The Instruments and Methods of Observation Programme (IMOP)

Established by WMO’s predecessor, the International Meteorological Organization, the Commission for Instruments and Methods of Observation (CIMO) ensures the accuracy of weather observation by facilitating the creation of international standards and, thus, the compatibility of measurements. The Commission is responsible for developing the guidelines and recommendations implemented through the Instruments and Methods of Observation Programme (IMOP), one of the key components of the World Weather Watch (WWW) Programme. For over a century it has coordinated collective actions by Members in respect to their observing systems, so that the end results of their efforts far exceed what each could individually accomplish to meet its critical needs; the Commission then disseminates those results worldwide.

Today, CIMO is facing new challenges, particularly in the areas of integration and new technologies. The transition from manual observations to automatic and, now, remote-sensing wind profiler and satellite observations requires the development of guidelines on the use and performance of these and, possibly, conducting intercomparisons to assess their relative performance. The ever growing demand for higher resolution meteorological observations in both time and space, such as for nowcasting and severe weather forecasting, and for the optimization of financial resources have obliged meteorological services to use observational data from various different sources – different systems as well as different providers – including external and private data providers. In addition, national security issues make these observations extremely sensitive. In this context, CIMO is challenged to support WMO Members in developing guidelines to assess the quality of the observational data provided by various systems and shared through metadata.

The Commission will use the same strategies and tools that have yielded successful results in the past to face these challenges:

  • The promotion of standards,
  • Development and publication of guides on instruments and methods of observation,
  • Instrument intercomparisons, and
  • The organization of capacity building activities such as training workshops and technical conferences.

It will also continue to actively collaborate with instrument manufacturers – primarily through the Association of Hydro-meteorological Equipment Industry (HMEI) – the scientific community and other international organizations.

The CIMO Guide

The Commission already has in preparation a new section dealing with standardization of observational procedures and techniques for satellite observation for the WMO Guide to Meteorological Instruments and Methods of Observation (CIMO Guide) (WMO-No. 8). The CIMO Guide, which was first published in 1954, deals with the standardization of observational procedures and techniques, and provides comprehensive and up-to-date guidelines on the most effective practices for carrying out meteorological observations and measurements. It contains guidelines on the measurement of variables related to weather and climate applications as well as to environmental (ozone, atmospheric composition), marine/ocean observations and water (precipitation, evapouration, soil moisture) applications.

As new technologies and observing techniques become available, the CIMO Guide needs to be updated, hence important updates are regularly in preparation. This does not mean that older technologies and techniques are set aside. Mature technologies and methods are tried and true, and are promoted as such by CIMO, and will be considered for inclusion as part of the WMO Technical Regulations within the framework of the WMO Integrated Global Observing System (WIGOS).

Improving measurements through intercomparisons

Instrument intercomparisons are one of the CIMO flagship activities. To date, the focus has been on the intercomparison of surface-based observation systems to improve quality and cost-effectiveness by providing advice and recommendations to WMO Members and manufacturers on the performance of, and improvements to be made to, instruments and observing methods. WMO Members rely on these CIMO intercomparison reports to select or confirm the instruments that best meet their particular needs. The CIMO intercomparisons also provide an incentive for manufacturers to constantly improve their systems.

The requirements for instrument testing and intercomparisons have grown apace with the availability and variety of high quality instruments of different designs by various manufacturers, which also use different measuring principles. Characterizing the performance, accuracy and suitability of instruments under different environmental and climatic conditions is in many cases the only way to establish their interoperability and the compatibility of their data. This intercomparison process has even greater importance today as improvements are needed to reduce measurement uncertainties to support climate service delivery.

The first WMO Solid Precipitation Measurement Intercomparison started in the northern hemisphere winter of 1986/87 and concentrated mainly on manual measurements of snow. But today, a number of NMHSs are in the process of upgrading to automated solid precipitation systems. Guidelines on the performance of these automatic instruments are now required, as well as information on how automatic methods perform in comparison to manual methods to account for possible data discontinuity issues occurring in climate records at the time of the change of the systems. Therefore, CIMO has recently commenced a new intercomparison, the WMO Solid Precipitation Intercomparison Experiment (SPICE), which will document the differences between various automatic systems, and between automatic and manual measurements of solid precipitation using equally exposed/shielded gauges, including their siting and configuration. SPICE will also recommend appropriate automated field reference system(s) for the unattended measurement of solid precipitation in a range of cold climates and seasons, and provide guidance on the performance of modern automated systems for measuring precipitation and snow depth in cold climates for all seasons.

Double Fence Intercomparison Reference with automatic gauge serving as reference system for SPICE

Reference system for SPICE, © Osmo Aulamo

SPICE test sites

WMO Solid Precipitation Intercomparison Experiment (SPICE), © Rodica Nitu, Canada

Remote-sensing systems, like radars, wind-profilers and lightning detections systems, are also being increasingly used and are likely to be the focus of future CIMO intercomparisons. Already underway is CIMO’s Radar Data Quality and Quantitative Precipitation Intercomparison (RQQI). Its aim is to identify, document and exchange the best techniques for quality control of ground-based Doppler weather radar data primarily for quantitative precipitation estimation in a variety of radar scenarios, and in different weather and environment regimes, and to develop data quality metrics for global and regional applications.

CIMO will also soon include airborne and space-based observation systems in its intercomparison activities. In order to respond to the needs of WMO Members, it will also have to provide intercomparison of traceability in the transfer from one system to another. These changes are necessary so that future CIMO intercomparisons can take into account the increased use of remote-sensing observations, aircraft-based and satellite observations and assess the performance of these systems.

