A Mediterranean drifters' dataset

the cnr realised 138 experiments in the mediterranean basin with surface lagrangian drifters in 12 years, not continuously, between july 1998 and april 2022 (month of the last recovery), at coastal and offshore level. lagrangian drifters produced and sold by 4 different enterprises have been used in the years, with different characteristics in data transmission, structure, repeatability of the experiments, dimensions, batteries, management of the experiments. the four drifters were used in different periods: in 1998-1999 the coastal lagrangian drifter (cld), by italian company innotech s.c.r.l., designed just for coastal use with gps transmission of its position, by a trimble lassen™ sk8, at a frequency of 5 minutes by a gsm mobile phone. the cld had a housing in pvc with electronic unit, rechargeable battery pack and antennas at its top. its dimensions were 140 cm high x 27 cm in diameter with a weight of 12.5 kg. a drogue was used below the cld; in 2009-2010 the argodrifter or code drifter by technocean (fl, usa) consisting in a cylinder of 100 cm height x 10 cm in diameter with four sails placed at 90°, for a total area of about 2 m2. its not rechargeable batteries permitted transmissions till a year by an argos satellite transmitter, a gps for its localisation and a temperature sensor. its position at sea was given by both satellite triangulation and gps; in 2014 the iridium ocean drifters (odi) by the spanish albatros marine technology sa were small, low-cost, and compact surface buoys localised by a gps module based on iridium satellite data transmission system (short burst data – sbd). its housing were two identical halves of a spherical drifter, sealed with an o-ring of 20 cm in diameter and 3 kg of weight. drogues were used below drifters; in 2015-2022 coastal and offshore nomad drifters by the spanish southtek sensing technologies s.l. were coastal gprs, namely the coastal nomad, and offshore satellite, namely the offshore nomad. both types were made in plastic, yellow colour, 72 cm in height x 22 cm in diameter and 2.895 kg of weight. the lithium rechargeable batteries allowed operations up to 7 days to the gprs and several months to the satellite drifters. in the water, only 16 cm of the cylindrical head were over the sea surface. the nomad drifters were of different types: lca (gprs), lce (satellite), lch (hybrid, gprs and satellite), lcf (satellite with temperature sensor).drifter data were pre-processed and repeated positions or wrong date/time, usually a failure of gps receiver and visible on plotted tracks, were manually deleted. this was followed by an editing procedure implemented at ogs (gerin and bussani, 2011; menna et al., 2017) starting with the retrieve of the deployment information then filled into the ogs postgresql database, enriched with other important metadata as the type and characteristics of the instruments, the owner, the principal investigator. here location errors were also replaced with nans based on the evaluation of different potential origins of error like positions outside the mediterranean or on land, duplicated data or data acquired outside the date/time of the experiment or wrong velocities.further remained erroneous data were then manually removed through a visual check. in some cases, the drifter trajectory was considered as two different deployments and split into more segments due to important temporal gaps or acquisition frequency modifications during the experiment. a new recovery/deployment information were included in the database and the automatic editing procedure is relaunched.a following step was the interpolation of edited data at uniform intervals using a kriging optimal interpolation method (hansen and poulain, 1996): at 1-hour intervals data with a frequency in acquisition between a few minutes and 2 hours; at 3-h intervals with frequency till 6 hours; at 6-h intervals with frequency higher than 6 hours. the velocities were calculated as finite differences of the interpolated position.at the end, a final dataset of 158 interpolated drifter tracks was generated.the presented datasets are available in two formats: copernicus and nasa/noaa-like (manageable by panoply, a nasa-developed data viewer). they are both composed of the interpolated data in netcdf files which include time, latitude, longitude, zonal and meridional speed, and metadata. ancillary data like temperature, battery level or drogue presence were not considered as not available for all platforms. the dataset includes drifters’ data with subsurface drogue (in the first metres) apart from a few experiments when the drogue was at 14 or 20 m depth. these experiments correspond to the files arib_lce234 and brib_lce234 (20 m), arib_lce236 and arib_lce354 (14 m) of the dataset. the dataset is publicly available also at the seadatanet infrastructure at[...]

在过去十二年（1998年7月至2022年4月，即最后一次数据恢复的月份）中，地中海盆地通过使用表面拉格朗日漂流器，由四家不同企业生产的，具有不同数据传输、结构、实验重复性、尺寸、电池和实验管理特性的漂流器，进行了138次实验，并非连续进行。这些漂流器分别在1998-1999年、2009-2010年、2014年和2015-2022年间使用，具体包括意大利Innotech S.c.r.l.公司生产的沿海拉格朗日漂流器（CCL），Technocean公司生产的Argo漂流器，西班牙Albatros Marine Technology SA公司生产的Iridium海洋漂流器（ODI），以及西班牙Southtek Sensing Technologies SL公司生产的沿海和离岸Nomad漂流器。漂流器的数据经过预处理，手动删除了重复位置或错误日期/时间的数据，这些错误通常由GPS接收器故障引起，并在绘制的轨迹上可见。随后，在OGS（Gerin和Bussani，2011年；Menna等，2017年）实施了编辑程序，首先检索部署信息，然后将其填入OGS PostgreSQL数据库，并添加其他重要元数据，如仪器类型和特性、所有者、主要研究员。根据评估不同潜在错误起源（如地中海或陆地之外的位置、重复数据或实验日期/时间之外获取的数据或错误的速度），也用NaN替换了位置错误。随后，通过视觉检查手动删除了剩余的错误数据。在某些情况下，由于实验期间存在重要的时间间隔或采集频率的修改，漂流器的轨迹被视为两次不同的部署，并分割成更多段。新的恢复/部署信息被纳入数据库，并重新启动了自动编辑程序。随后的一步是使用克里金最优插值方法（Hansen和Poulain，1996年）在均匀间隔内插值编辑后的数据：在1小时间隔内，采集频率在几分钟到2小时之间；在3小时间隔内，采集频率达到6小时；在6小时间隔内，采集频率高于6小时。速度是通过插值位置的计算有限差分得到的。最终，生成了包含158条插值漂流器轨迹的最终数据集。所提供的数据集以Copernicus和NASA/NOAA类似格式（可通过NASA开发的Panoply数据查看器管理）提供。它们都由包含时间、纬度、经度、纬向和经向速度以及元数据的NetCDF文件中的插值数据组成。辅助数据如温度、电池水平或浮标存在情况，由于并非所有平台都可用，因此未予考虑。该数据集包括带有水下浮标（前几米）的漂流器数据，除了少数实验中浮标位于14或20米深度。这些实验对应于数据集中的文件arib_lce234和brib_lce234（20米）、arib_lce236和arib_lce354（14米）。该数据集也公开可在Seadatanet基础设施上获取。