This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640276.
G2.13 Missing microwave standards maintained by national/international measurement institutes
Submitted by Anna Mikalsen on 12 June, 2017 - 10:43
Gap abstract:
The traceability of ground-based microwave radiometer (MWR) estimates and their uncertainty requires the traceability of MWR calibration to SI standards. Currently, no SI standard is available for MWR at any national/international measurement institute. Thus, full SI-traceability of ECVs from MWR is currently not feasible. However, at least one national measurement institute is currently developing SI standards for MWR. It is expected that SI-traceable standards for MWR will be available in the next few years. This will then allow the availability of transfer standards to MWR manufacturer and user communities.
Part I Gap description
Primary gap type:
- Knowledge of uncertainty budget and calibration
Secondary gap type:
- Uncertainty in relation to comparator measures
- Governance (missing documentation, cooperation etc.)
ECVs impacted:
- Temperature
- Water vapour
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.)
- Climate research (research groups working on development, validation and improvement of ECV Climate Data Records)
Non-satellite instrument techniques involved:
- Microwave Radiometer
G2.13 should be addressed together with G2.36
The remedy of G2.13, i.e. the development of MW standards maintained at national/international measurement institutes and the availability of transfer standards, will set the basis for SI-traceability of MWR observations and retrievals. However, tools for evaluating the MWR total uncertainty budget can be developed independently of the solution of G2.13.
Detailed description:
The traceability of the microwave radiometer (MWR) estimates and their uncertainty requires the traceability of MWR calibration to SI standards. This implies the use of certified black-body (BB) targets and temperature sensors (measuring the target physical temperature). Commercial BB targets have reached a mature state, but their characterization is usually limited. Despite this, many realizations of microwave brightness temperature standards exist in the form of heated or cooled calibration targets, although none are currently maintained as a standard by a national/international measurement institute (Walker, 2011). Thus, despite the efforts for fully characterizing the MWR absolute calibration, the traceability of any ECVs from MWR to national/international standards is currently not feasible. However, the development is ongoing (Houtz et al., 2015; 2016; 2017). This gap shall be addressed by national/international measurement institutes, and cannot be addressed within GAIA-CLIM.
Operational space missions or space instruments impacted:
- Other, please specify:
Microwave and Infrared temperature and humidity sounders
Validation aspects addressed:
- Radiance (Level 1 product)
- Geophysical product (Level 2 product)
- Gridded product (Level 3)
- Assimilated product (Level 4)
- Time series and trends
- Calibration (relative, absolute)
- Spectroscopy
Gap status after GAIA-CLIM:
- GAIA-CLIM has partly closed this gap
This gap will be considered closed when MW standards are available in at least one national/international measurement institute for calibrating secondary standards to be used for MWR calibration. The role of GAIA-CLIM is to follow and report the technological developments at national/international measurement institutes (e.g. NIST) and to inform MWR users and manufacturers about these developments.
Part II Benefits to resolution and risks to non-resolution
| Identified benefit | User category/Application area benefitted | Probability of benefit being realised | Impacts |
|---|---|---|---|
Traceable intra- and inter-MWR data characterization |
|
| Traceable MWR characterization will allow proper reconciliation of historical time series of MWR observations at any given site as well as uniformly across the network |
Increased confidence in MWR data quality |
|
| Traceable MWR data characterization will yield increased confidence and utilization of MWR observations in reanalyses and climate research |
| Identified risk | User category/Application area at risk | Probability of risk being realised | Impacts |
|---|---|---|---|
Non-traceable MWR-based validation for satellite ECVs |
|
| Difficult to reconcile historical time series of MWR observations. Ground-based MWR will not reach the requirements for climate monitoring |
Non-traceable MWR-based validation for satellite ECVs |
|
| No traceable validation for satellite boundary layer thermodynamical profiles |
Part III Gap remedies
Gap remedies:
Remedy 1: Development and testing of MWR standards and secondary standards
Primary gap remedy type:
Technical
TRL 4-6
Secondary gap remedy type:
Laboratory
Deployment
Research
Proposed remedy description:
Metrology applicable to microwave remote sensing radiometry is currently under development at national/international measurement institutes (e.g. National Institute for Standards and Technology, USA). These efforts include the development of a standard radiometer and standard high-emissivity black body (BB) targets. It is expected that SI-traceable calibration for BB targets and transfer standards in the form of calibrated BB targets will be available at NIST in the next few years. The current status is presented in an open literature paper (Houtz et al., 2017). The uncertainty in the BB Tb is around 0.1 K (1-sigma), covering the frequency range from 10 to 200 GHz. NIST plans to be able to calibrate other BB targets against their standards, which could then be used as transfer standards. Thus, the primary gap remedy type is technical/technological (the development of MW standards), but it involves laboratory and research work (testing and characterization) as well as deployment (transfer standard to manufacturer and user communities).
Relevance:
The remedy will make microwave standards available at least at one measurement institute (NIST). GAIA-CLIM aims at monitoring and effectively communicating the progress to MWR manufacturers and users, in order to promote the uptake of certified targets.
Measurable outcome of success:
The successful outcome is to make MWR users and manufacturers aware of the above developments. The effective characterization of existing and/or new MWR units against microwave standards would be an additional measure of success, which is subject to the availability of the transfer standards before the end of GAIA-CLIM.
Expected viability for the outcome of success:
- Medium
Scale of work:
- Single institution
Time bound to remedy:
- Less than 5 years
Indicative cost estimate (investment):
- Medium cost (< 5 million)
Indicative cost estimate (exploitation):
- No
Potential actors:
- Academia, individual research institutes
- SMEs/industry
- National measurement institutes
References:
- Houtz D. A., D. K. Walker and D. Gu, Simulations to characterize a passive microwave blackbody design, 2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Milan, pp. 3485-3488, DOI: 10.1109/IGARSS.2015.7326571, 2015.
- Houtz D. A., D. K. Walker, D. Gu (2016), Cryogenic Design and Uncertainty Analysis of the NIST Microwave Blackbody, 14th Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment (MicroRad), Espoo, Finland, April 11-14, 2016.
- Houtz D. A., W. Emery, D. Gu, K. Jacob, A. Murk, D. K. Walker, and R. J. Wylde, Electromagnetic Design and Performance of a Conical Microwave Blackbody Target for Radiometer Calibration, IEEE Transactions on Geoscience and Remote Sensing, vol. 55, no. 8, pp. 4586-4596, doi: 10.1109/TGRS.2017.2694319, Aug. 2017.
- Walker D. K., Microwave radiometric standards development at US NIST, IEEE GRSS Newsletter, 161, 2011.