This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640276.
G2.37 Need for more complete metrological characterisation of spectroscopic information
Submitted by Anna Mikalsen on 12 June, 2017 - 11:02
Gap abstract:
Molecular spectroscopy provides the primary link between radiance and atmospheric gas composition. Full knowledge of the spectroscopic properties of a measurement could, in theory, provide a route to formal traceability for that measurement. The exact nature of the influence of spectroscopic uncertainties on the derived ECV products will vary according to the spectral region being measured and the specific details of the measurement technique being employed – and a series of related gaps have been identified. However, there would be a clear benefit in a top-level spectroscopic coordination activity that identifies and disseminates common issues and solutions, including a harmonised process for dealing with spectroscopic uncertainties and establishing spectroscopic traceability.
Part I Gap description
Primary gap type:
- Knowledge of uncertainty budget and calibration
Secondary gap type:
- Governance (missing documentation, cooperation etc.)
ECVs impacted:
- Temperature
- Water vapour
- Ozone
- Carbon Dioxide
- Methane
User category/Application area impacted:
- Operational services and service development (meteorological services, environmental services, Copernicus Climate Change Service (C3S) and Atmospheric Monitoring Service (CAMS), operational data assimilation development, etc.)
- International (collaborative) frameworks and bodies (space agencies, EU institutions, WMO programmes/frameworks etc.)
- Climate research (research groups working on development, validation and improvement of ECV Climate Data Records)
Non-satellite instrument techniques involved:
- Lidar
- Microwave Radiometer
- FTIR
- Brewer/Dobson
- UV/VIS zenith DOAS
- UV/VIS MAXDOAS
- Pandora
-
This gap represents the top-level coordination and harmonisation activity required across the general spectroscopic measurement field. There are two gaps identified under this broad topic, G2.26 and G2.27 which address issues related to particular spectral regions and specific issues in individual measurement techniques. In both cases, this coordination activity should take place in parallel with the more specific gap assessments
Detailed description:
Molecular spectroscopy provides the primary link between radiance and atmospheric gas composition, and is a primary component of the theory of radiative transfer through the atmosphere. The spectroscopic properties of a gas are constant and therefore, if they are robustly characterised and all of the external and instrumental influence factors on a spectroscopic measurement method are assessed, then formal traceability could, in theory, be realised for any measurement using that method.
In addition to the spectroscopic issues relating to those techniques that directly use spectroscopic measurement methods to derive information on ECVs, spectroscopic parameters are also an integral part of radiative transfer (RT) codes. RT codes constitute the core of radiometric physical retrievals, such as optimal estimation methods. In addition, any data intercomparison/validation method that includes the use of RT codes will also be influenced by spectroscopic uncertainties. Such uncertainties will contribute to the overall uncertainty of the data intercomparison, and could be the source of, potentially unexpected, correlation between the different data sources.
The exact nature of the influence of spectroscopic uncertainties on the derived ECV products will vary according to the spectral region being measured and the specific details of the measurement technique being employed – and a series of related gaps have been identified that give examples of this. However, there would be a clear benefit in a top-level spectroscopic coordination activity that took an overview of the more detailed technical developments; identified and disseminated common issues and solutions; and potentially developed a harmonised process for dealing with spectroscopic uncertainties and establishing spectroscopic traceability. This final goal of formal traceability based purely on the spectroscopic assessment of the measurement is a very challenging one that is unlikely to be resolved in the short term. However intermediate steps to improve the knowledge of spectroscopic uncertainties and their impact on measurement methods and intercomparison results, will have immediate impact which will be enhanced through an overall spectroscopic coordination activity.
Historically, other sources of uncertainty have tended to be much larger than spectroscopic uncertainties such that spectroscopic uncertainty has tended to be seen as an ignorable effect. As satellite and non-satellite instrumentation become more stable and better characterised and understanding of collocation effects improves it is increasingly the case that spectroscopic uncertainties become important or even the limiting factor in the comparison, particularly as they are a potential source of long term correlation within individual measurement methods but also in comparisons between methods. It is thus increasingly important that spectroscopic uncertainties be considered afresh and better quantified.
Operational space missions or space instruments impacted:
- Independent of specific space mission or space instruments
This gap relates to all space instruments that rely on spectroscopic parameters knowledge in their measurement procedure or could use a sub-orbital spectroscopic-based technique as a validation tool.
