User:Kbernstein/SLDMB

Self-Locating Datum Marker Buoys (SLDMB) – A 70% scale Coastal Ocean Dynamics Experiment (CODE)/Davis-style oceanographic surface drifter with drogue vanes between 30 and 100 cm deep. This particular surface drifter is designed specifically for deployment from a U.S. Coast Guard vessel or airframe and for unattended operation during a 30-day lifetime. Similarly to other SLDMB systems, the METOCEAN SLDMB is accompanied by an onboard electronics package, which includes Global Positioning System (GPS) positioning and sensor data Service Argo, Inc, receives the data and forwards it to the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting n-series satellites every 30 minutes. The data is transmitted to a secure U.S. Coast Guard website for use by trained Search and Rescue Personnel.

Mechanical Design
The SLDMB design is based upon the Davis-style drifting buoy, which minimizes the affects of wind and waves on the drifter allowing for a more accurate representation of the surface ocean current. The SLDMB is shown in Figure 1 with four orthogonal drag vanes that are constructed of nylon fabric and supported by PVC arms that extend from a cylindrical hull. Four floats attach to the PVC arms that maintain the buoyancy of the SLDMB.

Prior to launch, the SLDMB is packaged in a circular cylinder, which can be launched through a hatch or door in any fixed or rotating wing aircraft or from any surface vessel moving up to 35 knots. The SLDMB is made up of a Deployment Assembly and a Surface Unit. The Deployment Assembly controls the aerial decent and breaks away along with the parachute when the buoy hits the water while the Surface Unit consists of an aluminum cylinder with the drogue panels attached. All of the electronics are switched on after the arms deploy.

The SLDMB parachute is square with two diagonal slits offset from the corners. The chute is 27 inches per side. The slits allow some airflow through the chute providing a flight time of 3 to 5 seconds. This design prevents the buoy from drifting off course and ensuring that it lands within 100 meters of the aircraft track. Tables 1 and 2 list the SLDMB dimensions and SLDMB construction.

Electronic Design
The SLDMB electronics package consist of the METOCEAN Model MAT 906 (Argos package), the Sensor Scientific Thermistor Model WM 103 that measures sea surface temperature, the Precision resistive divider for battery voltage, and the GPS receiver (Conexant Jupiter Model TU30-D140-231). All electronics are located at the bottom of the Surface Unit along with a power supply consisting of 10 “D” sized cells providing a minimum 15-day operating life. The antenna assembly is spring-loaded and raises the antenna to approximately 15.8 inches above the ocean surface. The ARGOS Data Transmission Format as well as the decoding equations are located in the METOCEAN User’s Manual. Tables 3 and 4 briefly list the electronics and sensor characteristics located on the SLDMB.

Deployment Methods
A very versatile design, the SLDMB can be deployed from fixed and rotary wing aircraft and vessels. Specific instructions for each USCG aircraft are available through the METOCEAN User’s manual as well a Coast Guard SAR publications. In general, personnel operating rotary aircraft should not deploy the SLDMB with a speed greater than 80 knots or height greater than 150 feet. Personnel operating fixed wing aircraft should not deploy the SLDMB with a speed greater than 150 knots and an altitude greater than 1000 feet.

Environmental Characteristics
The SLDMB is designed to operate at a minimum for 15 days and turn off automatically after 30 days. The specific operating environment and survival environment characteristics are listed in Tables 5 and 6. The SLDMBs are designed for storage up to 24 months and are typically not used in an official capacity after expiration..

Search and Rescue Application
The search and rescue of vessels and people inshore and on the high seas are highly reliant upon accurate and timely surface current information. The United States Coast Guard (USCG) uses the Self-Locating Datum Marker Buoys (SLDMB) developed by METOCEAN Data Systems as part of the search and rescue (SAR) system. Since the SLDMB has a very small surface area above the ocean surface and a high underwater surface area, there is very little leeway in response to the direct forcing of winds and waves. Additionally, the CODE design is an inexpensive design allowing a large number to be deployed. This is advantageous for the USCG who conducts approximately 5,000 searches per year and who maintains at least 600 SLDMBs for use in operational cases. The USCG uses these drifters to construct current vectors from sequential SLDMB positions. In conjunction with the Search and Rescue Optimal Search Planning System (SAROPS) the USCG is able to establish the ocean surface motion of a component of the object of the search.

One or more SLDMBs should be deployed for any case where higher resolution current data is needed to effectively plan a search. One example is a case that lies in or near the Gulf Stream where there are strong horizontal current variations. SLDMBs should be deployed as early as possible during the case as the goal is to provide timely and accurate drift of the search and rescue object. SLDMBs may even be pre-deployed at the beginning of period where higher boating traffic is expected such as at the start of a long weekend during the summer or at the beginning of a fishing tournament

The number and placement of SLDMBs are dependent upon the type of case and location that is presented to the SAR controller. A single SLDMB can be used in the vicinity of the last known position where the time lag between the distress incident and deployment is reasonable short. Multiple SLDMBs should be used where the last know position is not known. This is the case for an overdue vessel or vessel and crew who were fishing in a known fishing area

The use of METOCEAN SLDMBs provides valuable real-time current information to the search and rescue controller and ultimately provides a better search area.