Bias of the geopotential altitude at 10 hPa for 7 radiosonde comparisons (simultaneous measurements). The two dotted lines represent a qualitative envelope of all individual results.
© P. Jeannet, C. Bower, B. Calpini & G. Romanens


Collaboration with partners

Over the years, where synergies exist, CIMO has partnered with other international organizations to achieve common goals. These include the Bureau International des Poids et Mesures (BIPM), the International Organization for Standardization (ISO) and the direct involvement of CIMO experts into metrology research such as with the European Metrology Research Programme (EMRP).

CIMO Radiosonde Intercomparison, Yangjiang, China, 2010. The first international intercomparisons were conducted on radiosondes in the 1950s. The last two radiosonde intercomparisons led to the conclusion that pressure sensors were not required on GPS radiosondes. This should eventually lower the prices of some radiosondes.

CIMO Radiosonde intercomparison, © Holger Vömel/Franz Immler, DWD

Collaboration with BIPM:
Reference standard for solar radiation

Ensuring the quality and long-term stability of observations requires traceability to recognized reference standards. Therefore, CIMO advocates for the procedures and reference standards established by BIPM to ensure traceability of observations to the International System of Units (known by its French acronym SI).

Solar radiation is a key component of the Earth energy budget. Therefore, in the context of climate change monitoring/assessment, the precise measurement of solar radiation over long periods of time is crucial to understand the physical processes taking place and to determine the origins of climate changes. CIMO coordinated development of the solar radiation measurement reference, the World Radiometric Reference. In use since 1979, the reference is maintained by the Physical Meteorological Observatory of Davos (PMOD), which also serves as the WMO World Radiation Centre.

Solar tracker at PMOD with the radiometers of the World Standard Group (lower right) and a cryogenic radiometer (lower left)
© Osamu Ijima, JMA

Solar tracker

A group of radiation instruments, the World Standard Group, is used to materialize this reference. But the technology is improving and it is possible that in the future, cryogenic radiometers will be able to better define the scale in use for solar irradiance. PMOD is developing such radiometers. CIMO will continue its collaboration with BIPM and PMOD in order to assess the performance of these new technologies and determine, on one hand, whether the realization of the World Radiometric Reference by the World Standard Group needs to be changed and, on the other, whether solar radiation measurements could be better defined if referred directly to the International System of Units. This may have far-reaching implications as all solar radiation measurements have been reported using the World Radiometric Reference since 1979. This would obviously create data continuity challenges in the context of climate applications, which would need careful consideration.

Collaboration with ISO: Towards the first WMO-ISO Standard

CIMO experts participate in development of ISO standards such as the draft standard on ground-based remote sensing by Doppler wind lidars and the recently proposed development of a common WMO-ISO standard based on the WMO Siting Classification for Surface Observing Stations on Land. This classification tool is used to assess the quality of measurements originating from various networks contributing to WIGOS, including from non-WMO networks, it is likely to have a significant impact on the monitoring of climate variability and change.

The proposed common WMO-ISO standard is likely to be the first of many. The publication of a WMO standard in regulatory documents, such as WMO Manuals and Guides, suffices for the meteorological community; however, there is added-value to having some standards published as a common WMO-ISO standard. As such, they would reach other communities interested in meteorological measurements but not necessarily aware of the existence of WMO publications like the CIMO Guide.

The WMO Siting Classification for Surface Observing Stations on Land offers a good example. A number of different entities perform meteorological measurements for their own reasons – for one, highway operators interested in the meteorological conditions along the roads they maintain. Private companies or individuals who perform meteorological measurements for their own purpose may also be willing to share them with NMHSs, but the data they contribute may be of variable quality. NMHSs have started to make use of third party data, which have a large potential, but they require careful treatment as their quality and the conditions in which the measurements were made are generally not known. Such groups may not be aware of the latest developments, practices and recommendations in use within the meteorological community and WMO. Publishing the Siting Classification for Surface Observing Stations on Land as a common WMO-ISO standard will help to reach out to such communities to improve the overall quality of meteorological observations and to provide guidance on the methods used for various meteorological observations.

CIMO will continue to assess the added value that a common WMO-ISO standard may bring and will engage in such projects on a case-by-case basis.

Capacity development and outreach

Capacity development and outreach are critical to reduce the gap between developed countries and developing/least developed countries. This key activity of CIMO will remain important in the future, especially in the context of increasing automation and complexity of observing systems, and in the evolving context of climate change. The range of CIMO capacity development activities includes:

  • The publication and dissemination of guides and reports;
  • The organization of the Technical Conference on Meteorological and Environmental Instruments and Methods of Observations (TECO), in combination with exhibitions of meteorological instruments;
  • Training programmes developed to address major gaps impacting quality of data. The training lectures are published as reports to ensure they can be widely used, while dedicated regional workshops are carried out to train technicians, for example, on Upper-air Observations, Metrology and Calibration; and
  • Strengthening Regional Instrument Centres, Regional Marine Instrument Centres and Regional Radiation Centres and informing Members on the services these centres can provide to them to ensure the traceability of their standards to SI.

CIMO Training workshop

CIMO training

More than a century of progress

Since its establishment, the scope of IMOP has widened considerably, providing worldwide services in the area of instrumentation and measurements standards. It is an important pillar in WMO’s work in meteorology, climate and hydrology. As the global community continues to increase its scientific collaboration, work in this field will continue to progress, to keep pace with the ever-increasing demand for new and high-quality observational measurements of the atmosphere and the environment around the world, such as required for the Global Framework for Climate Services and the Global Cryosphere Watch. CIMO’s success will, of course, continue to rely on the experts from WMO Members who dedicate both time and effort.

Information on CIMO and the WMO Instruments and Methods of Observation Programme.


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