What is the difference between a drifter and a mooring

Primary tool for determining essential physical properties of sea water. Made up of a set of small probes attached to a metal body, and measurements can be done at up to 30 readings per secondCTD is lowered on a cable down to the seafloor collecting data on the way. A CTD cast, depending on water depth, requires 30 minutes to 2 hours.

Water sampling is often done at specific depths so scientists can learn what the physical properties of the water column are at that particular place and time. Rosette sampler Some analysis need to be done in the lab, or just to calibrate the CTD readings. The samples can be triggered from the vessel at preselected depths. ADCP What is it and why do we use it? The ADCP measures water currents with sound, using a principle of sound waves called the Doppler effect.

The ADCP transmits "pings" of sound at a constant frequency into the water. As the sound waves travel, they encounter particles suspended in the moving water, and are reflected reflect back to the instrument. Due to the Doppler effect, sound waves bounced back from a particle moving away from the profiler have a slightly lowered frequency when they return. The difference in frequency between the waves the profiler sends out and the echoes it receives is called the Doppler shift.

The instrument uses this shift to calculate how fast the particle and the water around it are moving. XBT How do they work? An XBT is a small probe that is dropped from a ship and measures the temperature as it falls through the water.

Two very small wires unroll while the probe is falling, and transmit the temperature data to the ship where it is recorded for later analysis. The probe is designed to fall at a known rate, so that the depth of the probe can be inferred from the time since it was launched. The probe is not recovered Advantages Can be deployed underway. Rapid transfer of temperature. Schott, F.

Union, — Stanitski, D. GOOS Rep. WMO , : Detailed requirements. WMO Tech. Zhang, H. The white dots cover the remainder of the ocean surface. This is a with-tropical-moorings simulation, for which no drifter observations are required in the near-equatorial band. Error bars indicate the standard deviation over the final 2 years of the simulation. Error bars indicate the standard deviation in the final 2 years of the simulations. A key component of the GOOS that measures these essential climate variables is the global array of surface drifters.

The statistics for these simulations are derived from the evolution of the actual global drifter array. It is concluded that drifters should be deployed within the near-equatorial band even though that band is also in principle covered by the tropical moored array, as the benefits of not doing so are marginal.

For in situ SST, crucial for bias correction of satellite observations and accurately determining temperature trends, the goal was to collect measurements at a temporal resolution of 25 observations per week, at a spatial resolution of km Needler et al. The requirement for in situ SST observations has subsequently Zhang et al.

No analogous study has been conducted for SSV, and it is unknown how the recommended sampling impacts errors in satellite-derived surface currents or how accurately it resolves seasonal and lower-frequency circulation. Citation: Journal of Atmospheric and Oceanic Technology 33, 4; The global drifter array is primarily supported by the U. Drifter data are available online NOAA A GDP drifter consists of a surface float attached by a tether to a holey-sock drogue sea anchor centered at m depth Niiler ; Lumpkin and Pazos ; Maximenko et al.

The surface float includes alkaline batteries, a satellite modem, and a thermistor that measures subskin SST. Because a single drifter provides approximately hourly measurements of SST and location Elipot and Lumpkin ; Elipot et al. The GDP relies on numerous national and international partners such, as the Office of Naval Research, to provide additional drifters meeting GDP instrument requirements and to provide deployment opportunities worldwide.

Other important partners are meteorological agencies that use sea level atmospheric pressure observations from the drifters to improve numerical weather prediction Centurioni et al.

Since then, this goal size has been used to assess the health of the global drifter array. In this study, observations of all drifters in the historical database are used to simulate the global drifter array under various lifetime assumptions, both with and without a completed array of tropical moored buoys.

Observations from Volunteer Observation Ships VOS are not considered, but they may reduce the need for sampling along the major shipping lanes e. Because many actual drifters are deployed from these ships, it is shown that fewer observations are needed on these lanes in the simulations even without explicit inclusion of ship observations.

The number of drifters deployed per year and the steady-state size of the global array are determined as a function of lifetime. Emphasis is placed upon the instrument cost per year; no attempt is made to quantify deployment costs, which vary widely based on location and lead times. The spatial distribution of deployments needed in the simulations is compared to the actual deployment distribution, revealing where additional efforts and regional deployment partners are most needed.

This was done as follows: First, the world was divided into an array of regular bins. Second, all drifters were identified that passed through each bin. More recently, Maximenko et al. Both drogued and undrogued drifters are used, and all seasons are included, in order to increase the robustness of results in regions of sparse observations.

Future refinements could include seasonal variations as in van Sebille et al. Because the PDFs are not normalized to conserve the number of drifters from one time step to the next, simulated drifters will disappear from various bins with the same odds as determined by the actual observations.

A comparison of Figs. These regions are indicated by dark gray shading in Fig. In the ocean interior away from death zones Fig. This is close to the design goal of days. The effect of this design goal can be examined in this study by replacing the background odds of dying with values consistent with quit half-lives of T hl e. At each time step, all open-ocean regions away from death zones Fig. If so, a drifter is deployed in the center of the bin.

Note that these simulations completely neglect the logistical challenges and associated costs of deploying drifters whenever a gap develops in the global drifter array. In practice, the GDP is not funded to charter vessels for deployments, relying instead on VOS traveling shipping lanes and on already-planned cruises for which the drifter deployments are a value-added side project.

These simulations also do not consider drogue loss, which often occurs before the drifter dies and negatively impacts the accuracy of SSV measurements. Finally, it should be noted that the statistics governing the simulated drifter motion are based on few drifters where the historical observational density is low see Fig. By construction, the simulations realistically evolve the simulated drifter array from one time step to the next.

Measurements from the mooring include surface variables wind, air and sea surface temperature, salinity, air pressure , as well as subsurface temperatures down to a depth of plus meters. They are generally upgraded or serviced yearly. They need to be constructed of very hardy materials to avoid problems in storms or high seas, the tether line which holds the buoy in the desired location needs to be especially strong.

The design also needs to counter intentional vandalism or accidental damage. Many different designs exist for moored buoys depending on the ocean area. As they are recording so many measurements, the moorings often store more data on-board than they send in real time, so when a moored buoy is recovered, processing and analysis of the data is performed at the buoy owner's data center. If a moored buoy goes adrift it represents a potential loss of costly equipment and a possible hazard to navigation.

For this reason a backup location system is used to ensure that an alert is sent if the buoy leaves a certain area. It is deployed in depths of up to meters. Measurements from the mooring include surface variables, as well as subsurface temperatures down to a depth of meters. Many different sorts of Wave Buoys exist to capture and model information about ocean dynamics on the surface.

These buoys measure the frequency and size of wave energy known as the spectra from which significant wave height, dominant wave period, and average wave period are derived.

Even the direction of wave propagation is measured on many moored buoys. This information can be used to greatly improve the prediction and warnings for dangerous storms.