly done, or not. We also planned for the next day’s dives. Setting up the gear in the morning, loading everything in the dive center van, transferring the gear into the RHIB, the half hour boat trip to the cave, and everything in reverse on the way back, plus rinsing the gear, taking care of the rebreather and the camera, charging all video lights and strobes, sorting and processing the daily pictures—the week was gone before I noticed.

The map plan view is completed once back at the dive center thanks to the videos.

During this week, our common efforts bring the stick map length and the sketched plan and profile views to a total distance of 410 m/1345 ft. We replaced 590 m/1936 ft of the old line and took many cool pictures. Most importantly, we all learned a lot and came back with new friendships and awesome memories! There is still a lot of work to be done, and the project will continue with additional survey sessions.

I would like to thank my teammates Joana, Sebastian, Oliver, Marco, and Vas for this great session!

Videos of each day of the June project can be found here:

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This month we’re launching a survey panel on dive computing. Please help us by sharing your thoughts & practice at: Dive Computers-Exploratory Survey. 

References

Cabras S, De Waele J, Sanna L. 2008. Caves and Karst Aquifer Drainage of Supramonte (Sardinia, Italy): A Review. Acta Carsologica / Karsoslovni Zbornik. 37. 227-240. 10.3986/ac.v37i2.148.

D’Angeli IM, De Waele J, Ruggieri R, Sanna L. 2013. Pleistocene sea level changes as revealed by flank margin caves in telogenetic limestones in Sicily and Sardinia (Italy). Proceedings of the 16th International Congress of Speleology, Brno 19-27 July 2013. 3.

Sanna L, De Waele J. 2010. Karst landscape and caves in the Gulf of Orosei (Central-East Sardinia): a scientific and cultural resource. 10.13140/2.1.2783.0728.

Dive Deeper

Website: Phreatic: Citizen Science and groundwater research. 

Website: Ariane’s Line

InDEPTH: EXPLORING AND DOCUMENTING SA CONCA ‘E LOCOLI CAVE by Andrea Marassich.

InDEPTH: Data for Divers: Mexican Explorers Go Digital to Chart Riviera Maya by Michael Menduno


Gatien Cosendey is a Swiss underwater photographer and technical/CCR instructor. When not traveling across Europe to enjoy caves, mines, and wrecks, he mainly dives the cold and dark Swiss lakes around his hometown. He loves shooting photos in all sorts of environments, ranging from deep caves to frozen mountain lakes. Besides diving, Gatien holds a PhD in Photonics and works as an optical engineer in the field of augmented and mixed reality.

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Cave

Plan The Shoot, Shoot The Plan

Gas planning is an essential part of tech diving but how does it apply if you’re planning to conduct a photoshoot in multiple specific locations in the overhead environment of a cave? Arguably one of the most artful cave photographers today, and a high-level tech diver, Fan Ping explains how he calculates gas requirements when making pretty pictures in the dark!

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By Fan Ping. Header image: Bedding Plane at Jug Hole by Fan Ping.

Plan the dive, dive the plan. That’s something I have been hearing since the beginning of my diving career but never really mastered until I started my cave diving training with Global Underwater Explorers (GUE). I was surprised by how powerful dive planning can be as a tool, down to a minute, a meter and a few bars. Of course, there is flexibility, but the whole point is you will be aware of what is going to happen next, and have control over the entire process of the dive.

Planning can also apply to underwater cave photoshoots and filming. As a fulltime underwater photographer and director of photography (DP), I plan my shoots in the caves all the time and teach it as a part of my Underwater Cave Photography Course. It definitely makes my job much safer and more efficient. There are two parts of the shoot plan: diving and photography. They work together and can sometimes be complicated, especially when shooting at more than one location. I usually start with the diving part. Knowing exactly where I am going for the photo, I can easily calculate how much time and gas I am going to use to get to the location, and then recalculate a third so I know how much time I have to shoot the photo.

Then I plan the photo part, usually based on a sketch with lighting indicated. Having a sketch of the photo can be very helpful, as it tells me how many lights I am going to need in total and where to put them, both on location as well as when traveling with them. I will also know how much time I am going to need to place and retrieve them, and that adds to the total bottom time too, so I can have a relatively accurate time for actually clicking the shutter.

Plan The Shoot on CCR

It’s the diving part again after the shoot—whether to a second location or to the exit—and in the end, I will have a deco time and total runtime, so I can make sure we are not locked in the park and have somewhere to go for dinner.

Red is in, blue is out, shoot location is in yellow. Map created by Jeff Hancock, partially shown for planning purpose only.

Let’s start with a more straightforward example with one location on rebreather. My buddy Derek Dunlop and I planned a photoshoot at the fissure on Sweet Surprise line in Ginnie Springs. We wanted to scooter to the jump at 670 m/2200 ft on mainline in 20 minutes, drop DPV and sidemount bailout, then swim for another 200 m/656 ft to the shoot location in 20 minutes. The depth of the location is about 28 m/92 ft, which is also the maximum depth of this dive, and the average depth is about 24 m/79 ft before 6 m/20 ft deco, so it was well within our bailout radius, somewhat conservative considering the flow in this cave. (I have LP50 or 7.8L doubles + 1x sidemount 11L, Derek has 2x LP85 or 12L OC bailout. Assume we both have 11L x 2 x 200bar = 4400L OC bailout gas, SCR = 20L/min, ATA = 4, so we have 4400/20/4 = 55min to get back to the cavern. Swim speed = 10m/min, DPV speed = 40m/min, and it will take no more than 40 min in a real situation.)

