Uncertainty estimation for temperature, salinity & chlorophyll-a. D#5.5. Version 1.

Abstract

This document constitutes Deliverable 5.5 of the JERICO project. It is intended to furnish members of the JERICO community with a basic understanding of how to proceed when attempting to establish measurement uncertainty for marine temperature, salinity and chlorophyll-a sensors. The document presents descriptions of the three measurands from a metrological standpoint, and discusses the approaches that could be taken to prepare uncertainty budgets for relevant sensors with some suitable examples and useful advice. The estimation of the uncertainty associated with the results of a measurement is an objective way to numerically depict the trustworthiness of those results. It is, therefore, a crucial part of the measuring process. Any measured value can be considered complete only if accompanied by a relative estimate of uncertainty. However, the latter characteristic is rarely discussed in marine observing circles and in the marine data management community despite its intimate link to sensor performance, data quality and data usability issues. This disregard arises from ignorance concerning the rigor required of modern measuring activity and the complexity of the underlying metrological system supporting it. There is a pressing need to begin to address this state of affairs, and the present publication, intended as a guidance document for members of the JERICO community, is a first step. The document deals with outlining a possible approach to determining uncertainty for sensor measurements of seawater temperature, salinity and chlorophyll-a. The approach is based on the generally accepted methodology for uncertainty evaluations given in the BIPM (Bureau International des Poids et Mesures) publication “Evaluation of measurement data - Guide to the expression of uncertainty in measurement”, commonly referred to as the GUM (2008). In all three cases, the conceived blueprint for action is based on the following topical cornerstones: the specification of the measurand, the descriptions of the realized quantity and the relative reference value, and finally, the identification of the uncertainty components and the quantification of the uncertainty.

The present document is intended to be used in conjunction with the GUM, which continues to remain the master reference document for the evaluation of uncertainty in measurement at this time.