Validation aspects addressed:
- Radiance (Level 1 product)
- Geophysical product (Level 2 product)
- Spectroscopy
Gap status after GAIA-CLIM:
- After GAIA-CLIM this gap remains unaddressed
Part II Benefits to resolution and risks to non-resolution
| Identified benefit | User category/Application area benefitted | Probability of benefit being realised | Impacts |
|---|---|---|---|
A robust and consistent approach to the handling of uncertainties and traceability in spectroscopic measurements would significantly extend the availability of reference quality data across a wide range of techniques and ECVs. |
|
| The provision of a formalised route to spectroscopic traceability would enable reference quality data to be realised in an efficient and consistent manner at any location. The contribution to uncertainty due to spectroscopic parameters can be fully accounted in the uncertainty budget of retrieved products and the associated time series and trends. |
An improved understanding of the common issues in spectroscopic measurements would identify sources of correlated uncertainties between different measurement and modelling techniques |
|
| Improved quality and understanding of the intercomparison between sub-orbital and satellite based measurements, and between measured and modelled atmospheric distributions. Understanding the spectroscopic uncertainties will yield increased confidence and utilization of observations in reanalyses and climate research. |
| Identified risk | User category/Application area at risk | Probability of risk being realised | Impacts |
|---|---|---|---|
If a coordinated activity is not carried out then the situation will remain as a series of separate activities linked to individual techniques / instruments. |
|
| ECV retrieval uncertainty lacks a coordinated contribution of RT models, which may potentially affect time series and trend recognition. Intercomparison / validation activities remain inefficient with none of the synergistic benefits that a coordinated spectroscopic assessment could bring. |
The potential effects of correlated uncertainties in the comparison of results from different techniques due to spectroscopic issues are not identified. |
|
| A key element in assessing the comparability and/or consistency of different measurements is not properly addressed, potentially undermining validation studies. |
Part III Gap remedies
Gap remedies:
Remedy 1: Establish traceability of spectroscopic properties of Essential Climate Variables
Primary gap remedy type:
Research
Secondary gap remedy type:
Education/Training
Governance
Proposed remedy description:
Establishment of a top-level cooperation and networking activity to coordinate and review spectroscopic uncertainty activities across the range of spectral regions and measurement techniques, with the long-term goal of developing harmonised processes to establish spectroscopic traceability in ECV determination. This may be achieved either by a large-scale coordinated project or piecemeal for specific cases. A large-scale coordinated project approach would benefit from synergies and commonality of approaches and may be preferred. Experts in laboratory and theoretical spectroscopy, metrology and the instruments would be required, and would need to link to the exiting collaborative activities involved in the development of spectroscopic reference databases such as HITRAN and GEISA. A key aspect of this work will be the introduction of metrological traceability in the determination of new spectroscopic data, covering both the target gas concentrations and path lengths being measured but also the ancillary parameters such as temperature, pressure and matrix gas composition that are crucial in derivation of spectroscopic model parameters and their uncertainties. The top level project should include a focus on the development of common procedures and robust methods that could be deployed across the wider spectroscopic community, to ensure consistency and comparability amongst data providers in the generation of the spectroscopic parameters, and understanding amongst data users in the application of the parameters and related uncertainties.
Relevance:
The proposed coordination activity is required to ensure a harmonised approach to addressing specific gaps in spectroscopic knowledge. This will lead to the efficient development of an improved understanding of spectroscopic uncertainties and a unified methodology in establishing traceability in spectroscopic measurements.
Measurable outcome of success:
Successful outcome of the activity will be demonstrated in the short term through transfer of knowledge from one area of spectroscopic research to another, and through the development of common processes and procedures. An additional measure of success would be the implementation of the estimated uncertainties in the retrieval methods exploited by the satellite and ground-based user community.
Expected viability for the outcome of success:
- Medium
Scale of work:
- Programmatic multi-year, multi-institution activity
Time bound to remedy:
- More than 10 years
Indicative cost estimate (investment):
- Medium cost (< 5 million)
Indicative cost estimate (exploitation):
- Yes
Potential actors:
- Other, please specify:
European funding mechanisms such as COST or EMPIR.