Because it has a small above-water surface and high underwater surface area, the effect of surface winds and waves has a negligible effect, instead moving with the flow of the upper 1m of the water column. The USCG has found that this instrument behaves as a 'zero-leeway' object, moving with the top meter of the water column, with no additional motion due to the direct effect of the wind on the SLDMB's exposed areas. The USCG maintains several hundred SLDMBs for deployment and responds to more than 5,000 SAR cases each year. In the year 2006, more than 400 SLDMBs were deployed in SAR applications, with an average lifetime of 22 days. The USCG may release SLDMBs at their discretion to aid in search efforts. In remote areas, SLDMBs are deployed via C-130 aircraft or helicopters. The GPS unit on each SLDMB calculates its position every 30 minutes, and transmits the data via the ARGOS data collection system to USCG Operational Support Center (OSC). During high traffic periods, the USCG may pre-deploy units in order to have existing data in areas where SAR operations are more likely, reducing the time required to collect ocean current data during the SAR process. SLDMB may be released as single units or as a group, depending on the situation required. In cases where the last known position is known and the time lag to SLDMB deployment are minimal, only a single unit may be necessary. However, if a sufficient time lag exists, or the last known position is not available, multiple SLDMBs should be used. An example of this second case would be a downed fishing vessel, in which only the approximate area of the vessel is known.
Read more about this topic: Self-locating Datum Marker Buoy
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