2006 Projects

 

The Lamont Rapid Deployment Ocean-Bottom System

Andrew Barclay, Patrick Jonke, James Gaherty, Spahr Webb

            The proposed Lamont Rapid Deployment Ocean Bottom System (LRDOBS) is a seafloor delivery/recovery and datalogger system that is lightweight, inexpensive, and easy to operate.  Although the LRDOBS has potential use for general time-series measurements (e.g., seismometers and hydrophones; pressure, current and flow meters; magnetometers; temperature and chemistry probes; acoustic profilers; and optical backscatter/transmissometer sensors), it meets an immediate and well-defined need in active-source seismology.  The seafloor seismometers that are used for marine seismic refraction/tomography experiments and that also provide crucial seismic velocity information for reflection surveys are typically designed for broader applications and are unnecessarily large, complicated and expensive.  With fixed capabilities that are matched to the requirements of active-source seismology (e.g., a single hydrophone recording continuously for one month at a fixed sample rate), the LRDOBS will be a low-cost, reliable, and low-maintenance instrument that can be stored on board ship and efficiently used at sea.  Automated pre-deployment programming, battery recharging, and data download are necessary to minimize the time and personnel required for LRDOBS operation.  OTIC funding will be used to develop a prototype instrument for demonstration and testing.  Many of the prototypeÕs components will be off-the-shelf; design and construction will focus on the datalogger for which the critical challenge is to minimize cost, size, weight and power consumption for 1-2 months of single-channel, 24-bit recording. 

 

A portable universal water sampler for dissolved gases

 

Martin Stute (martins@ldeo.columbia.edu)  Brice Loose (brice@ldeo.columbia.edu)

 

Concentrations and isotope ratios of gases dissolved in surface and ground waters give us important clues about fluid flow and transport dynamics (e.g. CFCs, SF6, SF5CF3, 3He), past climate conditions (e.g. noble gases, N2), and biogeochemical processes (e.g. CO2, H2, H2S, CH4, N2).

We are proposing to build a suitcase size, portable, user-friendly, self-contained sampler that will separate dissolved gases based on an in-line equilibrator with a fast semi-permeable membrane (Polypropylene, manufactured by Liqui-Cel¨, www.liqui-cel.com). We expect that the new system will yield reliable uncontaminated samples for all (or at least most) gases of interest.

At the heart of the system is a ÔcontactorÕ manufactured by Liqui-Cel¨, which consists of thousands of 300mm diameter polypropylene hydrophobic membranes that act as barrier for water, but are permeable for all gases. Gases being pumped in a closed circuit through the fibers equilibrate with passing water on the other side of the membrane. The characteristic equilibration time in the fibers is of the order of seconds (Liqui-Cel, 2006) and depending on the volume of the attached sample containers, the entire gas phase is expected to equilibrate over a period of minutes to tens of minutes. Partial pressures of the individual compounds in the gas phase depend on the temperature of the membrane and the (known) solubility of the gases in water. In order to determine the concentrations of dissolved gases in water from the mixing ratios in the gas phases, a precise temperature and total gas pressure measurement is required, and the whole system needs to be stabilized at the water temperature by placement into an thermally insulated box. The sampler will also require a small 12V battery to run the membrane pump and various gauges.

If successful, this universal sampler might revolutionize how environmental gas samples are collected and will benefit a wide range of current and proposed projects being conducted at Lamont.

 

2007  Projects

 

Satellite Telemetry for ShakeNet Strong-Motion Sensor Networks

 Colin P. Stark, David Gassier, Tarik Hussein, Andrew Barclay

Collaborating engineer:   Alberto Behar (JPL/NASA)

We are designing a prototype satellite telemetry interface for the ShakeNet project as a means of building LDEO institutional expertise in the use of satellite communications to scientific instrumentation. ShakeNet is an Earth Institute (CCI) funded pilot program to design and deploy low-cost networks of smart strong-motion sensors in impoverished, highly populated regions at great seismic risk.  Its aims are to enable the rapid assessment of shaking and damage following a destructive earthquake, to promote awareness of earthquake risk, and to provide vital data on attenuation, site effects, and infrastructural vulnerability.  Since landline and cellular networks will inevitably be compromised or overloaded in a damaging earthquake, satellite communications will be needed for emergency-mode communication between the sensors and a remote server.  Our key aims are therefore: (1) to understand the constraints and possibilities offered by low-cost satellite telemetry, and (2) to develop a prototype interface system that integrates off-the-shelf sensors, microcontrollers and satellite transponders into an adaptable tool for use both in the ShakeNet project and in future LDEO field projects.

 

Ice Thickness Spar

Doug Martinson (dgm@ldeo.columbia.edu), Xiaojun Yuan

 

We are proposing to build an affordable (<$6 k) functioning prototype of an ice thickness-measuring spar (ITS). The ITS will be a thick-walled PVC pipe, with thermistors located every 5-8 cm epoxied into small holes in the side of the spar. The spar is designed to be deployed in open ocean and frozen into the ice pack when it forms, operate for a minimum of 1 yr transmitting back the temperature profile via iridium (or, ideally, using ShakeNet being developed by Stark et al. in another OTIC project). The spar, can be any length, but the prototype will be designed for the nominal Antarctic seasonal sea ice cover, requiring a spar that can accommodate 1.5 m of sea ice/sea water and a 0.7 m snow cover. Buoyancy requirements are simple and show that we can easily accommodate enough batteries to allow more than 1 year of continuous operation. Experience during our ANZFLUX project in the Weddell gyre, using T-profiles through the ice and snow with similar non-transmitting PVC tubes show that the conversion from T to ice thickness is easy and precise, even allowing good estimation of the ice and snow conductivity and heat flux. Standard off-the-shelf parts will make this affordable, with the hopes that after successful testing of the prototype even supplements to our existing Antarctic grants will allow purchase of many spars allowing good coverage of ice thickness in regions we are currently studying in detail (for DGM this is within a dense grid of ocean stations along the mid-western margin of the Antarctic Peninsula; for XY, the target area is in the Pacific center of the ADP to complement mooring observations). Our dream is to have these continuously sampling throughout the pack ice, and low-cost is the key to this.