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Tools and In-Situ Data

Argo float


In support to SMOS cal/val, the objective is to provide an extended and validated in-situ dataset and the corresponding gridded fields at the sea surface. The Coriolis data centre mainly provide the in-situ observations. Argo international array of profiling floats is the principal source of data, reporting temperature and salinity from 2000m to near surface level (4-5m). More isolated measurments from CTDs, sensor equipped marine mammals and moorings (such as TAO/PIRATA in the tropics) complement the dataset but provide little information on the surface levels. Within the GLOSCAL context, we intent to incorporate data from surface dedicated instruments that are not yet in the Coriolis standard flow. First priority has been put on those collected with Thermosalinographs.
Quality control of these data is a prerequisite before they could be intergrated to the objective analysis ISAS.

ISAS surface processing

As ISAS has not been specifically developed for the surface (nor data neither processing), a preliminary work was required to adapt it to this need.

We considered a surface layer extending from 0 to 20 meters. For profile data, the surface layer is assumed perfectly mixed above the level of the last measurement, which is then repeated up to the surface. For TSG data, the level sampled by the instrument is assumed to represent the whole surface layer and is repeated over this layer. Most of the time the thermosalinographs measure temperature and salinity at levels varying between 3m and 15m, depending on the vessels and their draught. The error associated with extrapolated data is increased proportionally to the distance from the measurement level.

Furthermore, ISAS has been adapted to include the thermosalinographs data because of their specificity (timeserie data, data format, high frequency sampled).

The ISAS tool

ISAS (In Situ Analysis System) has been developed by Gaillard et al. (2009b), as a tool to produce these gridded fields from objective analysis of in-situ data coming from multiple sources. All the documentation could be find here.

The ISAS grid covers the globe from 80°S to 90°N with 1/2° Mercator resolution, on 151 standard depth levels between 0 and 2000m. A priori statistics are needed for the analysis: they were obtained from a previous analysis of the period 2002-2008 (von Schuckmann, et al. 2010), providing the following reference fields:

  • a mean seasonal cycle, or climatology, of temperature and salinity representative of the period
  • the corresponding variances (deviation between profiles and monthly mean field)
  • spatial scales deduced from the Rossby radius of the annual climatology

These reference fields and statistics are also used by ISAS for preliminary controls on the dataset and by the CATDS (Centre Aval de Traitement et des Données SMOS) for the real time validation of SMOS data.
We can consider that the ISAS
processing constitutes an additional control in the sense that it allows to check with a single processing the consistency of simultaneous datasets and the agreement with climatology. In the context of SMOS cal/val, we provide monthly gridded fields of SSS and SST and the corresponding dataset in near real time, taking into account as many validated observations as possible.

In-situ data and Quality Control

Coriolis Near Real Time dataset

The in-situ observations used to build our dataset are mainly collected and processed by the Coriolis data centre, which apply a real time quality controls in two steps. First, a set of automatic tests (location and date, spikes...) is applied to the database, followed by a visual checking. The result is that quality flags ranging from 0 (no control) to 9 (missing value) are assigned to each individual measurement. Then, after running daily objective analysis, a diagnostic test detects outliers by screening the analysis residuals. Anomalous profiles are visually checked by an operator. The Coriolis Processing is described in Coriolis report-04-047.

For the needs of GLOSCAL, Coriolis data centre has implemented a near-real time data flow. At the beginning of each month, a new analysis is performed with the data of the previous month, thus providing a dataset of improved quality.

Thermosalinograph datasets

The TSG data are collected within the context of GOSUD international project (Global Ocean Surface Underway Data). The GOSUD dataset is hosted by Coriolis that performs the project agreed real time quality controls on this dataset. For our analysis, only data that have passed delayed mode processing are used. The delayed mode quality control on TSG data is performed by the scientists at LPO, IRD Centres and LEGOS using the software TSGQC (TSG-QC link) developed by US-IMAGO (IRD). There are two levels of control: quality flags and corrections. The quality flags used follows the Coriolis definition and depends on the quality of the data with respect to the climatology, spikes, noise, etc. Then when needed, the time series are adjusted to fit the external data which can be either the water sample analysis (taken aboard) and/or the Argo co-localized data with ship tracks (provided by the LOCEAN). The TSG data set so produced are a contribution

to the GOSUD project and are available in NetCDF Gosud format

The processing flow can be summarized as follows:

  • For French Research vessels, the TSG real time data are available on the corresponding GOSUD FTP site. Water sample analysis are provided by Coriolis. The delayed mode processing is performed at Laboratoire de Physique des Océans (LPO) in Brest.

  • ORE-SSS merchant ships delayed mode data are processed at the IRD Centres in Nouméa and Brest, then at LEGOS in Toulouse and made available on a FTP site.
  • Experimental sailing ships (CANOE project) are provided by Coriolis or sent directly to LPO. Some water samples are available. Delayed mode processing is done at LPO.

Further information on the LPO website.