We plan to shoot until the batteries of the lights die, which will take 40-45 minutes, plus 10-15 minutes to place and retrieve the lights, so it’s a 1 hour shoot at the location. That gives us a 150 minute bottom time plus 25-30 minutes of deco at 6m/20 ft (O2 setpoint: 1.2 bar), 3 hour total runtime.

Derek at the fissure. Most walls are very dark as it’s less traveled.

I usually use the GUE EDGE, i.e., GUE’s predive checklist, for planning, as it is a very good base to start with, no matter if you were trained with GUE or not, and it is very difficult to miss important information with it:

Goals: Photo at fissure on Sweet Surprise line. 

Unified Team: Derek diver # 1 and model, Ping diver # 2 and photographer.

Equipment match: Derek has 1 light on tripod, Ping has camera and 4 lights.

Exposure: Max depth 28m, average depth 20m; 20 min on DPV to jump, 20 min swim to shoot location, turn at 100 min. Total runtime 180 min.

Decompression: 30 minutes deco.

Gas: Sufficient OC bailout gas for each diver, 5.7L AL tank filled with oxygen to 200 bar.

Environment: Normal flow.

Filming at Jug Hole back in 2019.

Plan the Shoot—Open Circuit Edition

Here is another example of a short but multiple location photo shoot at Jug Hole in Ichetucknee Springs State Park, Florida, with my buddy cave diving instructor Joseph Seda as the model.

We planned to take a photo at the Diamond Sands restriction first, then an HDR panorama photo in the bedding plane right after the reaper sign, and a cavern shot if not too late.

The Diamond Sands restriction is only 80 m/262 ft on the mainline, but the flow in this cave is strong, and the bedding plane at the beginning is very low, so my swim speed would be about 8m/s, and it will take me 10 minutes to get to the first shoot location from the cavern. 

Average depth for this part is about 15 m/49 ft, maximum depth is 22 m/72 ft at the restriction. I have a very standard 20L/min SCR, so with 2 sidemount LP85 steel tanks (12L) I am going to use roughly 30 bar in each tank (5 bar/5 min with 12L doubles) before I can start playing with the lights.

Map created and authorized by Adam Hughes.

My tanks are filled with 32% to 260 bar (welcome to cave country!), so theoretically I have 260-30-30×2=170 bar to use for the first shot, with the depth of 22 m/72 ft, it gives me about 35 minutes before I have to turn the dive. 

Lighting is relatively simple here, just 1 light from the model’s back and 2 on the camera, so it will take only a couple of minutes to set up. Diamond Sands restriction is famous for the rolling sands in the flow when a diver passes, and that’s what we want in the photo, obviously from the exit side, and that makes my job easier, as Joseph will be the one placing the light in the back and coming back out of the restriction to pose. So he is diver #1, going in with two lights on tripod (one as backup and for shot two).

Going back to the bedding plane for the second shot only takes about 5 minutes, and getting out of the cave from there will take no more than 5 minutes too, which is about 15 bars in each tank. So usable gas for the second shot is 260-30-170-15-15×2=15 bar.

Diamond Sands restriction. Enlarge to see the rolling sands.

At 15 m/49 ft it gives me only 5 minutes, and I am supposed to get out of the cave with at least 50 bar in each tank, so we will have to shorten the first shot in order to get the second shot, which is a lot more complicated with 6 lights in total to light up the whole scene.

In the end, we got a shoot plan like this with GUE EDGE:

Goals:  Photos at Diamond Sands restriction and in bedding plane.

Unified team: Joseph diver # 1 and model + light monkey for shot 1, Ping diver # 2 and photographer + light monkey for shot 2.

Equipment match: Joseph has 2 lights on tripod, Ping has camera and 4 lights.

Exposure: Max depth 22 m/22 ft, average depth 18 m/59 ft; 10 min to location one, 20 min for shot 1; 5 min to location two, 30 min for shot two, 5 min to cavern.

Total runtime: 70 min.

Decompression: Minimum deco.

Gas: 260 bar to start, 170 bar to finish shot 1, 80 bar to finish shot 2.

Environment: Strong flow, restriction and sandy bottom at location one, very low bedding plane at location two.

*This calculation is relatively conservative, we have twice the amount of gas we need to get out of the cave at any point.

Plan for Safety

The purpose of planning the photo shoot is to make sure we don’t put ourselves in danger while being too focused on the camera in underwater caves. Open water photography is a lot less stringent in terms of planning; however, overhead environments require more precise ideas for how much time it takes to do the job, especially on open circuit. Good planning also makes the shoot more efficient by reducing unnecessary communication and setting up the scene as a team, which eventually leads to a safer dive. There is not one single photo worth a diver’s life, but there are countless caves that are worth diving with a camera

“There is not one single photo worth a diver’s life, but there are countless caves that are worth diving with a camera.”

Dive Deeper

InDEPTH: Cameras Kill Cavers… Again by Natalie Gibb

Here are some of Ping’s other stories:

InDEPTH: Close Calls: I Ripped My Drysuit a Kilometer Back In The Cave by Fan Ping

InDEPTH: Underwater Galaxy by Fan Ping


Fan Ping is a photographer and filmmaker based in Atlanta, Georgia, USA, and is dedicated to showing the beauty of the underwater world to people through his lens. He is specialized in combining artistic elements with nature and complex lighting skills in overhead environments, and this artistic style has brought him international acclaim, including awards from many major underwater photo/video competitions. You can follow his work on Facebook and Instagram: Be Water Imaging.


Be Water Imaging’s Underwater Cave Photography Course is a modular course that includes unique lighting skills and advanced photography techniques in underwater caverns and caves, and shoot planning is a very important part of the course. For more details please check my Be Water Imaging website, and contact Ping at: info@bewaterimaging.com.

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