Essential Climate Variable
An Essential Climate Variable (ECV) is a geophysical variable that is associated with climate variation and change as well as the impact of climate change on Earth. GCOS has defined a set of ECVs for three domains, atmospheric, terrestrial and oceanic, see The Second Report on the Adequacy of the Global Observing Systems for Climate in Support of the UNFCCC, 2003, GCOS-82.
Fundamental Climate Data Record
A Fundamental Climate Data Record (FCDR) is a well-characterised, long-term data record, usually involving a series of instruments, with potentially changing measurement approaches, but with overlaps and calibrations sufficient to allow the generation of products that are accurate and stable, in both space and time, to support climate applications (Strategy Towards an Architecture for Climate Monitoring from Space, 2013). FCDRs are typically calibrated radiances, backscatter (for active instruments), or radio occultation bending angles. FCDRs also include the ancillary data used to calibrate them. The term FCDR has been adopted by GCOS and can be considered as an international consensus definition.
(Thematic) Climate Data Record
A Thematic Climate Data Record (TCDR – also known as a Climate Data Record (CDR)) refers to the counterpart of the FCDR in geophysical space (Strategy Towards an Architecture for Climate Monitoring from Space, 2013). A (T)CDR is equivalent to an ECV Product covering only one geophysical variable. For instance, the ECV Cloud includes six different geophysical variables, each of them constituting an ECV product or (T)CDR. The term (T)CDR has been taken up by many space agencies and can be considered as a de facto standard.
Interim Climate Data Record
An Interim Climate Data Record (ICDR) regularly extends in time a Fundamental or Thematic Climate Data Record using a system having optimum consistency with and lower latency than the system used to generate the FCDR or TCDR [N.B. This definition of an ICDR was endorsed at the 9th session of the joint CEOS/CGMS Working Group Climate Meeting on 29 March 2018].
Many GCOS ECVs are sub-divided into so-called ECV Products. The term “Product” denotes long-term data records of values or fields of ECVs derived from FCDRs (Systematic Observation Requirements for Satellite-based Products for Climate: Supplemental details to the satellite-based component of the “Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC” (2010 Update), 2011, GCOS-154)). For instance the water vapour ECV has 3 ECV Products: total column water vapour, tropospheric and lower-stratospheric profiles of water vapour, and upper tropospheric humidity, which describe different aspects of water vapour in the atmosphere. However, the definitions provided for ECV Products in GCOS-154 are not always consistent for all ECVs. For some cases, e.g. the ECV Sea Ice, there is only one ECV Product that covers 4 different variables/parameters for which requirements are provided. The ECV Inventory, and the associated questionnaire, names each variable/parameter for which requirements are to be provided per ECV Product. A consistent mapping is provided in ECV Inventory: Questionnaire Guide v2.2, 2016.